Structural basis for the phase transitions of Cs2HgCl4

Titelangaben

Bagautdinov, Bagautdin ; Jobst, Andreas ; Lüdecke, Jens ; van Smaalen, Sander:
Structural basis for the phase transitions of Cs2HgCl4.
In: Acta Crystallographica Section B. Bd. 57 (2001) Heft 3 . - S. 231-236.
ISSN 2052-5206
DOI: https://doi.org/10.1107/S0108768100020322

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Abstract

The a0 × b0 × 2c0 twofold superstructure of dicaesium mercury tetrachloride, Cs2HgCl4, at T = 120 K has been determined by single-crystal X-ray diffraction using synchrotron radiation. Lattice parameters were found as a = 9.7105 (2), b = 7.4691 (1), c = 26.8992 (4) Å, and [beta] = 90.368 (1)° with the supercell space group P21/c. Refinements on 1828 observed unique reflections converged to R = 0.053 (wR = 0.057) using anisotropic temperature factors for all atoms. This phase is the stable phase of Cs2HgCl4 below 163 K. A quantitative comparison is made of the distortions of the 2c0 superstructure with the undistorted phase that is stable at room temperature, and with the 3c0 and 5a0 superstructures that are stable at temperatures between 163 K and room temperature. The principal difference between the 2c0 superstructure and all other phases of Cs2HgCl4 is that the Cs cations are displaced away from the centers of their coordination polyhedra in the 2c0 superstructure. The structural basis for the driving force of the series of phase transitions in this compound is found in the variations of the environments of Cs atoms and in the variations of the distortions of the HgCl4 tetrahedra.