Synthesis of nanocrystalline Cd–Zn ferrite by ball milling and its stability at elevated temperatures

Abstract

High energy ball milling of stoichiometric (0.5:0.5:1 mole fraction) mixture of CdO, ZnO and α-Fe 2O 3 powders in air at room temperature results in formation of a non-stoichiometric Zn-rich (Zn,Cd)Fe 2O 4 phase with normal spinel structure having tetrahedral vacancies. The ferrite phase is initiated at 1 h of milling and after 25 h milling, 0.96 mole fraction of ferrite is formed and 0.04 mole fraction of CdO phase remained unreacted. The phase stability study of nanocrystalline non-stoichiometric (Zn,Cd)Fe 2O 4 powder annealed at elevated temperatures reveals that the Zn-rich ferrite phase remained stable up to 973 K and then slowly transformed towards Cd-rich (Cd,Zn)Fe 2O 4 phase following the release of divalent cations from ferrite lattice of normal spinel structure. The non-stoichiometric ferrite phase with almost similar composition has also been obtained by conventional ceramic route by sintering the same stoichiometric mixture at 973 K for 1 h. Microstructure characterization in terms of several lattice imperfections, relative phase abundances, cation distribution, and phase stability studies of unmilled, ball-milled and annealed samples is made by employing the Rietveld's structure refinement methodology using X-ray powder diffraction data. The analysis reveals that the particle size of ferrite phase reduces to ∼7 nm after 25 h of milling and after annealing at 1273 K for 1 h it grows up to ∼700 nm. However, in case of ferrite prepared by ceramic route it grows up to ∼250 nm which is quite less than the annealed ball-milled samples.