Abstract
The electrical conductivity, Seebeck coefficient, and thermal conductivity of polycrystalline M0.6Fe2.4O4 (M = Ni, Ni0.5Mg0.5, Ni0.5Zn0.5, Zn) were measured to elucidate cation distribution-dependent changes. Preferential occupation by the doped cation in the iron spinel has been noted: Zn2+ ions prefer to occupy the tetrahedral A-site, while Ni2+ and Mg2+ prefer to occupy the octahedral B-site. While the electrical conductivity and Seebeck coefficient are almost cation distribution-independent, the thermal conductivity at room temperature is sensitive to the cation distributions. The lowest thermal conductivity of 2.0 W m−1 K−1 at room temperature is observed for Zn0.6Fe2.4O4. The value is about one third of that of Ni0.6Fe2.4O4. The thermal transport of MxFe3−xO4 is mainly affected by cation distribution at the A-site, while the electrical transport is affected by the B-site, which is discussed in terms of the point defects at the A- and B-sites. Due to the disordering at the A- and B-sites, the thermal conductivity of MxFe3−xO4 could be reduced without decreasing the electrical conductivity. Doped spinel-ferrite MxFe3−xO4 would be a kind of “phonon-glass electron-crystal” material.
