engleski

Structural study of Mn-doped gahnite

Oxide spinels include a very large group of structurally related compounds having a considerable technological significance. Among them, zinc aluminate (ZnAl2O4, gahnite) is of interest due to its good combination of desirable properties. It is a widely used ceramic and catalytic material. Furthermore, it is a well known wide-band-gap semiconductor transparent for light wavelengths greater that 320 nm, so it can be used for various photoelectronic devices. When doped with Co2+, Mn2+, or rare-earth ions, it exhibits luminescence and can be used as a cathodoluminescent material. Gahnite is cubic with normal spinel structure, the space group Fd-3m. In contrast to zinc aluminate, the structure of manganese aluminate (MnAl2O4, galaxite) displays a pronounced inversion of spinel structure even at room temperature. It is expected that Mn-doping of zinc aluminate could induce an inverse spinel structure in ZnAl2O4. Powder samples of gahnite doped with 0, 4, 8 and 12 at% Mn (on account of Zn) were prepared by a sol-gel technique and additionally annealed at 800 oC for 2 h. Structural changes due to Mn incorporation in zinc aluminate lattice were studied by XRD, and crystal structures were refined by the Rietveld method. Oxidation state and location of manganese in the doped samples were determined by EPR spectroscopy. XRD patterns of the prepared samples indicated that all samples had a characteristic spinel-type structure. The unit-cell parameter a increased with Mn-doping level, the increase was not linear. EPR spectra of the prepared samples were characteristic for Mn2+ ions being likely in both tetrahedral and octahedral coordination. The Rietveld structure refinement confirmed appearance of the inverse spinel structure in gahnite on manganese doping.

Mn-doped gahnite; X-ray diffraction; Rietveld structure refinement; EPR spectroscopy

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