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 (σ) of the pv-CaIrO3 specimen decreased from 1.74 × 104 to 1.45 × 104 Sm-1, while the σ of the ppv-CaIrO3 specimen increased from 5.0 × 101 to 9.8 × 102 Sm-1 with increasing temperature from 298 to 1023 K. The Seebeck coefficient (S) of the pv-CaIrO3 specimen was around -44 μVK-1 at room temperature and increase to the highest value of 40 μVK-1 at 1023 K. The S of the ppv-CaIrO3 specimen decreased with increasing temperature and had an almost constant value of about 60 μVK-1 above 600 K. The thermal conductivity (κ) of the ppv-CaIrO3 specimen decreased from 2.7 to 1.2 Wm-1K-1 and that of the pv-CaIrO3 specimen decreased from 1.5 to 1.2 Wm-1K-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.