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Synthesis and Microdiffraction at Extreme Pressures and Temperatures
Published on: October 7, 2013
Hydrostaticity-Sensitive Structural Phase Transition and High-Pressure Phase Diagram in Fluorite: Evidence of Raman
Mingyu Wu1,2, Lidong Dai3, Haiying Hu3
1Key Laboratory of High-Temperature and High-Pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China.
The structural phase transition in fluorite is highly sensitive to hydrostaticity, with transition pressures varying significantly based on pressure-transmitting media. This study characterizes the reversible phase transition using Raman spectroscopy and electrical conductivity under high pressure.
Area of Science:
- Mineral Physics
- High-Pressure Geophysics
- Materials Science
Background:
- Fluorite (CaF2) exhibits structural phase transitions under high pressure.
- Understanding these transitions is crucial for interpreting geophysical data and developing new materials.
Purpose of the Study:
- To investigate the pressure-induced phase transition of fluorite using Raman spectroscopy and electrical conductivity.
- To determine the influence of hydrostaticity on the transition pressure.
- To characterize the reversibility and high-temperature behavior of the fluorite phase transition.
Main Methods:
- Raman spectroscopy in a diamond anvil cell (DAC) from 0.5-20.5 GPa.
- Electrical conductivity measurements from 298-873 K and 1.2-19.6 GPa.
- High-resolution transmission electron microscopy (HRTEM) for microstructural analysis.
Main Results:
- The cubic (α) to cotunnite (γ) phase transition in fluorite is sensitive to hydrostaticity, with transition pressures ranging from 7.5 to 10.4 GPa depending on the pressure-transmitting medium.
- The transition is reversible, confirmed by decompression experiments and HRTEM.
- Electrical conductivity measurements show an Ohmic response, and the transition temperature exhibits a negative dependence on pressure, defining a phase boundary.
Conclusions:
- Hydrostaticity significantly impacts the fluorite phase transition pressure.
- The phase transition is reversible and can be characterized by Raman spectroscopy and electrical conductivity.
- The determined phase diagram provides insights into the stability of fluorite and related minerals under extreme conditions.
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