  We present here the thermoelectric properties of olivine-type Fe2GeCh4 (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 Fe2GeCh4 is in
good agreement with the experimental reports at room temperature, with the
carrier concentration around 1018-1019cm-3. All the investigated systems show
an anisotropic nature in their electrical conductivity, resulting in a value
less than the order of 102 along the a-axis compared to the b- and c-axes.
Among the studied compounds, Fe2GeS4 and Fe2GeSe4 emerge as promising
candidates with good thermoelectric performance.
