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Report No.

Site dependent hardening of the lanthanum metal lattice by hydrogen absorption

Machida, Akihiko; Watanuki, Tetsu; Omura, Ayako*; Ikeda, Tomohiro*; Aoki, Katsutoshi; Nakano, Satoshi*; Takemura, Kenichi*

The compressibility of lanthanum (La) metal and its hydrides were measured at room temperature by high pressure synchrotron X-ray diffraction. La metal pressurized in a hydrogen medium forms a hydride with an fcc metal lattice, which likely contains hydrogen at a concentration close to 3.0. Equations of state have been determined by helium compression experiments for LaH$$_2$$ with tetrahedral interstitial sites fully occupied with hydrogen atoms and for LaH$$_{2.46}$$ with octahedral interstitial sites partially occupied with hydrogen atoms and tetrahedral sites fully occupied. Both hydrides possess fcc metal lattices. These values are three times larger than that of La metal and are very close to each other despite the difference in hydrogen occupation states. The hardening of the metal lattice by hydrogenation is attributed predominantly to hydrogen-metal interactions at the tetrahedral sites and is most pronounced for La, which has the largest ionic radius among rare-earth metals.



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Category:Physics, Condensed Matter



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