How do transition metals form metallic hydrides?

Metallic hydrides, also known as interstitial or alloylike hydrides, are formed by heating transition metals or their alloys with hydrogen gas.12

During this process, the metal's crystal lattice often expands to accommodate the hydrogen atoms, which occupy interstitial spaces within the metal structure. While some of these compounds are stoichiometric, many are nonstoichiometric, meaning they possess a variable composition.21

The formation of these hydrides is generally characterized by the absorption of hydrogen and the release of heat. Because the dissociation energy of molecular hydrogen is very high, elevated temperatures are typically required to achieve significant reaction rates. Once formed, these materials retain metallic characteristics such as lustre and electrical conductivity, which are attributed to the relative freedom of electron movement within the hydride structure.12