Nanophase oxalate precursors of thermoelectric CoSb3 by controlled coprecipitation predicted by thermodynamic modeling

Abstract

The precursors for the formation of thermoelectric skutterudite CoSb3 nanoparticles are predicted by thermodynamic modeling of the complex chemical species. Based on the results, equimolar mixture of CoC2O4 center dot 2H(2)O and Sb(C2O4) OH are successively co-precipitated under controlled conditions of pH = 2.7 and concentration of reactants. The as synthesized powder was decomposed at 350 degrees C to remove the organic molecules and further reduced to CoSb3 phase by heating at 530 degrees C under hydrogen flow. The obtained powder was consolidated by spark plasma sintering (SPS). CoSb3 prepared by controlled chemical co-precipitation has p-type behavior with a positive sign of the Seebeck coefficient. TE transport properties were measured, which revealed that the Seebeck coefficient increased 2.5 times with increasing the temperature and it is lower than the ball milled CoSb3. Thermal conductivity of sintered CoSb3 at 773 K starts from 0.06 W/cm K at room temperature and decreases to 0.04 W/cm K at 700 K, which is lower than the bulk counterpart. The ZT of coprecipitated CoSb3 and SPS consolidated at 773 K shows 2 times higher than the ball milled one. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.