High-Throughput Screening of Sulfide Thermoelectric Materials Using Electron Transport Calculations with OpenMX and BoltzTraP

The electron transport properties of 809 sulfides have been investigated using density functional theory (DFT) calculations in the relaxation time approximation, and a material design rule established for high-performance sulfide thermoelectric (TE) materials. Benchmark electron transport calculations were performed for Cu12Sb4S13 and Cu26V2Ge6S32, revealing that the ratio of the scattering probability of electrons and phonons (kappa(lat)tau(-1)(el)) was constant at about 2 x 10(14) W K-1 m(-1) s(-1). The calculated thermopower S dependence of the theoretical dimensionless figure of merit ZT (DFT) of the 809 sulfides showed a maximum at 140 mu V K-1 to 170 mu V K-1. Under the assumption of constant kappa(lat)tau(-1)(el) of 2 x 10(14) W K-1 m(-1) s(-1) and constant group velocity v of electrons, a slope of the density of states of 8.6 states eV(-2) to 10 states eV(-2) is suitable for high-ZT sulfide TE materials. The Lorenz number L dependence of ZT (DFT) for the 809 sulfides showed a maximum at L of approximately 2.45 x 10(-8) V-2 K-2. This result demonstrates that the potential of high-ZT sulfide materials is highest when the electron thermal conductivity kappa(el) of the symmetric band is equal to that of the asymmetric band.