Four microcrystalline rutile powder samples, which had been prepared at 930 to 980C from material that was doped with 0 to 0.8%Al2O3, were investigated. Synchrotron X-ray diffraction and Rietveld refinement methods were used to determine the unit-cell parameters and crystallite sizes. It was found that, with increasing amounts of dopant, the a and c cell parameters decreased steadily. Two rutile lattice vibrations which were sensitive to O vacancies were steadily weakened, and a vibrational mode of the same symmetry appeared that was characteristic of Me-O octahedra in corundum. The results proved that the Al2O3 was incorporated into the rutile lattice, and revealed the defect structure. At low dopant contents, Al3+ substituted for Ti4+ and was charge-compensated by O vacancies. At high dopant contents, the Al3+ was also present at interstitial sites. The crystal size of the rutile increased with temperature, but was not influenced by Al3+-doping.

Crystal Growth and Defect Structure of Al3+-Doped Rutile. Gesenhues, U., Rentschler, T.: Journal of Solid State Chemistry, 1999, 143[2], 210-8