Distribution of Fe2+ and Fe3+ and next-nearest neighbour effects in natural chromites: comparison between results of QSD and Lorentzian doublet analysis

The Mössbauer spectra of one chromite at 298 K and one chromite at 298, 200, 170, 140 and 90 K have been analyzed in this study. A Voigt-based quadrupole splitting distribution (QSD) method was used to analyze the spectra. The tetrahedral site Fe²⁺ and the octahedral site Fe³⁺ quadrupole splitting distributions (QSDs) were obtained from the Mössbauer spectra of chromites, and the multiple tetrahedral site Fe²⁺ Gaussian QSD components and the large widths σ _Δ of the Gaussian QSD components of the tetrahedral site Fe²⁺ QSDs for chromites were attributed to next-nearest neighbor effects. In addition, temperature dependences of the isomer shift and the quadrupole splitting were presented and discussed. Comparisons between the Mössbauer parameters for thickness-corrected folded spectra and raw-folded spectra of chromites were made, and the results show that the two sets of the Mössbauer parameters and ratios of ferric to total iron as well as χ² are very close to each other. This is because of the small absorber thickness of chromites in this study. Comparisons between the Mössbauer parameters of chromites obtained using the Voigt-based QSD method and a Lorentzian doublet method were also made. The results show that there are some differences between the two sets of the Mössbauer parameters and ratios of ferric to total iron, but not significant. However, much larger χ² were obtained when the Lorentzian doublet method was used to fit the spectra of chromites. This indicates that the Voigt-based QSD method is more adequate to analyze the Mössbauer spectra of chromites from the point of view of statistics.