Site dependent hardening of the lanthanum metal lattice by hydrogen absorption

水素吸収によるランタン金属格子の硬度化の水素占有サイト依存性

町田 晃彦; 綿貫 徹; 大村 彩子*; 池田 智宏*; 青木 勝敏; 中野 智志*; 竹村 謙一*

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

ランタンとその水素化物の圧縮率を高圧下放射光X線回折実験により調べた。ランタンを水素中で圧縮するとその組成がH/La=3に近い組成までの水素化物が形成される。水素原子が四面体サイトをすべて占有しているLaHと四面体サイトに加えて八面体サイトを一部占有しているLaHの状態方程式を決定したところ、体積弾性率は水素濃度が異なるにもかかわらず同じであるが、ランタンに比べ約3倍になることがわかった。水素化による結晶格子の硬度化は四面体サイトを占有した水素の影響が大きいことを明らかにした。

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 with tetrahedral interstitial sites fully occupied with hydrogen atoms and for LaH 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.