High-pressure structural trends of Group 15 elements: simple packed structures versus complex host-guest arrangements

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Chemistry

Background:

• Group 15 elements (P, As, Sb, Bi) exhibit layered structures at ambient conditions.
• Under high pressure, these elements transition to a body-centered cubic (bcc) structure.
• Intermediate pressure ranges show unique structural behaviors for P versus heavier congeners.

Purpose of the Study:

• To investigate the high-pressure structural phase transitions of phosphorus (P) and arsenic (As).
• To elucidate the electronic mechanisms governing the distinct intermediate pressure structures.
• To validate theoretical calculations against experimental findings for these elements.

Main Methods:

• Ab initio density functional calculations were employed.
• Pseudopotentials and a plane wave basis set were utilized.
• The incommensurately modulated structure of As was approximated using a supercell model.

Main Results:

• Calculations accurately reproduced the experimentally observed pressure stability ranges for P's simple cubic (sc) and simple hexagonal (sh) structures.
• The theoretical model successfully predicted the host-guest structure for As under pressure.
• Stabilization of sc and sh structures in P is attributed to d-state admixture (s-d mixing), which is pressure-dependent.

Conclusions:

• The distinct high-pressure behaviors of P and As are driven by differences in s-d mixing and its effect on electronic band structure.
• For P, band energy contributions dominate, leading to simple packed structures (sc, sh) due to increased s-d mixing with pressure.
• For heavier congeners like As, complex structures arise from a balance between Madelung energy and band energy.