Thermoelectric properties evolution of spark plasma sintered (Ge _0.6Pb_0.3Sn_0.1)Te following a spinodal decomposition

The pseudoternary (Ge,Pb,Sn)Te system is characterized by demixing to both Pb- and Ge- rich telluride submicrometer and nanosized domains. The present study is concerned with the thermoelectric (TE) properties of the quasi-ternary (Ge_0.6Pb_0.3Sn_0.1)Te compound at 390 °C, during the demixing process over lengthy periods of time up to 695 h. The dimensionality of the various physical metallurgy patterns evolved was correlated to the lattice thermal conductivity, κ_L, values. Excluding an initial period (<90 h) of increasing κ_L, associated with a coarse lamellar structure formation, an opposite decreasing trend (down to ∼0.8W/mK after 695 h), associated with nucleation of submicrometer (∼200 nm) circular phases, twinning and dislocation networks, all considered as effective phonon scattering centers, was observed. Expansion of these submicrometer sites, all over the samples, during the heat treatments, without any subsequent coarsening, clearly demonstrates the potential of retaining, or even improvement of the TE properties of (Ge,Pb,Sn)Te alloys following a spinodal decomposition reaction, during long-term operation in practical TE devices, at 390 °C. The presented approach, paves a route for design of stable bulk TE materials, consisting of physical metallurgy driven nano and submicrometer domains, without undesirable coarsening effects, upon elevated temperature operation, which are usually unavoidable while starting with nanopowders.