Influence of the annealing atmosphere on the structural and microstructural properties of the mechanosynthesized (Fe2O3)0.25–(Al2O3)0.75 system

The high-energy ball milling (HEBM) technique has emerged as a non-expensive route to processing nonequilibrium materials in several varied forms. In this work, structural and microstructural analysis of the as-milled and annealed isostructural (α-Fe2O3)0.25–(α-Al2O3)0.75 system were carefully conducted, focusing the annealing atmosphere effects on the final products. SEM micrographs for as-milled samples show agglomerated particles of different nanosizes, some smaller than 100 nm. The lattice parameters, the unit cell volumes, and the phase's fractions were obtained from the X-ray diffraction patterns by Rietveld structural refinement for the as-milled and annealed samples. It was verified that the annealing reduced the line broadening as a consequence of the re-crystallization of the milled batch, consequently releasing the lattice strains, with little grain growth. Besides that, it was verified that the argon atmosphere favors the formation of ferrous phases, while the oxygen annealing favors the formation of the ferric solid solutions, which are promising to be applied as lead-free perovskite magnetoelectric materials.