Highly Disordered Crystal Structure and Thermoelectric Properties of Sn3P4

Abstract

The crystal structure of Sn3P4, a long-known tin phosphide, has been determined. It crystallizes in the trigonal space group R3m with unit-cell parameters a = 4.4315(1) A and c = 28.393(1) A (Z = 3). The crystal structure of Sn3P4 is disordered. It consists of alternating layers of phosphorus and tin atoms that are combined into five-layer blocks and propagate along the c-axis. The major structural feature is the disordered orientation of the P24– dumbbells, which link the tin atoms. The latter possess two types of coordination. One third of the tin atoms reside inside the block and are octahedrally coordinated by phosphorus atoms. The rest of the tin atoms confine the block and possess a [3 + 3] environment made up of three close phosphorus neighbors and three rather distant (3.4 A) tin atoms of the adjacent block. The coordination of the tin atoms is confirmed by 119Sn Mossbauer spectroscopy. The electron diffraction and high-resolution electron microscopy data reveal ordered regions at the microscopic...