Tunable Low-Temperature Thermoelectric Transport Properties in Layered CuCr(S1-xSex)2 System

Abstract

We have characterized the layered CuCr(S,Se)2 system for the spin-polarized electronic band structures and low-temperature thermoelectric transport properties. The electronic band structure calculations reveal semiconducting behavior for CuCrS2, CuCr(S0.5Se0.5)2 and CuCrSe2 with an indirect bandgap of 0.42, 0.30 and 0.10 eV, respectively. The systematically decreased bandgap with increasing Se content is in line with the experimental observations showing a semiconductor-to-metal transition with increasing Se-substitution level in the CuCr(S1-xSex)2 system because of an increase in the charge carrier density. The p-type Seebeck coefficient shows a linear temperature dependence for the samples, like in degenerate semiconductors or metals. The remarkably large Seebeck coefficient even in metallic samples is due to a relatively large effective mass of charge carriers. As the thermal conductivity is intrinsically low owing to the layered crystal structure and is further decreased for the Se-substituted samples because of the increased phonon scattering from point defects, the thermoelectric characteristics are promising. The highest dimensionless figure-of-merit values were seen for the x=0.5 sample, e. g., 0.04 at 400 K.