Metal-semiconductor-insulator transitions in R sub 3 Ni compounds induced by hydrogenation

Electrical resistivity and ac magnetic susceptibility measurements of R sub 3 Ni and their hydrides R sub 3 NiH sub x were carried out. It is shown that the conductivity of R sub 3 NiH sub x compounds with a large amount of hydrogen have semiconductor and insulator conductivity type as compared with metallic conduction in the original compounds R sub 3 Ni. The resistivity of the original compounds is discussed on the basis of a conduction electron scattering model. Strongly modified transport processes of the hydrides are discussed on basis of a hopping model.