Influences of texture, off-stoichiometry, and phases on thermoelectric properties of Sn–Se polycrystals sintered by SPS from millimeter-scale crystal sheets

Abstract

Sn–Se based layer crystals, including both SnSe and SnSe2, are promising thermoelectric materials with intrinsic ultra-low thermal conductivity due to strong anharmonicity of phonon spectrum and special bonding circumstances. In contrast to the rigid growth condition, high cost, and poor mechanical property of single crystals, Sn–Se based polycrystalline samples prepared by spark plasma sintering (SPS) or hot-pressing are more friendly for industrial scale-up. Also, it is possible to take advantage of the anisotropic transport characteristics of the Sn–Se based compounds by introducing texture in polycrystalline samples. To investigate the influences of texture and off-stoichiometry on the thermoelectric property, Sn-rich millimeter-scale SnSe crystal sheets were used as precursor in SPS. Three types of polycrystalline samples with different composition, phase structure, and texture strength were obtained. The formation mechanism and their influences on the thermoelectric properties were studied and correlated. For comparison, Se-rich millimeter-scale SnSe2 crystals were also prepared and sintered by SPS to achieve polycrystalline samples. The phase evolution, texture, thermoelectric properties and its difference and similarity with SnSe were also analyzed.