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

CaCoO 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 CaCoO. We firstly synthesize CaCoO powders and subsequently obtain surface modified Cu/CaCoO 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/CaCoO samples suggest that the plated Cu has been doped into the CaCoO after sintering. The doped Cu substitutes Ca ions, creates local oxygen deficiency and increases the ratios of Co and Co, 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 CaCoO-based ceramics by altering the chemical composition and microstructures