Morphological evolution of pre-perturbed pore channels in sapphire

Abstract

Internal pore channels having sinusoidal perturbations of controlled amplitude α and wavelength λ oriented along the [1 1 00] and [11 2 0] directions were produced in undoped sapphire. The morphological evolution of these features at elevated temperature was monitored. Three regimes of behavior, dependent upon the perturbation wavelength, were identified. An orientation dependent minimum wavelength for perturbation growth was identified. In some instances, the behavior was not one of amplitude decay, but instead stabilization by facetting. For these cases, the minimum wavelength is referred to as λ facet. In other cases, after sufficiently long anneals, perturbation decay did occur, allowing an experimental determination of λ min. At intermediate wavelengths, channels broke up into isolated pores having spacings that were equal to the imposed wavelength, at rates that depended upon wavelength. The wavelength of maximum evolution rate is termed λ max, and is of the order of 2·λ facet or 2 · λ min. At long wavelengths, perturbations of relatively shorter wavelength developed naturally, albeit slowly, and resulted in the ultimate formation of isolated pores with spacings less than those imposed. Results are compared with those obtained previously when pore channels having no large amplitude perturbations were allowed to evolve at elevated temperatures.