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Structural properties of titanium doped gahnite

Recently, there has been considerable interest in titanium doped materials with spinel-type structure as the active media for solid-state lasers. Among them, titanium doped spinel (Ti: MgAl2O4) was found to have strong blue luminescence at ~490 nm, the luminescence originated from Ti4+ on B cation site in the spinel structure. Furthermore, titanium doped alpha-ZnAl2S4 spinel-type crystals exhibit luminescence in the IR spectral range 0.8-1.4 µm, the emission bands arising from Ti4+ on octahedral cation site. In both described cases, titanium doping level was low (≤ 1.0 at%). We have studied titanium incorporation in gahnite, ZnAl2O4. Gahnite possesses a normal spinel structure, the space group Fd-3m. When doped with Co2+, Mn2+ or rear-earth ions it exhibits luminescence and can be used as a cathodoluminescent material. There is no literature data on titanium doping of gahnite. Powder samples of gahnite doped with titanium were prepared by a sol-gel technique using zinc nitrate hexahydrate, aluminum-sec-butoxide and titanium(IV) butoxide as starting components. The excess of zinc component was used for the purpose of charge balance in the prepared samples. Samples could be described by formula Zn(Al2-2xTixZnx)O4, with 0.25 ≥ x ≥ 0.04. X-ray diffraction patterns indicated that all samples had a characteristic spinel-type structure. Unit-cell parameter a was determined using the UNITCELL program, and refined by WPPF program. The unit cell increased with the increase of Ti-doping level. Small amounts of the second phase, namely ZnO, were noticed in the samples. Rietveld structure refinement confirmed that Ti4+ was incorporated on B cation site in the normal spinel-type structure of gahnite with Zn excess.

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

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