Ukrainian Journal of Physical Optics 

Number  4, Volume 4,  2003

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Thermal Expansion and Phase Transformation Observation in Cs2BX4 (B=Hg, Cd; X=Br, Cl) Crystals 
1. Cs2HgCl4 crystals
Krupych O., Girnyk I., Trach I., Vlokh R., Vlokh O.

Institute of Physical Optics, 23 Dragomanov Str., 79005, Lviv, Ukraine

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The results of thermal expansion study and the domain structure observation in Cs2HgCl4 crystals are presented. It is shown that the phase transformations in caesium mercury chloride crystals pass through the heterophase regions. The phase transition between the normal and incommensurate (IC) phases is of the first order. The observed “devil’s staircase” in the range 143K<T<181K means that the wave vector of the modulated structure has a jump-like temperature dependence, leading to appearance of a complicated sequence of commensurate and IC phases. The non-compatible, inhomogeneous deformations existing in the temperature range 183K<T<225K are, most probably, the reason for appearing the electric polarization. The appearance of ferroelastic domains at 8K below Tc1 is explained by the existing heterophase structure.

Key words: incommensurate phase, domain structure, thermal expansion.
PACS: 65.70.+y, 77.80.Dj, 78.20.Fm

doi 10.3116/16091833/4/4/155/2003

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