Effect of Bi Substitution on Microstructure and Thermoelectric Properties of Polycrystalline [Ca2CoO3] pCoO2

概要

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Partially Bi-substituted [Ca2CoO3] pCoO2 ceramics were synthesized using a hot-forging technique. Then, the effects of Bi-substitution on microstructure and thermoelectric properties were evaluated. The average grain size of the precursor powder prepared by a solid-state reaction increased concomitant with the increase in Bi content. Furthermore, the electrical resistivity ($\rho$) of the hot-forged sample was decreased accordingly. Seebeck coefficient ($S$) was increased slightly by Bi-substitution and was less affected by grain size. Therefore, power factor ($\mathit{PF}=S^{2}/\rho$) was improved. On the other hand, the $\rho$ of the hot-forged sample was reduced using a large-grained precursor powder prepared by a solution growth method. Different from the case of the former samples made from as-sintered powder, the $\rho$ of the sample made from large-grained powder was increased slightly with the increase in Bi content. These results indicate that the main advantage of Bi-substitution for the decrease in the $\rho$ of the hot-forged sample is the enhanced grain growth during the heat treatment processes.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-05-15