CRYSTAL-STRUCTURE REFINEMENTS OF INXFE3-XO4 (X-LESS-THAN-OR-EQUAL-TO-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 wei ght function with a form w(Yi) = 1/Y-oi(2) (Y-oi = the observed profil e intensity at the ith step) was incorporated in the present Rietveld refinement. Structures thus refined were satisfactory not only in thei r internal consistency but also in their conformity with single crysta l data. These results corroborate earlier study, which indicated a pre ference of In3+ for the tetrahedral site. In-iv-O distances in the pre sent specimens [1.97(3) Angstrom-2.00(5) Angstrom] were close to the v alue calculated from a bond-valence scheme. In InxFe3-xO4, calculated Fe-vi(2+)-O distances increased with increasing x, and they were in be tween two Fe-vi(2+)-0 distances in Fe3O4 and gamma-Fe2SiO4 (spinel str ucture). A change of semimetallic nature to semiconductive one by In-d oping in Fe3O4 would be responsible for the elongation of Fe-vi(2+)-O distance.