M. Sinha

Phase Stability of Nanocrystalline Mg?Zn Ferrite at Elevated Temperatures

Nanocrystalline Mg–Zn ferrite phases obtained by high-energy ball milling a stoichiometric (0.5:0.5:1) powder mixture of MgO, ZnO, and α-Fe2O3 at room temperature are subjected to postannealing treatment to study the stability of nanocrystalline ferrite phases at elevated temperatures. An X-ray diffraction (XRD) study using the Rietveld method of structure refinement reveals that ferrite phases generally decompose by releasing MgO and ZnO from ferrite lattices at 873 K. A nonstoichiometric Zn–ferrite is observed in the unmilled mixture at 973 K without MgO in the ferrite lattice, with a particle size four times (approximately 23 nm) larger than that obtained in the high-energy ball-milled samples (approximately 5 nm) at room temperature. The particle size of the unmilled and ball-milled samples increases rapidly to approximately 350 nm after postannealing at 1473 K and the XRD results agree well with the results of the direct observation of ferrite grains by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM).

Complex electric modulus and dielectric relaxation of nanocrystalline zinc ferrite

We report the complex electric modulus and dielectric relaxation studies of nanocrystalline zinc ferrite. The dielectric constant exhibits strong temperature dependence at higher temperature and lower frequencies and this has been analyzed in terms of electric modulus vector. The real part of complex impedance has also been modeled by an ideal equivalent circuit consisting of grain and grain boundary resistances and capacitances. The metallic electrode and semiconductor junction forms Schottky diode, whose parameters like built in voltage and space charge density have been extracted from the capacitance-voltage characteristics.