YTTRIUM AND LANTHANUM HYDRIDE FILMS WITH SWITCHABLE OPTICAL-PROPERTIES

We discovered that yttrium-, lanthanum- and rare earth-hydride films e xhibit remarkable optical properties near their metal-insulator transi tion: the dihydrides are metallic and shiny while the trihydrides are semiconducting and transparent. The transition between the shiny and t ransparent state is reversible and can simply be induced by changing t he H-2 gas pressure or the voltage in an electrolytic cell. No deterio ration of the films is detected if they are protected by a thin pallad ium caplayer. The optical switching is also observed in hydrides of al loys of Y and La. Several theoretical models leading to an insulating and transparent trihydride state are discussed.