Hydrogen in Pd/Nb multilayers

Several Pd/Nb multilayers with various modulation periods have been prepared by laser deposition. Hydrogen was doped into the samples electrolytically or from the gas phase. The elastic response of the multilayers upon absorption of hydrogen, their relaxation and phase separation were studied by x-ray diffraction in reflectional, transmissional, and tilting geometries. It was found that the elastic expansion of the Nb layers after the first two cycles of hydrogen loading and unloading can be described well by a model allowing expansion in one dimension only. Phase separation is observed in the Nb layers as well as in the Pd layers. The phase separation is believed to be initiated by a plastic instability of the film due to hydrogen incorporation. The relaxation and change of strain mode in the multilayers due to hydrogen loading and unloading are discussed concerning the possible defects in the sample formed during sample preparation. {} 1996 The American Physical Society.