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

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