Microstructures define melting of molybdenum at high pressures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Geophysics

Background:

• High-pressure melting defines material phase diagrams and atomic ordering.
• Molybdenum's melting behavior under pressure has been debated, with conflicting experimental and theoretical results.
• Previous experiments suggested a nearly constant melting temperature with increasing pressure, contrary to theoretical predictions.

Purpose of the Study:

• To investigate the melting curve of molybdenum at high pressures.
• To resolve discrepancies between theoretical expectations and previous experimental findings on molybdenum's melting behavior.
• To identify reliable criteria for detecting melting under extreme pressure conditions.

Main Methods:

• Synchrotron X-ray diffraction analysis of microstructures.
• Laser-heated diamond anvil cell for generating high pressures (up to 130 GPa).
• Rapid quenching of samples to preserve post-melting microstructural changes.

Main Results:

• A high-slope melting curve for molybdenum was determined.
• Distinct microstructural changes, observed exclusively after melting, provided a reliable melting criterion.
• A novel high-pressure, high-temperature transition in molybdenum was discovered, forming textured body-centered cubic nanograins.

Conclusions:

• The study confirms a steep increase in molybdenum's melting temperature with pressure.
• The identified microstructural changes offer a robust method for determining melting points at extreme conditions.
• The newly discovered transition provides new insights into molybdenum's phase behavior under extreme conditions.