What is it about?
The atomic structure of Cs3Sb2I9 single crystals was refined using X-ray diffraction data (sp. gr. P3m1). The phase transitions found to be accompanied by the appearance of superstructural reflections at Tc1 = 86 K, the reflections indicating doubling of the c parameter at Tc2 = 73 K, a first-order phase transition takes place. In the temperature range from 73 to 78 K, an incommensurate phase providing the satellites h, k + 1/2 + δ, l + 1/2 is formed.
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Why is it important?
Comparing the X-ray diffraction and NQR data, one can assume that splitting of one iodine line is indicative to splitting of the iodine-atom position without the change of the trigonal symmetry.
Perspectives
The Cs3Sb2I9 compound belongs to the A3B2X9 family, where A is the alkali metal ion; B = Fe, As, Sb, Bi, Tl, or Mo; and X = Cl, Br, or I. All the structures of this class are built by hexagonal layers of AX3 and B ions occupying two-thirds of the octahedral cavities located between these layers. We found hat the phase transition at Tc1 = 86 K is really associated with the doubling of the c parameter.
Dr Bagautdin Bagautdinov
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This page is a summary of: Structure and phase transitions in trigonal Cs3Sb2I9 crystals, Crystallography Reports, January 2001, Pleiades Publishing Ltd,
DOI: 10.1134/1.1343121.
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