Crystal growth and defect structure of Al3+-doped rutile

Four microcrystalline rutile powders doped with 0-0.8% Al2O3/ TiO2 and grown at 930-980 degrees C from the same precursor material were investigated. By synchrotron X-ray diffraction and Rietveld refinement, unit cell parameters and crystallite sizes were determined, Also, FTIR reflectance spectra were recorded for possible contributions from free electrons and lattice, vibrations. With increasing amounts of dopant, cell parameters a and c decrease steadily while the positional parameter II has a maximum value with intermediate amounts, Two rutile lattice vibrations sensitive to oxygen vacancies are steadily weakened, and a vibrational mode of the same symmetry appears that is characteristic of Me-O octahedra in corundum, These results prove that Al2O3 is incorporated into the rutile lattice and reveal the defect structure: With low amounts of dopant, Al3+ substitutes Ti4+ and is charge-compensated by oxygen vacancies, and with large amounts of dopant, Al3+ is additionally put on interstitial places. The crystal size of rutile increases with temperature, but is not influenced by Al3+ doping, (C) 1999 Academic Press.