Hard boron rich boron nitride nanoglasses

Abstract

AbstractBoron‐rich amorphous boron nitride (BxN1−x, 0.55 ≤ x ≤ 0.95) alloys are generated by means of ab initio molecular dynamics simulations and their local structure, mechanical properties and electronic structure are exposed. BN:B phase separations are perceived in all amorphous networks, suggesting that these materials can serve as nanoglass ceramics. The sp2 hybridization is the main building unit in the BN‐rich regions for low boron concentrations, and the models carry locally the signature of the two‐dimensional hexagonal BN structure. The amorphous states having both sp2 and sp3 hybridizations form for boron contents between 70% and 80%. At higher boron concentrations, sp3 hybridization with a fraction of ~90%‐98% is detected as seen in the cubic or wurtize BN crystals. In the boron rich regions, the ideal and defective pentagonal pyramids emerge at 60% boron content, and the first complete B12 molecule develops at 70% boron concentration. In addition to the B12 icosahedron, the formation of a cage‐like B16 molecule is, for the first time, discovered in some amorphous alloys. The isolated B16 molecule is, however, found to be unstable. The Vickers harness calculations reveal that some of these amorphous alloys can serve as hard materials. When their electron properties are considered, all amorphous materials are predicted to be semiconducting.