19F NMR comparative investigation of some ZrF4-based fluoride glasses and some crystalline phases in the BaF2ZrF4 system

Pergamon

Solid State Communications, Vol. 89, No. 12, pp. 983-988, 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-1098/94 $6.00+.00 0038-1098(94)E0078-P

19F NMR COMPARATIVE GLASSES

INVESTIGATION

AND SOME CRYSTALLINE

J.SENEGAS,

J.M.BOBE

Laboratoire 351 cours

OF SOME

PHASES

ZrF4-BASED

FLUORIDE

IN T H E B a F 2 - Z r F 4 S Y S T E M .

and J.M.REAU.

de Chimie

du Solide

de la Liberation,

du CNRS,

F-33405

Universit~

Talence

de Bordeaux

I,

Cedex,France.

(Received 1 December 1993, in revisedform 8 January 1994 by P. Burlet) The

19F NMR comparative

ZrF4-based belonging

fluoride

study

glasses

of some

to the BaF2-ZrF 4 system

of low-temperature B-EaZr2Fl0.

This

spectra

model

proposed

nate glass

on the basis

with

the validity

free phases

the large

glasses

confirms

for

metal

crystalline

has shown

of fluoride

investigation

structural

alkali

and selected

analogy

t h a t of of the

t h e B a F 2 : 2 ZrF 4 f l u o r o z i r c o -

of the B-BaZr2F10

i. INTRODUCTION.

structure.

se composition [13], it was judicious to undertake

Fluoride glasses based on the ZrF4-BaF 2

simultaneously an 19F NMR investiga-

tion of both types of materials. Selecting the

system have attracted much attention because

series of alkali metal free ZrF4-based glasses

of the potential ability for infrared opti-

of ZrF4{0.55)-AIF3(0.O4)_BaF2(0.385_x}_LaF3 (

cal materials [1-4]. These fluoride glasses

0.025+x)

offer, on the other hand, interesting elec-

(0 ~ x ~ 0.07) and ZrF4(0.55)-AIF3(

0-04)-BaF2(0-37-x)-YF3(0.04+x)

trical properties due to the F- ion mobility.

(0 ~ x ~ 0.05)

formulations, we have investigated the 19F NMR

It results from many studies reported [5-11]

study of some glassy compositions and, by ti-

that the fluoride ion conduction in the alka-

tle of comparison, of the crystalline low-tem-

li metal free ZrFa-based glasses is of the or-6 7-1 . der of 1 0 lQ.cm) at 200°C, it i n c r e a s e s with the increasing average polarizability of

perature form a-BaZE2FIo and high-temperature form ~-BaZE2FI0 phases [14]. Valuable informations relative to the existence of various

glass-constituting cations.

possible sites for the F- ions [12,15,16] and

An 19F NNR investigation of glasses inside

to the diffusion of mobile fluoride ions could

the ZrF4-BaF2-ThF4_Li F system has allowed to

be expected from such a 19F NMR comparative

show that the F- ion conduction properties are

investigation.

bound to the carriers mobility and to the anionic distribution between different fluoride

2. EXPERIMENTS.

sublattices [12]. Knowledge of local order in the fluoride glasses appears consequently as

The glasses have been prepared in open cru-

essential to propose conduction mechanisms in these materials.

cibles at room atmosphere using an experimental method which has been described elsewhere

As many structural features are similar in

[17-19] : the starting materials were the oxi-

the glasses and the crystalline phases of clo-

des (ZrO2, A1203, La203, Y203 } and the fluori-

983

984 de

19F NMR COMPARATIVE INVESTIGATION BaF 2. BaF 2 and the d i f f e r e n t

oxides w e r e

Vol. 89, No. 12

r a t u r e range is shown in Fig.

m i x e d w i t h an excess of a m m o n i u m bifluoride.

sy

The mixed c o m p o n e n t s w e r e p r e h e a t e d for I h.

0°025} c o m p o s i t i o n

at about 400"C to a c h i e v e the f l u o r i n a t i o n

BaF 2 rate.

re-

action and g r a d u a l l y h e a t e d up in a dry gas to temperature

for melting.

T h e liquid was then

Ic for the glas-

ZrF4(O.55)-AIF3(O.04)-BaF2(0.385)-LaF3( that offers

At very low t e m p e r a t u r e s ions can be c o n s i d e r e d

(123 K),

as =frozen".

the FIn other

c o o l e d and p o u r e d into a brass mould at room

words,

temperature.

and the NMR s p e c t r a r e l a t i v e to very low tem-

An I.R.

spectroscopy

investiga-

tion has a l l o w e d to c h e c k up the absence g l a s s e s of OH- g r o u p s c h a r a c t e r i z e d p r e s e n c e of a peak at 3000 nm. B-BaZr2FI0

the p r e v i o u s l y d e s c r i b e d m e t h o d

sealed g o l d tube then q u e n c h i n g a-BaZr2Fl0

according

ture then q u e n c h i n g NMR e x p e r i m e n t s

at 540"C in

at that tempera-

123K 293K 403K

.~.~/

in water. on a Bruker

(B 0 = 4.7 T) e q u i p p e d

with a standard

variable

the t e m p e r a t u r e

range : 123 K to 423 K.

follows

on

B- form from 540"C to

were p e r f o r m e d

spectrometer

Spectrometer

to

in water from

is obtained,

a three days a n n e a l i n g

MSL-2O0

of the rigid fat-

by the h e l p of a slow c o o l i n g

of the high t e m p e r a t u r e 4O0"C,

are c h a r a c t e r i s t i c

by the

[14], by syn-

thesis of BaF 2 and ZrF 4 f l u o r i d e s

the other hand,

peratures

in the NMR time scale

[18].

has been prepared,

that temperature,

in

they a r e ' f i x e d

the largest

operating

temperature

conditions

unit in

"b-

have been as

:

-Spectrometer

frequency

: 188.283

;/

MHz.

J

- S p e c t r a l width

: 1 MHz.

-Filter width

: 2 MHz.

-Delay time

: 5s.(glasses)

//

/

123K 293K

/ and

----'~~ "

403K

107s.(crystalline phases). -c-

A O Echo s e q u e n c e with a

./2 pulse length of

Simulations formed using by Bruker. position, Gaussian

p r o g r a m has been u s e d 1.8 ps.

of the 19F NMR lines were per-

the "LINESIM"

This p r o g r a m peak height,

linewidth,

and L o r e n t z i a n

lative p e r c e n t a g e

123K 193K 233K 253K 273K 293K 313K 333K 353K

program provided

allows to adjust peak

functions

ratio of and the re-

of their areas.

393K

~_~:/i .~_r-~

3. Fig.l

RESULTS.

(a,b) give8

some t e m p e r a t u r e s

the 19F NMR s p e c t r u m

a- and B- BaZr2FI0

the other hand,

the thermal in the

phases.

0

413K 423K

-200 (ppm)

at

, 293 and 403 K} for

the c r y s t a l l i n e 19F NMR s p e c t r u m

200

DISCUSSION.

(123

~

Fig. I - 1 9 F NMR s p e c t r a On

v a r i a t i o n of the

(123K - 423 K) tempe-

for a - B a Z r 2 F l 0

at v a r i o u s (a),

temperatures

B-BaZr2FIO

(b} and

the g l a s s of Z r F 4 ( 0 . 5 5 } - A I F 3 ( 0 . 0 4 } - B a F 2 (0.385)-LaF3(0.025)

composition

(c).

Vol. 89, No. 12

19F NMR COMPARATIVE INVESTIGATION

tice of s t u d i e d increases, mobile

materials.

When t e m p e r a t u r e

the F- ions become

and their motions

more c h a n g e d

result

NMR spectra.

the case of 8-BaZr2FI0 low temperature

and of the glass,

spectra

of w h i c h

modifications

the contrary,

no c h a n g e

of the a-phase

in a larger glass

(Fig.l

spectrum (Fig.

F- mobility

appear

those relative

ZrF 6 [20]

(Table i),

glass

only

and the

ratio cor-

is intermedia-

to BaZr2Fl0

pare the l o w - t e m p e r a t u r e

spectrum

spectra

shows

materials.

a large

analogy

Table BaY 2 percentage

BaZr2FI0

probably

with

[13]

structural

those of B-BaZr2F10

This result e m p h a s i z e s

structural

from

that the

that the choice

as basic material

to propose

a

model of the BaF 2 : 2 ZrF 4 glass

was judicious.

is a Zr2Fl2 sociation

bipolyhedron

of two edge sharing

is c h a r a c t e r i z e d

sence of a d o u b l y

F-bridged

units

twisted

of i n t e r p e n e t r a t e d

so formed

Ba sheets

Deconvolution

The

by c o r n e r - s h a r i n g

of ZrF 7 pentagonal

layers

by the pre-

Zr-Zr pair.

join together

to form a 2D network

by the as-

ZrF 7 Dolyhedra.

This bi[x~lyhedron

Zr2FI2

structure

constituted

[21]

zig-

bipyramids.

are joined

The

together

by

(Fig.3).

attempts

of

the

19F NMR

of

the spec-

i. ratio

in the

and BaZrF 6.

BaY 2 ~

Lanthanum

involves

P-BaZr2FI0

to com-

Comparison

and a n i o n / c a t i o n

studied glasses,

[21].

It results

at low temperature

analogous

double

of the glass

between

glass

features

and Ba

with those of a-BaZr2Fl0 , B-BaZr2FI0 and -BaZrF 6. Fig.2 gives the 19F NMR spectra at 123 K for these various

studied

zag chains

it was important

and B-BaZr2FI0.

that 19F NMR study

The basic unit of the B-BaZr2FI0

--BaZr2Fl0.

to the studied

te between

123

I a}.It results

in 8-BaZr2Fl0

tra of glass

~of

b,c}. On

As the value of the a n i o n / c a t i o n responding

the

at

and s i g n i f i c a t i v e

temperature

than in

offer

is seen h~tween

and 293 K for a-BaZr2Fl0 for a higher

in more and

It is for instance

293 K notable

changes

progressively

985

anion/cation

series

Zr0.55A10.04Ba0.385_x La0.025+xF3.165+x

Yttrium

x

=

x

= 0.07

0.00

38.5

3.165

31.5

3.235 Slmllllltcu c u l v c

series

ZrF4(0.55 )-AIF3(0.04)-BaF2(0.385 )-LAY3(0.025~

.~ . . . . .

i

Zr0.55A10.04Ba0.37_x

200

lOC

i

i

i

0

-I00

-200

(pprn)

Y0.04+xF3.18+x = 0.00

37

3.18

x = 0.05

32

3.23

x

Fig.2-19F

NMR s p e c t r a

a-BaZr2Fl0

at 123 K for a-BaZrF6,

, B-BaZr2FI0

and the g l a s s

ZrF4(0.55)-AIF3(0.O4)-BaF2(0.385)-LaF BaZr2FI0

33.3

3.333

BaZrF 6

50

3.00

(0.025)

of 3

composition.

-Deconvolution

of the 19F NMR s p e c t r u m

123 K for the Z r F 4 ( 0 . 5 5 ) - A I F 3 ( 0 . 0 4 ) - B a F (0.385)-LAY3(0.025)

glass.

at 2

986

19F NMR COMPARATIVE INVESTIGATION

spectrum

of B-BaZr2FI0

at 123 K are failing,

due to the very i n t r i c a t e Baterial. six u n l i k e

Indeed, sites

structure

of this

the F- ions are located

on

[21] and the 19F NMR spec-

tr%ua results

from the sum of each of indis-

tinguishable

contributions.

the m a g i c - a n g l e - s p i n n i n g

On the other hand,

(MAS) NMR experiments

which

allow

Vol. 89, No. 12

to s e p a r a t e

of a s p e c t r u m

the various

because

the spectrum

respect

to the r o t a t i o n

T h e structural fluorozirconate

is too w i d e speed

model

(60 kHz) w i t h

(5.5 kHz).

for the BaF 2 : 2 ZrF 4

glass w h i c h has been proposed

on the basis of X-ray s c a t t e r i n g simulation

results

structure.

The basis

Zr2FI3

derives module

of fluoride

and computer

from the B-BaZr2FI0

structural

bipolyhedral

three kinds

components

could not be used for B-BaZr2FI0

unit

(Fig.4)

ions

is the

which offers

: five Fnb

bridging

ions and two types of bridging

internal

bridging

fluoride

form an e d g e - s h a r i n g

entirely

fluoride

ions

(6 F b) w h i c h

modules.

The ratio

nFnb

investigation by EXAFS

are shared by two

/ (nFbi + nFb) calcu-

is equal

technics

to 50

: 50. An

has allowed

structure

to study

around

Zr [22]:

value of the Zr-Zr mean d i s t a n c e

( 3.60 A ) is c o n s i s t e n t ce in the

brid-

bridging

of some ZrF4-BaF 2 binary

the near neighboring the e s t i m a t e d

double

to the module,

lated for this module glasses

{2 Fbi) w h i c h

Zr-(2 Fbi)-Zr

ge and belong

recent

ions

nonanions,

Zr2FI2

with

(B-BaZr2F10

the Zr-Zr d i s t a n crystal)

and

Zr2FI3 ( BaZr2FI0 glass) polyhedra. C o n s e quently, the structural model proposed for the BaF 2 : 2 ZEF 4 glass FI0 structure,

on the basis

is c o n f i r m e d

Zr3

-a-

~4

I

Zr6

I

Zr4

F //~/

B-BaZr2FI0

structure

tion of a d o u b l e nal b i p y r a m i d s interpenetration rallel picture

to [i01]

layer

the p e n t a g o n a l

of ZrF 7 p e n t a g o from

of zig-zag

chains

(a) and [201]

bipolyhedron

bipyramid

Zr2F12

[21].

\

Zr7

nb

'~3

Zr8

: Representa-

(c) r e s u l t i n g

in the left u p p e r

//Fb""'-

Fnb b, Fb Fnb _ ( ~

Zr5 Fig.3-The

/

Irnb Fb

~Fnb~b / Fbi~ \

/F b

of the B-BaZr 2

not only by EXAFS

the pa-

Fnb

: Non-bridging

Fbi

: Internal

bridging

fluoride

fluoride

ion.

Fb

: Bridging

fluoride

ion.

ion.

{b). T h e

corner

shows

ZrF 7 a n d

the

Fig.4-The

Zr2FI3

the basic

bipolyhedron structural

2 ZrF 4 g l a s s

[13].

proposed

to be

unit of the BaF 2 :

Vol. 89, No. 12

19F NMR COMPARATIVE INVESTIGATION Table 2

987

1ogy with the ZrF4(0.55)-AIF3(0.04)_BaF2(0.315 )

-LaF3(0.095) glass [23].

19F NMR lineshape simulation data of the

Simulation data relative to spectra at 123 K

glasses studied at 123 K.

of other vitreous compositions studied are gathered in Table 2° The pl/P2 ratio appears as Glass composition Lineshape Chemical width Area! (mole ~) c o m p o n e n t Shift (kHz) (~)

of the Vitreous composition in the-

( 41 ~) of network modifiers (BaLF2 + LaF3 ,

(ppm) +3

i~ependent

se glasses characterized by a similar rate

+0.5

Bad~2 + YF3). Consequently, as the Fnb ions

+3

rate is straightly bound to network modifiers rate, the Fnb/F b ratio is quasi-constant for ZrF4AIF3BaF 2 L a F 3

the studied glasses. On the other hand, the value of the Fnb/F b ratio equal to about 60:40

55

4

38.5

2.5

Pl

77

35.8

60

in the studied glasses is higher than that cal-

P2

-72

27.2

40

culated for the Zr2FI3 bipolyhedral module

Pl

71

36

62

higher percentage of network modifiers and

P2

-76

27.3

38

(50:50). This result can be attributed to a 55

4

31.5

9.5

Consequently of Fnb ions in the glasses studied than in the BaF 2 : 2 ZrF 4 glass.

ZrF4AIF3BaF 2 YF 3 55

55

4

4

37

32

i F

4

9

Pl

87

35.8

64

I

P2

-72

28

36

i i i

Pl

81

36

62

i

P2

-73

28.1

38

4. CONCLUSIONS. The 19F NMR investigation of extrema glassy compositions belonging to series of alkali metal free

ZrF4(0.55)_AIF3(0.04)_BaF2(0.385_X)_

LaF3(0.025+X)

(0 ~ x ~ 0.07) and ~rF4(0.55 )_

experiments but also by 19F N~R investigation

AIF3(0-04}-EaF2(0-37-X)~YF3(0.04+x)

of ZrF4-based fluoride glasses at low tempera-

0.05) fluoride glasses has been undertaken.

ture. The 19F N ~

The Fnb/F b ratio, determined at low temperaspectrum at 123 K obtained for

(0 ~ x

ture (123 K) is equal to about 60:40 for each

the ZrF4(O.55)-AIF3{0.04)-BaF2(0.385)-LaF3{ 0.025) glass could be simulated by the help of two Pl and P2 gaussian functions (Fig. 2 ). The simulation data are gathered in Table 2. The gausslan shade of the Pl and P2 functions indicates that fluoride ions are not mobile at

material studied. It is consequently independent of the vitreous composition inside these materials which involve close rates of network modifiers (41~). On the other hand, the large analogy of the low temDersture spectra of these glasses with

that temperature. The Pl and P2 functions are

that of B-BaZr2FI0 confirms the validity of

in the ratio 60 : 40 and have been assumed to

the structural model proposed for the BaF 2 :

IM~ proportional to the fraction of non-bridging

2 ZrF 4 glass on the basis of the B-BaZr2F10 structure.

(Fnb} and bridging (F b) fluoride ions, by ana-

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19F NMR COMPARATIVE INVESTIGATION

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