X-ray emission study of the electronic structure of nanocrystalline Al2O3

Valence states of metal ions and the phase composition of nanocrystalline Al2O3 (of the original oxide and the oxide irradiated by high-energy Fe+ ions) are studied by using x-ray emission Al L-2,L- 3 and O Kalpha spectra. It is established that the shape of the Al L-2,L- 3 spectra strongly changes as one goes from the original (bulk) Al2O3 to nanocrystalline oxide, while the O Kalpha spectra remain practically unchanged. Moreover, irradiation by high-energy Fe+ ions results in slight additional changes in the x-ray spectral characteristics of the aluminum oxides under study. The obtained experimental data are compared with the results of theoretical calculations of the electronic structure of alpha and gamma phases of Al2O3 performed using the LDA formalism. Using the results of x-ray spectral studies, electronic structure calculations, and x-ray diffraction analysis, it is shown that the revealed spectral differences between the nanocrystalline state of aluminum oxide and the bulk material can be interpreted as a phase transition from the alpha phase to the gamma phase of Al2O3 with an addition of bayerite. (C) 2004 MAIK "Nauka/Interperiodica".