Structural transitions induced by hydrogen absorption in metallic hydrides

Abstract Intermetallic compounds are able to store reversibly large amount of hydrogen. The hydride formation usually takes place through a two-phase domain for which an equilibrium plateau is observed between the metallic phase and its hydride. Such phase transformation induces important structural changes such as volume expansion (either isotropic and anisotropic), symmetry lowering, hydrogen ordering and phase transitions. In some cases, change of the electronic structure, from metallic to iono-covalent state, is reported. Finally, amorphization can occur leading to disproportionation of the parent compound. In this overview we give some examples of these different behaviors to illustrate the fascinating structural properties of these materials that are of potential interest from the fundamental point of view and for practical applications like energy storage either by solid-gas or electrochemical routes.