Ni-doping effect on thermoelectric properties of c-axis-oriented CuFeO₂ ceramics

The combined effect of chemical doping and grain orientation on the thermoelectric properties of delafossite-type CuFeO₂ ceramics was investigated. Ni was chosen as the dopant, whereas the reactive templated grain growth method was used for the fabrication of grain-oriented bulk ceramics. Nanorods of Ni-doped α-FeOOH with a nominal Ni content of up to 5 mol% were synthesized by the hydrothermal method and were then used as the template to fabricate Ni-doped CuFeO₂ ceramics with a preferred c-axis orientation. The electrical conductivity, Seebeck coefficient, and thermal conductivity of the Ni-doped CuFeO₂ ceramics along the in-plane direction (perpendicular to the orientation axis) were measured at temperatures between 300 and 1100 K. Ni doping was found to effectively increase the electrical conductivity and decrease the thermal conductivity, whereas it maintained a high Seebeck coefficient of around 400 μV K⁻¹. Consequently, the c-axis-oriented CuFeO₂ ceramics doped with 1 and 3 mol% Ni showed an enhanced dimensionless figure of merit of 0.08 at 900 K.