Synthesis of superhard cubic BC2N

Abstract

Cubic BC2N was synthesized from graphite-like BC2N at pressures above 18 GPa and temperatures higher than 2200 K. The lattice parameter of c-BC2N at ambient conditions is 3.642(2) Å, which is larger by 1.48% than would be expected based on ideal mixing between diamond and cubic boron nitride. The bulk modulus of c-BC2N is 282 GPa which is one of the highest bulk moduli known for any solid, and is exceeded only by the bulk moduli of diamond and c-BN. The hardness of c-BC2N is higher than that of c-BN single crystals which indicates that the synthesized phase is only slightly less hard than diamond.

Exploring the high-pressure behavior of superhard tungsten tetraboride

“…Broadly, two approaches are used to design and synthesize materials with high hardness. A first approach is to imitate natural diamond by combining light first row elements (B, C, N or O) to produce materials that maintain short bonds with high-covalency, such as c-BN, 1 B 6 O, 2 and BC 2 N. 3 A second route is to start with elemental metals that are intrinsically incompressible, but not hard, and try to improve their hardness by incorporating light elements into the metal structure to simultaneously optimize covalent bonding and valenceelectron density. 4 This class, which generally contains late, transition-metal borides, carbides, nitrides, and oxides contains many candidate hard materials.…”

Fracture Strength ofAlLiB14

“…[1][2][3] The orthorhombic borides, formulated as XYB 14 where X and Y are metal atoms, have been of interest to scientists and engineers for the past decade due to a report [4,5] that AlMgB 14 prepared by mechanical milling can achieve a hardness between 32 and 46 GPa. The reason for the observed superhardness is not understood.…”

Evidence for a low-compressibility carbon nitride polymorph elaborated at ambient pressure and mild temperature

“…Thus, the bulk modulus of the cubic carbon nitride appears remarkably high with a compressibility equivalent to 73% and 91% of diamond (this work) and c-BN [2] compressibilities, respectively. Moreover, its performances appear better than the low-density cubic BC 2 N phase and comparable with this heterodiamond high-density polymorphs recently claimed (all BC 2 N polymorphs being elaborated under high pressure and temperature) [3,[30][31]. Finally, despite the fact that c-CN x exhibits a bulk modulus lower than theoretical values calculated for dense C 3 N 4 polymorphs, its very low compressibility remains impressive and of the same order than values predicted for CN phases involving sp 2 bonds [9].…”

“…Cubic boron nitride (c-BN) ranks second among superhard materials and is widely used as abrasive [2]. Recently, BC 2 N heterodiamond was synthesized and found to exhibit an unusual combination of mechanical parameters as its bulk modulus is lower than that of c-BN while its Vickers hardness ranks second only after that of diamond [3]. Since 1989, the C-N binary system also aroused deep interest because exceptional mechanical properties were theoretically predicted for three-dimensional (3D) C 3 N 4 by Liu and Cohen [4].…”

“…Consequently many efforts were devoted to the experimental and theoretical studies of highly incompressible carbon nitrides (CN x ). Ab initio calculations first proposed several crystallographic networks (either hexagonal or cubic) for dense CN x with C 3 N 4 composition where carbon and nitrogen are in tetrahedral (C sp 3 ) and trigonal (N sp 2 or sp 3 ) coordinations, respectively [4][5][6][7][8].…”