Pipe diffusion in sapphire: A dislocation dipole annealing study

When annealed at high temperature, dislocation dipoles and elongated loops in sapphire break up into smaller dislocation loops in a sequential manner and the process is controlled by pipe diffusion. The pipe diffusion coefficient is obtained by studying the dipole annealing process using TEM.; Based on Lagerlöf's break-up model for semi-dipoles, a model for the break-up of elongated loops was established using the energy criterion. Using the models, two methods were employed to calculate the pipe diffusion coefficient from the experimental data of sequential dipole annealing. The results of these two methods are similar: the pipe diffusion is about 10 5 times faster than bulk diffusion in sapphire.; In the temperature range of 1250∼1485°C, the pipe diffusion coefficient can be expressed as: Dp =9.19×10^-4 exp-4.4eVkT m²/ sforundopedsa pphireusingMethod 1 Dp= 1.45exp&parl0;-5.1eVkT &parr0;m²/sfor undopedsapphireusing Method2 Dp= 4.27×10^-4exp&parl0;-4.2eV kT&parr0;m²/s for30ppmMgO- dopedsapphire Pipe diffusion in MgO-doped sapphire is slightly faster than that in undoped sapphire.