Effect of partial substitution of Ca for Al on the microstructure and high-temperature thermoelectric properties of CuAlO 2

Abstract

The sintered CuAl 1− x Ca x O 2 (0 ≤ x ≤ 0.2) bodies contained the CuAl 1− x Ca x O 2 solid solution with a rhombohedral structure, R 3 ¯ m , along with second phases such as CuO, CaO, Ca 3Al 2O 6, and CaAl 4O 7 phases. It was found that, as the amount of Ca in the CuAl 1− x Ca x O 2 samples increased, the grain size increased from 0.94 to 3.01 μm and the porosity decreased from 29.3 to 6.8%. The substitution of Ca up to x = 0.1 for Al in the CuAl 1− x Ca x O 2 samples gave rise to an increase in both the electrical conductivity and the Seebeck coefficient. On the other hand, the higher Ca substitution ( x ≥ 0.15) decreased both the electrical conductivity and the Seebeck coefficient. The highest value of power factor (7.82 × 10 −5 Wm −1 K −2) was attained for CuAl 0.9Ca 0.1O 2 at 1140 K. We demonstrate that the Ca substitution is highly effective for enhancing high-temperature thermoelectric properties.