Thermoelectric properties of Nb3Sb2Te5

Nb3Sb2Te5 was prepared by reacting the elements in the respective stoichiometric ratios at 600 °C. Its crystal structure was re-determined via X-ray single crystal structure studies to check for Sb/Te ordering. In a prior study Nb3Sb2Te5 was reported to crystallize in the Ir3Ge7 type, space group Im3¯m, with a = 9.8155(8) Å, with mixed Sb/Te occupancies. We found that complete Sb/Te ordering, which lowered the symmetry by removal of the inversion center, yielded improved residual factors, e.g. from R1 = 2.97% in Im3¯m (a = 9.8180(4) Å) to R1 = 2.47% in I4¯3m. Because of this ordering, no Te–Te contacts <3.4 Å prevail. Electronic structure calculations predicted nonmetallic properties, which were verified by temperature-dependent conductivity studies. The investigation of the thermoelectric properties yielded at 300 K a Seebeck coefficient of −29 μV K−1, electrical conductivity of 75 Ω−1 cm−1, and thermal conductivity of 5.7 W m−1 K−1. The thermoelectric figure-of-merit improves rapidly with increasing temperature.