The diffusion of F- ions in the garnet was induced here for the first time, and was investigated by using magneto-optical techniques. Crystals with the composition, Y3-xCaxFe5O12-xFx (with x ≈ 0.3) were grown, and diffusion of F- ions out of the sample was induced by high-temperature annealing in O. The replacement of F- by O2- ions produced Fe4+ ions, whose magnetic circular dichroism in the near-infrared was used as a sensitive probe of the diffusion process. This results could be well described in terms of classical diffusion:

D (cm2/s) = 6.5 x 100 exp[-3.42(eV)/kT]

These values were suggested to indicate that microscopic F-, O2- ion exchange occurred via the intervention of an anion vacancy.

Diffusion of Fluorine Ions in Yttrium Iron Garnet. B.Antonini, P.Paroli: Physical Review B, 1983, 28[6], 3422-6