Abstract:

Bi- and Cu-substituted Ca₃Co₄O₉ samples were prepared by conventional solid-state reaction method and the e?ect of element substitution on the microstructures and thermoelectric properties was investigated. Partial substitution of Cu for Co leads to an increase in electrical conductivity and a decrease in Seebeck coe±cient due to the rise of hole concentration. The microstructure of Cu-substituted sample is almost unchanged compared with undoped Ca₃Co₄O₉. On the other hand, partial substitution of Bi for Ca gives rise to a significant increase in the grain size, and c-axis-oriented structure can be formed in Ca_2.7Bi_0.3Co₄O₉, resulting in an obvious increase in electrical conductivity. Cu and Bi co-substitution further increases the grain growth and the electrical conductivity of Ca_2.7Bi_0.3Co_3.7Cu_0.3O₉. Thus, Cu and Bi co-substitution samples possess the optimal thermoelectric performance at high temperature and the highest value of power factor can reach 3.1×10^-4 Wm^-1?K^-2 at 1000 K.

Key words: Ca₃Co₄O₉, Element substitution, Microstructure, Thermoelectric properties