Exchange model for proton relaxation in disordered metallic hydrides

The experimental frequency and temperature dependences of proton spin-lattice relaxation in metallic hydrides are often treated within the Bloembergen-Purcell-Pound model. However, even the consideration of activation energy (or correlation time) distribution does not provide a satisfactory agreement with experimental data. It was experimentally detected that in metallic hydrides hydrogen atoms can be in two states: mobile and bounded to the lattice. Here, we suggest treating the proton spin-lattice relaxation in such systems within the model, which implies an exchange between these two states. The correlation times and activation energies values for the hydrogen motion in a hydride of the disordered TiV0.8Cr1.2 alloy have been estimated applying this exchange model.

Research highlights
► Temperature dependence of proton T1 provides information on hydrogen mobility.
► BPP model fails to explain several features of this dependence in metallic hydrides.
► In metallic hydrides hydrogen atoms can be in mobile and bounded states.
► We suggest treating the proton T1 in such systems within an exchange model.
► This model implies an exchange between two hydrogen states: mobile and bounded.