Related Experiment Video
Updated: Feb 18, 2026
08:55
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
9.0K
Multiple pathways in pressure-induced phase transition of coesite
Wei Liu1, Xuebang Wu1, Yunfeng Liang2,3
1Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, People's Republic of China.
Summary
High-pressure experiments reveal coesite transforms into a novel octahedral phase (HPO) and amorphous states. Molecular dynamics simulations explain these diverse transformation pathways under hydrostatic pressure.
Area of Science:
- Geophysics and materials science
- Mineral physics under extreme conditions
Background:
- Coesite, a dense silica phase, is known for pressure-induced amorphization.
- Previous studies observed different transformation pathways under hydrostatic pressure, leading to ambiguity.
Purpose of the Study:
- To elucidate the transformation mechanisms of coesite under high-pressure hydrostatic conditions.
- To explain the formation of the high-pressure octahedral (HPO) phase and amorphous silica.
Main Methods:
- High-pressure single-crystal X-ray diffraction with precise hydrostatic control (He or Ne).
- Ab initio parameterized potential molecular dynamics simulations.
Main Results:
- Reproduced experimental observations, including transformation to an HPO phase with a defective hcp oxygen sublattice.
- The HPO phase transforms into the α-PbO2 phase upon further compression.
- High-pressure amorphous silica phases are characterized by a mixture of fcc and hcp sublattices.
Conclusions:
- The HPO phase forms via continuous oxygen sublattice rearrangement towards an hcp arrangement.
- Molecular dynamics simulations successfully model diverse coesite transformation pathways under pressure.
Related Concept Videos
02:39Phase Diagrams
50.6K
A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. These diagrams indicate the physical states that exist under specific conditions of pressure and temperature and also provide the pressure dependence of the phase-transition temperatures (melting points, sublimation points, boiling points). Regions or areas labeled solid, liquid, and gas represent single phases, while lines or curves represent...
50.6K
01:19Phase Diagram
7.1K
The phase of a given substance depends on the pressure and temperature. Thus, plots of pressure versus temperature showing the phase in each region provide considerable insights into the thermal properties of substances. Such plots are known as phase diagrams. For instance, in the phase diagram for water (Figure 1), the solid curve boundaries between the phases indicate phase transitions (i.e., temperatures and pressures at which the phases coexist).
7.1K
02:31Phase Transitions
23.4K
Whether solid, liquid, or gas, a substance's state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the solid pack closely together, generally in a pattern. The particles vibrate about their fixed positions but do not move or squeeze past their neighbors. In liquids, although the particles are closely spaced, they are randomly arranged. The position of the particles are not fixed—that is, they are free to move past their neighbors to...
23.4K
02:33Phase Transitions: Sublimation and Deposition
20.4K
Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and standard pressure, a piece of dry ice (solid CO2) sublimes, appearing to gradually disappear without ever forming any liquid. Snow and ice sublimate at temperatures below the melting point of water, a slow process that may be accelerated by winds and the reduced atmospheric pressures at high altitudes. When solid iodine is warmed, the solid sublimes...
20.4K
02:39Phase Transitions: Melting and Freezing
15.3K
Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
15.3K
00:59States of Matter and Phase Changes
5.0K
The internal energy of a substance—the total kinetic energy of all its molecules and the potential energy of their associated forces—depends on the strength of the intermolecular forces in the condensed phases and the pressure exerted on the substance. The internal energy of a substance is the highest in the gaseous state, the lowest in the solid state, and intermediate in the liquid state. Phase transitions are caused by changes in physical conditions, such as temperature and...
5.0K