Coexistence of multiple metastable polytypes in rhombohedral bismuth

TL;DR

This study discovers multiple metastable polytypes coexisting with the rhombohedral A7 structure in bismuth, supported by experimental microstructure analysis and first-principles calculations, explaining variations in physical properties.

Contribution

It reveals the coexistence of metastable polytypes in bismuth at ambient conditions, supported by experimental and theoretical evidence, and suggests this phenomenon may be common in other elements.

Findings

Identification of three new polytypes with atomic positions close to A7

Simulated diffraction data match experimental microstructure analyses

Variations in physical properties may be due to polytype formation

Abstract

Derivative structural polytypes coexisting with the rhombohedral A7 structure of elemental bismuth (Bi) have been discovered at ambient condition, based on microstructure analyses of pure Bi samples treated under high pressure and high temperature conditions. Three structures with atomic positions close to those of the A7 structure have been identified through first-principles calculations, showing these polytypes energetically comparable to the A7 structure under ambient condition. Simulated diffraction data are in excellent agreement with the experimental observations. We argue that previously reported variations in physical properties (e.g., density, melting point, electrical conductivity, and magnetism) in bismuth could be due to the formation of these polytypes. The coexistence of metastable derivative structural polytypes may be a widely occurring phenomenon in other elemental materials