Power factors of Ca3Co2O6 and Ca3Co2O6-based solid solutions

A polycrystalline sample of Ca3Co2O6 was prepared by solid state reaction of CaCO3 and Co3O4 at 1243 K in air. The electrical resistivity (rho) of Ca3Co2O6 exhibited semiconducting behavior and ranged from 1.6x10(2) to 1.3x10(-1) Ohm cm with temperature from 400 to 1170 K. The Seebeck coefficient (S) showed positive value, and decreased from 660 to 140 muV/K with increasing the temperature from 350 to 1170 K. The power factor (S-2/rho) tended to increase with increasing temperature, and the maximum value was 1.6x10(-5) W/(m K-2) at 1150 K. Samples with the starting compositions of (Ca(1-x)A(x))(3)Co2O6 (A=Y, La, and Bi, x=0.03) and Ca-3(Co1-yMy)(2)O-6 (M=Cr and Cu, y=0.03) were also heated at 1243 K in air to prepare Ca3Co2O6-based solid solutions. The changes of lattice parameters and widths of X-ray diffraction peaks for the obtained samples indicated substitutions of Y, La, Bi for Ca, Cr and Cu for Co, although the samples included trace amount of impurities. Substitutions of Bi and Cu increased the power factors of the solid solutions, and the maximum values were 3.4x10(-5) W/(m K-2) (A=Bi at 1130 K) and 2.3x10(-5) W/(m K-2) (M=Cu at 1150 K). The Seebeck coefficients of the solid solutions with Y and La were negative below 400 K. (C) 2003 Elsevier B.V. All rights reserved.