Abstract
We have studied crystal structure and high temperature thermoelectric properties of delafossite-type oxide CuFe1–xNixO2 (0 ≤ x ≤ 0.05). There is no significant difference in the lattice parameter a among the Ni-doped samples and CuFeO2 due to the decrease of Fe–O distance and simultaneous increase of O–Fe–O angle by the Ni doping. The lattice parameter c is slightly longer in the doped samples than that of CuFeO2, reflecting the increase of Cu–O distance. The decrease of the Fe–O distance indicates hole doping in the Fe-site. Because of the hole doping, the electrical conductivity σ is enhanced to 18 S/cm. The Seebeck coefficient S decreases slightly by the Ni doping, but remains high (S > 250 μV/K). The obtained Seebeck coefficient at high temperature agrees well with theoretical values based on the generalized Heikes formula that takes the spin entropy flux into account. The thermal conductivity κ of CuFe1–xNixO2 is relatively high (κ > 4 W/mK). The maximum ZT value, ZT = σS2T/κ = 0.14 is obtained with the sample of x = 0.01 at 1100 K.
