Influence of cationic size on the transition temperature of the AIIBIIIF5 compounds of SrAlF5 type

74

164 INFLUENCE

OF CATIONIC

TEMPERATURE

SIZE ON THE TRANSITION

OF THE A”B”‘Fs

J. Ravez, V. Andriamampianina, Laboratoire

COMPOUNDS

OF SrAlFs TYPE

A. Simon, J. Grannec,

J. M. RCau

de Chimie du Solide du CNRS, Universite

35 1 tours

de la Liberation,

33405

Talence

de Bordeaux

I,

(France)

and S. C. Abrahams AT&T Bell Laboratories, Murray Hill, NJ 07974 (U.S.A.) and Institut fur Kristallographie der Universitat Tiibingen, Charlottenstrasse D-7400

Ttibingen

The

prediction

temperature

of

published

as

Tc measurement

[l T

members

oft the

increasing

685K,

and

]

made

.

on5

later both

The

cation

is

SrAlF

was

determined

between

increase

that

structure,

= 715K

33,

(F.R.G.)

basis

confirmed by

heat

present radius

isomorphous

ferroelectric

the

with

radius.

substitutions

on

Example

by

reports

Curie

a

dielectric correlation

environment

family. radius is

a

previously

experimental

and

electronic

AIIBr1'F5 vIIIA2+ ionic

with increasing VIB3+ ionic

its

an

capacity

study or

with

of

T

C

and

BaFeF

is

for

found

decrease

with

T

to with

= 730K

5 = '620K and and r( '11'Ba2') = 1.42 i, Bag 5Sr0 5FeF5 with T VIIIsr2+ = 1.26 i) for r(A2') 'as the variable. I"t is possible r( 2+ to substitute Pb for Sr2+ or Ba2+, thereby introducing the 2+ influence of the Pb into the structure. The effect lone pair of

these

results

1

will

S.C. J.

be

Abrahams,

Appl.

Phys.

T

C

have

been

determined

discussed.

J. 52,

Ravez,

A.

4740

(1981).

Simon

and

J.P.

Chaminade,

and

the