Crystal chemistry and its significance on the growth of technological materials: Part II; Octahedrally coordinated compounds

Prog. Crystal Growth and Charact. 1992, Vol. 24, pp. 269-359

0146-3535/92 $15.00

Printed in Great Britain. All rights reserved

© 1992 Pergamon Press Ltd

CRYSTAL CHEMISTRY AND ITS SIGNIFICANCE ON THE GROWTH OF TECHNOLOGICAL MATERIALS: PART I; SILICATES, PHOSPHATES AND THEIR ANALOGUES K. Byrappa* and D. Yu. Pushcharovskyt * Mineralogical Institute, University of Mysore, Manasagangotri, Mysore - 570 006, India t Department of Crystallography and Crystal Chemistry Geology Faculty, Moscow State University, Leninsky Gori, Moscow, Russia

l.Introduction The

discovery

understanding

of

crystal

their a p p l i c a t i o n s

X-rays chemistry

of most

developed

in X-ray d i f f r a c t i o n

determined

complex

Some exceeded

compounds.

Majority

mostly

natural

natural

minerals

practical fusibility,

Several

covering

external

e x t e n s i v el y

characters, fracture,

composition,

paragenetic

properties,

However,

most

structural and

an

properties

properties

cases

recent

of minerals

the c o n c l u s i o n s

increase

between

in

were

began during

and properties 269

have

is based

1930's,

to

find

in many

synthetic

earlier

were

X-rays,

based on

the their

properties

of the crystals,

Today the

and it

and

structures

in the m a j o r i t y

out

etc.

chemical

between

[3,4].

like

chemical

properties

on the

correlation

been

and

properties,

geochemical

to s p e c u l a t i o n s

the new p o s s i b i l i t i e s

the structure

physical

in the

structures

of

and classified

and

of

reported

chemical

Although,

nearer

natural

the d i s c o v e r y

some

classification

[1,2].

tendency

number

structures

malleability,

the

total

in

properties

new techniques

both

But even before

studied

trend

find great a p p l i c a t i o n s

ago the

of the inorganic

were

revolutionary

is an i n c r e a s i n g

and they

years

i00,000

minerals.

uses,

There

structures.

three

a

and in turn the m a t e r i a l s

in technology.

discovery

technologies.

generated

of

there

the is

correlation has

been

270

K. Byrappa and D. Yu. Pushcharovsky

well

established

zeolites doubt

at

[5], micas

crystal

engineering,

least

for the most

[6], quartz

chemistry

has

well

[7], diamond played a

known

compounds

[8], garnet

significant

[9],

role

like

etc.

in

the systematic t a i l o r i n g of crystal properties.

No

crystal Recently,

Th. Halin has made an attempt to r e v i e w briefly the i m p o r t a n c e of crystal c h e m i s t r y in m a t e r i a l s the

crystal

growth

science

[10]. Later H.Arend has briefly d i s c u s s e d

and crystal c h e m i s t r y which

he

quotes

m a t e r i a l s research is often based on a "closed loop circuit"

[ii]

that

the

shown below

:

Substance Preparation

iroperties

Crystal irowth

/

T a i l o r i n g of Mapping

of p r o p e r t i e s

However,

there

crystal

chemistry

reason the

is

< ......

no b r e a k t h r o u g h in

Structure the

etermination

correlation

or structure and crystal growth.

is due to the fact that the crystal growth,

Perhaps although

the started

previous century has reached it's climax only during the

period.

Today crystals c o n s t i t u t e the heart of our advanced

Crystals

are being grown e x t e n s i v e l y by various methods,

still

wide gap existing between the crystal

a

crystal structures. technique

nor

literature clearly

support

have

made

an

but

the techniques can produce the on the growth of all the known

this statement.

There is

an

same

having

attempt

to study such

t e c h n o l o g i c a l materials. tetrahedrally

germanates,

there

a

crystal.

synthetic

undoubtful

in war

is and

Here,

correlation

The part I deals

c o o r d i n a t e d anionic

phosphates,

groups

crystals

the authors

between

crystal

The r e v i e w

with

has

significance the

covering

sulphates and related compounds.

The

relationship

divided into two parts based on the crystal chemical the

main

technology.

technology

c h e m i s t r y and crystal growth of some selected compounds. been

post

the

Neither all the crystals can be o b t a i n e d by a single

all

survey

growth

e x i s t i n g between crystal c h e m i s t r y and crystal growth.

of

between

The

compounds silicates, part

II

Silicates, phosphates and their analogues

covers

the o c t a h e d r a l l y

tantalates and

etc.

Here

correlate

coordinated

in part

these

I

studies

compounds

the authors

The f o l l o w i n g

aspects

diversity

of

and the chemical

silicate types and of

silicates

structures,

of t e t r a h e d r a l distinction

crystal anions

physico-chemical

complexes,

of t e c h n o l o g i c a l These

chemical

significance

are

specific

- silicates

the compounds

containing

with oxygen,

which

(table

Bond

and bond angles

Si-O-Si small

to their mean values: = 140 ° . Si atoms groups

coordination

basically

is favoured

i.

silicon

and

crystal

of Si-atoms

by the ratio

silicates

: rO = 0.28 tend =

in

and

ratio

< 0.15 0.15-0.22 0.22-0.41 0.41-0.73 0.73-1.37

be

relatively in

of coordinations of of ionic radii ratio

radii

to

109°.47';

compounds.

Ionic

Their

in a 4-fold

rSi

pressure

Dumb-bells Triangle Tetrahedron Octahedron Cube

upon

oxygen.

of

2 3 4 6 8

crystal

bond Si-O

coordination

Coordination

influence

and their analogues.

in 6-fold

C N

similarity

and

= 1.62 A; angle O-Si-O

The Different types cations as a function

new

significance

light

are found high

of

tetrahedral

in S i - t e t r a h e d r a

in some of the o r g a n o s i l i c a t e

Table

of

chemical

a

is the presence

d(Si-O)

of silicates,

compounds,

and the c h ~ m l c a l

coordination

close

throw

of silicates

feature

lengths

concepts

and their analogues,

structural

i).

crystal

would d e f i n i t e l y

of silicates

main

configuration

chemistry,

of the growth

diversity

Silicates main

studies

on the

related

I: structural

and their analogues, silicate

mainly

and

in part

classification

niobates,

silicates

germanates

bond Si-O,

and synthetic

crystal

materials

growth.

2. S t r u c t u r a l

chemical

conditions

comparative

deal with

have been covered

in silicates

of natural

like titanates,

with phosphates,

compounds.

271

5-fold

272

K. Byrappa and D. Yu. Pushcharovsky

The

structures

tetrahedral

anions

pyrogroups, a nal y s i s

of

rings,

of

different

chains,

considerably

crystalline

materials.

t hei r

spread

wide

silicates

frameworks, scientific

The a t t e n t i o n

abundance

variability

of t e t r a h e d r a l

wide

application

of silicates

widely

being

used

optoelectronic, Table

in

etc.

2. Bulk

ceramic,

If

one

anions, types

such of

content

possible around It have

which

dominate Liebau compares elements.

the the

[15]

is

connected

anions

optical,

(table

in their

with

2.),

structures

technology.

of

the

and

Silicates

electronic,

a are

piezoelectric,

[12]

Total

% % % % %

Total

the most

number

crust

specific

96.5

%

features

of

(Si,O)

in the chain period, in

different

of silicate

or

layers,

tetrahedral

the

it

is

anions

as

[13]. to assume

IVth main most organic

that this

compounds

diversity

of carbon,

group of the p e r i o d i c

abundant

inorganic

chemistry.

the d e f i n i t e

the nature

crust

in c o n t i n e n t a l

can be c o n s i d e r e d

reason with

in the are

to silicates

of t e t r a h e d r a

the total

possible

common

silicon w hic h

as the number

to e s t i m a t e

is

comparative

structures

in modern

64.0 9.0 18.0 4.0 1.5

into account

one hundred

Their on

of silicates

+ Amphiboles

rings

tetrahedron,

ideas

Percentage

takes

(single

contain

industries.

Mineral

Feldspars Pyroxenes Quartz Biotite Olivine

compounds

etc.).

in the c o n t i n e n t a l

exceptional spread

related

configuration

layers,

extends

and

However,

distinctive

of the bonds

formed

of

which

is

table.

compounds, according

features

silicates situated Like carbon

compounds

to Bragg

and carbon

above

silicates,

can be r e v e a l e d

by silicon

should

[14]

and

if

one

with other

Silicates, phosphates and their analogues

i)

Si - atoms

2 s 2 2 p 2.

Thus,

double

(bond

2)

C

higher

Therefore, silicon

become

and o x y g e n

atoms

components

Diversity The

which

are p h o s p h a t e s

with

term

phosphate

be used

P-O

may

linkages

simple

and c o m p l e x

For

free

a

valence

cell

over

[20].

oxides

bonds

(bond the

d-orbitals

and

bonds

A

atoms. between

(Si-O)calc

lines

connecting

coesite,

SIO2)[17]

as

elecrton

density

be

much

atoms

the

(Si-O)ex p = 1.626

can a l s o

are

of the o x y g e n

reinforce

analogues

the

well

silicon as

their

maps

attributed

=

(for

with

-

of s i l i c a t e s

to s i l i c a t e s

350 m i n e r a l s .

to i n c l u d e Similarly

obtained

a t o m of p h o s p h o r u s is w r i t t e n

2p-orbitals

and

[16].

f r o m the

are n e a r e r

sense

contain

to the

of the e m p t y

atoms

[19].

in t h e s t r u c t u r a l

compounds

the e n e r g y

[18].

fig.l.

= 222 KJ/mol)

Silicon

on the d e f o r m a t i o n

bonds

Si

In the

(for example,

in Si-O

Si -

= 452 K J / m o l ) .

components

A l 2 S i O 5)

bonds

-

shorter

Si-O

of the p e a k s

andalusite,

Si-Si

much

C

strong

consequently

symmetry

the

are

while

form very

closer

d - p

and

A. D e v i a t i o n s

example,

Si-O

3s23p2d,

C - atoms

while

C, Si atoms

decreases

additional

nonspherical

2.1.

with

charge

they

oxygen

between

C-C = 346 KJ/mol,

C-O = 358 KJ/mol,

energetically

electrons

= C can be formed,

energies

nuclear

1.760

the v a l e n c e

distances

In c o n t r a s t

energies

and

the

bonds

weaker

have

273

in the c r y s t a l

According

to C o r b r i d g e

all p h o s p h o r u s the a u t h o r

the d i s t r i b u t i o n

compounds

[21]

from phosphoric of

chemical

acid

calls as

the which

all

the

phosphates.

electrons

in

the

to

3p

as follows:

3 s

3 p

St It

means

electrons atom

that

phosphorus

and a n o t h e r

participates

two o w i n g

atom

can

form

the

to 3s e l e c t r o n s .

in the r e a c t i o n

with

oxygen

bonds

Hence,

to e x i s t

due

the in

phosphorus a

trivalent

274

K. Byrappa and D. Yu. Pushcharovsky

f~

sii ~

"

Fourier

maps

forming

As a r e s u l t

: a)andalusite

phosphides

orbits

oxygen,

it l e a d s

However, (

~

develop

bonds),

but

as w e l l .

to t h e

condensation

O-P-

or P - O

the

p orbit

the

plane

bonds. follows: 109.4

angle, along

the

= 1.54

and

P-O-P

large

and

that

length

bond

angle

tends P-O-P

linkage [22].

not

angles

= 156

of

is o b t u s e

to f i n d

are

bond

of

P

ordinary

bonds

-Pmake to

a t o m s to f o r m

A,

are

given

angle

rotation

as

O-P-O =

=

1.64~. the b o n d

flexibility

orientation

of

of p h o s p h a t e s ,

it

and bond to

(

susceptible

(bridging)

chemistry

an a n a l o g u e

PO4].

perpendicular

related

lengths

[

of s u c h b o n d s

= 1.51

the

with

bonds

to i t ' s m e a n v a l u e ,

and

a variety

in t h e

short

in P t e t r a h e d r a

to be c l o s e

similar

group

of b r i d g i n g

of t h e

to 167 ° . P - O

four

be p u r e l y

is a r r a n g e d

(terminal)

phosphates.

phosphorus

tetrahedra

formation

From the crystal

it is d i f f i c u l t

will

d orbits

P-O

allows

the v a r i a t i o n

of

fraction

(which

with

P-O-P

of P)

tetrahedral

the P-O

to t h e

oxygen

and

forming

of the d e v e l o p m e n t

+ 0.02 A,

angle

tetrahedra that

distinct

due

interact

lengths

the b o n d

evident

quite

bond

especially

adjacent is

to

interaction

of a s t a b l e

a

The possibility

POP)

5°

Although,

reactions

the

state

3p o r b i t a l s

a tetrahedron

known

of t h e b r i d g i n g

d(P-O)

+

in s u c h

It is w e l l

(M).

The

(is a n d

and during

it i n c l u d e s

bonds)

coesite,

in a p e n t a v a l e n t

to the formation

the P-O bonds

; b,c)

S i - O - S i = 1 8 0 ° (c). and

of sp 3 h y b r i d i z a t i o n

energy

%

,..

S i - O - S i = 1 8 0 ° (b); state,

--

'....

' .., ...

Fig.l.

-

angles

is

[PO4]-tetrahedra

Silicates, phosphates and their analogues

among

the

crystal

inorganic

chemistry

of

understand

crystal

vanadates,

arsenates,

2.2. C o n d e n s a t i o n Germanates

compounds

[23]. Hence a

silicates

and

boratesa

in

compounds

tetrahedra

ability

etc.)

nearer

significantly

property

of

suitable

value

respect ratio

germanates

and

Si tetrahedra

for

Si

formation of

tetrahedra

(0.38)

the tetrahedral out

of

more

synthetic

cation) than

only

[25], CdS207

canaphite

in

having

and

9

observed

factors: to

(i)

one

(this

radius

ratio

for which

In

the

limit states

this radius

of

the

and

the

capable of forming oxide complexes shown in table

3

form

for different

structures four

cations.

refined

structures

for

viz,

Structurally

pyrophosphate

the (T is

For example, natural

K2S207

[26] and Te(S207) 2 [27], the pyrogroups

recently.

a

the linking of [TO4]-tetrahedra

is different

six hundered

have been established mineral

Besides,

with

(i0

coordination.

(0.41). The possible valent

BeF 4

characteristic

(ii) characteristic

table 3. All these elements

sulphates

nK2S207.V205

This

the when

BO4,

connected

nearer to the upper stability

numbers of basic cations

coordination.

types

but

SO4,

based on two

differ from Ge tetrahedra

coordination

in

[13].

tetrahedral

coordination

tetrahedral

silicates

P:O and Ge:O ratios

can be explained

from phosphorus),

the

rGe4+:rO 2-

given

(VO4, AsO4~

silicates

tetrahedral

are

of

of valence charge of silicon equivalent

silicon

rSi4+:rO 2-

germanates~

when compared with a similar Si:O which is 28 as

phosphates,

separates

to

radicals,

This is probably

lower number of different

respectively) in

ionic radii.

helps

is high for silica tetrahedra

Ge, P and other tetrahedra

having

the

All the three

[SiO 4, GeO 4 and PO4] form condensed

with

like

form the nearest analogues

to undergo polycondensation

compared

turn

of

etc.

owing to the nearer ionic radii and charge values. of

study

complexes

of the tetrahedral

and phosphates

thorough

phosphates

chemistry of analogous sulphates,

275

and [24],

[$207]

a very important phosphate

groups

[P207 ]

formed

by

the

276

K. Byrappa and D. Yu. Pushcharovsky

linking

of

Before

two

the

opinion

tetrahedra

discovery

with

although,

regard

more

vanadates

than

which

oxygen,

contain

Pb2V207

having

teterahedra [29].

In

[As207]

at

of

this

to

the

320

complexes

of

such

have

Table

-

3.

Group

V

VI

to

concept

of

1988,

there

condensed are

and

formed

been

by

Valency

2

3

4

-

+

5

[VO4]so

far i.e.

Coordination

Si

+

-

-

Ge

+

5

6

+

+

+

-

+

--

+

+

+

P

-

+

+

+

-

-

+

V

+

+

+

+

-

-

+

As

-

+

-

+

-

-

+

S

+

-

+

+

-

+

state of the coordination.

-

element

which

structures

structures

with

[30]. big

(Si~O)-complexes with

two

numbers

+

fragments

commensurable

of

arsenates.

+

polyhedral

/Si207/~

with

chervetite;

pyrogroups~

-

cationic

contain

nature.

reported

or

-

the

always

However,

4

(Si,O)-tetrahedral

which

in

3

silicate

the

minerals

6

structures

by

phosphate

been

groups

States

silicate

confirmed

unanimous

linking

has

[28].

an

Valency states and coordination of basic oxide complexes

In

was

was

example,

the

among

recently

coordinations

for

sharing

reported

known

6-fold

radical

+ indicates the valency can form the tetrahedal

3. M a i n

5-

corners

B

IV

reported

V-tetrahedra,

Element

III

4-~

condensed

not

of

was

minerals

[V207]

the

in

absence

condensed

one

contrary,

mineral

form

pyrogroup

with

vertices

phosphate

usually the

the

the

edges

of

anions In

particular

cations on

should

the

cationic

(K,

Na,

basis

be

this Car of

polyhedra.

adjusted principle RE

...),

pyrogroups

Silicates, phosphates and their analogues

Several approach.

quantitative For example,

formula

Ma[T207] b,

subdivided

; b)

T = As,

into two groups:

frontier

actually

there are more than

where

bichromate-like

the

correlations

Be,

between

both groups

Crn Ge,

corresponds

r - radii of t e t r a h e d r a l

cations

[31]

the i n c r e a s i n g

establish

tetrahedral

a quantitative

complexes

4. Crystal chemical There

are

discuss

relationship

general

They

with angle T-O-T

can

be

>

140 °

illustrates

to the equations

r/T/

(T) and n o n t e t r a h e d r a l

between

structures

the

= (M)

allows

configuration

of the n o n - t e t r a h e d r a l

that

of

cations.

classification of silicates and their analogues

several

classification

P~ S, Si.

number of refined

and properties

with a

< 140 ° . The fig.2

- i.i, where

to

this q u a l i t a t i v e

60 c o m p o u n d s

1.5r/M/

Thus,

complete

a) t o r t v e i t i t e - l i k e

with angle T - O - T

277

of

earliest

silicates

some of the recent

attempts

in

the

and their analogues.

approaches

in their

crystal Here,

chemical

the

authors

classification.

4.1. Crystal chemical classification of silicates Belov's groups

concept

[30].

of

there are several

The

feature

of

Liebau

7

common

(Si,O)-tetrahedral

this d i r e c t i o n [34].

[19] p r o p o s e d

criterions

polyhedra

with

branching

of anions

two

which

very

adjacent a

polyhedra

with

7) p e r i o d i c i t y

anions;

structures

approaches

The e a r l i e s t Naray-Szabo

number

(Si,O)-polyhedron anions~

are isolated

their

of chain or ring of

attempts

is

of of

5) dimensionality, (SisO)-anions.

in

oxygen (Si,O)-

connected,

fundamental

anions

the

on the basis

or are in contact

their f un d a m e n t a l

3 or more neighbours,

with

2) number

3)

their

[33] and Bragg

classification

Si-polyhedra,

into two to

is c o n n e c t e d

number of Si,

- (a) u n b r a n c h e d

b) branched

[32],

detailed

given

(SiOn)-polyhedra , which

others,

different

configurations.

; i) c o o r d i n a t i o n

between

2

a

of silicate

of all these

were made by M a c h a t s c h k i

localized

contain

the d i v i s i o n

However,

unde r s t a n d i n g . a nal y s i s

enabled

contain

4)

anions

with

1 or

(SiOn)-

6) multiplicity~

278

K. Byrappa and D. Yu. Pushcharovsky

0.4

V As

VVO~O V

V

oo oo

0.3 ICr

/

5i

o

v

~v/

/

o

o

oo

o oo

o

o

o

o

/ ~ortveitite-like

o0.2

/

bichromate-like

/

W

P

~

V/o

ooo

o o

o

o

! 0.1

/

I 0.5

5

°

I 1.0

0.8

i 1.5 radius

o f M m+

Fig.2. C o r r e l a t i o n between the stability of t o r t v e i t i t e like and b i c h r o m a t e like structures Ma[T207] Kostov of

(1975)

and radii of M- and T - cations [31]

[35] p r o p o s e d his c l a s s i f i c a t i o n partly on the

crystal structure, w h i c h is r e f l e c t e d from the ratio of Si-atoms

nontetrahedral

atoms

as

well

a s s o c i a t i o n of chemical elements Pushcharovsky

(1984)

as from

crystal

morphology,

phosphates

and

[13] c o n s i d e r e d the c o m p o s i t i o n of

germanates.

d i f f e r e n t Si:O ratios phosphates per

Thus,

compositions,

and

tetrahedral silicates,

it was shown that the number

(= 9). The average number

(K) in the anionic complexes

K = 8-(2m/n).

is c o n n e c t e d

subdivision

(table

4). These structures do not obey P a u l i n g ' s

in

Silicates d r a w the a t t e n t i o n of crystal chemists right

systematic

days owing to their abundance,

w i d e l y accepted.

classification

a

Thus there

for silicates,

which

of

special V

rule

from

structural d i v e r s i t y and

a p p l i c a t i o n in various technologies. structural

their

About 20 c o m p o u n d s with d i f f e r e n t types

in the same structure were included

spread

the

Obridg e

with

anions

earliest

of

of

tetrahedral

[36].

the

(= 28) is greater than the c o r r e s p o n d i n g values in

(= i0) and g e r m a n a t e s

tetrahedron

to

in minerals.

a n i o n s / T n O m / as the basic c r i t e r i o n in the c l a s s i f i c a t i o n of

wide

basis

the their

exists has

a

been

Silicates, phosphates and their analogues

279

4.2. Crystal chemical c l a s s i f i c a t i o n of phosphates In

c o n t r a r y to silicates the major structural

like phosphates do not have of

a

wide

variety

susceptibility condensation. anions,

of

of

analogous

a systematic classification. phosphates

is

connected

there

The

formation

with

reaction

p h o s p h o r o - o x y g e n anions to give various

As a result of such reactions among the develops

bridging

oxygen

compounds

degrees

phosphoro-oxygen

bonds

-P-O-P-

forming

p y r o p h o s p h a t e s -[P207 ] initially followed by more complex linear like

[PnO3n+l ], rings like [PnO3n ] (n < 3) and so on. It

difficult

to

complexity recently

classify

in

the

reported

structure

crystallographically to

the

phosphates unlike silicates,

phosphates

internal

nonequivalent

'a'-axis, the other along

tetrahedra.

This

pyrophosphate

compound

is

is

structures.

For has

of

infinite

(PO3)- chains, one running

parallel

'c'-axis, both with a period the

first

example

of

a

of

long

[38,39]. Normally,

-silicates

bear

detailed

here are

orthophosphates

anions

are

chains

of finite length in their structures.

called

observed

cyclophosphates. oxygen

in

whereas

the phosphates

p y r o p h o s p h a t e s followed

the

structures

of

with

by

with

silicates, phosphates

than

silicates

isolated

[P207 ]

sorophosphates

having

If p h o s p h o r o - o x y g e n

phosphates

they

The phosphates made of infinite chains

anions in their structures are called

phosphates

although

The phosphates with isolated p h o s p h o r o - o x y g e n anions are

called

are

At

respective

Since,

represented by a less number of structural classes

and germanates.

a

classification

Just as in

also mostly Greek and Latin prefixes are used.

chain

so far.

while giving nomenclature for phosphates,

n o m e n c l a t u r e of silicates are taken into account.

five

such

present there is no clear cut agreement in their nomenclature, class

a

two

with c r y s t a l l o g r a p h i c a l l y independent chains and

isostructural

high

example,

p e c u l i a r i t y has not been reported in silicates or germanates

its

anions

extremely

because

of(NH4)2Ce(PO3) 5 [37]

of

are of

called

phosphoro-

polyphosphates.

ribbon and layered types of anions are

rings

called

Finally, ribbon

280

K. Byrappa and D. Yu. Pushcharovsky

phosphates of

and p h y l l o p h o s p h a t e s

tetrahedra

in

sorophosphates so on.

infinite called

anionic

has been d i v i d e d

For example,

tetrahedra

the

respectively.

are

phosphates

called

chain

group

each

into tri-,

with

tetra-,

repeating

at e v e r y

4. C o m b i n a t i o n s

of t e t r a h e d r a l

from

pentaphosphates made of

and three

phosphates

fourth

anions

with

tetrahedron

are

triple

tetrahedron

band

ring

9-membered

chain chain

layer

layer

double

classification

of

of the t e t r a h e d r a l

3 indicates

meta

also.

silicates.

term u l t r a p h o s p h a t e s structures.

phyllotypes.

silicates

complexes. Many

It is c o n s i d e r e d

cyclometaphosphates,

their

triple

band

the

ring

band

double

phosphates

structure

triple tetrahedron 4 - m e m b e r e d ring 1 2 - m e m b e r e d ring chain band

3 - membered

composition

same

pyrogroup fivefold tetrahedron 4 - m e m b e r e d ring chain layer

pyrogroup

In

in the

II anion

orthotetrahedron

and

number

starting

Similarly,

I anion

in

class

the

tetrapolyphosphates.

Table

=

upon

a ring type of anions

tricyclophosphates.

structures

Depending

i.e. is used

a

layer

prefix

For example,

authors

use the

The u l t r a p h o s p h a t e s

same term in

naming

include

having

are grouped

silicates

the

of O/Si

with O/P = 3. Besides

for all the c o m p o u n d s

with

indicates the ratio

that m e t a p h o s p h a t e s

phosphates

In c o m p a r i s o n

chain

poly-

and

this,

the

branched

into ribbon

and p h o s p h a t e s

the

bonds types other

Silicates, phosphates and their analogues

analogous and

compounds

sulphates

borates,

vanadates,

arsenates

have not been studied in detail and they do not have

such

structural

less

abundance

diversities.

such as germanates,

281

classification. in

It

nature

This is probably connected

and

is noteworthy

also

lesser

that Belov's

degree

concept,

dominating

role of the cations,

can be used for the

mixed-anion

phosphate

(table 5).

structures

with

of

any their

structural

emphasizing

the

interpretation

of

Table 5. Mixed anions in alkali Ta - phosphates Compound

rM +, A

nM+/nTa(H)

anion I

anion II

CsTa2[P3OI0][PO4]2

1.69

1:2

P3OI0

PO 4

[40]

RbTa2[P5OI6][PO4]2

1.48

2:3

P5016

PO 4

[41]

KTa[PO3]2[P207]

1.33

i;i

PO 3

P207

[42]

chemical

classification

4.3.

Comparative

crystal

Ref

of

tetrahedral

the

substraction

complexes For of

the purpose of comparative

tetrahedral

corners.

or

framework

where

of

their the

orthosilicates,

if

of tetrahedra

classsification

tetrahedra

is absents

is

more

concept of mixed complexes.

was elaborated condensation

chemistry,

is very useful

If the condensation

structures

networks

fragments

crystal

of

by academician tetrahedra

Belov emphasized

absent.

the predominate

within

concept

As

of

the

with Si-tetrahedra

approach

was recently extended to the structures

the mixed

compounds

regard

to

in

which

structural

fragments.

of different

sulphates,

tellurides

Hawthorne's

classification

and so on.

of carbonates

the the

with

The mixed

fig.3 chain

This

chemical

and has been in the recent years used for the classification

carbonates,

of

silicon and oxygen do form

linkings

[43].

The

their

analysis

effective

that cationic polyhedra

bond forces are comparable with bonds between

classes

the

Belov considering

is

share

of

illustrates complexes

282

K. Byrappa and D. Yu. Pushcharovsky

Fig.3. Mixed chain complexes in c a r b o n a t e structures: a) dundesite, P b [ A I ( C O 3 ) ( O H ) 2 ] 2 H 2 0 : b) s a h a m a l i t e , ( R E ) 2 [ M g , F e ) ( C O 3 ) 4 ] : c)artinite, [Mg2(CO3).(OH)2(H20) ] : d) nesquehonite, [Mg(CO3)(H20)2](H20) : e) c h a l c o n a t r o n i t e ,

Na2[Cu(CO3)2(H20)3]

[43].

S t r u c t u r a l c l a s s i f i c a t i o n of sulphates on the basis of this proves

that

comparable

the

variability

of

mixed

complexes

in

concept

sulphates

with the d i v e r s i t y of tetrahedral anions in silicates

is (fig.

4) [44].

5. N e w types of t e t r a h e d r a l anions in s i l i c a t e s and t h e i r a n a l o g u e s The slowed

discovery down,

belonging

to

of new silicate structures

some all

new c o n f i g u r a t i o n s

formed

although~ by

has

silicate

the main s u b d i v i s i o n s were r e p o r t e d

in

actually tetrahedra

the

recent

years. 5.1. I n s u l a r silicates anions The structure of a s h c r o f t i n e K I o N a I 0 ( Y , C a ) 2 4 ( O H ) 4 ( C O 3 ) I 6 ( S i 5 6 O I 4 0 ) I 6 H 2 0 has the biggest insular anion built of 48 Si - t e t r a h e d r a Pyrophosphate mineral

with

groups

linked

(fig.5)

[P207] were d i s c o v e r e d in canaphite,

P - tetrahedra

[28].

It

was

supposed

[45].

the that

only its

Silicates, phosphates and their analogues

(

283

4

> •

b

c

d

•

Fig.4. Mixed insular complexes in sulphate structures: a) starkeyite, MgSO4.4H20 : b) VOSO45H20 : c) astrakhanite, Na2Mg(SO4)24H20 : d) Fe2(SO4)3.9H20 : e) Mause's salts, A5Fe30(SO4)6nH O, where A=Li, Na, K, Rb, Cs, NH4, TI, n=5-10 [44].

Fig.5. The isolated configuration built of 48 Si-tetrahedra in ashcroftine structure. Each vertex corresponds to the centre of Si-tetrahedron.

284

K. Byrappa and D. Yu. Pushcharovsky

formation

is

due

to

the

low

hydolysis

and

thus

do

not

break

such

isolated

5.2.

Tetrahedral There

are

germanate

found

[46].

Unlike

composition

large Table

in

While

of

of

3 4 5 6 8 9 i0 12 18

membered membered membered membered membered membered membered membered membered

-

ring

anions

tetrhedral 6).

The K,Na

tetrahedral

The

double

6 - membered

rings

which

P - O - P.

Today

has

considerably

rings

biggest -

in

prevent the

the

number

of

increased.

18

rings

- membered

which

and were

, were

phosphate rings

and

(fig.

6)

KNa8[Si9OI8(OH)9]I9H2

O

[SiO3] n double

3 - membered rings

silicate,

silicate,

KCa2Be2AI[SiI2030]H20

silicates

Anionic

Type

of

natural

simple

structure

6.

in

bonds

conditions

chains

(table

[ S i 2 0 5 ] n.

group

and

types

1990

the

rare.

milarite

rings

nine

the

tetrahedral

structures

were

rather

linear

temperature

rings

4 - membered first

later

have

the

rings

are

discovered found

in

in

the

quite

[47]. in

silicate,

Silicates

phosphate

Phosphates

+ + + + + + +

Fig.

6.

and

germanate

Germantes

+ + + + + + -

18

- membered

structures

+ + + -

silicate

ring

[46].

a

Silicates, phosphates and their analogues

Nearly (table

15

7).

different

Recently,

tetrahedra

in

types of tetrahedral 1989,

(fig.7)

[48]. Two main parameters

number

of tetrahedra

I/ (A)

chain period

(fig.8).

chain

with

[49], participating

coefficients

in size of the non tetrahedral

16

i)

fs

=

(A), i i - length of the edge

tetrahedra

The stretching

far

KEr[PO3]4-VII

2) stretching factor

of tetrahedral

decrease with the increase of the electronegativity, difference

so

can be used for their description~

li, where I - length of the repeat unit in

spiral

in the synthetic

in their repeat unit;

between bridging oxygens

chains are known

a new type of

in it's period was described

285

cations

Fig.7. Structure of KEr(PO 3)4 -VII containg with 16 tetrahedra in its period [48].

in

chains

the valence or

( table 8,9)

spiral phosphate

the

the

[18,49].

chains

286

K. Byrappa and D. Yu. Pushcharovsky

f

0.9~ 0.8-~

o..O.O o

o.5

-i 2

[p

I

l

I

I

I

I

4

6

8

10

12

14

Fig.8. Values of stretching factors in structures and Phosphates with even periods [49].

of chain silicate~

H Fig.9. a) b) c) d)

Branched chain silicate complexes

16

in structures

astrophyllite, NaK2Mg2(Fe,Mn)5-Ti2[Si4Ol2]O 2 [63], aenigmatite, Na2Fe5Ti[Si6Ol8]O2 [64], surinamite, Mg3Al4Si3BeOl6 [65], saneroite, HNal.15Mn5[(Si5.5V0.5)Ol8]OH [66].

of

Silicates, phosphates and their analogues

T ab l e

7. A n i o n i c

Types

of chain

1 2 3 4 5 6 7 8 9 10 12 14 16 22 24

tetrahedron tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra tetrahedra

T ab l e

chains

in silicate,

phosphate

Silicates

in in in in in in zn in in in in In zn zn zn

period period period period period period period period period period period period period period period

287

and g e r m a n a t e

Phosphates

structures

Germanates

_

_

+

+ + + + +

+ + + +

+ + + +

nu

_

_

+

-

_

-

2r

-

+

-

_

+ nu

-

-

8. Influence of valence and electron a f f i n i t y of cations of [PO 3] - chains in m e t a p h o s p h a t e structures

Compound

Period

Stretching factor

Cation valence

on shape

Electron affinity of cation (KJ/MOL)

Ref.

Rb[P03]

2

0.835

1

213.5

[50]

KIP03]

2

0.934

1

221.9

[51]

4

0.633

1

263.8

[52]

AI[P03] 3

6

0.626

3

1620.4

[53]

Nd[P03] 3

6

0.493

3

1101.2

[54]

Bi[P03] 3

6

0.466

3

1578.5

[55]

Zr[PO3] 4

8

0.708

4

1817.2

[56]

Na[P03]

5.3.

- A

Silicates

The

with

ratio

sili c a t e

Si:O

=

complexes,

"branched"

anions

tetrahedral tetrahedra

branched

chain -

i~3 is also typical

which [19]. or

anions

according

The basis

ring

"branches"

to Liebau,

a

specific

belongs

of these c o m p l e x e s

(figs.9 If

for

and

one marks

10) a

linked

pyrogroup

to

is

so

of

called

formed

with by

group

by

a

additional the

2~

and

288

K. Byrappa and D. Yu. Pushcharovsky

Table

9. Influnce of cation sizes on the shape of [PO3] - chains in m e t a p h o s p h a t e structures

Compound

Period

Stretching Av. valence factor

Difference of Ref. cation sizes,(A)

III-

KNd[P03] 4

4

0.747

2

0.34

[57]

III-

KEr[P03] 4

4

0.739

2

0.46

[58]

CdBa[P03] 4

4

0.733

2

0.52

[59]

CsPr[P03] 4

8

0.466

2

0.64

[60]

VI - CsNd[P03]4

8

0.464

2

0.66

[61]

CsTb[P03] 4

8

0.462

2

0.74

[62]

orthotetrahedron

- by the fig.l,

complex can be represented 1-2-2-,

the surinamite

2-1-1-1-1-2.

then the formula of the

as 2-2-2-,

the aenigmatite

complex as 1-1-1-2-

The branched ring complexes

astrophyllite

complex as

and the saneroite

are shown in fig.

complex

i0.

b

i Fig.10.

Branched ring silicate complexes

in the structures

2-2-1-

of :

a) eakerite, C a 2 S n A I 2 [ S i 6 0 1 8 ] ( O H ) 2 2 H 2 0 [67]; b) tienshanite, K N a 9 C a 2 B a 6 ( M n , F e ) 6 ( T i , N b , T a ) 6 S i 3 6 B I 2 O I 2 3 ( O H ) 2 1 6 8 ] ; c) branched [B4012] complex in the structure of uralborite, Ca2[B404(OH)4] [69].

as

Silicates, phosphates and their analogues

5.4.

Tetrahedral

bands

in

silicate

289

structures

Some silicate structures contain the bands formed by double The

chains.

structural connection between chain and band silicates is given

in

table 10. The d i f f e r e n t bands are shown in fig.ll.

a

e

b

c

d

h

f

7

Fig.ll. Different types of [Si20] 5 - bands in silicate structures a) sillimanite [76], b) v i n o g r a d o v i t e [77], c) epididymite [78], d) c a y s i c h i t e g) f e n a k s i t e

[79], e) tuhualite [83], h) canasite

[81], f) n a r s a r s u k i t e

[84].

[82],

:

290

K. BymppaandD. Yu. Pushcharovs~

Table i0.

Description

Chain silicate

period

CuGeO 3 [68] pyroxene~

3 CaMgSi206

wollastonite,

of different

[69]

(Si,O)

- bands

band silicate

sillimanite,

AI[AISiO5]

[76]

2 vinogra-Ne4(TiO)4[Si206][Si4Ol0]H20 ,dovite 3 epididymite; N a 2 B e 2 S i 6 O I 5 H 2 0 [78]

CaSiO 3 [70]

batl-,Na2Ba(TiO)2Si4012[71] site

4 caysichite, Y4Ca3RE(OH)Si8020(CO3)67H20)[79]

rhodonite,

5

CaMn4Si5015

[72]

inessite,

Ca2Mn7[Si5OI4(OH)2]5H20

s t o k e s i t e , C a S n S i 3 0 9 2 H 2 O [73] 6 tuhualitet 2+ 2+ (Na,K)2Fe 2Fe 2SII2030H20

[77]

[80]

[81]

The contact of two w o l l a s t o n i t e chains via corners of the o r t h o t e t r a h e d r o n leads to the formation of the xonotlite Ca6Si6OI7(OH) 2 band with composition [Si6017 ] [85]. The new types of bands were found Microscopy) pyroxenes, 3-,

in mica

and/or

the gradual

biopyribols~ (biotite)

333 pyroxene transition

which contain the

and amphiboles. chains

to layers

in

sections

elementse

Electron

similar

There are bands formed by

in their structures

which

to 2-,

demonstrate

[86].

There is another group of bands, contain

(through High Resolution

the different

the so called rings.

"tube - like"~

Some of them

are

which

listed

table ii. Table ii. Description

of tube - like bands

Silicate with tube - like bands

projection

of bands

Ref.

stilvellite

Ce[BSiO5]

3 - membered

ring

[87]

narsarsukite

Na2(TiO)(Si4Ol4)

4 - membered

ring

[82]

fenaksite

KNaFe[Si4OI4 ]

6 - membered

ring

[83]

agrellite

NaCa2[Si4OI0]F

6 - membered

ring

[88]

canasite

(K,Na,Ca)II[SiI2030](OH,F) 4

8 - membered

ring

[84]

myserite

KCa5[Si207][Si6OI5] (OH)F

8 - membered

ring

[89]

in

Silicates, phosphates and their analogues

Z-O

!

!

!

!

!

I

291

Y

X

Fig.12.

Fig.13.

a

Io

b

'

Structure of ganophyllite

Structure

of bementite

with double layered sheet

[91].

[90].

a

d

A

~ V V v

AA

d) antygotite,

c) sepyolite,

Mg6Si4OI0(OH)8 •

;

AI2Mg2[Si4OI012(OH)28H20 Mg8[Si401013(O,OH)48H20

b) palygorskite,

Fig.14. Tetrahedral layers Si O in structures of : a) pentagonite, Ca(VO)Si4OI04H20 ;

A A ~

;

o=

=

Q_

W

~o

Silicates, phosphates and their analogues

293

5.5 Layered silicates Eggleton with

a

and Gugenhiem

formula

(fig.12) layers.

[90]. At

membered

6

are

-

in

layers

rings

condensation

of

and

palygorskite

(fig.

5.6.

Framework A

new

grumantite

structure

many

complexes

in s e p y o l i t e

grumantite,

many and

examples and

occurs

(fig.15)

attempts

to f i n d o u t

configuration of

better

the

5

-

the The

layer most

and

there

is

a

formed formed

6

of

the

specific

are oriented For

was

common

contain

t h e m as a r e s u l t

in

example,

by t w o

one in

pyroxene

by t h r e e p y r o x e n e

values

which

sheets

The presence

[13].

decreases of f r a m e w o r k

In p r i n c i p l e

their more

the

the

negative

average reasonable.

of

negative

that

the with

till

1960

between

the

there

are

However, shape

of

charges

(Si,O)Si

-

are not typical

of

characterized (OH)

in

connection

correlation

the f r a m e w o r k s

are mainly

In

found

to m e n t i o n

anions.

between

of

recently

[92].

of s i l i c a t e

correlation

average 12).

was

it is n o t e w o r t h y

- complexes,

formation

of

within

bands

Na[Si204(OH)H20

the

tetrahedra

combination

direction.

framework

(table

tetrahedral

-

chains

- with bands

tetrahedron [T205]

7

However,

with

the

and

are polar

several

in

6 - membered

(fig.13).

the opposite

of t e t r a h e d r a l

of

composition

in

ganophyllite

silicates

type

were

in w h i c h

of

sheet

14).

structure

there

rings

to c o n s i d e r

- like chains.

layered

can be substracted

unusual

7 -membered

s u c h an i n v e r s i o n

- like chains

are

in c l a y m i n e r a l s

silicates

, while

structure

the

Mn7[Si6OI5](OH)8

pyroxene

- like chains

in

5 - membered,

It is p o s s i b l e

several

a new double

These

and

found

[19].

of l a y e r e d

direction

formed.

membered

reported

like fragments

of b a n d s ,

bementite,

tetrahedral

group

The amphibole

rings

revealed

membered

unit-(Si,Al)5Ol2

the contacts

membered,

recently

- groups charges

per

by in

the

simple

"grumantite" and

make

the

294

K. Byrappa and D. Yu. Pushcharovsky

Table 12. Polymorphic (Si,O)-radical formula

Si:O Average ratio negative charge/ Tetrahedron

forms of various Form

of

(SilO)

the

radicals*

tetrahedral

Isolated linear Rings Chains Ribbons groups /bands

Layers

SiO 4

0.25

4

Si207

0.286

3

Si3Ol0

0.3

2.67

Si4013

0.308

2.5

Si5016

0.312

2.4

SiO 3

0.333

2

Si7020

0.35

1.71

Si6017

0.353

1.67

+

+

Si5014

0.357

1.6

+

+

Si4Oll

0.364

1.5

+

Si7019

0.368

1.43

+

Si308

0.375

1.33

+

Si8021

0.381

1.25

+

Si5013

0.385

1.2

+

+

Si12031

0.387

1.17

+

+

Si205

0.4

1

+

+

Si3.5Bel.5Ol0 .

0.417

1

(OH,F) 2 Si7AiOl9

0.421

0.88

Si8019

0.421

0.75

SiI5AIO36(OH)2 0.429

0.67

Si10023

0.435

0.6

Si409

0.444

0.5

0.454

0.97

5.7 °22

Frame -work

+ +

+

+

+

+

0.69

Si307

4.3

+

radical

contd.

+

Silicates, phosphates and their analogues

295

(Si,O)-radical formula

Si:O Average Form of the tetrahedral radical ratio negative charge/ Isolated Tetralinear Rings Chains Ribbons Layers Frame hedron groups /bands -work

Si6.34A13.66022

0.454

0.87

+

Si2(Si,AI)4013

0.462

0.67

+

Si16A12039

0.462

0.44

SiI2AI8OI3(OH) 2 0.488

0.4

Si2AI208

0.5

0.5

SiO 2

0.5

0.0

+

In the lower part of the table given are the tetrahedra which simultaneously exist with (Si:O) radicals like A1 and Be. Other elements which can form isomorphous substitution with Si are Ge, Ps B, Ga and Fe.

o

0 0

~

0

s

b 0 "-'~

7 0

o

o

j

0

o

o o

0 °

o

t

o

o

°

e

0

I

o

~ o

Fig.15.

J

Structure of grumautite

[92].

0

o

296

K. Byrappa and D. Yu. Pushcharovsky

I

700

I o

50~

|

f

'

I

1

300 0.5

I 3

2

I

4

5

P H2 0 (arm) Fig.16. Crystallization ranges of different phases in the system M20-Nd205-P205-H20 under hydrothermal conditions [138].

I I

700

I

£J o

I 500

I 0.5

I I NdP04

NdP 30 9

NdP5 ° 14

1 P

H20

I

i

I

2

3

4

I i 5

(at,.)

Fig.17. Crystallization ranges of different phases in the system M20-Nd203-P205-H20 under hydrothermal conditions [138].

Silicates, phosphates and their analogues

6.

similarity

and d i s t i n c t i o n

297

between natural and

synthetic

silicate

compounds In

the

previous

section the structures

silicates

have been discussed together.

diversity

of mineral

physico-chemical known

(Si,O)

conditions

-

These compounds Their

tetrahedral

energetic (Si,O)

in nature.

configurations which

are

corrugated

is revealed

compositions

such correlations.

accordingly

configuration

these

the of

definite

However,

shape~

-

their many

complexes,

the average anions~

have

The

[T6017 ] and with these

whereas

[P6017 ]4"- and

silicate anions

in

5-

there are

complexes

in silicate

anions::

i)

phosphate values

[Si6014 ]4-

[P4Oll ]2- are also

of

the

the

layered

(table 14).

the tetrahedral

an unusual

complexes

shown in table.13

are

characterized

shape if one takes into account the value of the

charge per tetrahedron.

of [Si308]

[Si205]

all

Si - tetrahedron.

The silicate

configurations.

and [Si40912- , and in phosphate

definite

per

have basically the ribbon configuration,

charges per Si - tetrahedron

negative

ii)

between the shape of (Si,O)

negative

and

the

peculiarities:

two

types of rings etc.,

show layered

Thus

a

have a rather complicted

complexes

of

in

by

of silicate and phosphate anions with composition

[T4OII ] illustrates

in

structures

chains with 22 or 24 tetrahedra

of good correlation

comparison

in

the

synthetic

about 10% of

characterized

the average values of negative charges

shape

shows that

contain the elements which are quite rare in nature.

layers with different

examples

However,

were revealed only

- anions in these structures

period,

by

Their comparison

synthetic

(table 13).

disadvantage

tetrahedra,

same

and

is much more than that of the

configurations

synthetic compounds

and

natural

This is probably due to the existence of wide variations

ones.

fold

structures

of

complexes

complexes. energetic

For example,

and the framework

the layer is is an usual

These configurations

disadvantages,

which

are is

an

unusual

configuration

characterized

connected

average

with

by

a

their

298

K. Byrappa and D. Yu. Pushcharovsky

Table 13.(Si,O)-anions observed in the structures of synthetic compounds (Si,O) anion formula

Shape of (Si,O) - anion

compound

[Si5016]

linear group, built of 5 tetrahedra Na4Sn2(Si5OI6)H20

[SiO 3 ]

chains with the periodicity

22 tetrahedra 24 tetrahedra like

Mg0.8Sc0.1Li0.1(SiO3) Na3Y(Si309)

[95]

Ba3(Si5Ol3)

[96]

[Si5013]

band, built of 5 pyroxene chains

[Si308 ]

layer with 6-and 10- membered rings Na2Cu(Si308) layer with 6-, 8- and 12-membered rings

[Si205 ]

double 3- membered ring

[93] [94]

[97]

K8Yb3(Si6OI6)2(OH)

[98]

Ni(NH2CH2CH2NH2)3(Si6OI5)H20

layer with 4-, 5-, 6- and 8membered rings layerwith 4-, 5- and 12membered rings

NaNd[Si6OI2(OH)2]nH20

[99] [I00]

LiBa9(Si10025)C17CO 3 [i01]

Table.14 Average negative charge per tetrahedron as a controlling parameter in the tetrahedral configuration of anions Compound

Charge per tetrahedron

Form of the tetrahedral anion

Ref.

NaNd[Si6014 ]

0.67

Layer

[102]

Cd2[P6OI7 ]

0.67

Layer

[103]

Ca6[Si6OI7](OH) 2

1.67

Ribbon

[85]

(Xonothite) K2[Si409]

0.5

Layer

[104]

Ca[P4Oll]

0.5

Layer

[105]

Ca(Mg,Fe)2.5[Si4OII](OH)

1.5

Ribbon

[106]

(Actinolite)

complicated

geometry and unusual shape. It is obvious that only on

the

Silicates, phosphates and their analogues

basis

of

both

chemistry.

groups it is p o s s i b l e to

In this connection,

299

understand

silicate

it is a p p r o p r i a t e to quote

crystal

Prewitt:

have often noticed a p r o v i n c i a l i s m among some scientists; who only to

work

on

minerals

compound

has

customer"

[107].

7.

or who are not

important

Influence

of

physical

interested

unless

properties that can

physico-chemical conditions on

a

be

I

want

synthetic sold

to

a

the configuration of

tetrahedral complexes This forms an important part of the present r e v i e w dealing with configuration several

the

of tetrahedral complexes which is d i r e c t l y influenced

physico-chemical

factors.

The most important of

all

is

by the

tendency of P - t e t r a h e d r a not to share their vertices is the reason for a rather in

rare substitution of P for Si which is almost c o m p l e t e l y

mineral

authors

structures with condensed tetrahedral

anions.

absent

Hence,

have selected in this section the study of i s o m o r p h i s m

Si and other elements like P, As and V,

p a r t i c u l a r l y between

the

between Si and P.

7.1. Isomorphism between Si and P in minerals Isomorphism minerals apatite The

with

orthotetrahedra.

For

example,

zircon,

few

natural

pyromorphite,

can a c c o m m o d a t e both Si and P atoms in their tetrahedra

weak

isomorphism

extraordinary phosphates obvious

between Si and P has been fixed only in a

if

between

silicon

and

phosphorus

one considers the similarity

with

equivalent

between

chemical formula table 15

looks

with

insignificant

special

isomorphism

(si,P,As,S,Ge structures

some

etc.) with

Ag 6 [SO4][SiO~]

and

reasons. between

Moreover,

different

there

[109].

is

tetrahedral

in structures with isolated tetrahedra. an

orderly

distribution

(NH~)~H~[AsO~][SO~ ] [ii0].

of

such

quite

silicates

that the absence of such i s o m o r p h i s m between Si and P

connected

[108].

and

It

is

must

be

a

very cations

The

only

cation

are

300

K. Byrappa and D. Yu. Pushcharovsky

The

experiments

isomorphism factors. at

between

temperatures

Lithiophillite

and Munro show that a

Si and P in minerals

Thus for example,

high

LiMgPO 4

of Bradley

in laboratory

(500-900°C)

LiMnPO 4.

is mainly due

conditions

tephroite,

in

nature

crystallization

can

temperatures

be

appropriate

to discuss the role of phosphorus

isomorphism.

There

is a wide diversity

most

rock forming silicate melts

chemical

influence

properties

liquidus

polymerisation

crystallizes

[112-119].

(fosterite,

presence

mineral

silicate

phosphate Si 4+

formulas

the

later stages and

structures

[123-125]

and silicate

and

and

for the anions

other

it

the is

Since, increase

Mg2SiO 4 and

element

[115]

allows

Comparison

and

observed

Usually,

[126-128]

in

of silicate

of anionic

of

P205 the and

species

indicates

oxygen.

in the melt are(PnO3n+l )-n-2 and are capable

its

because

degrees

polymerization

with

in

portion of the systems

anions have very similar structures coordinated

the

protoenstatite,

to the fosterite.

and phosphate melts

that both the cations

to

physical

different

along with description

p5+ are tetrahedrally

indicating

Here

attention

The author

of cation other than Si 4+ [120-122].

phosphate in

of P205 for example,

is a minor

considerable

between minerals with

of Si-tetrahedra

in

lower

< 1 wt% P205 ). Despite

on phase relations

of the melts

boundaries

the addition

solid

containing

[iii].

in

pair

with

of opinion with regard

MgSiO 3) shift rapidly toward the silica-deficient with

the

there is a substantial

(generally

this element has attracted

strong

solved

in silicate melts.

P205 . It is well known that phosphorus

low abundance

that

connected

that

on the role of P205 in silicate melts and P and Si

of

its

for

with olivine bearing rocks

role

of

is typical

of pegmatites,

in comparison

in the data available

it was revealed

the absence of these

phosphates

the earlier works of Bradley and Munro,

weak

geological

be

primarily

(400-600°C)

to

Mn2SiO 4 can

The similar reaction

---> forsterite Mg2SiO 4. Therefore~

solutions

relatively

that

in which both The

general

(SinO3n+l)-2n-2

of forming chain and ring

Silicates, phosphates and their analogues

structures. of

the

The major difference

four

crosslinking The

bonds in a

of phosphate anions

~) indicates

bond

which

in the cationic radii of Si 4+ (0.42 ~) and p5+

for Si 4+ in silicate anions.

chromatograms

as

indicative

The authors

(0.35

containing

16

wt%

glasses and have interpreted

of Si 4+ entering

SiO 2 and

phosphate

0.6 wt% P205 . Notable

are the chain species SiP207,

occurrence

p5+

[130] have added up

furnace

among

Si2POI0 and

the

anions.

[131] have extracted anionic species from blast

extracted

limits

[129].

20 mol% silica to sodium phosphate

authors

double

that these cations may be capable of copolymerization,

substitutes to

between the anionic species is that one

phosphate-oxygen

closeness

301

the

The slags

anions

Si3+nPOl3+2n .

of such species shows that the substitution

of p5+ for

The Si 4+

is very common. Table 15. Structural

similarity between silicates

A.Scheme M3+Si 4+ ..... >

M2+p 5+

Silicates danburite, euclase,

hurlbutite,

herderite,

CaBOHSiO 4

goedkenite,

R2AI(OH)(SiO4) 2

synthetic .

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

(Sr,Ca)2AI(OH)(PO4) 2 Ca5(OH)(PO4) 3

2 whitlockiteCal4Ca4Mg2(PO4)12PO3(OH)

Na5Gd4(SiO4)4(OH) .

nefedovite, .

.

.

.

MnBeFPO 4

CaBeFPO 4

hydroxyapatite,

R3Ca2(OH)(Si04) 3

cerite,Rl4Ca4Mg2(SiO4)12(SiO3)(OH)

.

CaBePO 4

vayrynenite,

AIBeOHSiO 4

tornebohmite, britholite,

Phosphates

CaBSiO 4

datolite,

and phosphates

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Na5Ca4(PO4)4F .

.

.

.

.

.

.

.

.

.

.

B.Scheme M2+Si 4+ ..... > M+P 5+ Silicates merwinite,

Ca2CaMg(SiO4) 2

glaucochroite,

CaMn(SiO4)

Phosphates brianite,

Na2CaMg(P04) 2

natrophilite,

NaMn(PO 4)

2

302

K. Byrappa and D. Yu. Pushcharovsky

Simpson feldspar,

(1977)

NaAI2PSiO 8

structural in

[132] has s y n t h e s i z e d a l u m i n i u m p h o s p h a t e variants of and

KAI2PSiO 8 .

In

minerals~

[P04]

plays

role and always more or less similar to that of Si04,

the a l u m i n i u m bearing phase A1 + P substitutes for 2Si. The

substitution charge

of

aluminium

compensation,

minerals,

(3 + ) and p h o s p h o r u s

but

in v i e w of the

(5 + ) not

network

only

a

while coupled

provides

structure

of

such

m u s t also be i m p o r t a n t in a l l o w i n g p h o s p h o r u s to form 4 single

P-Obridg e bonds. In and of

v i e w of the s i m i l a r i t y b e t w e e n glassy and

p h o s p h a t e structures,

it is i n t e r e s t i n g to compare

P - O - M and Si-O-M bond formation.

crystalline

phosphates

crystalline

are

silicate

the

energies

The e n t h a l p i e s of f o r m a t i o n of

strongly

exothermic

and

the

becomes

more

e x o t h e r m i c as the e l e c t r o n e g a t i v i t y of the metal cation d e c r e a s e s

[133].

C o m p a r i s o n of the e n t h a l p i e s of f o r m a t i o n of c r y s t a l l i n e p h o s p h o r u s with the

analogous

indicates Si-O-M

silicates,

that P - O - M bond f o r m a t i o n is e n e r g i t i c a l l y more

bond

activity

formation.

of

attributed rather

Thus P205 p r o d u c e s a m a r k e d

SiO 2

in

P205

-

SiO 2

to

copolymerization

in

of

p5+

by

complexing

complexes. expands

in

The

with

M n+

the

P205 and

p o l y m e r i z a t i o n caused by P205 in

the g r a n i t i c - f e r r o b a s a l t i c

the f e l d s p a t h i c components,

the is

network,

M O xy

interact stronger

P205 - SiO 2

Si-O-M-O-Si

MxOy-SiO2-P205

liquid solvus by

than

SiO 2

generally

destroying

in

decrease

P205 p o l y m e r i z e s M O xy

cations

etc.

stable

decrease

This

melts p r o d u c i n g M-O-P bonds which are

the c o r r e s p o n d i n g M-o-si bonds.

melts

melts.

than it's action as a n e t w o r k modifier.

strongly than

i.e., o r t h o s i l i c a t e s Vs o r t h o p h o s p h a t e s

further

bond melts

enriching

Si, AI, K, Na in the granite while d e p l e t i n g

the high charge density cations,

Fe, Mg, Mn, Ca, Ti. The e n r i c h m e n t

of

K and Na in the granitic melt is i n d i c a t i v e of the a f f i n i t y for

network

forming

anions.

The

sites compared to the sites a s s o c i a t e d w i t h

phosphate

rare earth elements are also d e p l e t e d in the i m m i s c i b l e

granites

and

in

contrary,

the P205

bearing

granites

P205

causing

free their

Silicates, phosphates and their analogues

distribution

coefficients

to

increase

from

303

approximately

4

(approx). P205 is m o r e soluble in depolymerized silicate melts to polymerized. activity

to

15

relative

Hence, for given fugacities of CO 2, H20t F 2 and Cl 2

of CaO, apatite crystallizes from p o l y m e r i z e d melts

at

and lower

P205 contents than in more d e p o l y m e r i z e d melts. In

general

crystallization aluminium

the of

role

of P205 is

pegmatites.

greatly

noticeable

It controls not only the

during

the

stability

silicate m i n e r a l s but also the d i s t r i b u t i o n of some

of

elements

like AI, Li~ Mn, Be~ Ti,Nb, Tat W, U~ rare earth elements etc [134-137].

7.2. Isomorphism between Si and P in synthetic compounds In works

the

recent years there are innumerable number

dealing

containing

with

the

synthesis

of

various

a wide range of cationic elements

growth techniques.

of

experimental

inorganic

using

phosphates

different

crystal

M a j o r i t y of these works either d i r e c t l y or indierctly

discuss

the role of P205 in the c r y s t a l l i z a t i o n and

polymerization

various

phosphates

author

carried

out a series

in

both

ortho- and condensed.

The

[138]

of experiments under the hydrothermal

the system M 2 0 - N d 2 0 3 - P 2 0 5 - H 2 0

studies

tetraphosphate. to

the

(where M = Li; Na~ K; Rb; Cs, TI;

on

the

In hydrothermal

growth

of

mixed

alkali

Basically~ rare

process is quite important.

influence

At a constant

change. during increase

range In

1-600 atms, the boundaries of phase

this case the changes in phase formation

changes in

transformations

formation take

molar

take place~

fraction

of

water

the

on

the

In

the

do

not

place

in the c o n c e n t r a t i o n of water in the ampoule. the

earth

temperatures

increases with reference to the molar fraction of the water.

pressure

Ca,

system the pressure m e a s u r e d corresponds

pressure of the aqueous solutions and it's

crystallization it

were

has

conditions

Sr, Ba~ Pb, etc.) and arrived at some important conclusions. these

of

following

only

With

an

phase

304

K. ByrappaandD. Yu. Pushcharovs~

MNdP4OI2

..... > NdP309 ..... > NdPO 4

NdP5OI4 ..... > NdP309 ..... > NdPO 4 This

is

Geoscientists

to

explain the p o s s i b l e reasons for the absence of c o n d e n s e d p h o s p h a t e s

in

nature

an

i m p o r t a n t conclusion,

particularly

[138]. The e x p e r i m e n t s carried out under h y d r o t h e r m a l

showed that w h e n PH20 > 6 atmospheres~ or

conditions

c r y s t a l l i z a t i o n of p o l y p h o s p h a t e s

u l t r a p h o s p h a t e s ceases and is r e p l a c e d by c r y s t a l l i z a t i o n of

orthophosphates Similarly, leads

only

i r r e s p e c t i v e of the t e m p e r a t u r e

to d e c o n d e n s a t i o n ,

crystallizationt

[P207 ] ,

of

even an i n c r e a s e in the c o n c e n t r a t i o n of M20 and u l t r a p h o s p h a t e s

state or a complex anionic s t r u c t u r e of

for

[P309 ] ,

and

the

system.

in the

having a

higly

system

condensed

[P5014 ] d i s a p p e a r from the p r o d u c t s

and are r e p l a c e d by p o l y p h o s p h a t e s

[P4012 ]

simple

finally

[PO4]

with

(figs.16

&

radicals

17).

These

e x p e r i m e n t s d e m o n s t r a t e that the structures of c o n d e n s e d p h o s p h a t e s not stable at least not in the p r e s e n c e of water. the

magmatic

always presence

of

formation than

accompanied various which

many

by

a certain amount of water and

types of metals.

of o r t h o p h o s p h a t e s

180

natural by

alkali, can

conditions.

It is well known

or the p o s t - m a g m a t i c p r o c e s s e s of mineral

accompanied

be

a

These are the

connected

with

high f u g a c i t y of water

and

a l k a l i n e earth, d i v a l e n t and considered

However,

with

proceed

conditions

as

the

the

most

the high

d i s c o v e r y of

are

in

the

for

the

[138].

More

pegmatites

are

concentration

trivalent

stable

that

formation

and not c o n d e n s e d p h o s p h a t e s

phosphates

are

etc.

of

cations

phases

under

canaphite

[28],

these it

is

p o s s i b l e to expect in nature atleast p y r o g r o u p of c o n d e n s e d radicals

if

not the u l t r a p h o s p h a t e s or highly c o n d e n s e d radicals. The c o n c l u s i o n s drawn above can be very well of a more recent t e c h n o l o g i c a l m a t e r i a l several

like N A S I C O N crystals.

growth e x p e r i m e n t s d e a l i n g with the

p5+ in the recent years.

Here,

justified in the growth

s u b s t i t u t i o n of

There are Si 4+

the authors c o n s i d e r e d N A S I C O N system

and as

Silicates, phosphates and their analogues

an example to discuss such a substitution. x

< 3) was reported during

NASICON

structure of NASICON [140]. Subsequently,

the

structure of NASICON in great detail understand

introduction production silicate

of

yielded

small

and

which

and p5+ into the system never

phosphate end members.

However,

neutron scattering of these

interesting

various

amounts.

stopped

[141-143];

results

that

all

the

NASICON the

facilitated p5+.

The

in

the

either study

resultant

condensed radicals like P207 ~ P308 e Si308~

The formation of these condensed radicals could

the authors

[21~ 144] have solved the problems

adopting the hydrothermal method.

experiments

of

This is mainly because of the

involving

condensed radicals of solid

state

IRhave

products etco

in

not

be

methods.

flux

by

crystal

do not

P-tetrahedra.

reactions~

of

completely

growth experiments at elevated pressures of P205 and H20 crystallization

pure

compounds

in most of the works using solid state or flux growth

However,

the

studied

resulted are

0 <

reported

authors

stoichiometric compounds. Always they

very

contained

Si 4+

pure

spectroscopy

several

the isomorphous substitution between Si 4+ and of

or

(Nal+xZr2SixP3_x;

1976 [139]. At the same time Hong

the

to

305

permit All

growth

the and

hydrothermal growth have revealed that the NASICON system involving both Si

and

P

cations

(hydrothermal)

insist

synthesis.

high

temperature

< 800°C (flux growth) and 200-300°C is

generally

opined

other metals~ complexes.

than

carried

(solid state reactions)

that the growth

and Si together is always problematic. reaction susceptible

pressure

and

(hydrothermal).

silicate crystals is not problematic.

highly

high

The growth of pure phosphates can be

out at relatively lower temperature < 1000°C

It

and

of

pure

phosphate

But the growth of crystals with Also~

silicon.

and P

it is well known that P

is

Hence;

of

in the

presence

it readily forms complexes much earlier to silicon forming

306

K. Byrappa and D. Yu. Pushcharovsky

7.3. I s o m o r p h i s m b e t w e e n Si and As, V Under the specific conditions, are

the linear anions in some

built

of

chemically

association

of

a triple t e t r a h e d r o n

found

in

tiragalloite,

different

is

possible

to

in medaite,

compare

this

Mn4AI6[(As,V)O4][SiO4]2[Si3OI0](OH)6, composition,

as

ardennite

structure has

was

and

of

a

(fig.17) and

with quite

5-fold

ardennite, a

[Si3010]

similar and

can

be

considered

[145].

accordingly

or f a v o u r a b l e conditions

as

As-

Thus t i r a g a l l a i t e witnesses

for the h y d r o l y s i s

Linear tetrahedral anions in tiragalloite.

As-

anions

in t i r a g a l l o i t e is e m p h a s i z e d by the p o s i t i o n of the (fig.18)

Aswell

natural a r s e n a t e s contain only isolated

formation.

Fig.18.

tetrahedron

HMn6[VSi5016]O3

which

t e t r a h e d r o n e x c e p t i o n a l l y at one side

unfavourable

the

The d i f f i c u l t y in the formation of linear tetrahedral

[AsSi3OI2(OH)]

and

examples

[146]. The h y d r o l y s i s easily breaks the Si-O-As as

P-O-P bonds. Therefore,

tetrahedra.

[145]

but contains isolated triple t e t r a h e d r a

orthoterahedra

For

(Si3010) with As

Mn4[AsSi3OI2(OH)]

t e t r a h e d r a with a V - t e t r a h e d r o n it

tetrahedra.

structures

during

of

the their

Silicates, phosphates and their analogues

307

Conc o Se, atl( *

P Kbar

61.4 55.8 611

-

48.6 37.6

20.5

135

135

140

T - O - T

Fig.19. Decrease in T-O-T with the substitution of Si for Ge [172].

Conc. Ge, at% 100

a

/

|

P Kbars

80,

o

61.4 55.8

60

48.6

0

37.6

40 0

20

0

20.7

_!

J

0 L'j -161

j

I

I -20

I

I

I

I

I -25

I

Fig.20a. Decrease in the filt angles between tetrahedra.

K. Byrappa and D. Yu. Pushcharovsky

308

8. Comparative crystal chemistry of silicates One

of the main m o d e r n

predictions

of structural

crystal

chemical

transformations

problems

is c o n n e c t e d

of e l e v a t e d

with

temperatures

and

pressures. The

diversity

attributed

to

coordination unstable

a

silicates

advantage

of

Si-O can be linked

The

confirmed

With

fixed

d(Si-O)min forsterite The

=

stability

into

of

structures

with

M-cations.

with

under

followed

other

words~

M-cations equal.

by a d e c r e a s e chemical

of

ig

in

on

certain

with

longer and

greater,

more

compact and

and angles

/

the

is in

(Si-O-Si)/2.

= 180 ° , one

get~

structure

(Si-O)avg

properties

with

a high

in the c o o r d i n a t i o n these

easily have

to Brown

shown

of

that

(1978) in

with

of value

oxygen

transform

[19]. in

structures

Si-Obridging

distances

connected

of

structures

(table.16)

distances

According

the

of M - c a t i o n s

[164]

the

deformations

a

becomes

(Si-O-Si)max

depends

more

(1967)

show that

accidental

-

high p r e s s u r e s

Si-octahedra

them

[150].

to a d e c r e a s e

and C r u i c k s h a n k

become more

9 GPa

is

distances

value was o b t a i n e d

The p r e s e n c e

leads

electronegative

Oterminal

This

make

- 1.59 A leads

becomes

not

interatomic

Si--tetrahedra

Consequently~

McDonald

is

~.

electronegativity

of o x y g e n

is

= 3.06 A and /

lower

but also by edges

of S i - a t o m s

1.59 ~

between

M g 2 S i O 4 at P = 14,

nontetrahedral

atoms.

value

value

Si-octahedra

number

The

[147]

There

ig2/d(Si-O)avg./=Igd(Si-Si)

distances

1.59

studies

"critical"

because

been

structures

by Si-octahedra.

the d i s t r i b u t i o n

"critical"

Si-Si

in these

the

5 has

lower depths.

structural

the c o o r d i n a t i o n

[149].

in section

not only by corners,

by the c o r r e l a t i o n

Si-tetrahedra

of

Thus

at the same time

[148].

until

such t r a n s f o r m a t i o n s ,

by faces.

and

(2-3)

High p r e s s u r e

Si-tetrahedra

described

at r e l a t i v e l y

oxygen

of Si-O d i s t a n c e s

in

distances

stable

of

in the mantle.

change

even

(Si,O)-complexes,

numbers

the d e c r e a s e to

of

[165]

and

this

Si-

effect

Si-tetrahedra. the

presence

of

In M

Silicates, phosphates and their analogues

cations

with

structural

high electronegativity

309

is similar to

the

high

pressure

deformations.

Table 16. Correlation initiating [38,13]

the

between electronegativity

transformation

Compound

of

of cations and pressures

siIV-si VI

M-atoms

in

EM

silicate

P GPa

structures

T°C

Ref.

[(C6H402)3Si][C5H5NH] 2

N,C,H 3.0;2.5;2.1

10 -4

[151]

Si(NH4)2[P4OI3]

N,H,P 3.0;2.1;2.1

Ca~[Si(OH)~] [SO~] [COq]x dxI2H20 (TKaumasfte)

C,S,H 2.5;2.44;2.1

10 -3

SiP207

P

2.1

10 -3

800-1000 ° [154]

K2siVIsiIV09

Si~K

1.8;0.8

2-9

900-1200 ° [155]

SiO 2 (Stishovite)

Si

1.8

9

1200-1400 ° [156]

In2SiO 7 (s.t.pyrochlore)

In

1.7

Mg3(AIMg0.5Si0.5)VI[sio4]3

AI,Mg 1.5;1.2

10-4-10 -3

8-12

1300

i0

1.5

12.5

1.5;0.8

14.3

K(AI0.25Si0.75)VIo8

AI,K

MgSiO 3- s.t.ilmenite - s.t. Pervoskite

Mg Mg

1.2 1.2

22 27

NaAISiO 4

Na

0.9

24-30

structure

reformation

transformations polyhedra

emphasizing

under

( p )

z/d ~[166],

atoms.

The

from

O): 1.291

where d-distance of

~ - and

(~), 1.860

of the Mg-octahedra

between

(~) and 1.251

the

cations of

depends

ratios

(~). The significant

during the transformation

in

from t h e ~ -

the

cationic

cation

successively

[163]

structural of

which can be considered

with decreasing

[161] [162]

polyhedral

central

mainly

[160]

1000-1200

The compressibility

Mg2SiO 4 under high pressure ~ - modifications

1200-1400 1500 1830

role of

to

[158]

800-1000 ° [159]

interpretation

Si-tetrahedra

of the M-polyhedra,

For example~ to

high pressure.

behaviour

compressibility

used for the

is inversely proportional

density

[167].

be

the dominating

[157]

9OO

Mn

concept,

[152] [153]

Mn3(MnSi)VI[si04] 3

The

350 °

charge and on

as

Othe

initial

transforms (Mg-O)/(Si-

compressibility to the~ - form

310

K. Byrappa and D. Yu. Pushcharovsky

initiates the u n e x p e c t e d e x p a n s i o n of Mg2SiO 4

=

1.636

noteworthy, some

A,

that

while

in

the Si-tetrahedra;

- Mg2SiO 4

the structural a l t e r a t i o n s

=

d(Si-O)

in ~ -

[168].

It

is

in these compounds

as

in

1.655

A

other silicates result in oxygen atom p a c k i n g o r d e r i n g

(table.17)

[169]. According silicates This

to

can

idea

Ringwood

be studied

[170], high

transformations

on the basis of their

germanate

the

ratio

D e c r e a s e of d i s t o r t i o n ( s ) of c a t i o n i c polyhedra and Siduring ~ - @- f t r a n s f o r m a t i o n s in o l i v i n e - l i k e structures

Polyhedron

Co2SiO 4

Si-tetrahedron Ml-octahedron

13.2 88.7

2.3 18.2

M2-octahedron

50.7

20.0

M3-octahedron

-

10.7

16.6 77.6

3.1 12.3

47.5

19.5 15.3

48.9

11.2

71.6

29.3

19.0

O2-Octahedron

86.5

37.8

13.0

70.4

S = (~/x)2"i04 ~2=~x

distances

rcation/roxygen

0

-

56.7

03-Octahedron

Mg2SiO 4

15.2

Oi-Octahedron

(xj - ~)2/

0-0 in polyhedra.

(n-l)

57.9 , xj and x - the definite

O--octahedra~

unoccupied

should be increased under high pressure.

At

p r e s s u r e rGe 4+ is greater than rSi 4+ for 20 %. Therefore,

the

high

d e f o r m a t i o n s in silicates. pressure

deformations

in

s u b s t i t u t e d by Ge.

As an example~

structural changes in quartz

atmospheric

the structures

it's

structure,

where

the authors [171]

Si-atoms

and

by c a t i o n s .

of g e r m a n a t e s at normal p r e s s u r e reflect m a n y specific features of pressure

of

analogues.

can be u n d e r s t o o d if one takes into account that

Table 17. tetrahedra [169]

average

pressure

with were

high

compare chemical partially

Silicates, phosphates and their analogues

These

crystals

considered the

to

be unique

synthetic

tendencies for

Ge

bear

quartz

in quartz

angles

because;

crystals

with:

between

distortion

distances

tetrahedra

(table.18)

the GeO 2

never e x c e e d e d

i) d e c r e a s e

of i n t e r t e t r a h e d r a l

(Si0.86Ge0.14)O 2

hitherto,

under high p r e s s u r e

are connected

decrease

composition

which

0.13 m o l a r

% . The

of angle T-O-T iii)

iv)

similar

increase

The

parameter

explain with

different

change

stishovite

of Si

of

ii)

of

tilt

tetrahedral

134.2 2.925 3.064 -23.47

why GeO 2 does

GeO 2

130.1 3.024 3.193 -26.55

1.04

and

phenomenon.

- like form GeO 2 -- mineral

10.09

germanates

allows

One of them is

not c r y s t a l l i z e

with

argutite

high

of Si for Ge

142.2 3.304 3.406 -17.41

of silicates

chemical

under

(Si0.86Ge0.14)

5.51

comparison

crystal

Substitution

61.4 Kbar

0.67

the q u e s t i o n

w hil e

I atm.

143.73 3.331 3.411 -16.37

structural

common

[172].

Pressure

/ T-O-T inter-tetrahedral d i s t a n c e s O-O A tilt angle (O-T-O)-angle's dispersion

in

(fig.19)~

Table 18. C o m p a r i s o n of structural p a r a m e t e r s in quartz p r e s s u r e and after with the s u b s t i t u t i o n of Si for Ge

Structural

is

concentration

and with the s u b s t i t u t i o n

0-O~

(fig.20a),

311

to

connected

coesite

structure

is known

even

in

nature. The structural with

significant

smallest

angle

temperature angle factors reinforce

of

sharply

other

decreases.

of O I, which

atoms

the tendencies

= 180 ° .

under

in Si-O-Si

to 180 ° , increases

in other words OiSi

of coesite

dispersion

factor

equal

changes

high p r e s s u r e

angles.

Moreover;

up to about

decrease. and w o u l d

to the d i s p l a c e m e n t

connected

It is n o t e w o r t h y under

participates

are

in

high

bond

30%, w h i l e

Substitution

of

that the

pressure

the

S i - O l -Si the

Ge

temperature

for

lead to the structural of O 1 and the d i s t o r t i o n

with

Si

would

distortions~ in angle

Si-

312

K. Byrappa and D. Yu. Pushcharovsky Conc.Ge,at% I0( -

P Kbars 80-

"o

- 61.4 -- 55.8 - 48.6

60-

O

o

37.6

40

- 20.7

20

|

0 _/! 1 9.

Fig.20b. Increase of tetrahedral d i s t o r t i o n [172].

I

I

l

I

|

2

3

4

5

6

Crystal

chemical

I

I

I

i i0

significance

of

technological

silicates

their

and

analogues The

primary

device

r e q u i r e m e n t for any

potential

material/crystal/mineral

is the u n d e r s t a n d i n g of it's

scientific

the spatial a r r a n g e m e n t of atoms,

types of chemical bonds between them.

structure,

ions and m o l e c u l e s and also

It is the chemical bond more

anything

else

crystal.

A crystal chemical k n o w l e d g e helps in t a i l o r i n g a given

or

a

given

crystal

that d e t e r m i n e s the structure and the

structure that is

structure

properties.

and

Since,

to

optimize

defect s t r u c t u r e with respect

the p r e s e n t r e v i e w is confined to

complexes which are being e x t e n s i v e l y their

applications

ferroelectric, of

others.

structure with have

in

Thus followed

here

the

by phosphates~

compounds.

discussed

covering

all

as

than of

a

phase

classification~ to

the

the

desired

tetrahedral

laser~

superionic,

opto-electronics

initially

borates~

r e f e r e n c e to their properties. been

such

piezoelectric, authors

the

studied and c h a r a c t e r i z e d owing to

technologies

ion-exchanges

properties

chemical

a

foundationt

p a r t i c u l a r l y the c o n s e q u e n c e s of the s u b - m i c r o s c o p i c crystal i.e.

with

discuss

vanadates~

the

tetrahedrally

host

silicate

sulphates

Only some r e p r e s e n t a t i v e the

and a

etc.

compounds coordinated

Silicates, phosphates and their analogues

~

ee

Fig.21.

v~ e ~

(001) projection

g

e

~

of K-Vishnevite

A

e

[173].

Fig.22. Ca-form of Linde A [175].

313

K. Byrappaand D. Yu. Pushcharovsky

314

9.1.

Silicates To

begin

because

with

of their

such a study~

large

scale

it is better

industrial

quartz,

zeolite,

feldspar,

mica

9.1.1.

Framework

silicates

- zeolites

Here

the

authors

particularly

the

have

They are p r o d u c e d

properties

which permit

and

in s e l e c t i v e

characterised volume values

of

df

A12Si5014 [20].

Low d e n s i t y

molecules~ of

change

10H20

A) in zeolite

weakly

All

occupied,

zeolites wat e r

The voids sieves.

For

the weak

waste

remove

straight

in

example

of gasoline.

the natural chains

or b r a n c h e d

which

of

cations

The

SiO 2)

and

water

the p r o j e c t i o n

shown are

-

( 3.5 - 15

in

only

cations the

fig.21 partially

and

anionic

capability to m e n t i o n

of the

Na + as 2Na + can be r e p l a c e d of r a d i o a c t i v e

elements

dK2Na2Ca/AISi5OI2/8H20

permit

V

(NaCa0. 5)

- form

it is p o s s i b l e

Ca- form of Linde A

from

is

between

is the e x t r a c t i o n

structures

are

where

and channels

group

incorporate

by c l i n o p t i l o l i t e

frameworks

faujasite;

determine

For example,

exchanger

in the unit cell.

K-cations

These weak bonds

molecular

cyclic

of

ion

For example,

interaction

that

structural

different

framework.

from c a n c r i n i t e

by zeolites

example,

having

of

with

of their

(high p r e s s u r e

accommodate

all the p o s i t i o n s

in zeolite

voids

quality

connected

Another

small

presence

which

ion exchanger.

from the nuclear

Si)

there are big voids

framework.

by Ca2+(Mg2+).

+

synthetic

sievesl

T- atoms

means

emphasizing

softening

(AI

structures.

df = 1000 nT/V,

in coesite

that

like

120

tetrahedral

Here of

and

because,

Zeolite

(df).

from 12,7

vishnevite

as

minerals

up to 29.3

most

tetrahedral

42

n T - number

structures,

potassium

[173].

cell,

with m i n e r a l s

framework

them to use as m o l e c u l a r

low d e n s i t y

of the unit

the

commercially

shape catalysis.

by

silicates

etc.

having

compounds.

consider

utilization

considered

zeolites

to

them to be used as (fig.22)

gasoline

undesirable

burn with

hydrocarbon

[175]

molecular

with

rather

hydrocarbons

the explosion. molecules

[174].

Thus the

increase

the

Silicates, phosphates and their analogues

Zeolites

p a r t i c i p a t e in many processes

take place at high temperatures.

which

of zeolites is important. Si/AI

ratio

silica

315

(selective shape

Therefore,

the thermal

stability

This stability increases with the increase

(tablel9). Thus the interest in the

zeolites

catalysis)

synthesis of

of

high

-

can be justified.

Table 19. C o m p o s i t i o n and pore parameters of some zeolites

Type

Unit-cell c o m p o s i t i o n

Void Volume (ml/ml)

Linde A

NaI2(AIO2)I2(SiO2)I2

0.47

4.2

700

1.0

Linde X

Na86(AiO2)86(SiO2)106

0.50

7.4

772

1.23

Linde Y

Na56(AIO2)56(SiO2)I36

0.48

7.4

793

2.43

0.28

6.7 X 7.0

Mordenite Na8(AIO2)8(Si02)40

9.2.

Mixed

As

framework

silicates

- superionic

it was m e n t i o n e d earlier,

can

migrate

smaller voids. These and

tetrahedra.

realized

Thermal decomposition (°C)

5.0

silicates

However,

only inside the

Si/Al ratio

i000

the cations can c o m p l e t e l y

low density frameworks of zeolites. cations

Pore diam. (A)

leave

there are structures, where

frameworks~

which

contain

are mainly mixed frameworks built of

The

the

compounds in which the

transfer

of

the

octahedra charges

by the m i g r a t i o n of ions are called ionic conductors.

is

Several

fast ionic conductors are being reported in the literature time to

time

from

400-

the silicates family

700°C, P = 1-3 Kbars) 20

gives

a

literature. (Li4SiO4) that

the

list It

of

[176-180]. Hydrothermal

superionic silicates

[210-213].

For examples

reported

so

lithium

the authors

far

materials

range 300-400~C

in

in

Table the

[213] have shown

e s p e c i a l l y at lower

become very good ionic conductors [214].

=

orthosilicate

r e p l a c e m e n t of SiO 4 tetrahedral groups by PO 4, SO4~

groups can increase the conductivity; These

(T

is the most popular for fast ionic silicates.

all began with the d i s c o v e r y of

structure

synthesis

the

or

AIO 4

temperatures. temperature

316

K ByrappaandD Yu Pus~harovs~

Superionic

Na + silicates

became popular

Na5RESi4OI2

[RE = La - Lu, Sc~Y]

from

different

three

Na5FeSi4Ol2 their

was

[216]. Hydrothermal bearing the

reported

by

silicates

laboratories

of

is

by Bowen;

Schairer

of

isotypic

time to time.

The crystal

et al [217]

characterized

and

system

structure of Structure

by SiO 4 tetrahedra

[217]

could locate only 48/90 of the Na + atoms might be

measurements cal/mol earth

good Na +

showed

(200°C)

for Na5YSi4OI2. silicates

solid-state

ion

Further

prepared

reactions

conductor.

of

linked to

to the basal plane of the hexagonal

a

cell.

Subsequently

= 4 X 10 -2 (ohm.cm) "~I and investigations

by Maksimov

Willems

in 1930

Zn. AI~ etc,

rare

was earth

form

Si12036

The

authors

mobile

making

conductivity Ea

=

7.1

showed that the Na

hydrothermally

in

Na5RESi4OI2

parallel

compound

fact~

etc. has been reported

rings

this

In

during

In~ Mg~ Mo, Be~

(fig.23).

of

simultaneously

[178,200~205,215-217].

Na5ScSi4Ol2,Na5ErSi4Ol2,

Maksimov

almost

the Na20 - Fe203 - SiO 2

synthesis

Na5YSi4OI2,

literature

ring silicates,

first discovered

investigation

only after the discovery

could be

and that compounds with rare earth

rare

made

ions

K

by

having

even larger ionic radii than that of Y could be prepared. Table 20. Compound

NaAISiO 4 Nal.5AII.5Si0.504

List of Na + fast ionic conducting Reference

[181~182--184] [182]

silicates

Compound

Na4Zr2Si3Ol2 Na4Mg2Si3Ol0

Ref.

[179~197] [185~188~198]

Na2MgSiO 4

[185-189]

Na4ZrSi3Ol0

[199]

Na2ZnSiO 4

[190-192]

Na~MSi.O~_ [M D= F ~ , ~ , I n ~ M o ]

[199~201]

Na2ZnSi206

[190-192]

Na2BeSi206

[193-195]

Na_RESi_O~ [R[=Sm ff--~£u,Sc~Y]

[200-203, 178-180~ 204-208]

Na2BeSiO 5

[193-196] Na3YSi309

[207,209]

Silicates, phosphates and their analogues

317

o

Fig.23.

Structure of Na5RESi4012

The

other important silicate structure suitable for the fast

conductors

is

(structure

type

distorted not

[217].

the carnegieite structure. of Ca-ferrite;

hexagonal bottlenecks

stable at room temperature.

carnegieite

have

been

The

carnegieite

CaFe204) forms network [218]. Unfortunately; Hence;

prepared

ionic

(NaAiSiO 4 )

structure

with

the structure

is

several structural analogues

of

with

lots

of

other

divalent

and

t r i v a l e n t metals showing high ionic conductivity. Much work has been done on the NASICON family of silicates. is

a solid solution within the system NaZr2P3012

Only

a

few

conductivity. conductivity

members For

of

this

example,

system

show

Na4Zr2Si3012

- Na4Zr2Si3Ol2

considerable shows

high

moderate

In

chemical

consists

of

ionic

reactions

to

[214]. Itms physical

ZrO 2 ~ SiO 2

properties

The interest was rekindled only after the d i s c o v e r y of

contrary

ionic

which was first synthesized during

the 19th century and was later obtained in the system Na20

known.

[142].

of the order of 10 -4 S-%m -I [177]. A closer similarity

NASICON was e s t a b l i s h e d in Na2ZrSi05;

through

NASICON

to the structure of NASICON;

the

structure

ZrO6 o c t a h e d r a which are highly d i s t o r t e d by

of

were

not

NASICON. Na2zrSiO 5

sharing

the

K. Byrappa and D. Yu. Pushcharovsky

318

vertices linked and

and

by silica

the

High

forming

silicates~

(fig.24) rare

framework;

[Si308]

This

allowed

built

0.46A.

are

in

ionic in

6-,

chains

conduction

[219].

Ho.

of

family

of

A n e w type

of

these

structures rings.

coordination.

inside

and octahedra.

Thus

in

K-position

found

close to K 3

the o c c u p a t i o n

factor

The

Structural

distribution

was

are

such

8- and 12- m e m b e r e d

to find out the c a t i o n i c

Correspondingly,

chains

structural

feature

octahedral

additional

three

RE = Yb~ Gd~

is the p e c u l i a r

of t e t r a h e d r a

conductivity

distance

also r e p o r t e d where

These

atom links

to g e n e r a t e

layer c o n t a i n s

cations

determination

was

to the b-axis.

silicon

[Si6016] 2 (OH)t

layer

[220].

Each

the voids

mobility

earth

highest

fill

K8RE 3.

tetrahedral

parallel

tetrahedra.

Na + atoms

cationic

chains

the

Ho-phase

of K 3

with at

a

decreases

from 1 to 0.39. 9.3. M i x e d Like exhibit These

framework

mixed

phosphates

conductors

have

been reported. all

conductivity <

x

single

of

structures

these

structure

conductivity

poses

a

its s t r u c t u r e

etc.

substitutions

ionic

in the f r a m e w o r k ionic

in the N A S I C O N

derivatives types

viz.

is given

of

to

NASICON

in

of

Materials mechanism

of

analogues in

table

high

ionic

Na + ~ -alumina Scientists

due to the lack

composition.

investigated The basic

Na3Sc2P3012.

and anti N A S I C O N

A lot

(Nal+xZr2SixP3_xOl2;O

to that

the

[221].

that of

3-dimensional

-NASICON

tetrahedra.

conductors.

phosphates

have been

system

remains

ionic

also

in phosphates.

NASICON

and c o n d u c t i o n

non-stoichiometry

and

and

is equal

challenge

Many v a r i a t i o n s

phosphates

conductivity

to both N A S I C O N

discovery

crystals;

deficiency,

of fast

the

NASICON

understanding

with

such as

built of o c t a h e d r a

group

belonging

phosphates

analogues

to the ionic

A list of fast

began

< 3) w h e r e

[139].

structures

form a m a j o r

ionic

It

- superionic

structural

can c o n t r i b u t e

fast

21.

it's

framework

structures

Today~

phosphates

silicates~

by

appropriate

NASICON The

of

Zirconium

structure

[140~222].

in

of has

most two

structure

Silicates, phosphates and their analogues

of NASICON is highly complicated; There

are

difficult assuming

nearly to

because of it's solid solution nature.

hundred atoms per unit cell which

describe. However;

simplification

makes

can

be

(1976)

C2/c

structure

by

glaserite

super structure [223] (fig.25).

studied the structure of

NASICON~

in the region of x = 1.8-2.2 value [140].

Nal+xZr2SixP3_xOl2

The

Space group

first

crystal

of NASICON type material was performed in 1968 by Hayman

Kierkegaard~ Zr)

rather

introduced

solid solution series and reported a monoclinic deformation. is

it

that this type of structure is derived from that of

K3Na(SO4) 2 - a rhombohedral Hong

319

who studied the structure of NaM2(PO4) 3 (where M=Ge;Ti

and found them to be isomorphous

[224]. NASICON structure has

and and been

further studied by Sizova et al [198]. Table 21. List of Na + fast ionic conducting phosphates Compound

Ref.

Compound

Na3MZr(PO4) 3

[224]

NaCd4(PO4) 3

[255.260]

NaMg4(PO4) 3

[261--263]

[M = Mn,Mg,Zn]

Ref.

NaM(PO4) 3

[228]

NaPb4(PO4) 3

[264]

Na3M2(P04) 3

[225-233]

Na4TiP209

[265]

Na3PO4

[234-~236]

Na6CaP209

[265]

Na3Zr2Si2POl2

[140,143~139; NaCoP207 237-249] NaCaMn2(P207) 2 [143,250] [M = Yb;In;Cr] [251] Na2(R~M3+)M4+(PO4) 3

Na3ScZrSiP2Ol2 Na3.2Hf2Si2.2P0.8012 Na7(MP207)4PO 4

[252]

[R=Rare earths~

Na4Ni7(PO4) 6

[253]

NaFeP207

[254]

M 3+= Co~Cr;Fe;Ga

NaZr2(PO4)P 3

[223,224~ 238~255]

M 4+= Zr~Ti ]

Na5Zr(PO4) 3

[256]

NaTi2(PO4) 3

[224,238~ 257~258]

Na2M2+Zr(P207) 2

[266] [266]

[144,221. 267-269]

[270~271]

[M= Ni~Co~Mn,Zn~Cd] (Na2/3Zrl/3)2P207

[272]

320

K. Byrappa and D. Yu. Pushcharovsky c s~e B

Fig.24. Structure of K8Yb3[Si6OI6]2(OH)

Fig.25. Structure of glaserite [223].

[220].

Silic~es, pho~h~esandtheiranalogues

Tranqui

et

al

[177]

nonstoichiometry A.Clearfield al

reported

multiple

in NASICON compound,

5 different

sites

Boilot

[257]~ Delbecq et al [233]e

[229] reported

Na +

321

leading

et al [142],

to

Baur

the

[238].

Susman et al [273]~ Collin

lattice sites for Na+; out of which

et only

the Na + is mobile. Stoichiometry,

structure

several

and

studied

by

NASICON

is highly complicated;

authors time to

to develop new superionic are

time.

Materials

conductors

of

a three dimensional

analogues

like

with

C=Ln

NASICON

Since;

the

Scientists

are

structure

continue to

Structure of

framework.

these

A series

(A=Li~Na,Ag,K~

and Bi)

relatively

[275]

simple

M=Cr,Fe)

(M=Sc,Cr,Fe)

structures.

contain only the ortho-group them. Recently,

first

time

The

method

of

new

Na2M2+Zr(P207)2,

[276], were

symmetric.

shares two opposite

groups Na +

of radicals

(A=K~Rb,Cs

synthesized

A

M 2+

=

Ni;

Co,

conductivity

did

variety for

the

grown

Mn;

conductors

Zn;

by

The metal octahedron

(AI~ Zr, anions.

share an

edge

considered.

are comparable conductors.

numbers

are

(Na2/3Zrl/3)2P207;

of these pyrophosphates

and other metals

distances

superionic

compounds

has reported

superionic

edges with two diphosphate

Zr

distances

only

composition

of a wide

are

Nit

highly

Co~Mn~Zn)

The distorted 06 forming

which are linked together by the two pyrophosphate

interatomic

sodium

these

irrespective

ions lie in cavities with coordination

2.564

all

showing high ionic

etc. The structures

about

However,

pyrophosphate

where

Na2AIH3(P207) 2

octahedra

NASICON

[268-270].

important

pseudo-centro

strive

phosphates

[274]i ABC(PO4) 3

the group of Mysore University

pyrophosphates

hydrothermal

of

Phosphates

an intention to develop compounds with stoichiometric

and

being

Na3M2+(PO4)3, (M=Sr~Mg,Fe,Mn) [225]~ Na2(R,M3+)M4+(PO4)3

[2681, A3M3+(P04)3~ B=Ca,Sr,

of

with simple structures.

found to be the most suitable ones.

consists

of

conductivity

isolated

anions.

that depend

on

The the

Average Na(1)-O = 2.628A and Na(2)-O = to the values

A conduction model

encountered for the

in

other

pyrophosphate

322

K. Byrappa and D. Yu. Pushcharovsky

s u p e r i o n i c conductors has been p r o p o s e d based on a systematic crystal

structure,

conductivity

i s o m o r p h i s m between various elements and

values.

Followed

by these

reports

c o n s i s t i n g of c o n d e n s e d p h o s p h a t e anionic group; have been r e p o r t e d in the l i t e r a t u r e

two

PO4r Ge04,

possible content

the

more

[265]. complexes~

cations.

The compounds with

a

the

general

where M = Fe, Set Ins can be used as an

this conclusion. transport.

such as

SO 4 and MoO 4 shows that the highest ionic t r a n s p o r t

alkaline

Li3M2[P0413,

ionic

compounds

m a i n l y in structures with o r t h o - t e t r a h e d r a and with of

of

N a 4 T i P 2 0 9 and Na6CaP209

The r e v i e w of solid e l e c t r o l y t e s with tetrahedral SiO4n

study

is high

formulae

illustration

for

They are c h a r a c t e r i z e d by an i n t e r e s t i n g model of ionic

Their

structures also contain the mixed

networks.

At

the

t e m p e r a t u r e 518K there is a m o n o c l i n i c - o r t h o r h o m b i c phase t r a n s f o r m a t i o n and

the compounds become superionic conductors.

a c c o m p a n i e d by r e a r r a n g e m e n t of Li-atoms, structure at 293°K, Pcah)

[274].

anisotropy situated

group.

which is shown

of

conductivityt

along

because the c o m p l e t e l y

the

occupy

the p o s i t i o n Lils

(a.

significant positions~

As a

(fig

is

space group

filled

a-axis hinders the cationic transport. Li3-atoms

in fig.26

b. structure at 573°K,

The r e a r r a n g e m e n t of Li-atoms leads to

rearrangement belong

space group P21/n;

This t r a n s f o r m a t i o n

result

26b),

to one point system with Li I in the frame of o r t h o r h o m b i c The p e n e t r a t i o n of this atom through the triangle face,

of

which space

common to

t e t r a h e d r o n and trigonal b y p y r a m i d looks enigmatic. Here

it

is a p p r o p r i a t e to m e n t i o n the comments

metallographer

This was taken as a criticism.

d i f f r a c t i o n people took it as a compliment; only

significant

one

classical

: "The trouble with X-ray methods is that they raise more

problems than they solve".

given

of

for

a good question°

p o s i t i o n s hinder the cationic transport.

X-ray

because a good answer may be

It is of interest

a n i s o t r o p y of conductivity~

But the

because the

that

there

completely

is

a

filled

Silicates, phosphates and their analogues

Fig.26a.

Mixed network

structure

323

of Li3M2[P04] 3 [274].

O~o, .

0

1

15

03

Fig.26b.

Rearrangement

of Li atoms

J06

[275].

324

K. Byrappa and D. Yu. Pushcharovsky

9.4.

Tetrahedrally

The

coordinated

in s o l i d s t a t e lasers

m a t e r i a l s w h i c h carry a great t e c h n o l o g i c a l

lasers and luminophors. with

complexes

i m p o r t a n c e are

the

Their specific p r o p e r t i e s are d i r e c t l y c o n n e c t e d

the so called active ions usually situated in isolated

polyhedra.

During 1970s the p o s s i b i l i t i e s of d e v e l o p i n g m i n i a t u r e laser m a t e r i a l crystals c o n t a i n i n g a high c o n c e n t r a t i o n of Nd ions was proved 281].

Today there are over 20 such

different

from

other

Nd:La2S 3,

CaF2:Nd,

Nd

in

[282].

The

compounds

LaCl3:Pr,

c o n c e n t r a t i o n quenching.

suitable Nd (like

CaWO4:Nd3+~

compounds,

YAG:Nd;

[220,277which

These compounds have been d i s c u s s e d in quenching

weak i n t e r a c t i o n of the Nd ions

rare

[283,284].

is

The compounds wherein

earth ions go in the form of islands and their p o l y h e d r a

interconnected

with each other in the structure are called

are

term nezoites more c o r r e c t l y reflects their crystal c h e m i s t r y the

structure

distinguish

a

of any Nd compound for lasers,

nezoite

complex made up of isolated

ligands often having tetrahedral feature along

of

ions

(fig.27)

Nd

exist in a state of inter-isolation.

throws

a

the not

the

[282]. can

easily

polyhedra

polyhedra

by

so that Nd p o l y h e d r a in the structure of

always

to

and

[282]. The c h a r a c t e r i s t i c

such a complex is the bonding of Nd

its long axis,

one

the

"nezoites"

For the compounds having an a n a m o l o u s l y low c o n c e n t r a t i o n quenching,

In

low

detail

result of the i s o l a t e d Nd p o l y h e d r a in the crystal structure leading a

are

LaMgAIIIOI9:Nd,

etc.) with an a n a m o l o u s l y

reason for such a low c o n c e n t r a t i o n

in

This p r o p e r t y

light upon the t e c h n o l o g y of o b t a i n i n g them in

of the

ligands nezoites nezoites form

of

monocrystals. 9.5. C r y s t a l The

chemical

significance

of b o r a t e s

- optoelectronic

other recent crystals with great t e c h n o l o g i c a l

optoelectronics reference structural

are borates,

which have been studied

to their crystal chemistry. types,

applications extensively

Borate anions exist

since the boron atom is capable of

materials

in

in with

numerous

coordination

in

Silicates, phosphates and their analogues

325

r04]

Fig.27.

either

trigonal

that the rather

Structure

or tetrahedral

of

shorter wavelengths

of

new UV nonlinear UV

spectral

structures in

the

basic

regions.

a)

(BO3)3-,

f)

(B307)5-,

b) g)

(B04)5~ ~ c) (B308)7-,

units.

The

the transmission

for use in the

there

are

groups

However~

pointing

d)

(B309)9-,

calculations

of UV radiation and

development

of

interest e)

i) (B5010)5-,

(SHG)

[285,

and

different

structural

there are only a few

are shown in fig.28. generation

of the B and

hundreds

(B207)8-T.

out

intermediate

as basic

of practical

(B205)4-, h)

It is worth

in the identification

Todays

units of borates

the second harmonic

structural

favours

borate anionic

All these configurations studied

[i~285].

materials

known borate crystals.

[282].

in the electronegativities

and helps

optical

with various

structural

mode

large difference

0 atoms on a B-O bond certainly

far

of nezoite

units

types

of

286]~

(B306)3-, j) (B409)6-

The authors

coefficients

[286] have

for all

of these coefficients

these

have led

to

326

K. Byrappa and D. Yu. Pushcharovsky

understand guide

structural

in the

optical

regularities

identification

crystals

of b o r a t e

in b o r a t e s

and d e v e l o p m e n t

which

serve

as

of n e w u l t r a v i o l e t

a

useful

nonlinear

series.

a

b

c

d Fig.28. B a s i c s t r u c t u r a l u n i t s of b o r a t e s [286].

e

f

% g

h

j The

authors

possessing

a

structural

unit

provided

that

[286]

6 - ring capable

the b o r a t e

observed

that

conjugated

the

- orbital

of e x h i b i t i n g crystal

planar

is not

large

(B306)3-

system

nonlinear

can

anionic be

an

optical

centrosymmetrical

on the

group ideal

effects~ whole.

Silicates, phosphates and their analogues The as

n o n - c e n t r o s y m m e t r i c barium borate

327

( ~ - phase) has been w i d e l y

a UVNLO crystal for NLO devices like harmonic generators

[287] and dye lasers even for tunable trigonally

[288], optical p a r a m e t e r oscillators

SHG

barium

c o o r d i n a t e d B atoms in the planar

[289-291]

and three

(B306)3- anionic group the Z-components

c o e f f i c i e n t s will be enhanced to an higher borates.

Nd:YAG

VUV/XUV radiation devices [292]. When one of the

LiB305 is changed over to tetrahedral coordination, the

of

used

order than

in of

in ~ -

LiB305 crystallizes in the space group Pna 21

and

is

D_

up

made

of

(running by

a continuous network of

parallel to the

sharing O atoms

all

these

endless

(B305)

Z- axis) formed from (B307)

[293]. The authors

spiral 5-

chains

anionic

[286] have been able

groups

to

SHG coefficients for LiB305. Their work concludes

measure that

the

anionic group model is indeed a sufficiently good w o r k i n g model for

the

identification

and

d e v e l o p m e n t of new n o n l i n e a r optical

materials

borate crystals as well as in crystals of other structure

types.

A m o n g crystals~ which are of interest for q u a n t u m electronics; is

a

special

group of ferroelectrics,

which

produce

in

the

so

there called

harmonic waves with frequencies two or three times greater in comparison with

the

incident beam. The recent developments in

connected

of

laser

ferroelectrics displacement. influence an

(220)

LiNbO 3 However,

beam and in

[294].

Thus

it

KDP there is LiNbO 3 the

was

not

shown

any

ins

structural

changes

d i s o r i e n t a t i o n of crystalline blocks

KDP crystals an additional

reflections.

peak

that

in

significant

of laser beam are connected with an increase angular

Whereas

studies

is

with the structural i n v e s t i g a t i o n of crystals which are under

exposition

i.e

their

of

the

atomic

under

the

extinction~

(5.1"

is fixed

in

8.6"). section

This fact can be considered as an indication of

the

r e c o n s t r u c t i o n in their domain structure. Thus, properties

the like

tetrahedral superionic,

complexes show laser,

very

interesting

optoelectronic,

etc.

A

physical systematic

328

K. Byrappa and D. Yu. Pushcharovsky

study

of their

obtain

crystal

the d e s i r e d

chemistry

physical

helps

liquid

or

solid

scheme

growth

much

as

science since

the

of

difficult

present

of the crystal

field

growth

form

crystal

on

has

various this the

of silicates

homogenous

and

All

the

to

the

according

growth

covering

is

a

solid or

arrangement.

to discuss

review

involving

classified

subject,

an i n t e r d i s c i p l i n a r y

scope

to

developed

branches

as a w h o l e crystal

of

here,

chemical

it's analogues.

Crystal growth of silicates

The

artificial

growth

[295,296].

Till

1940s

understand

the

mineral

diopside,

feldspar

importance phases

of

growers alkali

on rare

silicates

was

carried

work

and germanates.

as

especially

discuss

the crystal

germanates

followed

quartz

required studies

phosphates. chemical

was

Thus

time.

by p h o s p h a t e s

by

metal This

these

for

the extended

in the present

mica,

Several and

new

70s

silicates

further

works

an

crystal

silicates,

like etc.,

led to

an

revealed

the

crystallization

of

to other review

of the growth

and borates.

to

technological

Soviet

of complex

was

augite,

1960s

the

century

growth

the

During

All

were

importance

19th

revealed.

technology.

on germanates.

Such

1940s

transitional

in

the

hornblende,

out e s p e c i a l l y

alkali

conditions

silicates well,

during

at this

during

of the silicate

and c h a r a c t e r i z a t i o n

applications

research

physico-chemical

only

especially

silicates,

find enormous

extensive

But

began

of quartz,

discovered

the growth earth

objective

genesis

etc.

research

of silicates

the main

of silica were

extensive

whic h

22. The

to

atomic

can be b r o a d l y

and it is e x t r e m e l y

significance

i0.I.

in table

process

or t o g e t h e r

a 3-dimensional

processes

presented

chemical

individually

having

structures

tetrahedral complexes

is a h e t e r o g e n o u s

gas w h e t h e r

substance

crystal

so

growth

their

properties.

i0. Crystal growth of compounds with Crystal

in t a i l o r i n g

Since,

compounds

the

authors

of silicates the

number

and of

Silicates, phosphates and their analogues

Table

i. S o l i d

22.

- Solid

Classification

Solid

of c r y s t a l

T .... >

Solid

329

growth

processes

Devitrification Strain annealing Polymorphic phase change Precipitation from solid Solution

2. L i q u i d - S o l i d Molten

(i) M e l t G r o w t h

Material

dec.T .... >

Crystal

Bridgman-Stockbarger Kyropoulos Czochralski Zoning Verneuil

(ii) (iii)

Flux Growth Solution

Solid(s)

+ Flux Agent(s)

Growth Solid(s)

+ Solvent

dec.T ..... > Crystal(s)

low T ..... > Crystal(s)

Evaporation Slow cooling

Boiling solutions

(iv)

Hydrothermal

Growth Solid(s)

high T ...... > Crystal(s) high P

+ Solvents

Hydrothermal sintering Hydrothermal reactions Normal temperature gradient Reversed temperature gradient

(v)

Gel growth Solution + Gel medium

low T ..... > Crystal

Reaction Complex decomplex Chemical reduction

Solubility reduction Counter - flow diffusion Solution

...... > Crystal(s)+products

3. Gas ......... > S o l i d Vapour(s) ....... > Solid

the processes given processes u~ed in the analogues.

in b o l d growth

Sublimationcondensation Sputtering Epitaxial proocesses I o n - implantation letters indicate the crystal growth of silicates, phosphates and their