  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.
