Pressure tuned incommensurability and guest structure transition in compressed scandium from machine learning atomic...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Scandium (Sc) exhibits a host-guest (H-G) incommensurate structure under gigapascal (GPa) pressures.
• The guest structure can adopt multiple forms and exhibit disorder under compression.

Purpose of the Study:

• To explore the global potential energy surface of scandium under various pressures.
• To investigate the solid-phase transition mechanisms in compressed scandium.

Main Methods:

• Utilized a global neural network (g-NN) potential.
• Employed the stochastic surface walking (SSW) global optimization algorithm.
• Analyzed structures containing hundreds of atoms to probe global minima.

Main Results:

• The solid-phase transition between Sc-I and H-G Sc-II phases is fully reconstructive.
• Above 62.5 GPa, the face-centered tetragonal (fct, Sc-IIa) guest structure destabilizes to a body-centered tetragonal (bct, Sc-IIb) phase.
• The host structure remains stable while the guest structure transforms.

Conclusions:

• The study reveals the reconstructive nature of the Sc-I to Sc-II phase transition.
• Identified a new body-centered tetragonal (bct) guest structure in compressed scandium.
• Provides insights into the complex structural modifications of metals under extreme pressure.