Influence of annealing process on phase transition of Cu-Al nanoferrites synthesized by a coprecipitation method

As-synthesized CuAl0.8Fe1.2O4 nano-crystalline samples prepared by the co-precipitation method were annealed at different temperatures T. The nanoferrite samples were characterized using X-ray diffraction and FT-IR and Mössbauer spectroscopy. This study proved that the structural phase of the nanoparticles was transformed with T from cubic to tetragonal due to the tetragonal distortion of a Jahn-Teller effect (JTE) of Cu2+ ions. The transformation process was pronounced at 600 °C and predominated at 1000 °C. All spectra and parameters were affected by JTE. The crystallite size, strain, distortion parameter and inter-chain distance showed dependence on T, whereas the lattice parameters did not. Six absorption bands were observed in the IR spectra, where their position and intensity, threshold frequency and Debye temperature were T dependent. The Mössbauer spectra were affected by T. The hyperfine magnetic field of the A- and B-sites, magnetization and area ratio of B/A-sites were deduced and discussed as functions of T. The estimated cation distribution explained the motion of metallic ions between the crystal sublattices as T increases.