Thermoelectric properties of chalcogenides with the spinel structure

Many compounds with the spinel structure type have been analyzed for their thermoelectric properties. Published data was used to augment experimental results presented here and to select promising thermoelectric spinels. Compounds studied here include Cu_0.5A1_0.5Cr₂Se₄, Cu_0.5,Co_0.5Cr₂Se₄, Cu_0.5In_0.5Cr₂Se₄ and CuIr₂Se₄. Many exhibit low lattice thermal conductivity of about 20 mW/cmK, independent of temperature. Two representative series of compounds Ga_xCu_1-xCr₂Se₄ 0<x < 0.6 and Cu_xZn_1-xCr₂Se₄ 0<x< 0.3 have been studied to examine the doping region of interest for both high and low temperature thermoelectric applications. Ferromagnetic, small polaron semiconductors are found in both series of compounds. Ga_xCu_1-xCr₂Se₄ shows a metal insulator transition, from a p-type metal at x=0 to a p-type and then n-type semiconductor as x crosses 1/2. The maximum figure of merit ZT is of order 0.1. Cu_xZn_1-xCx₂Se₄ transitions from a p-type semiconductor to a p-type metal as x increases.