Diffusivity of Al vacancies in corundum (αAl2O3)

The diffusivity of Al vacancies in corundum has been experimentally determined from 1300 degrees C to 1500 degrees C, by annealing high-purity single crystals in the presence of water at a high pressure (similar to 1.5 GPa), followed by spatially resolved Fourier transform infrared spectroscopy on slabs cut from the cores of crystals. Infrared spectra recorded from the experimental products show bands at 3263 and 3421 cm(-1), with the former having a shoulder at 3278 cm(-1). These bands are interpreted to represent H (as protons) charge-compensating vacant Al sites, likely as (V-Al ''' 2H(i)(center dot))', (V-Al ''' H-i(center dot))', and/or H-i(center dot), although their exact assignment is unclear. Regardless, the Arrhenius relationship derived for the diffusivity of (assumed) protonated vacancies, based on fitting profiles of band absorbance versus distance from the crystal edge from the three experiments, is: log(10)D=0.73(+/- 0.70)m(2)s(-1)+-421.8(+/- 22.7)kJmol(-1)/2.303RT Uncertainties are 2 sigma. The activation energy (equivalent to 4.4 eV) and absolute diffusivity values are consistent with previously published values representing Al vacancy diffusion in corundum, supporting the interpretation of the identities of the absorption bands.