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 (σ) 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.