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


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.


Includes supplementary material


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

"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."


CC BY 4.0 (Attribution), ©2017 The Authors