Nucleation and growth of ice XI; Study suggests the existence of ferroelectric ice in the Universe

氷XIの核生成と成長; 宇宙における強誘電体の氷の存在について

深澤 裕; 星川 晃範*; Chakoumakos, B.*; Fernandez-Baca, J. A.*

Fukazawa, Hiroshi; Hoshikawa, Akinori*; Chakoumakos, B.*; Fernandez-Baca, J. A.*

米国オークリッジ国立研究所で実施の中性子回折の実験結果について報告する。氷XIの核生成と成長の過程を時間分割の粉末中性子回折実験で分析した。冥王星等と同じ温度圧力領域にて氷XIが発生可能であることを発表する。

From neutron powder-diffraction experiments, we have studied the growth process of ferroelectric ice XI with deuteron-ordered arrangements. We measured time-resolved neutron diffraction of compressed KOD or NaOD doped DO-ice. We observed the growth of ice XI at 58 74 K. The mass fraction f (the ratio of mass of ice XI to that of the doped ice) linearly increased with time for about 5 days. The de-transformed ice Ih, obtained after warming above the transition temperature of 76 K, retransformed to ice XI at 60 66 K. The observed increase of f with time is in good agreement with the nucleation process of the ordering and the constant growth of the ordered domain. The results suggest that large quantities of ice on cold icy bodies (such as Pluto and Charon) in our solar system are able to transform to ice XI, which may be detectable by space telescope and planetary exploration.