Hydridites

Hydridites are a proposed class of crystalline materials defined by the incorporation of hydridic hydrogen, that is hydrogen with negative charge (H−), into a solid lattice. In this usage, hydridites describe interstitial compounds whose bonding and structure give rise to significant hydridic character while preserving solid-state integrity. The concept is used in both mineralogical discussions of hydrogen-bearing phases and in materials science research on hydrogen storage and diffusion.

Most hydridites are described in synthetic systems, where metal or alloy hosts trap hydrogen within interstitial sites of a metal framework, often achieving nonstoichiometric compositions MHx with x ranging widely. The hydridic occupancy leads to distinctive vibrational spectra and diffusion pathways compared with conventional hydrides, and may produce metallic or semiconducting behavior depending on composition and pressure.

Natural occurrence of hydridites is not well established. Experimental evidence for hydridite-like phases has emerged in high-pressure studies of metal-hydrogen systems and in hydrided minerals formed under laboratory conditions. In practical terms, hydridites are studied for hydrogen storage, electrochemical compatibility, and catalytic properties, owing to their high hydrogen density and tunable release kinetics.

Synthesis generally involves exposing metal hosts to hydrogen under controlled temperature and pressure, sometimes with catalysts or dopants to improve kinetics and stability. Challenges include maintaining reversibility, preventing excessive embrittlement, and ensuring safety during hydrogen cycling.

See also: metal hydrides, hydrogen storage materials, interstitial alloys, hydride minerals.