Cation Distribution Dependence on Thermoelectric Properties of Doped Spinel M_0.6Fe_2.4O₄

Abstract

The electrical conductivity, Seebeck coefficient, and thermal conductivity of polycrystalline M_0.6Fe_2.4O₄ (M = Ni, Ni_0.5Mg_0.5, Ni_0.5Zn_0.5, 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 Zn_0.6Fe_2.4O₄. The value is about one third of that of Ni_0.6Fe_2.4O₄. The thermal transport of M_xFe_3−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 M_xFe_3−xO₄ could be reduced without decreasing the electrical conductivity. Doped spinel-ferrite M_xFe_3−xO₄ would be a kind of “phonon-glass electron-crystal” material.