Migration of hydrogen in rare-earth metals at the disorder-order transition

The migration energies, which are obtained using the hydrogen disorder-order transition, of hydrogen atoms in rare-earth metals divide into two groups, high values and low values. The high values are approximately double the low values. The cause of the discrepancy is discussed and explained as a misestimate of the order of the reaction in the rate equation for the low-value group. The high and low values of the migration energy agree well with each other on using the correct order of the reaction. The same explanation has been given for the case of Pd-H alloys.