Improved thermoelectric performance of BiCuSeO via increased bond covalency and carrier mobility.

BiCuSeO oxyselenides have been successfully fabricated by self-propagating high-temperature synthesis (SHS). Compared with the SHS process of the binary or ternary alloys, thermal analysis indicates the ignition temperature of quaternary layered BiCuSeO oxyselenides approaches the second lower melting point of the compound. The ZT value of SHS-synthesized BiCuSeO is almost 1.5 times larger than that of the solid state reaction (SSR) product at 873K. This is attributed to the existing amorphous region, nano-pores, and optimized grain size. Furthermore, with the partial substitution of Pb 2+ for Bi 3+ , ZT was enhanced through the optimization of charge carrier concentration and band gap narrowing. This achieved a ZT of 0.91 at 873K for Bi1-xPbxCuSeO (x=0.04). Combining with the Debye-Callaway model

Point defects and nano-grains are very effective ways to control the thermal conductivity in oxide-based thermoelectrics. Here we use the optimised Debye-Callaway model to understand how the effect of point defects and nano-grains to reduce the thermal conductivity by inducing normal process and oxygen vacancy in oxide-based thermoelectrics. Our results reveal that this model can be effective to fit the experimental data of thermal conductivity in ZnO-, CaMnO 3 -, BiCuSeO-, SrTiO 3 -and In 2 O 3 -based systems, which indicate that the normal scattering process and the oxygen vacancy will make obvious contribution to the thermal conductivity as compared with alloy compounds system. These calculations also propose that it could be desirable to obtain higher ZT by controlling the concentration of oxygen vacancy in the nano-grained thermoelectric oxides.

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