Hydrogen-induced microstructural changes of Pd films

•Nanocrystalline, polycrystalline and epitaxial Pd films were deposited on sapphire.•Defects in Pd films with various structures were examined by positron annihilation.•We report structural changes in the Pd films charged with hydrogen.•In all films studied hydrogen causes plastic deformation which creates new defects.•Above certain critical hydrogen concentration buckling of films can be initiated.

The development of the microstructure in nanocrystalline, polycrystalline and epitaxial Pd films loaded with hydrogen is investigated. Structural changes in Pd films loaded with hydrogen were characterized by positron annihilation spectroscopy combined with electron microscopy and X-ray diffraction. It was found that hydrogen charging causes plastic deformation which leads to an increase of the defect density in all Pd films studied. Moreover, the formation of buckles was observed in nanocrystalline and polycrystalline Pd films loaded above a certain critical hydrogen concentration. Buckling leads to detachment of the film from the substrate and this is accompanied with in-plane stress relaxation and plastic deformation of the film.