Electronic Structure and Transport Properties of Ba8Cu6Ge40 Clathrate Calculated by Density Functional Theory

Semiconducting clathrates are attracting a great deal of attention as potential candidates of thermoelectric material based on a design concept called Phonon Glass and Electron Crystal (PGEC). Since most of the thermoelectric clathrates are n-type, developing a p-type clathrate with high thermoelectric performance is an important issue. In this study, the electronic structure and thermoelectric properties of Ba8Cu6Ge40 clathrate are calculated based on density functional theory (DFT) to search for new p-type clathrates. An energy gap is formed in the electronic band structure of Ba8Cu6Ge40, and the Fermi energy lies in the valence band, indicating that Ba8Cu6Geぃis a p-type semiconductor. The effective mass of the valence
band is larger than that of the conduction band. The Seebeck coefficient for p-type is larger than that for n-type, reflecting the difference in effective mass. According to the dependence of Seebeck coefficient and electrical conductivity on the chemical potential, adjusting the Fermi energy, corresponding to the carrier concentration, to the optimum value improves the power factor. Therefore, the results of DFT calculation show that Ba8Cu6Ge40 has excellent properties as a candidate for p-type thermoelectric materials.