Predicted thermoelectric properties of olivine-type Fe < inf > 2 < /inf > GeCh < inf > 4 < /inf > (Ch = S, Se and Te)

Abstract

We present here the thermoelectric properties of olivine-type Fe 2 GeCh 4 (Ch = S, Se and Te) using the linear augmented plane wave method based on first principles density functional calculations. The calculated transport properties using the semi-local Boltzmann transport equation reveal very high thermopower for both S and Se-based compounds compared to their Te counterparts. The main reason for this high thermopower is the quasi-flat nature of the bands at the valence and conduction band edges. The calculated thermopower of Fe 2 GeS 4 is in good agreement with the experimental reports at room temperature, with the carrier concentration around 10 18 -10 19 cm -3 . All the investigated systems show an anisotropic nature in their electrical conductivity, resulting in a value less than the order of 10 2 along the a-axis compared to the b- and c-axes. Among the studied compounds, Fe 2 GeS 4 and Fe 2 GeSe 4 emerge as promising candidates with good thermoelectric performance.