Pressure-induced landau-type transition in stishovite

Area of Science:

• High-pressure geophysics
• Materials science
• Mineral physics

Background:

• Stishovite, a high-pressure polymorph of silica, exhibits unique structural properties under extreme conditions.
• Understanding phase transitions in minerals is crucial for interpreting Earth's deep interior.

Purpose of the Study:

• To investigate the structural behavior of stishovite at ultra-high pressures.
• To determine the pressure-induced phase transformations and their characteristics.

Main Methods:

• Rietveld structural analysis using angle-dispersive x-ray diffraction.
• Synchrotron radiation source at the European Synchrotron Radiation Facility (ESRF).
• Yttrium-aluminum-garnet (YAG) laser heating to manage deviatoric stress.

Main Results:

• A CaCl2-type structural distortion of stishovite was confirmed at 54 ± 1 gigapascals (GPa).
• No further phase transformation was observed up to 120 GPa.
• The tetragonal distortion occurred without a substantial change in volume, fitting a single Birch-Murnaghan equation of state.
• Pressure-induced lattice modifications at 54 GPa were analogous to Landau-type temperature-induced transitions.

Conclusions:

• The CaCl2-type distortion represents a significant phase transition in stishovite under pressure.
• The transition is characterized by lattice modifications similar to temperature-induced transitions.
• It is proposed that the critical temperature for this transition increases with pressure, favoring a lower entropy form above 54 GPa.