Ultra-fast non-equilibrium synthesis and phase segregation in InxSn1−xTe thermoelectrics by SHS-PAS processing

Abstract

The self-propagating-high-temperature-synthesis (SHS) in combination with plasma activated sintering (PAS) is applied for the first time to SnTe-based thermoelectric materials and produces single-phase structures. Thermodynamic and kinetic parameters of the SHS process relevant to SnTe compounds were determined. InTe is supersaturated in In_xSn_1−xTe during the non-equilibrium SHS process. After annealing, doping SnTe with In gives rise to phase separation and the formation of InTe nanoinclusions, which affect the carrier density and, in turn, the transport properties. The presence of the InTe nanophase dramatically reduces the lattice thermal conductivity as low frequency heat carrying phonons are strongly scattered. Moreover, the ensuing deficiency of Te in the SnTe matrix gives rise to Te vacancies which reduce the density of hole carriers and thus enhance the Seebeck coefficient. Compared to samples synthesized by the traditional methods, the SHS-PAS technique shortens the synthesis time from several days to merely 15 min which bodes well for low cost mass production of SnTe-based materials. The phase separation process observed here for the first time effectively adjusts both the microstructure and the carrier density of SnTe-based materials and offers a new approach to optimize their thermoelectric properties.