Three metallic BN polymorphs: 1D multi-threaded conduction in a 3D network.

In this paper, three novel metallic sp2/sp3-hybridized boron nitride (BN) polymorphs are proposed by first-principles calculations. One of them, denoted as tP-BN, is predicted based on the evolutionary particle swarm structural search. tP-BN is composed of two interlocked rings forming a tube-like 3D network. The stability and band structure calculations show that tP-BN is metastable and metallic at zero pressure. Calculations for the density of states and electron orbitals confirm that the metallicity originates from the sp2-hybridized B and N atoms, forming 1D linear conductive channels in the 3D network. According to the relationship between the atomic structure and electronic properties, another two 3D metastable metallic sp2/sp3-hybridized BN structures are constructed manually. Electronic property calculations show that both of these structures have 1D conductive channels along different axes. The polymorphs predicted in this study enrich the structures and provide a different picture of the conductive mechanism of BN compounds.