Three-Dimensional Buckled Honeycomb Boron Lattice with Vacancies as an Intermediate Phase on the Transition Pathway from α-B to γ-B

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Abstract

In the phase diagram of elemental boron, an unknown high-pressure form was identified as γ-orthorhombic boron (γ-B₂₈), provoking studies of the extraordinary properties of its main building blocks, B₁₂ icosahedra and B₂ dumbbells. Although two low-pressure phases, α- and β-rhombohedral boron (α-B₁₂ and β-B₁₀₆), are also composed of icosahedra, the detailed kinetics and mechanisms of the structural transition from α-B₁₂ or β-B₁₀₆ to γ-B₂₈ remain poorly understood. We report on new metastable boron phases formed during the transition in high-pressure high-temperature conditions that were discovered using the crystal structure search method. The metastable phases are understood to be a three-dimensional buckled defective honeycomb lattice in which boron vacancies lead to a dynamically and mechanically stable structure with triangular motifs. We suggest that the metastable phases act as intermediate states on the transition pathway from α-B₁₂ to γ-B₂₈ owing to their structural flexibility and low enthalpies, in the framework of Ostwald's step rule.

Description

Includes supplementary material

Keywords

Boron, Crystals, Polymorphism (Crystallography), Design, Materials science

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"This work was supported by Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08 and by the Brain Korea 21 PLUS Project of Korea Government."

Rights

CC BY 4.0 (Attribution), ©2017 The Authors

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