Crystal structure and switchable optical properties of yttrium hydride films covered by palladium layer

The palladium/yttrium films were prepared using magnetron sputtering technique. The changes of crystal structure, morphology and optical properties of the films during the hydrogen absorption/desorption process were investigated. The results of SEM and AFM analysis show that yttrium films have columnar structure, and the Pd cover layers on the surface of the yttrium films are composed of nanometer-sized Pd particles, which contain a large amount of smaller crystalline grains. During the gas hydrogen absorption/desorption process, YH3 and YH2 hydrides form on the sites of Pd grains contacting with Y grains. Upon hydrogenation, YH, hydride forms and the switchable optical properties can be observed. The light transparency of the films increases with the increasing of hydrogen loading time and the light wavelength, and the absorption limitation occurs at lambda = 400 nm. Upon dehydrogenation, YH3 hydride dissociates into YH2 hydride, and the maximum transparency occurs at lambda = 689 nm.