Icosahedra boron chain and sheets: new boron allotropic structures

TL;DR

This paper introduces new boron allotropic structures based on icosahedra, including chains and sheets with various symmetries, characterized by unique bonding and electronic properties, using advanced molecular dynamics simulations.

Contribution

The study reports the discovery and detailed characterization of novel icosahedra-based boron structures, expanding the known boron allotropes with specific bonding and stability features.

Findings

New boron icosahedra chain and sheets identified

Distinct bonding types and deformation observed

Energy gaps and stability barriers quantified

Abstract

The icosahedra boron chain and three icosahedra sheets (with {\alpha}, {\delta}4, and {\delta}6 symmetries), constructed by the icosahedra B12, have been obtained as new members of boron family using a highly efficient molecular dynamics scheme based on a transferable and reliable semi-empirical Hamiltonian. The icosahedral B12 in the icosahedra chain is slightly elongated along the china direction and directly bonded each other with the two-center covalent bonds. A deformation of the icosahedra B12 was also found in the two-dimensional icosahedra sheets. In addition to the three-center bonding nature inside the icosahedra B12, there are two types of directional inter-icosahedra bonds in the icosahedra sheet structures, one is the single strong covalent bond, and the other is a pair of the weak covalent {\delta} bonds. In contrast to the boron monolayer, there is no buckling found in these icosahedra sheets. The deformation of the icosahedra B12 and the special bonding nature in these new icosahedra structures induce the energy band gap of 0.74 eV in the icosahedra chain, 0.52 eV in the icosahedra {\delta}6 sheet, 0.39 eV in the icosahedra {\delta}4 sheet, and the gapless in the icosahedra {\alpha} sheet, respectively. The energy barrier per atom from the icosahedra {\delta}6 sheet to the icosahedra {\alpha} sheet is estimated to be 0.17 eV while it is estimated as 0.38 eV from the icosahedra {\delta}6 sheet to the icosahedra {\delta}4 sheet and 0.27 eV from the icosahedra {\alpha} sheet to the icosahedra {\delta}4 sheet, respectively. Such high energy barriers indicate that these icosahedra sheets are relatively stable.