Thermoanalytical study of the polymorphism in LiIO3

Mat. Res. Bull. Vol. 7, pp. 869-872, 1972. in the United States.

THERMOANALYTICAL

Pergamon Press, Inc.

STUDY OF THE POLYMORPHISM

Printed

IN LiIO 3

H. Arend, M. Remoissenet and W. Staehlin Laboratory of Solid State Physics, Institute of Technology, ZUrich~ Laboratoire de Di~lectriques et Ferro~lectriques, Universit~ de Dijon, France~ and Swiss A l u m i n u m Ltd., Research Laboratories, Neuhausen, Switzerland.

(Received July 3, 1972; Communicated by G. H. Jonker)

ABSTRACT A t h e r m o a n a l y t i c a l study showed that the contamination of LiIO 3 by small amounts of HIO 3 influences markedly the polymorphism. A reversible e-y transformation could be observed only in pure samples, whereas a nucleation of and gradual conversion to the B-phase occurs at the same temperature in impure samples.

Introduction Contradictory made

observations

at atmospheric

an irreversible According

transition

B-LiIO 3. Desvignes

loss.

in the past.

in hexagonal

(2) the newly

and Remoissenet

~-8 transition

Recently

sequence

pressure

to Liebertz

irreversible

on the p o l y m o r p h i s m

Matsamura

as a function

was

~-LiIO 3 ~

~

(1) found

~-LiIO 3 at about

(3) observed

accompanied

of the thermal

250°C.

that the

by a small weight

the following

history

phase

of the sample:

~285°C ~-LiIO 3

~200Oc The reversible

Herlach

formed phase was tetragonal

(4) determined

~247°C

of LiIO 3 were

u-y transition

=

~

8-LiIO3~

~390Oc ] is endothermic 869

Liquid I

on heating,

whereas

870

POLYMORPHISM

the reversible effect.

Once the

temperature needing

7-8 transition B-phase

further

irreversibly

change

to the

the obvious

is the behaviour

reversibly

an exothermic

it is stable between

Consequently

elucidation

which may either

is connected with

is formed,

and melting.

Vol. 7, No. 9

room

question

of the e-phase

to the y-phase

or

B-phase.

E x p e r i m e n t a l P a r t and Results Single

crystals

acid solutions showed

of e-LiIO 3 can be grown either (2,3).

that a chemical

types was necessary. contained

0,59

All samples

Different

grown

On heating

processes

were observed

in oxygen below

250°C.

The second effect

of a d i s t i n c t

decomposition excess

occurred step.

of different cycles,

and a sample

HIO 3 was removed

to demonstrate of 8-LiIO 3 were shown in Table

250°C

of traces

in the form only in

loss ranged

the chemically

shows

determined

that the HIO 3-

samples was checked

e-LiIO 3 grown of acid grown by melting,

in repeated

from neutral crystals,

were

the role of the nucleation

and

in which

studied.

In order

of the B-phase

added to HIO 3 free a-LiIO 3. The results i.

the

incomplete.

and cooling

the excess

loss from 0,1 to

HIO 3 and its weight

amount of free acid the lower value

acid solutions

weight

It was observed

0.2 to 0.4%. As compared with

heating

thermogravimetric

the first heating

around

between

The DTA-behaviour

thermo-

due to the presence

containing

was

differential

could be reduced by annealing

samples

decomposition

of both

acid could be

in a M E T T L E R

two different

at ll0°C and is evidently

of water.

no excess

300°C during

This effect

(5)

from acid solutions

of simultaneous

The first one was a continuous

0,4% below sample

by means

or

solutions.

and t h e r m o g r a v i m e t r y

analyser.

cycle.

samples

from neutral

measurements

of crystals

of HIO 3, while

were examined

analysis

absorption

characterization

to 0,76%

found in crystals

thermal

Infra-red

in neutral

seeds are

Vol. 7, No. 9

POLYMORPHISM

TABLE DTA-Behavlour

871

1

of Different

LiIO 3 Samples Observations

Sample i. a-LiIO 3 from neutral solution

Reversible a-7 transition occurring at 249oc on heating and at 202°C on cooling unchanged in I0 cycles between 150 ° and 270Oc. Changes irreversibly to S-LiIO 3 at 300°C

2. u-LiIO 3 from acid solution

Gradual disappearance of a-7 transition while c y c l l n g b e t w e e n 150 ° and 270 ° during 2 to 5 cycles. Subsequently no exothermic process at 300oc detectable.

3. a-LiIO 3 from neutral solution + 10% B-LiIO 3

Gradual disappearance of reversible a-7 transition while cycling between 150 ° and 270oc. Complete after 7th cycle. No further exothermlc process at 300oc detectable.

4. a-LiIO 3 from m o l t e n acid grown crystal + 30% B-LiIO 3 seeds

Gradual disappearance of reversible transition while cycling between 150 ° and 270 ° , complete after 6th cycle. No change detectable at 300°C.

Discussion of Results The reversible

a-7 transition

was found only in samples (sample

temperature

to the S-phase

150 ° and 270°C portion

occurs

two processes

while

i.e.

at 300°C.

A steadily

follows M a t s a m u r a ' s

an increasing

HIO 3

The irreversible above the

If, however,

2) is cycled repeatedly

compete.

(4)

no excess

in this sample well

one,

LiIO 3 (sample

of the sample

transition,

150 ° and 270°C).

of the reversible

HIO 3 c o n t a m i n a t e d

by M a t s a m u r a

of a-LiIO 3 containing

I - cycling between

transition

as described

between

decreasing

reversible

amount of the sample

~-7 is

872

POLYMORPH~M

Vol. 7, No. 9

changed irreversibly into the S-phase.

From the absence of a

specific effect in the DTA curve we can judge that the sample may change completely to the S-phase at a temperature coinciding with the ~-7 transition. Such a behaviour can be understood by assuming that the small HIO 3 contamination leads to a nucleation of the S-phase at lower temperatures in acid grown crystals.

Once the seeds

are formed they gradually convert the remaining sample to the S-phase already at the temperature of the a-7 transition. This assumption was checked by intentionally adding S-seeds to two types of acid free a-LiIO 3 (samples 3 and 4 in Table I). After seeding neutral crystals or samples in which the excess acid is destroyed thermally by melting and which follow originally Matsamura's phase pattern, an irreversible transition into the S-phase occurs already at 250°C. Thus the nucleation of the S-phase, which is favoured in the presence of HIO 3 impurities, is the deciding factor in the phase pattern LiIO 3 follows upon heating.

In cooling down liquid

LiIO 3 a similar behaviour was found earlier by Liebertz

(2).

Acknowledgment The assistance of Mr. Garandet from the Dijon University, who grew most of the crystals used, is gratefully acknowledged. The authors are further indebted to Prof. S. Hauss~hl from the University of KSln for the remaining samples.

References i.

F. Herlach, Helv.Phys.Acta 34, 305 (1961).

2.

J. Liebertz,

3.

J.M. Desvignes, M. Remoissenet, Mat. Res. Bull. 6, 705

4.

S. Matsamura, Mat.Res. Bull. 6, 469

5.

J.M. Crettez, R. Gard and M. Remoissenet, to be published

Zeitschr.Phys.Chem.

N.F. 67, 94 (1969). (1971).

(1971).