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-Fe 2 O 3 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).