Influence of hydrogen loading on the microstructure of niobium-palladium multilayers

Nb-Pd multilayers were prepared by laser deposition. Samples were loaded el ectrolytically with hydrogen up to 0.3 H/Nb, others were submitted to four complete loading-unloading cycles and remained loaded. The microstructure o f these samples as well as that of as-prepared samples were studied by high resolution electron microscopy. After several hydrogen loading and unloadi ng cycles the change in microstructure consists mainly of a new arrangement of dislocations. Further transmission electron microscopy studies reveal t hat beta-NbH grows in columns parallel to the growth direction of the films after phase separation. X-ray studies show that after unloading from the b eta-NbH phase the stress in the film changes to the reverse mode. This is v alid for completely loaded as well as partially loaded specimens.