Microstructure characterization and phase transformation kinetic study of mechanosynthesized non-stoichiometric CdFe2O4 by Rietveld's analysis

Nanocrystalline non-stoichiometric cadmium ferrite (CdFe2O4) has been synthesized by high-energy ball milling the mixture (1 : 1 mol%) of CdO and alpha-Fe2O3 at room temperature. Formation of nanocrystalline CdFe2O4 as normal spinet structures has been noticed after ball milling the mixture for different durations. The structural and microstructural evolution of CdFe2O4 caused by milling is investigated by X-ray powder diffraction. The relative phase abundances, particle sizes, r.m.s strains, lattice parameter changes of different phases have been estimated employing Rietveld powder structure refinement analysis of XRD data. Particle size and amount (wt%) of CdO reduce very fast in comparison to alpha-Fe2O3 and a significant amount of nanocrystalline CdFe2O4 is formed within 5 h ball milling of CdO+alpha-Fe2O3 powder mixture. It appears that solid state diffusion of nanocrystalline CdO and alpha-Fe2O3 particles results in formation of nanocrystalline CdFe2O4 spinel. A significant amount of alpha-Fe2O3 did not take part in ferrite formation within 25 h of milling time and even after post annealing the 5 It milled samples at different temperatures (up to 1273 K) for different durations, similar to 13 wt% of alpha-Fe2O3 remained as an excess phase. It indicates that the ferrite prepared by ball milling is a non-stoichiometric Cd-riched phase. However the ferrite phase content increases considerably when the 5 h milled sample is annealed at different elevated temperatures for different durations.