Thermoelectric Properties of Ca-Ir-O Compounds Prepared by Spark Plasma Sintering

Abstract

Ca-Ir-O compounds in various molar ratios of Ir to Ca (RIr/Ca) from 0.2 to 1.2 were synthesized by solid-state reaction and compacted by spark plasma sintering (SPS). Ca4IrO6 and CaIrO3 with a small amount of second phase were obtained at RIr/Ca=0.25 and 1.0, respectively, whereas Ca2IrO4 in a single phase was obtained at RIr/Ca=0.5. The electrical conductivity was 4×10−4 to 150 Sm−1 at room temperature and exhibited a semiconducting behavior for all the samples. The Seebeck coefficient at RIr/Ca=0.4 to 0.7 showed negative values whereas samples with RIr/Ca=0.25 and 0.9 to 1.2 showed positive values. The thermal conductivity was 1.1 to 2.7 Wm−1K−1 at room temperature and slightly decreased with increasing temperature. The highest ZT value of p-type was 0.006 at 1023 K and RIr/Ca=1.1 and 1.2, while that of n-type was 0.0022 at 800 K and RIr/Ca=0.5.