Single crystal growth of Sn0.97Ag0.03Se by a novel horizontal Bridgman method and its thermoelectric properties

SnSe-based single crystal has attracted much attention due to its outstanding thermoelectric behaviors, however, the fabrication of large size crystal seems difficult as it is very easy to cleavage during crystal growth. In this work, a novel horizontal Bridgman method was employed to produce SnSe crystal with 3 mol% Ag substitute for Sn. The Sn0.97Ag0.03Se raw material was in-situ synthesized in the horizontal Bridgman furnace and the crystal was grown in a PBN crucible. B2O3 encapsulant was used to prevent Se volatilization. The as grown Sn0.97Ag0.03Se crystal was about 105 g in weight and a 25 mmx20 mmx 15 mm single crystal was obtained. The density of the single crystal of 6.178 g/cm(3) close to the theoretical value was measured. X-ray powder diffraction measurement indicated Sn0.97Ag0.03Se single crystal had orthorhombic Pnma structure at room temperature. The thermoelectric properties along a axis were analyzed and the Figure-of-merit, ZT=0.95 was obtained at 793 K mainly due to the low thermal conductivity near the Pnma-Cmem phase transition temperature