Volume 29A, number 9 PHYSICS L E T T E R S 28 July 1969

A N T I F E R R O E L E C T R I C T R A N S I T I O N IN C s P b C 1 3

M. NATARAJAN, S. RAMDAS and C. N. R. RAO Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, India

Received 20 May 1969

The transformation of Csl~oC13 at 47°C is associated with a change from the antiferroelectric phase to the paraelectric phase.

M~ller [1] repor ted a phase t r an fo rma t ion of CsPbC13 at 47oc f rom a te t ragonal s t r uc tu r e to a cubic perovski te s t ruc tu re . Recently, Sakudo et al. [2] have identif ied a new phase t r ans i t i on around 40oc based on X- ray , e las t ic and acoust ic m e a s u r e m e n t s ; they observed s u p e r s t r u c t u r e at this t r ans i t i on t empera tu re . We have examined the phase t r ans i t i ons in CsPbC13 by employing D. T .A . , X - r a y and d ie lec t r ic m e a s u r e m e n t s .

The D. T .A. s tudies show that the t r ans i t i on at 47°C is associa tedlwi th a ve ry low enthalpy (~ 20 ca lo r i e s mo le - ); DTA curves , however, fai led to show any t r a n s f o r m a t i o n a round 40°C as repor ted by Sakudo et al. [2]. The low enthalpy and the absence of t he rma l h y s t e r e s i s indicate that the t r ans i t ion at 47°C may be of higher o rder [3]. The d ie lec t r i c constant of CsPbCI 3 shows an anomaly at 47°C as shown in fig. 1. There is a l -

so a marked i nc r ea se in the d ie lec t r i c constant in the 35-40°C region poss ib ly due to the new t r ans fo rma t ion proposed by Sakudo et al. [2]. No d ie lec t r i c hys t e r i e s was observed in CsPbC13 in the t r ans fo rma t ion region (25-60°C).

The p r e se n t f indings along with the obse rva - t ion of s u p e r s t r u c t u r e [2] indicate that below 47°C Cs~?bC13 is an t i f e r roe lec t r i c . The t e t r a - gonal (C~,.- P4mm) to cubic t r ans fo rma t ion probably-~or responds to a change f rom the an t i - f e r r o e l e c t r i c phase to the pa rae l ec t r i c phase. We find that the to le rance factor for the p e r - ovskite CsPbCI 3 is 0.826; this would favour the d i s tor t ion f rom the nonpolar cubic phase to the an t ipolar te t ragonal phase. Such to le rance fac- to r s of l ess than unity a re a lso found in other a n t i f e r r o e l e c t r i c s such as P bZr O 3 [4] and PbHfO 3 [5].

1201 ! l

80 I 40

I 25 4s 66 t ,°c

Fig. 1. Variation of the dielectric constant of CsPbC13 with temperature.

The authors a re thankful to the U. S. National Bureau of Standards for a r e s e a r c h gran t (G-51) under the i r Special In te rna t iona l P r o g r a m m e .

Rej-C~?-~nc~ s

1. C.K. MCller, Mat. Fys. Medd. Dan. Vid. Selsk., 32 No. 2 (1959).

2. T. Sakudo, H. Unoki, F. Fujii, J. Kobayashi and M. Yamoda, Phys. Letters 28A (1969) 542.

3. C.N.R. Rao and K. J. Rao in Progress in solid state chemistry, ed. H. Reiss, Vol. 4 (Pergamon Press, Oxford, 1967).

4. G. Shirane, H. IYanner, A. Pavlouic and R. Pepinsky, Phys. Rev. 93 (1954) 672.

5. W. Kanzig, Ferroelectrics and antiferroelectrics (Academic Press, London 1957).

528