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

The Mossbauer 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 Mossbauer spectra of chromites, and the multiple tetrahedral site Fe2+ Gaussian QSD components and the large widths σΔ 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 Mossbauer parameters for thickness-corrected folded spectra and raw-folded spectra of chromites were made, and the results show that the two sets of the Mossbauer 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 Mossbauer 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 Mossbauer 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 Mossbauer spectra of chromites from the point of view of statistics.