Changes in the sizes of second-phase precipitates in Co-doped single crystals were examined in samples which had been subjected to progressive annealing at 600 to 1500C. The precipitate sizes and spatial locations were measured by means of light scattering, before and after annealing in flowing Ar. Absolute light scattering angular distribution measurements were used to obtain size distributions using a Mie theory deconvolution procedure. A comparison of

Ostwald ripening theory with the time evolution of the precipitates indicated that the growth could be described by a dislocation or grain boundary diffusion ripening mechanism. This mechanism was also consistent with ultramicroscope measurements before and after each anneal. The depletion region surrounding the ripening particles was observed via backscattering in the measured angular distributions. The results for diffusion within the boundary regions gave:

D (cm2/s) = 1.60 x 10-7 exp[-1.36(eV)/kT]

for the Co ions. This equation was in agreement with previous diffusion-couple measurements of non-enhanced diffusion in the grain-boundary regions of this material.

R.M.Bunch, W.P.Unruh, M.V.Iverson:  Journal of Applied Physics, 1985, 58[4], 1474-82