engleski

A study of the systems HfO2-Fe2O3 and ZrO2-Fe2O3 by XRD and 57Fe Moessbauer spectroscopy

The existence of solid solutions in the HfO2-Fe2O3 system and ZrO2-Fe2O3 system was studied by X-ray powder diffraction and Mössbauer spectroscopy. A series of samples at the HfO2- or ZrO2-rich side were prepared from amorphous precursors, precipitated from aqueous solutions of the corresponding salts, followed by calcination at 500, 800 and 1100oC. The thermal behavior of the systems was monitored using differential scanning calorimetry. Crystallization temperature increased with an increase of the Fe2O3 content and proved to be ~100 oC higher for the HfO2-Fe2O3 system. X-ray diffraction powder patterns were taken by step-scanning and determination of unit-cell parameters was performed by means of the powder-pattern-fitting methods. In the HfO2-Fe2O3 system there exist two types of solid solutions, H and F, of the form Hf1-xFe2xO2+x, very closely structurally related to m-HfO2 and a-Fe2O3, respectively. In case of the ZrO2-Fe2O3 system two different ZrO2-type solid solutions appear, Zm and Zc, closely structurally related to m-ZrO2 and c-ZrO2, respectively. The volume fraction of the Zc phase increased with an increase in the iron content and a decrease in the temperature. The solubility of Fe2O3 in the HfO2 and ZrO2 decreased with an increase of temperature. The status of the Fe3+ ions in the HfO2- and ZrO2-type lattice and the process of their segregation into the a-Fe2O3 phase were examined by Mössbauer spectroscopy. A good correlation between the results of XRD and those of Mössbauer spectroscopy was obtained.

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