Thermoelectricity of CaIrO3 ceramics prepared by spark plasma sintering

Polycrystalline bulk CaIrO3 as a main phase with minor phases of IrO2 and/or Ca2IrO4 was prepared by spark plasma sintering (SPS) at 1273 K. Metastable CaIrO3 with a perovskite-type structure (pv-CaIrO3) formed by heat-treatment at 1273 K for 43.2 ks and transformed into a post-perovskite structure (ppv-CaIrO3) by heat-treatment at 1273 K for 259.2 ks. The electrical conductivity (sigma) of the pv-CaIrO3 specimen decreased from 1.74 x 10(4) to 1.45 x 10(4) Sm-1, while the sigma of the ppv-CaIrO3 specimen increased from 5.0 x 10(1) to 9.8 x 10(2) Sm-1 with increasing temperature from 298 to 1023 K. The Seebeck coefficient (S) of the pv-CaIrO3 specimen was around -44 mu VK-1 at room temperature and increase to the highest value of 40 mu VK-1 at 1023 K. The S of the ppv-CaIrO3 specimen decreased with increasing temperature and had an almost constant value of about 60 mu VK-1 above 600 K. The thermal conductivity (kappa) of the ppv-CaIrO3 specimen decreased from 2.7 to 1.2 Wm(-1)K(-1) and that of the pv-CaIrO3 specimen decreased from 1.5 to 1.2 Wm(-1)K(-1) with increasing temperature from 298 to 1023 K. The highest dimensionless figure of merit values (ZT) of the pv-CaIrO3 and the ppv-CaIrO3 specimens were 0.02 and 0.003 at 1023 K, respectively. (C) 2009 The Ceramic Society of Japan. All rights reserved.