Structural Rietveld refinement and vibrational study of MgCrxFe2−xO4 spinel ferrites

Spinel ferrites with the general formula MgCrxFe2−xO4 (0≤x≤1) were synthesized by the standard ceramic technique and characterized by X-ray diffraction. The XRD patterns confirmed that the mixed ferrite samples are in the cubic spinel structure which is further validated by Rietveld refinement in the space group Fd3m. The crystal structure and cell parameters were refined by Rietveld analysis. The vibrational study was achieved using Fourier Transform-InfraRed (FT-IR) and Raman spectroscopy. From FT-IR band frequencies, the force constants Kt and Ko , for tetrahedral (A) and octahedral (B) sites respectively, have been calculated and discussed with the trend of bond lengths obtained from Rietveld refinement. For all compositions, Raman spectra revealed the five active modes showing the vibration of O2− ions at both the A-site and B-site ions. The frequencies trend with chromium content of both FT-IR and Raman spectra showed a shift toward higher values for all modes.