Structural phase transformations of as-synthesized Cu-nanoferrites by annealing process

Samples of the as-synthesized CuFe₂O₄ nanoferrites by co-precipitation route were annealed at different temperatures T. X-ray diffraction, infrared and Mössbauer spectroscopy and vibrating sample magnetometry were used for characterizing the samples. The sample structure phase was transformed from cubic-to-tetragonal-to-cubic as T increases. This transformation was attributed to the tetragonal distortion of Jahn–Teller effect of Cu²⁺ ions (d⁹). The crystallite size R, lattice parameters, density, porosity P, strain and stiffness constant showed dependence on annealing temperature T. Seven absorption bands were observed in the IR spectra. The two characteristic bands of spinel ferrites, ν₁ and ν₂, force constants and Debye temperature showed a decrease against T. The absorption bands ν₁ and ν₂ proved dependence on bond length; d_AO and d_BO, and saturation magnetization Ms, respectively. Hyperfine magnetic fields, line widths, area ratio of B- to A-sites, isomer shifts and quadrupole shifts (splitting) were deduced and discussed as functions of T, where the cation distribution were estimated. XRD patterns, Infrared spectra and RT temperature hysteresis loops proved the transformation process. Saturation magnetization showed dependence on T, P and R. - Highlights: • Amounts of as-synthesized Cu-nanoferrites were annealed at various temperatures T. • Structural phase was transformed from cubic-to-tetragonal-to-cubic with T by JTE. • IR band positions showed dependence on bond lengths and saturation magnetization Ms. • The deduced parameters showed dependence on T and affected by JTE. • Ms proved dependence on porosity and crystallite size