Structure and properties of tin-doped metal oxides

Tin-doped Fe3O4 prepared by solid state reactions is shown by X-ray powder diffraction and extended X-ray absorption fine structure to contain tin in the octahedral sites of the inverse spinel-related structure. In situ Fe-57 Mossbauer spectroscopy performed at elevated temperatures in vacuo shows the Curie temperature to decrease with increasing concentrations of tin and, after prolonged heating at elevated temperatures, the partial segregation of tin to form tin dioxide at the magnetite surface. Thermal treatment under oxidising conditions causes the oxidation of tin-doped Fe3O4 to tin-doped gamma-Fe2O3 and tin-doped alpha-Fe2O3. Tin-doped gamma-Fe2O3 prepared by precipitation techniques also contains tin in the octahedral sites of the inverse spinel-related structure. Fe-57 Mossbauer spectroscopy at elevated temperatures has been used to derive a Neel temperature for tin-doped gamma-Fe2O3 and to examine the stabilising influence of tin on the conversion of gamma-Fe2O4 to alpha-Fe2O3. Tin-doped alpha-Fe2O3 prepared by hydrothermal methods contains tin in both interstitial- and substitutional-octahedral sites in the corundum-related matrix. The defect structure is unusual and is rationalised by crystallographic- and chemical- arguments.