Superdiffusion of4T-Hydrogen in Vanadium

Room-temperature x-ray diffuse scattering experiments are reported for hydrogen in solution in vanadium. Uniaxial stress (below the elastic limit) results in transformation of all hydrogen atoms from $1T$ into $4T$ states; each hydrogen is delocalized over four neighboring $T$ sites via tunneling. The diffusion coefficient of the $4T$ hydrogen, $D_{4T}$, is measured from 340 to 200 K under an external $〈111〉$ stress. It is extraordinarily large as compared to the existing data and satisfies the relation $D_{4T}=D_0\exp \left(\frac{-E}{kT}\right)$, where $D_0=1.6\mathrm{}\times {10}^{-3\mathrm{}}$ ${\mathrm{cm}}^2$/s and $E=6\mathrm{}$ meV.