Hydrogen in rare earths: a wealth of structural and electronic phenomena

After discussing a typical R–H phase diagram, some relevant examples are selected, from (i) the α*-RHx solid solution, (ii) the superstoichiometric β-RH2+x dihydride, and (iii) the substoichiometric RH3−x trihydride phase. Thus, in (i) we show the influence of hydrogen upon the magnetism of Er and discuss the possible origin of the uni-dimensional configuration of the α*-phase; in (ii), the role of the order/disorder transformation in the excess hydrogen sublattice upon the magnetism of β-TbD2+x, and, in (iii), the electrical as well as the optical metal–insulator transitions and their relation with structural disorder in the H-sublattice.