Planar Defect Layers Template a High-Pressure InBi Polymorph

Area of Science:

• Materials Science
• Condensed Matter Physics
• Crystallography

Background:

• The high-pressure behavior of III-V materials, particularly their order and structure, remains a complex area of research.
• Previous studies on Indium-Bismuth (InBi) under high pressure suggested a site-disordered β-Sn structure, which is inconsistent with analogous III-V systems.
• Experimental data like X-ray diffraction suggested disorder, but theoretical calculations indicated extremely high temperatures (above 3000 K) were required for such disordering.

Purpose of the Study:

• To investigate and propose alternative structural models for Indium-Bismuth (InBi) under high pressure, focusing on planar defects.
• To reconcile experimental observations of apparent site disorder with theoretical predictions of high disordering temperatures.
• To establish InBi as a model system for understanding unique high-pressure planar defects and their influence on material properties.

Main Methods:

• Symmetry analysis of crystallographic transitions to derive potential planar defect structures.
• Density Functional Theory (DFT) calculations to investigate the stability and electronic structure of proposed defects.
• Comparison of calculated diffraction patterns with experimental data and theoretical disorder barriers.

Main Results:

• Identification of two sets of planar defects in InBi that replicate the diffraction signature of a site-disordered β-Sn structure.
• These proposed defects are thermodynamically stable under high pressure, supported by DFT calculations showing stabilization with decreasing interlayer separation.
• One identified defect structure closely matches the known high-pressure phase of InBi (InBi-ϵ), suggesting defects act as templates for phase growth upon heating.

Conclusions:

• The apparent site disorder in InBi under high pressure is likely due to specific planar defects, not a bulk disordered structure.
• These defects provide a mechanistic explanation for the observed trends in superconducting critical temperature with increasing pressure.
• The methodology for defect identification is generalizable to other materials exhibiting reported high-pressure site disorder.