Thermoelectric properties of two-dimensional slabs of Ba8Ga16Ge30 from first principles

Thermoelectric effects enable the direct conversion between thermal and electrical energy and provide an alternative route for power generation and refrigeration. The clathrate Ba8Ga16Ge30 has the highest figure of merit (ZT ~

1. among other members in the family of type-I inorganic clathrates. Enhancement of the thermoelectric properties have been observed in multilayered superlattices, quantum wires and in nanostructured materials, either due to the increase in power-factor (S^{2}\sigma) or due to the reduction of lattice thermal conductivity (\kappa). Here, we investigate the thermoelectric properties of two-dimensional slabs with varying thickness of Ba8Ga16Ge30 using semi-classical Boltzmann transport theory with constant scattering approximation. We observe that, there exists a delicate balance between the electrical conductivity and the electronic part of the thermal conductivity in reduced dimensions and the insights from these results can directly be used to control particle size in nanostructuring experiments. The calculated properties are consistent with the recent, first measurements on bulk nanostructured samples.