Exploring thermoelectric performance of Ca3Co4O9+δ ceramics via chemical electroless plating with Cu

Ca3Co4O9+δ ceramic is a potential p-type thermoelectric material for high temperature applications, however, its thermoelectric performance is limited by the strongly interrelated thermoelectric parameters. In this work, we develop an effective method to simultaneously tune the electrical and thermal transport properties of Ca3Co4O9+δ. We firstly synthesize Ca3Co4O9+δ powders and subsequently obtain surface modified Cu/Ca3Co4O9+δ through a well-controlled electroless plating technique followed by a fast Spark Plasma Sintering process. The detailed characterizations of microstructures and chemical compositions of Cu/Ca3Co4O9+δ samples suggest that the plated Cu has been doped into the Ca3Co4O9+δ after sintering. The doped Cu substitutes Ca ions, creates local oxygen deficiency and increases the ratios of Co3+ and Co4+, which reduces the carrier concentration and induces Ca-missed regions, thus, reducing the electrical and thermal conductivity. This study indicates that introducing metallic Cu phase by chemical electroless technique is a promising method to tune the thermoelectric properties of Ca3Co4O9+δ-based ceramics by altering the chemical composition and microstructures.