Thermoelectric properties of plasma sprayed of calcium cobaltite (Ca2Co2O5)

The thermoelectric properties of calcium cobaltite deposits produced by the plasma spray process are investigated from room-temperature to 873 K. Synthesis of Ca3Co2O6 and Ca2Co2O5 powders were prepared by the solid-state reaction from CaO and CoOx starting powders. During their subsequent plasma spray Ca particles experience preferential evaporation within the plasma, resulting in a complex interplay among process conditions, stoichiometry, and resultant phases. The as-sprayed material predominantly contains amorphous and secondary phases. Upon annealing, the deposits show sensitivity to phase evolution and therefore thermoelectric properties. Through screening studies, optimal annealing conditions were identified which show a p-type Seebeck coefficient value of 180 mu V K-1, electrical conductivity of 1.09 x 10(4) S m(-1), thermal conductivity of 1.16 W m(-1) K-1 at 873 K. The resultant figure of merit value reached 0.266 for this combination of processing and thermal treatment and is in line with data reported from other techniques for this system.