Exchange model for proton relaxation in disordered metallic hydrides

NMR study of metal-hydrogen systems for hydrogen storage

“…And one can suppose that there is an exchange between these two states. To treat the temperature dependences of 1 H T1 in Ti-V-Cr hydrides we applied the modified Bloembergen-Purcell-Pound (BPP) model [14] assuming a fast exchange between mobile and bounded to the lattice hydrogen states [15]. This model can be applied in a case when the life time of hydrogen in these states ( m , b ) is much less the spin-lattice relaxation time m,b < < T1 and the relaxation functions can be described by an average exponential function:…”

“…[15]), the only contributions taken into account were from 1 H-1 H dipole interactions and from conduction electrons:…”

Hydrogen diffusion in metal-hydrogen systems via NMR and DFT

“…Despite the presence of a local minimum energy at the O-site, its probability of occupancy must be rather low, and the lifetime of the hydrogen in the site is no longer enough to observe a resonance within the NMR experiment time. Moreover, no trace of hydrogen was detected from the O-site relaxation analysis [20]. The magnetization recovery traces fit well with a single exponential decay in the whole studied temperature range.…”

“…In more details this problem and the most successive attempts to solve at least partly [13,14,19] was discussed in Refs. [20], in which the authors proposed to consider an exchange model between hydrogen in two states with different mobility.…”

“…As shown in Section 4.3, this value fairly agrees with that resulting from diffusion measurements, however below 12 MHz the observed behavior reveals the presence of a second diffusion mechanism, even more intense at higher temperature. It is worth to note that the frequency dependence of 1/T 1 can be fairly fitted according to the exchange model [20,57]. In the model, it was supposed that the fractions of 'mobile' and 'bonded' hydrogen can be considered as two different states in between them takes place exchange correlations, with a characteristic time estimated to 0.02 ms << t ex << 10 ms [57].…”