Observation of anomalous site occupancy in Ni-Co-Cu-Cr ferrite system synthesized by sol-gel method

Anomalous variation in cation distribution in chromium doped Ni-Co-Cu-Cr ferrites synthesized by sol-gel method has been observed the formation of spinel structure and explained with the help of DTA/TG and X-ray diffraction analysis. Error estimated between theoretical and calculated lattice parameter based on proposed cation distribution is found be in range of 0.0014% to 0.00005%, which confirms the cation distribution predicted for the present samples. In this present work, it appears that most of the cobalt and 50% of nickel ions are observed to occupy A-sites instead of B-sites of spinel lattice, which is a drastic deviation from the reports published till date. The g-value have been found to be lower for x = 0.02 concentration as observed from ESR analysis. Fourier transform infrared spectroscopic techniques (FTIR) show no variation in peak position of vibrational bands, indicates the uniform bond length in the spinel ferrite, even for different concentration of chromium. This is further confirmed by the bond length calculation using empirical formulas and experimental lattice parameters, showing least error for shared and unshared ion for tetrahedral or octahedral sites. •Observed changes in cation ion distribution are supported by FTIR and ESR studies.•Minor change in bond lengths of tetrahedral and octahedral sites observed for Cr3+ < 0.04 but remain constant for Cr3+ > 0.04.•The observed g-value from ESR is approximately equal to standard value.