The wake of hydrogen in V, Nb and Ta at elevated temperatures: Irreversibility and non-central forces revisited

At elevated temperatures U and Do of the Arrhenius equation for diffusion describe the amplitude and relaxation rate, respectively, of the stern wave wake of H. The key evidence for this hypothesis is the close correlation between the isotope dependence of U derived from measurements of the Gorsky effect and the shear distortion of the orthorhombic phases of NbH(D) and TaH(D). The isotope dependence of U can be described in closed form: U=axsqrt(M)+bxsqrt(m), where M and m are the atomic weights of host metal and H isotope: a and b are 7.4 and 37 for Nb and Ta, and 0 and 55 for V, respectively, in units of meV. I explain this correlation in two steps: a) the cubic symmetry of the nearest neighbor strain field of the interstitial H is the result of a dynamic superposition, possibly caused by a JT resonance, of two orthorhombic variants of ordered NbH0.75 and b) the successful characterization of the diffusion process as jump diffusion eliminates the transition state from considerations.