Substitutional defects enhancing thermoelectric CuGaTe2

Abstract

It is known that phonon scattering by point defects is effective for reducing the lattice thermal conductivity due to the mass and strain fluctuations between the host and guest atoms. Therefore a high concentration of defects having big mass and strain fluctuations is desired. Based on this strategy, this work focuses on the effect of Ag/Cu substitution on reducing the lattice thermal conductivity in CuGaTe₂. It is seen that the lattice thermal conductivity can be significantly reduced by a factor of 4 when >30% Cu is substituted by isovalent Ag, which further leads to a great enhancement in the thermoelectric figure of merit, zT in the entire temperature range. The peak zT of ∼1.0 at 750 K is obtained in the samples with an optimal carrier concentration, which is one of the highest reported so far for this material in a single phase at the same temperature. This work demonstrates CuGaTe₂ as a promising thermoelectric material and the point defect scattering as an effective strategy for enhancing its zT.