Switchable metal hydride films

This chapter summarizes various studies carried out on different generations of rare earth metal switchable mirrors based on polycrystalline, epitaxial layers, rare earth–Mg alloys, rare earth–Mg multilayers structures, and nanoparticles. In case of polycrystalline and epitaxial rare earth metals, switching behavior measured in terms of optical and electrical contrast, switching and recovery times and transparency and color neutrality of the trihydride state is explained in terms of intrinsic effects such as crystal structure change, phase modification, lattice contraction/expansion, and lateral and longitudinal H diffusion during hydrogenation and dehydrogenation. Moreover, a large scope for fabricating a variety of devices based on hydrogen induced structural, optical, and electrical changes and the possibility of new physics required to explain the intriguing phenomenon accompanying the switchable mirror effect – provided the necessary impetus for applied and basic research in this area. More work needs to be carried out to understand R metal–palladium (Pd) interface. Use of Pd nanoparticles has been shown to improve the switching properties and it may be possible to modify Pd layers by other means. It may also be possible to use chemical methods for growing rare earth layer.