High temperature crystal structure and DSC of Sn 2P 2S 6

Abstract

We report the single crystal X-ray diffraction of Sn 2 P 2 S 6 at 110°C. The crystals are monoclinic, with space group P 2 1 / n, a =9.362(2) A, b =7.493(1) A, c =6.550(3) A, β=91.17(3)°, and Z =2. The structure consists of P 2 S 6 −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 A. At room temperature, Sn 2 P 2 S 6 crystallizes in the space group P c 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 P 2 S 6 −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, M 2 P 2 X 6 .