Thermogravimetric Study and High-Temperature Thermoelectric Properties of [Ca2(Co1-xAx)O3]0.62CoO2

Abstract

Systematic ion substitution has been performed on the Co site in the rock-salt (RS)-type [Ca₂CoO₃] subsystem of misfit-layered cobalt oxide [Ca₂(Co_1-xA_x)O_3-delta] _0.62CoO₂ (A = Nb, Ru, Ta, Pb, W, La and Zr). The oxygen deficiency delta and the decomposition temperature T_d of the substituted samples have been determined by means of the thermogravimetric analysis (TGA). Upon heating, the oxygen atoms are gradually released from the RS-type subsystem up to delta~0.10. A small amount (x = 0.10) of the substitution remarkably increases T_d from 1173 K (x = 0) up to 1246 K (A = Nb). The Pb-substituted samples show substantial decrease in electrical resistivity p from 19.2 mOmegacm to 13.8 mOmegacm (x = 0.10) at 950 K. The highest thermoelectric power, S²p^-1 = 2.1times10^-4 WK^-2 m^-1 , is realized for the Pb-substituted sample with x = 0.10 at 950 K