Synthesis and thermoelectric characterization of polycrystalline Ni1-xCaxCo2O4 (x= 0-0.05) spinel materials

Ca doped NiCo2O4 spinel materials were synthesised by conventional solid state reactions at 900 C. Thermoelectric properties of polycrystalline products were characterised at a high temperature range of about 800 C in air. Direct current conductivity of the prepared polycrystalline 5 mol% Ca doped NiCo2O4 was about 60 S/m at 300 C. The value of dc conductivity increased with increasing temperature. Thermoelectric voltage of polycrystalline Ni1-xCaxCo2O4 (x = 0-0.05) was positive at 300-800 C, showing p-type thermoelectric properties. The Seebeck coefficient of 5 mol% Ca doped NiCo2O4 was about 300 microV/K at 600 C. The value of the Seebeck coefficient of Ni1-xCaxCo2O4 polycrystalline products decreased with increasing temperature. The thermal conductivity of 5 mol% Ca doped NiCo2O4 was about 2.2 W/m.K at 600 C. The estimated thermoelectric figure-of-merit of 5 mol% Ca doped NiCo2O4 spinel polycrystalline product was about 3.5 x 10 exp(-5)/K at 600 C. 17 refs.