Efficient thermoelectricity in Sr2Nb2 O7 with energy-dependent relaxation times

We evaluate theoretically the thermoelectric efficiency of the layered perovskite Sr2Nb2O7 via calculations of the electronic structure and transport coefficients within density-functional theory and Bloch-Boltzmann relaxation-time transport theory. The predicted figure-of-merit tensor ZT, computed with energy-, chemical potential-, and temperature-dependent relaxation times, has one component increasing monotonically from around 0.4 at room temperature to 2.4 at 1250 K at an optimal carrier density of around 2×1020cm-3, while the other components are small. The Seebeck coefficient is about 250 to 300 μV/K at optimal doping and reaches 800 μV/K at lower doping. We provide a python code implementing various approximations to the energy-dependent relaxation-time transport, which can be used to address different systems with an appropriate choice of material parameters.