Unusual behaviour of the band structure and electronic-induced phase transitions in metallic hydrides

Progress in theoretical and experimental investigations aimed at achieving a better understanding of the structural transformations in the transition metal hydrides is reviewed. Tetragonal distortion in the titanium group dihydrides and the light rare earth trihydrides and the metal-to-semiconductor transition in the trihydrides are discussed. Both theoretical band structure calculations and experimental investigations indicate that the phase transitions are electronically induced. The theoretical description was based on the excitonic dielectric model.