engleski

Manganese incorporation in gahnite

Zinc aluminate (ZnAl2O4), known by the mineral name gahnite, is a technologically important material. It has attracted interest as a wide- band-gap semiconductor with good optical properties for use in various photoelectronic devices, as a phosphor host material for applications in luminescent displays, as well as a catalyst and catalyst support material. When doped with Mn2+, Co2+ or rare-earth cations, gahnite exhibits luminescence and can be used as a cathodoluminescent material. ZnAl2O4 possesses a normal spinel structure, in the space group Fd-3m. Under specific temperature conditions it can adopt a partial inverse spinel structure in which Al and Zn share both available tetrahedral and octahedral cation sites of the spinel structure, respectively. Powder samples of gahnite doped with 0-75 at% Mn (on account of Zn) were prepared by a sol-gel technique and additionally annealed at 800 °C for 2 h. Prepared samples were characterized by X-ray diffraction at RT, and their crystal structures were refined by the Rietveld method. The XRD patterns showed that all samples had the spinel- type structure. The unit-cell parameter was precisely determined using silicon powder as an internal standard, and refined by the WPPF program. It increased with the increase of Mn- doping level. EPR spectroscopy revealed that manganese was present as Mn2+ ion in the samples, being in both tetrahedral and octahedral coordination. Rietveld structure refinement results showed that doping of gahnite with manganese induced the inverse spinel structure already at 4 at% Mn. The inversion parameter δ increased with the increase of Mn content, from 0.03 for 4 at% Mn to 0.13 for 75 at% Mn. Both metal-oxide distances in the (Zn, Mn, Al)O4 tetrahedra and (Al, Mn)O6 octahedra increased as the Mn-doping level increased, causing the unit- cell parameter enlargement.

Mn-doped gahnite; Spinel structure; X-ray powder diffraction; Rietveld method

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