Diffusion of deuterium and hydrogen in doped and undoped MgO crystals

Infrared absorption of O${\mathrm{D}}^{-}$ and O${\mathrm{H}}^{-}$ ions is used to study diffusion rates of ${\mathrm{D}}^{+}$ and ${\mathrm{H}}^{+}$ in doped and undoped MgO crystals heated at high temperatures in ${\mathrm{D}}_2$O and ${\mathrm{H}}_2$O vapors. Crystals doped with H, Li, Na, Al, V, Cr, Fe, Co, Ni, Cu, Ga, Ag, and Yb are studied. With the exception of the H- and Li-doped crystals, the diffusion characteristics of the doped and undoped MgO crystals are essentially the same. The minimum temperature observed for ${\mathrm{D}}^{+}$ diffusion is 1750 K, and the diffusion coefficient is ∼1×${10}^{-6\mathrm{}}$ ${\mathrm{cm}}^2$/sec at 1873 K. The ratio of the diffusion coefficients of ${\mathrm{H}}^{+}$ and ${\mathrm{D}}^{+}$ at 1873 K is $\frac{D\left({\mathrm{H}}^{+}\right)}{D\left({\mathrm{D}}^{+}\right)}=1.1\mathrm{}\pm 0.1$. Complete removal of soluble ${\mathrm{H}}^{+}$ can be accomplished by application of an electric field at 1300 K. In H-doped crystals an exchange of ${\mathrm{H}}^{+}$ for ${\mathrm{D}}^{+}$ results in large concentrations of O${\mathrm{D}}^{-}$ ions. In Li-doped crystals, deuterons diffuse much more readily; the threshold temperature for ${\mathrm{D}}^{+}$ diffusion is only 800 K. The higher diffusivity is attributed to a catalytic behavior of ${\mathrm{Li}}_2$O precipitates.