High Temperature Thermoelectric Properties of Ca_1-xY_xMnO_2.98 (0.05≤x≤0.30)

Abstract

High temperature thermoelectric properties of Ca_1-xY_xMnO_2.98 (x=0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) have been measured in the temperature range from 300 to 1273 K. Ca_1-xY_xMnO_2.98 (x=0.05, 0.10, 0.15, 0.20) exhibited the metal-insulator transition (T_t) in the relation between electrical resistivity and temperature, and the transition temperature increased with increasing x content. Electrical resistivity in the metallic region above T_t decreased with increasing x content, reflecting the increase of Mn³⁺ ions. In the semiconductor region below T_t, the band gap increased with increasing the doped x content. The Seebeck coefficients of all samples were negative, and the absolute value of Seebeck coefficient at low temperature decreased with increasing x content. Thermal conductivity decreased with increasing x content due to the increase in phonon scattering by the doped Y ions. Among substituted CaMnO₃, the highest figure of merit of Z=1.77×10^-4 K^-1 was obtained for x=0.15 at 1273 K.