Crystal structure refinements of InxFe3-xO4 (x≤0.3) spinels by the Rietveld method

The distribution of In3+ between tetrahedral and octahedral sites and coordinate of oxygen in InxFe3-xO4 (x = 0, 0.1, 0.2, and 0.3) spinels have been determined on powder samples by the Rietveld method. The weight function with a form w(Yi) = 1/Y-oi(2) (Y-oi = the observed profile intensity at the ith step) was incorporated in the present Rietveld refinement. Structures thus refined were satisfactory not only in their internal consistency but also in their conformity with single crystal data. These results corroborate earlier study, which indicated a preference of In3+ for the tetrahedral site. In-iv-O distances in the present specimens [1.97(3) Angstrom-2.00(5) Angstrom] were close to the value calculated from a bond-valence scheme. In InxFe3-xO4, calculated Fe-vi(2+)-O distances increased with increasing x, and they were in between two Fe-vi(2+)-0 distances in Fe3O4 and gamma-Fe2SiO4 (spinel structure). A change of semimetallic nature to semiconductive one by In-doping in Fe3O4 would be responsible for the elongation of Fe-vi(2+)-O distance.