The effect of nanostructure on the thermoelectric figure-of-merit of La0.875Sr0.125CoO3

Nanostructured thermoelectric materials prepared by mechanical alloying and sintering have already shown enhanced values of the dimensionless thermoelectric figure-of-merit (ZT) for different families of materials. Oxide materials, however, are still far from reaching competitive values of thermoelectric efficiency. In this work we report results regarding a nanostructuring approach on thermoelectric transport properties of La0.875Sr0.125CoO3 obtained by solid-state reaction combined with ball milling and sintering. This simple method allows us to obtain a set of samples with very different nanostructures, with grain sizes ranging from 19 nm to 0.7 μm. Both, thermal and electrical properties, were found to be dependent on the grain size. The grain size reduction results in an enhancement of the electrical resistivity whereas the thermal conductivity is strongly reduced. Interestingly, the thermoelectric power of the sample with the smallest grain size increases significantly compared to the microcrystalline sample over the whole temperature range. As a result the thermoelectric figure of merit of the sample with the smallest grain size is enhanced by 30% compared to the microcrystalline sample above room temperature. This finding confirms the validity of the nanostructuring approach on thermoelectric oxides in order to improve their thermoelectric efficiency.