Abstract
Ice is a material of fundamental importance for a wide range of scientific disciplines including physics, chemistry, and biology, as well as space and materials science. A well-known feature of its phase diagram is that high-temperature phases of ice with orientational disorder of the hydrogen-bonded water molecules undergo phase transitions to their ordered counterparts upon cooling. Here, we present an example where this trend is broken. Instead, hydrochloric-acid-doped ice VI undergoes an alternative type of phase transition upon cooling at high pressure as the orientationally disordered ice remains disordered but undergoes structural distortions. As seen with in-situ neutron diffraction, the resulting phase of ice, ice XIX, forms through a Pbcn-type distortion which includes the tilting and squishing of hexameric clusters. This type of phase transition may provide an explanation for previously observed ferroelectric signatures in dielectric spectroscopy of ice VI and could be relevant for other icy materials.
Highlights
Ice is a material of fundamental importance for a wide range of scientific disciplines including physics, chemistry, and biology, as well as space and materials science
A break-through in hydrogen ordering ice VI came with using hydrochloric acid (HCl) as a dopant which led to the discovery of the antiferroelectric hydrogen-ordered ice XV6
The diffraction pattern at 230 K is consistent with fully hydrogen-disordered ice VI with P42/nmc space group symmetry
Summary
Ice is a material of fundamental importance for a wide range of scientific disciplines including physics, chemistry, and biology, as well as space and materials science. Upon cooling HCl-doped ice VI at pressures above ~1 GPa, the hydrogen-ordering phase transition from ice VI to ice XV is suppressed progressively even though the glass transition temperature of the molecular reorientation dynamics has been lowered significantly by the acid dopant[6,15,16,17,18]. These unusual doped samples have been called deep-glassy ice VI19. Upon heating at ambient pressure, deepglassy ice VI shows the phenomenon of transient ordering as the metastable ice VI state first undergoes irreversible hydrogen ordering to ice XV and reversible hydrogen disordering to ice VI15,17
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