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Vibrational states of atomic hydrogen in bulk and nanocrystalline palladium studied by neutron spectroscopy

Kofu, Maiko  ; Hashimoto, Naoki*; Akiba, Hiroshi*; Kobayashi, Hirokazu*; Kitagawa, Hiroshi*; Iida, Kazuki*; Nakamura, Mitsutaka; Yamamuro, Osamu*

The vibrational states of hydrogen atoms in bulk and nanocrystalline palladium were examined in a wide energy region $$0 le hbar omega le 300$$ meV using neutron spectroscopy. In bulk PdH$$_{0.73}$$, the vibrational excitations of H atoms were roughly reproduced by the quantum harmonic oscillator (QHO) model. In PdH$$_{0.42}$$ nanocrystals with a diameter of 8 nm, however, additional vibrational excitations were found at energies above 80 meV. The energies and intensities of the additional states were not explained by QHO but reasonably described as vibrations in a highly anharmonic trumpet-like potential. The additional excitations are attributed to the vibrations of H atoms at tetrahedral sites in the subsurface region stabilized by surface effects. This is an experimental work which clearly detects hydrogen vibration ${it inside}$ metal nanoparticles.



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Category:Materials Science, Multidisciplinary



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