Structure and phase transitions in trigonal Cs3Sb2I9 crystals

The atomic structure of Cs3Sb2I9 single crystals was refined using X-ray di ffraction data (sp. gr. P (3) over bar m1; wR = 1.58% and R = 3.07%). The p hase transitions revealed earlier were found to be accompanied by the appea rance of superstructural reflections. At T-cl = 86 K, the reflections indic ating doubling of the c parameter. At T-c2 = 73 K, a first-order phase tran sition takes place accompanied by "freezing" of the satellites h, k + 1/2, l + 1/2 reflections. In the temperature range from 73 to 78 K, an incommens urate phase providing the satellites h, k + 1/2 + delta, l + 1/2 is formed. (C) 2001 MAIK "Nauka/lnterperiodica".