Thermoelectric properties of Zn-doped Ca_(3)AlSb_(3)

Polycrystalline samples of Ca_(3)Al_(1)−_(x)Zn_(x)Sb_(3), with x = 0.00, 0.01, 0.02, and 0.05 were synthesized via a combined ball milling and hot pressing technique and the influence of zinc as a dopant on the thermoelectric properties was studied and compared to the previously reported transport properties of sodium-doped Ca_(3)AlSb_(3). Consistent with the transport in the sodium-doped material, substitution of aluminum with zinc leads to p-type carrier conduction that can be sufficiently explained with a single parabolic band model. It is found that, while exhibiting higher carrier mobilities, the doping effectiveness of zinc is lower than that of sodium and the optimum carrier concentration for a maximum figure of merit zT is not reached in this study. We find that the grain size influences the carrier mobility, carrier concentration, and lattice thermal conductivity, leading to improved properties at intermediate temperatures, and highlighting a possible approach for improved figures of merit in this class of materials.