An analysis of Mn-Zn ferrite microstructure by impedance spectroscopy, scanning transmission electron microscopy and energy dispersion spectrometry characterizations

Abstract

AC resistivity measurement results on Mn-Zn sintered ferrite were analyzed in the 0.1-500 MHz range. From electrical point of view, the material could be represented by an equivalent circuit of parallel resistance-capacitance cells connected in series corresponding to the contributions from bulk grains in one hand, and grain boundary layers in the other hand. The experimental resistivity curves were fitted with the model. The as obtained parameters give information on dielectric properties and conductivity of both bulk grains and boundary layers. For the studied material, it appears that the resistivity at low frequencies is increased 27 times due to the boundary layers effects. STEM (Scanning Transmission Electron Microscopy) and EDS (Energy Dispersion Spectrometry) characterization where performed in order to detect impurities at a grain boundary layer which can explain those wide differences between bulk grains and boundary layers electrical properties. It appears that the two components have close chemical compositions, but some calcium impurities segregate at the boundary which increases dramatically the resistivity of these layers. Furthermore, the bulk grains show relative permittivity around 350 at low frequency which is much smaller than the one measured for the whole material which is in the 50,000-100,000 range. This giant-dielectric behaviour can be explained by an internal barrier layer (IBLC) at the grain boundaries. At last, the components of classical eddy current losses including losses due to ohmic effects and (true) dielectric losses on both bulk grain and boundary layers are distinguished.

Effect of High‐Pressure Oxygen Annealing on Electrical and Magnetoelectric Properties of BaSrCo2Fe11AlO22 Ceramics

“…Complex impedance spectroscopy is one of the most powerful tools to separate the contributions of the bulk, grain boundaries, and electrode interface to the current conduction of ceramic devices. The method has been widely used to study the conduction mechanisms of ZnO, SrTiO 3 , and some types of ferrite materials …”

“…(c). Many papers have reported and discussed the contribution of grain‐boundary resistivity to the resistivity of ferrite ceramics, especially Mn–Zn ferrites, using this technique …”

Magnetic and Electrical Properties of Magnesium-Substituted Ni–Zn Ferrites

“…5. The dielectric loss factor tan δ = ε /ε conveys the ability of the dielectric material that can convert electrical energy into thermal energy which produces heat in the material [24]. This arises because of the lag between polarization and applied field which is created by the impurities and imperfections in the crystal lattice [10].…”

Effects of TiO2 and Co2O3 combination additions on the elemental distribution and electromagnetic properties of Mn–Zn power ferrites

“…The additives of CaO, Nb 2 O 5 , ZrO 2 , TiO 2 and Co 2 O 3 play an important role in promoting the electrical and magnetic properties. The CaO and Nb 2 O 5 exsiting on the grain boundaries can increase the grain-boundary resistivity and then lower the eddy current losses [5,8]. The ZrO 2 can accelerate the grain boundary migration and increase the grain sizes by Zr 4þ increasing the cation vacancy, which could reduce the resistance of domain wall displacement [6].…”