Measurements were made of pure single crystals, using 86Rb tracers at 525 to 675C. The diffusion parameters were determined in the high-temperature region by means of a least-squares straight-line fit to an Arrhenius plot. The results were described by:

D(cm2/s) = 5514 exp[-2.01(eV)/kT]

H.L.Downing, R.J.Friauf: Physical Review B, 1975, 12[12], 5981-9