Room temperature thermoelectric properties of p-type CuMn1.1−xExO2 (E=Mg, Ca, Sr, x=0-0.2) ceramics

CuMn1.1−xExO2 (E=Mg, Ca, Sr, x=0-0.2) bulks with a delafossite structure were prepared via solid-state reactions and sintered at 1253 K for 2.5 h in argon. The phase, microstructure, and thermoelectric properties of the CuMn1.1−xExO2 (E=Mg, Ca, Sr, x=0-0.2) samples were discussed using different cation substitution contents. The crystallinity and microstructure of the bulks were analyzed using X-ray diffraction and scanning electron microscopy, respectively. The thermoelectric properties of the bulks were studied at room temperature. Both different dopants and cation substitution contents affected the phases and thermoelectric properties of sintered bulks. Bulks with the crednerite CuMnO2 phase were obtained in all samples, although the second phase Mn3O4 existed on Mg substitution samples with an x value of up to 0.15. The crednerite CuMn1.1−xExO2 (E=Mg, Ca, Sr, x=0-0.2) samples were p-type semiconductors. The thermoelectric properties of the CuMn1.1−xExO2 (E=Mg, Ca, Sr, x=0-0.2) bulks were enhanced by cation substitution, because electronic conductivity increased while thermal conductivity was suppressed and the Seebeck coefficient did not fall much. The CuMn0.9Mg0.2O2 sample showed the lowest thermal conductivity and the largest ZT at room temperature. This study demonstrates that Mg substitution was highly effective for enhancing the room-temperature thermoelectric properties of CuMnO2.