Discordant Distortion in Cubic GeMnTe and High Thermoelectric Properties of GeMnTe-%SbTe.

GeMnTe adopts a cubic rock salt structure and is a promising mid-temperature thermoelectric material. The pair distribution function analysis of neutron total scattering data, however, indicates that GeMnTe is locally distorted from the ideal rock salt structure with Ge cations being discordant and displaced ∼0.3 Å off the octahedron center. By alloying GeMnTe with SbTe, the carrier concentration can be tuned in GeMnTe-%SbTe ( = 15.1), leading to converged multiple broad valence bands and a high Seebeck coefficient of >200 μV K from 300 to 823 K. The system exhibits a large density-of-state effective mass of >10 and a high weighted mobility of 80 cm V s, leading to a power factor of 15 μWcm K at 823 K. The composition GeMnTe-15.1%SbTe exhibits very low lattice thermal conductivity of ∼0.5 Wm K at 823 K, attributed to the combination of off-centering cations in the rock salt structure, Ge/Mn positional disorder, dislocations, and abundant Ge-rich and Mn-rich nanoparticles. A value of ∼1.5 can be achieved for GeMnTe-15.1%SbTe with a of 0.96 in the temperature range of 400-823 K.