Powder XRD structure refinements and57Fe Mössbauer effect study of synthetic Zn1-xFexAl2O4(0 < x ≦ 1) spinels annealed at different temperatures
✍ Scribed by J. C. Waerenborgh; M. O. Figueiredo; J. M. P. Cabral; L. C. J. Pereira
- Publisher
- Springer-Verlag
- Year
- 1994
- Tongue
- English
- Weight
- 940 KB
- Volume
- 21
- Category
- Article
- ISSN
- 0342-1791
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✦ Synopsis
Members of the solid solution series Znl_xF%A1204 (x = 0.2, 0.4, 0.6 and 1.0) with spinel structure were synthesized by direct solid-state reaction of the simple metal oxides and metallic iron in evacuated silica ampoules at 1175 ~ C. Two aliquots of the single-phase spinels obtained for each composition were annealed under vacuum at 1075 ~ C and 725 ~ C for 48 hours and then quenched in liquid nitrogen.
The cation distributions of all the quenched samples were determined by X-ray powder diffraction, using the Rietveld method of structural refinement. The degree of inversion increases with iron content and for spinels with the same chemical composition with quenching temperature. The relative areas estimated for the contributions to the M6ssbauer spectra of tetrahedrally-and octahedrally-coordinated Fe 2+ suggest that most of Zn 2+ cations remain at the tetrahedral site, as expected from the relative cation site preferences.
Failure to quench the equilibrium cation distributions, suggested by deviations between the observed composition dependence of the cation distribution and that expected from the thermodynamic model of O' Neill and Navrotsky (1983, 1984), may be explained by an enhancement of cation diffusion rates in the Znl_xF%A1204 (0 < x < 1) spinels caused by the presence of cation vacancies. Fe3+/vacancy defects are easily formed in these spinels due to partial oxidation of Fe z+ at high temperature.