B1-B2 transition in shock-compressed MgO

Area of Science:

• Planetary Science
• Geophysics
• Materials Science

Background:

• Magnesium oxide (MgO) is a key component of planetary mantles.
• Understanding MgO's high-pressure behavior is vital for exoplanet mantle dynamics.

Purpose of the Study:

• To experimentally determine the phase diagram of MgO at extreme pressures.
• To investigate the B1 to B2 crystal structure phase transition in MgO.

Main Methods:

• Laser-compression experiments along the shock Hugoniot.
• Simultaneous measurements of crystal structure, density, pressure, and temperature.
• Analysis of phase transitions and melting points.

Main Results:

• Identified the B1 to B2 phase transition between 397-425 GPa (~9700 K).
• Observed a mixed-phase region (B1 and B2 coexistence) from 425-493 GPa.
• Found B2-liquid coexistence above 500 GPa and complete melting at 634 GPa.

Conclusions:

• The experimental data align with theoretical predictions including phonon anharmonicity.
• The study provides critical insights into the timescale of MgO phase transitions under extreme conditions.
• This research bridges the gap between theoretical and experimental studies on MgO.