A window type of the environmental cell system for a high-voltage electron microscope was developed and applied to in situ observation of a palladium (Pd) thin film. For in situ hydrogenation of Pd thin films, the distances of the lattice fringes were 0.20 and 0.23 nm, which correspond to the lattice d spacings of β-phase (200) and (111) planes. Expansion of the Pd lattice happened as a result of phase transformation from the α phase to the β phase. In particular, the lattice fringes were clearly distinguished, and the dislocation behavior during Pd hydrogenation was easily recognized according to the corresponding inverse fast fourier transform images. Furthermore, significant growth in the number of dislocations was observed at the grain boundary during increasing hydrogen pressure in the cell.

Transmission electron microscope (TEM) observation of light metal hydrides is complicated by the instability of these materials under electron irradiation. In this study, the electron kinetic energy dependences of the interactions of incident electrons with lithium, sodium, and magnesium hydrides, as well as the constituting element effect on the interactions, were theoretically discussed, and electron irradiation damage to these hydrides was examined using in-situ TEM. The results indicate that high incident electron kinetic energy helps alleviate the irradiation damage resulting from inelastic or elastic scattering of the incident electrons in the TEM. Therefore, observations and characterizations of these materials would benefit from increased, instead decreased, TEM operating voltage. signals resulting from these phenomena allow for powerful microscopy and spectrometry applications in the TEM, e.g., imaging, diffraction, energy dispersive X-ray spectroscopy (EDS), and electron energy-loss spectrometry (EELS). However, these advantages are associated with detrimental beam damage, which limits the application of the TEM in materials that are sensitive to high-energy electron radiation.Unfortunately, most advanced hydrogen storage materials consisting of light elements are partially subject to this limitation. To achieve a high hydrogen capacity [1][2], the majority of currently studied hydrogen storage materials are composed of compounds and complexes containing light elements [3] such as lithium, sodium, and magnesium. These materials are

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We propose the microstructural change model of magnesium hydride catalyzed by Nb 2 O 5 during hydrogenation. The ball-milled composites, MgH 2 and 1 mol% Nb 2 O 5 , were dehydrogenated and then rehydrogenated for varied time at room temperature under 0.1 MPa H 2 atmosphere. The crystallite size of Mg and MgH 2 was evaluated by powder X-ray diffraction (XRD) measurement and confirmed by transmission electron microscopy (TEM) observation. The crystallite size of generated MgH 2 was smaller than that of Mg and did not change significantly with increasing time of hydrogenation. It is suggested that the number density of MgH 2 crystallites increases during the hydrogenation process.

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