Defect studies of hydrogen loaded Nb: bulk metals and thin films

Microstructure investigations of Nb loaded with H are presented in this work. The microstructure was examined by positron annihilation spectroscopy (PAS), combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The behaviour of H-loaded bulk samples and thin films was compared. First, the microstructure of the virgin (H-free) specimens was characterized. Subsequently, the development of the microstructure during step-by-step electrochemical H charging was studied. The investigations were performed mainly in the low H concentration region (α-phase), where the Nb-H system represents a single phase interstitial solid solution. In bulk samples it was found that new vacancy-like defects are introduced by H loading. Vacancies surrounded by H were detected also in the electron irradiated bulk samples. Nanocrystalline thin films were produced by sputtering at room temperature. They exhibit a significant volume fraction of grain boundaries with open volume defects which trap H.