What is it about?
Cs2HgCl4 has space group Pnma (Z = 4) in its normal phase at room temperature. On cooling a sequence of incommensurate and commensurate superstructures occurs. Cs2HgCl4 distinguishes itself from the other A2BX4 compounds by the fact that it has both modulated phases of a- and c- directions. The study of both types of superstructures might give insight into the different ways the local strain can be resolved by the formation of superstructures.
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Why is it important?
Cs2HgCl4 belongs to the family of A2BX4 compounds. These compounds are known for their phase transitions towards incommensurate and commensurate superstructures.
Perspectives
For the incommensurately modulated structures, the superspace group gives the complete symmetry, and these phases will show the behaviour according to a centrosymmetric symmetry. For the commensurate modulations, the appropriate section t of superspace needs to be determined in each case. It is noted that dependent on t, either a centrosymmetric or non-centrosymmetric supercell space group is obtained.
Dr Bagautdin Bagautdinov
Read the Original
This page is a summary of: Modulated structures of Cs2HgCl4: the 5a superstructure at 185 K and the 3c superstructure at 176 K, Acta Crystallographica Section B Structural Science, December 1999, International Union of Crystallography,
DOI: 10.1107/s0108768199008071.
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