What is it about?
The temperature behavior of lattice parameters and diffraction patterns of the reciprocal lattice in Cs2HgCl4 crystals is studied by x-ray diffraction in the temperature range from 4.2 to 300 K. A sequence of phase transitions is observed and attributed to the evolution of incommensurate and commensurate modulations along the crystallographic a and c axes of a unit cell in the initial Pnma structure.
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Why is it important?
Cesium tetrachloromercurate Cs2HgCl4 belongs to the family of A2BX4 crystals and has a β-K2SO4 structure (Pnma, Z = 4, c > a > b) at room temperature. Most of the known compounds with incommensurate phases belong to the A2BX4 family. Investigations into the physical properties of Cs2HgCl4 crystals revealed a series of phase transitions occurring upon cooling. In order to clarify the structural aspects of the sequence of phase transitions in Cs2HgCl4 crystals, we carried out a systematic x-ray diffraction investigation of the configuration of the reciprocal lattice and measured the interplanar spacings in a wide temperature range from 4.2 to 300 K.
Perspectives
Our analysis led to the conclusion that starting from Ti = 221 K, processes associated with a rearrangement in the modulated structure occur in Cs2HgCl4 crystals upon cooling. This manifests itself in the behavior of satellite reflections. As a result of cooling, the incommensurate and commensurate modulated states are formed in the structure with eight phase transitions.
Dr Bagautdin Bagautdinov
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This page is a summary of: X-ray diffraction study of a sequence of phase transitions in Cs2HgCl4 crystals, Physics of the Solid State, February 2001, Pleiades Publishing Ltd,
DOI: 10.1134/1.1349487.
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