Phases and thermoelectric properties in stoichiometric Sn1 − xMnxTe and non-stoichiometric Sn1 − yMn1.1yTe alloys

Abstract

Both series of stoichiometric Sn1−xMnxTe and non-stoichiometric Sn1−yMn1.1yTe 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 Sn1−xMnxTe 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 Sn1−yMn1.1yTe 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 Sn1−yMn1.1yTe alloys, resulting in the maximum figure of merit ZT of 1.22 in Sn0.9Mn0.11Te alloy at 873K, due to more Mn substituting for Sn in SnTe lattice. The excess Mn in the non-stoichiometric Sn1−yMn1.1yTe alloys is important for preparing the Mn-doped SnTe materials with high thermoelectric property.