Apparently, the diffusion coefficient is sensitive to impurities or structural difficulties while in the crystal, but that remains being quantified. For our tough estimates of time at temperature necessary to remove the hydrogen from our samples, the hydrogen diffusion coefficient preferred is always that given by Belonoshko et al. (2004), https://www.tumblr.com/thegemjournal/759696203354128384/understanding-the-unique-characteristics-of-yellow?source=share