Electronic structure and surface properties ofMgB2(0001) upon oxygen adsorption

Abstract

We use density-functional theory to investigate the bulk and surface properties of MgB2. The unique bonding structure of MgB2 is investigated by Bader's atoms-in-molecules, charge density difference, and occupancy projected band structure analyses. Oxygen adsorption on the chargedepleted surfaces of MgB2 is studied by a surface potential energy mapping method, reporting a complete map including low-symmetry binding sites. The B-terminated MgB2(0001) demonstrates reconstruction of the graphene-like B layer and the reconstructed geometry exposes a threefold site of the sub-surface Mg, making it accessible from the surface. Detailed reconstruction mechanisms are studied by simulated annealing method based on ab-initio molecular dynamics and nudged elastic band calculations. The surface clustering of B atoms significantly modifies the B 2p states to occupy low energy valence states. The present work emphasizes that a thorough understanding of the surface phase may explain an apparent inconsistency in the experimental surface characterization of MgB2. Furthermore, these results suggest that the surface passivation can be an important technical challenge when it comes to development of a superconducting device using MgB2.

Exfoliated Magnesium Diboride (MgB2) Nanosheets as Solid Fuels

“…The MgB 2 nanosheets were prepared via an ultrasound-assisted liquid-phase exfoliation method with etching acid . MgB 2 has an AlB 2 -type crystal structure with alternating close-packed Mg layers and graphene-like B layers along the c axis of the hexagonal unit cell . The in-plane bonding is mixed covalent/metallic, and the interlayer bonding is ionic.…”

“…21 MgB 2 has an AlB 2 -type crystal structure with alternating close-packed Mg layers and graphene-like B layers along the c axis of the hexagonal unit cell. 22 The in-plane bonding is mixed covalent/ metallic, and the interlayer bonding is ionic. The bulk MgB 2 used to synthesize the MgB 2 nanosheets are micrometer-sized with irregular shapes (Figure 1a).…”

Quasi-Two-Dimensional Nanostructures from AlB2-Type Metal Borides: Physicochemical Insights and Emerging Trends

“…MgB 2 is widely regarded as the flagship material of the layered metal diboride family. It has a hexagonal crystal structure and exhibits a P 6/ mmm space group with Mg atoms sandwiched between hexagonal boron layers . This material came into the limelight in 2001 for its superconductivity in bulk form at 39 K (critical temperature being the highest among conventional superconductors) .…”

“…It has a hexagonal crystal structure and exhibits a P6/mmm space group with Mg atoms sandwiched between hexagonal boron layers. 28 This material came into the limelight in 2001 for its superconductivity in bulk form at 39 K (critical temperature being the highest among conventional superconductors). 24 MgB 2 has also found its use in other areas like additives in blast-enhanced explosives and propellants in fuels.…”

Spontaneous dynamical disordering of borophenes in MgB2 and related metal borides

“…Suehara et al 16 observed from ab initio molecular dynamics (AIMD) that the stoichiometric B-terminated (0001) surface of ZrB 2 , when annealed, exhibited boron aggregation and formation of umbrella-like B 7 clusters, suggesting the existence of competing stable surface patterns. Similarly, based on AIMD simulations, Kim et al 27 predicted that the B surface of MgB 2 rapidly reconstructs upon adsorption of oxygen at 600 K, eliminating the E 2 g phonon mode coupling to the in-plane electronic states and disabling the high-T c superconductivity. Reconstruction has also been reported for other two-dimensional boron systems.…”