Crystal Growth and Defect Structure of Al3+-Doped Rutile

Four microcrystalline rutile powders doped with 0-0.8% Al2O3/TiO2and grown at 930-980° 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 parametersaandcdecrease steadily while the positional parameteruhas 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 Al2O3is 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.