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Ice XII in its second regime of metastability
Physical Review Letters
|September 16, 2000
Summary
Researchers confirmed the formation of ice XII, a novel crystalline ice phase, under new conditions by compressing hexagonal ice I(h). This new ice phase can be preserved at low temperatures and ambient pressure.
Area of Science:
- Materials Science
- Crystallography
- Thermodynamics
Background:
- The existence of various crystalline ice phases is crucial for understanding planetary science and atmospheric phenomena.
- The recently identified ice XII phase has unique structural properties that require further investigation.
Purpose of the Study:
- To provide unambiguous evidence for the formation of ice XII under novel conditions.
- To determine the accurate structural properties of ice XII.
- To establish the temperature and pressure limits for ice XII formation and stability.
Main Methods:
- Neutron powder diffraction was employed to analyze the crystalline structure of ice.
- Hexagonal ice I(h) was compressed at temperatures ranging from 77 to 160 K up to 1.8 GPa.
- High-resolution diffraction was performed at 1.5 K to obtain precise structural data.
Main Results:
- Unambiguous evidence for the formation of ice XII was obtained under compression of hexagonal ice I(h) at various temperatures (77-160 K).
- Ice XII was found to be stable at ambient pressure within the temperature range of 1.5 K to 135 K.
- The formation of ice III/IX alongside ice XII at higher temperatures (140-160 K) suggests an approximate upper limit of 150 K for ice XII synthesis using this method.
Conclusions:
- The study successfully demonstrates a new method for synthesizing ice XII.
- Accurate structural data for ice XII were obtained, enhancing our understanding of its properties.
- The findings provide critical insights into the phase diagram of water ice under specific temperature and pressure conditions.
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