Apparently, the diffusion coefficient is sensitive to impurities or structural concerns within the crystal, but that remains to get quantified. For our rough estimates of time at temperature needed to take away the hydrogen from our samples, the hydrogen diffusion coefficient chosen is that presented by Belonoshko et al. (2004), https://sparxsocial.com/story8332110/indicators-on-sri-lankan-yellow-sapphire-you-should-know