Statistical theory of diffusion. Quantum states, configurational shape of a potential, and two types of noncoherent transitions of a hydrogen atom in metals

The configurational shape of the potential of a light atom (hydrogen) in metals with bcc lattice is calculated using the methods of many-electron theory. It is shown that localized states of the proton are formed by local displacements of the atoms of the crystal, whereas in a “rigid” lattice the quantum states are delocalized in a time of the order of the ocsillation period of the proton. Two types of noncoherent transport of the hydrogen atom – “active” and “passive” hops – are investigated by means of data on the quantum states. It is shown that the rate of high-temperature noncoherent hopping of a light atom (“active” hopping) is determined by three processes: thermal activation, tunneling accompanied by motion of the deformation cloud, and intrasite transitions of the hydrogen due to two-phonon scattering. It is shown that the observed inflection in the temperature dependence of the activation energy is due to a change in the mechanism of the elementary hydrogen diffusion process, namely, the transition from passive to active transport.