Impedance spectroscopy and dielectric properties of multiferroic BiFeO3/Bi0.95Mn0.05FeO3–Ni0.5Zn0.5Fe2O4 composites

Multiferroic composites with equal weight fractions of bismuth ferrite/manganese doped bismuth ferrite and nickel–zinc ferrite with the chemical formulae, 0.5(BiFeO3)–0.5(Ni0.5Zn0.5Fe2O4) and 0.5(Bi0.95Mn0.05FeO3)–0.5(Ni0.5Zn0.5Fe2O4) have been prepared using sol–gel autocombustion and solid state methods and investigated to understand the effects of manganese on various structural, dielectric and impedance properties. X-ray diffraction analysis of the composites reveals the formation of di-phase compounds while retaining the spinel and rhombohedrally distorted perovskite phases for the nickel–zinc ferrite and bismuth ferrite/manganese doped bismuth ferrites, respectively. Scanning electron microscopy measurements on the sintered surfaces of the samples display uniformly well knitted fine grained microstructures with thin grain boundaries. Dielectric properties of the composites have been studied in a wide range of frequencies from 1 Hz to 1 MHz and at different temperatures in the range from 30 to 350 °C. Observed temperature dependent diffuse dielectric anomalies, one at around 180–270 °C and the other at around 270–340 °C, were attributed to structural inhomogeneities and dipole induced charge carrier hopping motions at low temperature, and to magnetic phase transitions at high temperatures. Impedance analysis on the samples help to understand the contributions of electrical conductivity and interfacial polarization, and the observed results are in support of the arguments made during the analysis of dielectric properties. The results of all these measurements clearly emphasize the presence of Mn to bring about significant changes in the microstructure, conductivity and impedance properties leading to reduced dielectric losses.