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

Ca doped NiCo2O4 spinel materials were synthesized by conventional solid state reactions at 90 degreesC. Thermoelectric properties of polycrystalline products were characterized at high temperature range of similar to 800 degreesC in air. d.c. conductivity of the prepared polycrystalline 5 mol % Ca doped NiCo2O4 was about S m(-1) at 300 degreesC. The value of d.c. conductivity was increased with the temperature increasing. Thermoelectric voltage of polycrystalline Ni1-xCaxCo2O4 (x+0-0.05) was positive at 300-800 degreesC, this showed p-type thermoelectric properties. The Seebeck coefficient of 5 mol % Ca doped NiCo2O4 was ca. 300 mu V/K at 600 degreesC. The value of the Seebeck coefficient of Ni1-xCaxCo2O4 polycrystalline products decreased with the increasing temperature. Thermal conductivity of 5 mol % Ca doped NiCo2O4 was ca. 2.2 W m(-1) K-1 at 600 degreesC. The estimated thermoelectric figure-of-merit, Z, of 5 mol % Ca doped NiCo2O4 spinel polycrystalline product was about 3.5 x 10(-5) K-1 at 600 degreesC. (C) 2004 Kluwer Academic Publishers.