Mössbauer study of the iron atom state in modified chromium dioxide

Powders of modified chromium dioxide produced by the hydrothermal method were studied using $^{57}$Fe Mössbauer spectroscopy at a temperature of 298 K. The content of the modifier, i.e., $^{57}$Fe compound, was varied from 2 to 10 mmol/mol Cr at a Sb content of 2.2 and 10 mmol/mol Cr. It was shown that, independently of concentrations, Fe$^{3+}$ ions are distributed between three magnetic solid solutions (sextets): based on CrO$_2$ (bulk material and iron-enriched surface layer), based on Cr$_{2}$O$_{3}$, and surface $\beta$-CrOOH (doublet). In this case, chromium atoms were not substituted in the CrSbO$_{4}$ nucleation (12 nm in size) phase with an accuracy up to the Mössbauer factor. It was assumed that the powder coercivity, in addition to the size factor, is controlled by the iron concentration in the CrO$_2$ surface layer.