Annealing effects on hydrogen ordering in KOD-doped ice observed using neutron diffraction

中性子回折実験で観測された氷中の水素秩序化のアニール効果

荒川 雅*; 鍵 裕之; 深澤 裕

Arakawa, Masashi*; Kagi, Hiroyuki; Fukazawa, Hiroshi

これまでの研究では、氷XIの核形成は65K以下で起こると考えられてきた。しかし、本研究では、過去に氷XIを経験した試料においては、これまでに報告されてきたよりも高い温度(70K, 72K)でXIの成長が観測された。水素秩序化を経験したことのある氷には、110Kにおいても微小(数nm以下)な水素秩序化領域が存在し、それがテンプレートとなり、XIの成長が起こったことが示唆された。本成果は、普通の氷Ihの中の短周期の水素秩序化構造の存在を示す、極めて重要な発見である。

We measured the neutron powder diffraction of 0.013 M KOD-doped DO ice to investigate the formation process of ice XI, a hydrogen-ordered phase of ice Ih. The doped ice Ih transformed to ice XI after annealing at 57 and subsequently at 68 K. The mass fraction of ice XI to that of the doped ice () was estimated using Rietveld analysis for each sample. The value of the doped ice, which had once experienced being ice XI ( = 0.23), was larger than that of the doped ice, which had never experienced being ice XI ( = 0.14). Results indicate that small hydrogen-ordered domains remained in the ice Ih, which had once trans- formed to ice XI, and accelerated the phase transition from ice Ih to ice XI. Results further suggest that large amounts of ice on icy bodies in our solar system can transform to ice XI, which might be detectable using infrared telescopes or planetary exploration in the near future.