Phases and thermoelectric properties in stoichiometric Sn_{1 - x}Mn_xTe and non-stoichiometric Sn_{1 - y}Mn_1.1yTe alloys

Both series of stoichiometric Sn_{1 - x}Mn_xTe and non-stoichiometric Sn_{1 - y}Mn_1.1yTe alloys were prepared through melting, quenching and spark plasma sintering to investigate their phases and thermoelectric properties. The experimental results show that the SnTe-based solid solution single phase was formed in both series of samples with lower Mn content. The minor secondary MnTe₂ phase was formed in the stoichiometric Sn_{1 - x}Mn_xTe alloys with x ≥ 0.06 due to the Mn needed for filling in the intrinsic Sn lattice vacancies of SnTe and volatilization lost during the preparation. The excess Mn in Sn_{1 - y}Mn_1.1yTe alloys compensates this need to avoid the formation of block MnTe₂ phase, which changed the phase relationship and guaranteed more Mn effectively substituting Sn in SnTe. All the samples show p-type conduction. The substitution of Mn in SnTe enhances its Seebeck coefficient and reduces its thermal conductivity. Much greater improvement on thermoelectric properties was found in the non-stoichiometric Sn_{1 - y}Mn_1.1yTe alloys, resulting in the maximum figure of merit ZT of 1.22 in Sn_0.9Mn_0.11Te alloy at 873 K, due to more Mn substituting for Sn in SnTe lattice. The excess Mn in the non-stoichiometric Sn_{1 - y}Mn_1.1yTe alloys is important for preparing the Mn-doped SnTe materials with high thermoelectric property.