Disproportionation reaction of LaH at high pressure and low temperature

低温高圧下におけるLaHの不均化反応

町田 晃彦; 綿貫 徹; 川名 大地*; 青木 勝敏

Machida, Akihiko; Watanuki, Tetsu; Kawana, Daichi*; Aoki, Katsutoshi

LaHは室温、11GPaで異なる体積の二相に分離することを放射光X線回折により確かめた。この相分離は自発的な水素の濃淡が生じることで説明が可能であり、圧力誘起の不均化反応といえる。この不均化反応は格子間サイトに位置する水素原子のサイト間移動を伴うため、低温で水素の拡散を抑制することで、不均化反応に影響があると考えられる。そこで、LaHの低温高圧下におけるX線回折実験を実施し、不均化反応への温度効果を調べた。その結果、200Kにおいて約13.5GPaで不均化が起こることを観測した。

We found that LaH decomposed into two different molar-volume phases at 11 GPa at room temperature through synchrotron radiation X-ray diffraction (SR-XRD) measurements. Observed decomposition suggests that the H-poor and H-rich phases are spontaneously formed by pressurization, namely, a pressure-induced disproportionation reaction. Observed disproportionation reaction accompanies the transfer of the H atoms between the interstitial sites. Diffusivity of the H atoms suppresses as the temperature decreases. Hence we have investigated this disproportionation of LaH in the low H diffusivity case at low temperature.SR-XRD measurements at high pressure and low temperature were carried out at BL22XU, SPring-8. We found the disproportionation at 13.5 GPa even at 200 K. The volume fraction of the H-poor phase at 200 K is larger than that at room temperature. The disproportionation at low temperature will be discussed on the basis of the X-ray diffraction data.