HIGH-TEMPERATURE CRYSTAL-STRUCTURE AND DSC OF SN2P2S6

We report the single crystal X-ray diffraction of Sn2P2S6 at 110°C. The crystals are monoclinic, with space group P21/n, a=9.362(2) Å, b=7.493(1) Å, c=6.550(3) Å, β=91.17(3)°, and Z=2. The structure consists of P2S6-4 anions linked together via S-Sn contacts. Each Sn atom is coordinated to eight S atoms. The S-Sn distances range from 2.914-3.227 Å. At room temperature, Sn2P2S6 crystallizes in the space group Pc and has a strong ferroelectric response. Using differential scanning calorimetry, the transition to the paraelectric state is determined to be 60±2°C. The DSC data are also consistent with the phase transition being second order. The major change in the structure results from movement of the tin atoms. The P2S6-4 units remain essentially unchanged. Neither the room temperature nor the high temperature phase exhibits a layered structure characteristic of the transition metal phosphorus chalcogenides, M2P2X6. © 1992 Academic Press, Inc.