title: Porous ice phases with VI and distorted VII structures constrained in nanoporous silica.
abstract: High-pressure compression of water contained in nanoporous silica allowed fabrication of novel porous ice phases as a function of pressure. The starting liquid nanoporous H2O transformed to ice VI and VII at 1.7 and 2.5 GPa, respectively, which are 0.6 and 0.4 GPa higher than commonly accepted pressures for bulk H2O. The continuous increase of pressure drives the formation of a tetragonally distorted VII structure with the space group I4mm, rather than a cubic Pn3m phase in bulk ice. The enhanced incompressibility of the tetragonal ice is related to the unique nanoporous configuration, and the distortion ratio c/a gradually increases with increasing pressure. The structural changes and enhanced thermodynamic stability may be interpreted by the two-dimensional distribution of silanol groups on the porous silica surfaces and the associated anisotropic interactions with H2O at the interfaces.
authors.affiliation: National Lab for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences , Beijing, 100190, China.
authors.forename: Jinlong
authors.initials: J
authors.lastname: Zhu
authors.forename: Zewei
authors.initials: Z
authors.lastname: Quan
authors.forename: Yu-Shen
authors.initials: YS
authors.lastname: Lin
authors.forename: Ying-Bing
authors.initials: YB
authors.lastname: Jiang
authors.forename: Zhongwu
authors.initials: Z
authors.lastname: Wang
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Zhang
authors.forename: Changqing
authors.initials: C
authors.lastname: Jin
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Zhao
authors.forename: Zhenxian
authors.initials: Z
authors.lastname: Liu
authors.forename: C Jeffrey
authors.initials: CJ
authors.lastname: Brinker
authors.forename: Hongwu
authors.initials: H
authors.lastname: Xu
keywords: DAC; Nanoporous ice; SAXS; WAXS; high pressure