Robust structural stability in tI2-La with constant axial ratio under pressures exceeding 330 GPa

Area of Science:

• Materials Science
• Condensed Matter Physics
• High-Pressure Physics

Background:

• Lanthanum's behavior under extreme pressure is not fully understood.
• Previous studies have not explored pressures as high as 337 GPa.

Purpose of the Study:

• To investigate the crystal structures, equations of state, and compressibility of lanthanum.
• To determine the phase transitions and stability of lanthanum at ultrahigh pressures.

Main Methods:

• Synchrotron X-ray diffraction was used to analyze lanthanum.
• Pressures up to 337.2 GPa were applied.

Main Results:

• A series of phase transitions were observed, with the I4/mmm (tI2) phase becoming stable at 82.8 GPa.
• The tI2 phase remained stable up to 337.2 GPa, exhibiting a constant c/a axial ratio above 260 GPa.
• Lanthanum showed ideal metallic properties and compressibility similar to simple metals like Al, Au, and Cu.

Conclusions:

• The study extends the known phase diagram and equation of state for lanthanum to record high pressures.
• The tI2 phase of lanthanum demonstrates robustness and near-ideal metallic compressibility under extreme compression.
• A constant lattice axial ratio under high pressure is a universal behavior observed in light rare-earth metals.