title: AB-stacked square-like bilayer ice in graphene nanocapillaries.
abstract: Water, when constrained between two graphene sheets and under ultrahigh pressure, can manifest dramatic differences from its bulk counterparts such as the van der Waals pressure induced water-to-ice transformation, known as the metastability limit of two-dimensional (2D) liquid. Here, we present result of a new crystalline structure of bilayer ice with the AB-stacking order, observed from molecular dynamics simulations of constrained water. This AB-stacked bilayer ice (BL-ABI) is transformed from the puckered monolayer square-like ice (pMSI) under higher lateral pressure in the graphene nanocapillary at ambient temperature. BL-ABI is a proton-ordered ice with square-like pattern. The transition from pMSI to BL-ABI is through crystal-to-amorphous-to-crystal pathway with notable hysteresis-loop in the potential energy during the compression/decompression process, reflecting the compression/tensile limit of the 2D monolayer/bilayer ice. In a superheating process, the BL-ABI transforms into the AB-stacked bilayer amorphous ice with the square-like pattern.
authors.affiliation: CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, CAS Center for Excellence in Nanoscience, University of Science and Technology of China, Hefei, Anhui 230027, China. wuha@ustc.edu.cn.
authors.forename: YinBo
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, CAS Center for Excellence in Nanoscience, University of Science and Technology of China, Hefei, Anhui 230027, China. wuha@ustc.edu.cn.
authors.forename: FengChao
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, NE 68588, USA. xzeng1@unl.edu.
authors.forename: Jaeil
authors.initials: J
authors.lastname: Bai
authors.affiliation: Department of Chemistry, University of Nebraska-Lincoln, NE 68588, USA. xzeng1@unl.edu and Hefei National Laboratory for Physical Sciences at Microscale and Collaborative Innovation Center of Chemistry for Energy Materials, University of Science and Technology of China, Hefei, Anhui 230026, China.
authors.forename: Xiao Cheng
authors.initials: XC
authors.lastname: Zeng
authors.affiliation: CAS Key Laboratory of Mechanical Behavior and Design of Materials, Department of Modern Mechanics, CAS Center for Excellence in Nanoscience, University of Science and Technology of China, Hefei, Anhui 230027, China. wuha@ustc.edu.cn.
authors.forename: HengAn
authors.initials: H
authors.lastname: Wu