Fabrication and thermoelectric properties of CuMn1+xO2 (x=0~0.2) ceramics

Crednerite CuMnO2 ceramic has been investigated for the first time in this study as a potential thermoelectric material based on its low band gap and layer structure. Undoped CuMn1+xO2 (0≤x≤0.2) samples with a delafossite structure were prepared via solid-state reactions and sintered at 1353 K for 2.5 h in argon. The phase, microstructure, and thermoelectric properties of the CuMn1+xO2 (0≤x≤0.2) samples were discussed by adjusting the sample composition. The crystallinity and microstructure of sintered bulks were analyzed using X-ray diffraction and scanning electron microscopy, respectively. The thermoelectric properties of the samples were studied from room temperature to 573 K. CuMn1+xO2 sintered bulks showed a relative density of 91% and a layered structure. The composition affected the phases and thermoelectric properties of sintered bulks. Bulks with the crednerite CuMnO2 phase were only obtained at x=0.1 or 0.143. The crednerite CuMn1+xO2 (0≤x≤0.2) samples were p-type semiconductors. The Seebeck coefficient (S) increased and the electrical conductivity (σ) decreased with Mn content up to x=0.1. Excess Mn content (x>0.143) decreased the Seebeck coefficient and increased electrical conductivity. The power factor (PF) of the CuMn1+xO2 (0≤x≤0.2) samples improved due to the significant increase in the Seebeck coefficient. The thermal conductivity (κ) decreased with increasing temperature. The lowest κ value (6.79 W m−1 K−1) was found for the CuMn1.1O2 sample at 573 K. The dimensionless figure of merit ZT values of the undoped CuMn1+xO2 bulks are too small for these bulks to be candidates for thermoelectric materials due to weak electrical conductivity.