Dielectric and impedance properties of NiFe<inf>1.95</inf>R<inf>0.05</inf>O<inf>4</inf> (R = Y, Yb and Lu)

The dielectric and impedance spectroscopic properties of NiFe1.95R0.05O4 (R = Y, Yb and Lu) were investigated. The materials were prepared by solid state reaction and crystallized in the cubic inverse spinel phase with a very small amount additional phase of RFeO3 (R = Y, Yb and Lu) as secondary phase. The scanning electron micrograph images clearly show grains (∼2μm) which are separated by thin grain boundaries. The presences of all elements were confirmed by the energy dispersive X-ray elemental mapping. The frequency variation of ϵ' shows the dispersion, following the Koop's phenomenological theory, which considers the dielectric structure as an inhomogeneous medium of two-layers of the Maxwell-Wagner type. Impedance spectroscopic analysis indicates the different relaxation mechanisms, which corresponds to bulk grain and grain-boundaries. Their contributions to the electrical conductivity and capacitance of these materials were discussed in detailed.