Naslov
Effect of cobalt doping on zinc aluminate structure

Autori
Popović, Jasminka ; Gržeta, Biserka ; Tkalčec, Emilija ; Kurajica, Stanislav

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
Sixteen Croatian-Slovenian Crystallographic Meeting. Book of Abstracts / Cetina, Mario ; Popović, Stanko ; Skoko, Željko ; Šantić, Ana ; Štefanić, Zoran - Zagreb : Hrvatska akademija znanosti i umjetnosti (HAZU) ; Hrvatska Kristalografska Zajednica, 2007, 39-39

Skup
Sixteen Croatian-Slovenian Crystallographic Meeting

Mjesto i datum
Petrčane, Hrvatska, 13.06.2007. - 17.06.2007

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Zinc aluminate; Spinel structure; Cobalt doping; X-ray powder diffraction

Sažetak
Zinc aluminate, ZnAl_2O_4 (mineral name gahnite), is a well known wide-band-gap semiconductor transparent for light wavelengths greater that 320 nm. When doped with Co^(2+), Mn^(3+) or rare-earth ions it exhibits luminescence and can be used as a cathodoluminescent material in multicolor displays. ZnAl_2O_4 possesses a spinel structure, in the space group Fd3m. Its unit cell contains 32 oxygen atoms in cubic close packing, 16 octahedral sites occupied by Al cations and 8 tetrahedral sites occupied by Zn cations. Under specific temperature conditions it can adopt an inverse spinel structure in which Al and Zn share both available cation sites. Powder samples of pure gahnite and ones doped with 4, 8 and 12 at% of Co (substituting for Zn) were prepared by a sol-gel technique. Samples were additionally annealed at 800oC for 2 hours. The cobalt/zinc atomic ratios in the samples were determined by means of PIXE (Particle Induced X-ray Emission) spectroscopy. Prepared samples were characterized by X-ray diffraction at RT using a Philips MPD 1880 counter diffractometer. Diffraction patterns indicated that all prepared samples had the spinel-type structure, no additional phases were detected. Unit-cell parameter a for the undoped and Co-doped gahnite samples was determined using silicon powder as an internal standard, and refined by the whole-powder-pattern fitting method. It decreased with increase of cobalt content in the samples. This behavior can be explained by considering ionic radii of zinc and cobalt. The ionic radius for the 4-coordinated Zn^(2+) (0.074 nm) is higher than that of Co^(2+) (0.071 nm) favoring a decrease in unit cell volume and therefore the lattice contraction when cobalt substitutes zinc. For higher level of cobalt doping, the inverse spinel structure could be expected similar to that of CoAl_2O_4 as reported by Fischer.

Izvorni jezik
Engleski

Znanstvena područja
Fizika, Kemijsko inženjerstvo

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