Discordant Distortion in Cubic GeMnTe 2 and High Thermoelectric Properties of GeMnTe 2 - x %SbTe.

GeMnTe 2 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 2 is locally distorted from the ideal rock salt structure with Ge 2+ cations being discordant and displaced ∼0.3 Å off the octahedron center. By alloying GeMnTe 2 with SbTe, the carrier concentration can be tuned in GeMnTe 2 - x %SbTe ( x = 15.1), leading to converged multiple broad valence bands and a high Seebeck coefficient of >200 μV K -1 from 300 to 823 K. The system exhibits a large density-of-state effective mass of >10 m e and a high weighted mobility of 80 cm 2 V -1 s -1 , leading to a power factor of 15 μWcm -1 K -2 at 823 K. The composition GeMnTe 2 -15.1%SbTe exhibits very low lattice thermal conductivity of ∼0.5 Wm -1 K -1 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 ZT value of ∼1.5 can be achieved for GeMnTe 2 -15.1%SbTe with a ZT ave of 0.96 in the temperature range of 400-823 K.