Influence of thermal history and 50 MeV Li ion irradiation on the structural properties of Al3+–Cr3+ co-substituted CuFe2O4

Abstract

50 MeV Li3+ ion irradiation-induced changes on the structural properties of slow-cooled (SC) and quenched (QC) CuFe2−2x Al x Cr x O4 (x=0.0, 0.2, 0.4 and 0.6) ferro-spinels have been studied. Polycrystalline samples were prepared by using a standard double-sintering ceramic technique and were characterized by energy-dispersive X-ray analysis, X-ray diffraction and infrared (IR) absorption spectroscopy. The investigations on the influence of thermal history of the spinel system CuFe2−2x Al x Cr x O4 showed that the SC and QC samples exhibit Jahn–Teller structural tetragonal deformation owing to the presence of Cu2+ and Cr3+ ions at octahedral sites of the spinel lattice. The study also showed that the distribution of cations is sensitive to the heat treatment and swift heavy ion irradiation (SHII) of the materials. The SHII reduces the tetragonal distortion in both the cases and significantly modifies the cation distribution in the case of the QC sample. The shifts observed in the IR frequency bands ν1 and ν2 for tetrahedral and octahedral sites are due to the perturbation taking place in the Fe3+–O2− bond caused by substitution of Al and Cr ions. The presence of Cu2+ and Fe2+ ions in a spinel ferrite lattice gives rise to a ‘shoulder’ or splitting of the IR absorption band. The IR spectra results show that the irradiation shifts ν1 and ν2 bands to higher frequencies, attributable to the transformation of Fe3+ to Fe2+ having larger Pauling radius by irradiation on both octahedral and tetrahedral sites.