High temperature thermoelectric properties of delafossite-type oxides CuFe0.98M0.02O2 (M=Mg, Zn, Ni, Co, Mn, or Ti)

We have measured the electrical conductivity sigma and Seebeck coefficient S of CuFe_0.98M_0.02O₂ (M=Mg, Zn, Ni, Co, Mn, or Ti) at high temperatures. The highest electrical conductivity of 30 S/cm was obtained with the Mg-doped sample above 600 K. The Seebeck coefficient of the doped samples were still high (higher than 210 muV/K). The maximum power factor P=sigmaS ²=4.1times10^-4 W/mK² at 1150 K was obtained with CuFe_0.98Mg_0.02O₂. The above results were well explained in terms of the valence states and ionic radii of the dopants. The chemical stability of the doped samples was discussed by measuring the temperature dependent power factor during the repeated cycles of heating and cooling processes.