A novel low compressible and superhard carbon nitride: Body-centered tetragonal CN2

Abstract

A novel body-centered tetragonal CN(2) (4 units per cell), named as bct-CN(2), has been predicted here using our newly developed particle swarm optimization algorithm for crystal structure prediction. Bct-CN(2) is energetically much superior (3.022 eV per f.u.) to previously proposed pyrite structure and stable against decomposition into a mixture of diamond + N(2) or 1/3(C(3)N(4) + N(2)) above 45.4 GPa. No imaginary phonon frequencies in the whole Brillouin zone indicate bct-CN(2) is dynamically stable. The electronic calculations indicate that bct-CN(2) is a wide gap dielectric material with an indirect band gap of 3.6 eV. The ideal tensile, shear, and compressive strength at large strains of bct-CN(2) are examined to understand further the microscopic mechanism of the structural deformation. Strikingly, it is found that bct-CN(2) has high calculated ideal strength, bulk modulus, shear modulus, and simulated hardness, indicating its very incompressible and superhard nature. The results provide new thoughts for designing and synthesizing novel superhard carbon nitrides, and insights for understanding the mechanical properties.

A Novel Superhard Tetragonal Carbon Mononitride

“…From Table 1, we find unusually high incompressibility along c-direction for P4 2 /m-CN, as demonstrated by the extremely large C 33 value (1156 GPa), which is slightly larger than the experimental data of diamond (C 33 : 1076 GPa). 43 This value is comparable to those of known potential superhard materials (β-C 3 N 4 (1053 GPa), 12 bct-C 4 (1189.9 GPa), 44 and Z-carbon (1184.5 GPa) 44 ) suggesting that the c-axial direction of P4 2 /m-CN is very stiff. The polycrystalline bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio v, and G/B of P4 2 /m-CN are also shown in Table 1.…”

“…As is known for carbon nitrides, four-coordinated carbon and three-coordinated nitrogen leads to high bulk modulus and large hardness values. 12 At 0 GPa, the calculated lattice parameters of P4 2 /m-CN are a = b = 4.666 Å and c = 2.373 Å in a unit cell in which two nonequivalent atoms C and N occupy the Wyckoff 4j (0.3323, 0.9737, 0.0) and 4j (0.8136, 0.7391, 0.0) sites, respectively. In more detail, the C−C bond length in the P4 2 /m phase is 1.584 Å at 0 GPa, slightly longer than that in diamond (1.535 Å) but shorter than that in Pnnm phase (1.606 Å).…”

A sp2+sp3 hybridized carbon allotrope transformed from AB stacking graphyne and THD-graphene

“…The ideal tensile strength in a specified direction is microscopically determined by bond strength and breaking nature under strain. 47 Fig. 5 shows the ideal tensile strength of TBBC-carbon along several high-symmetry directions.…”

Cubic C3N: A New Superhard Phase of Carbon-Rich Nitride

“…In light of the extensive applications of c -BN as superhard material, boron nitride compounds, such as Z -BN, Pbca -BN, w -BN, O -BN, and C 222 1 -B 3 N 5 , have been found to be superhard [1,2,3,4,5,6]. Except boron nitrides, carbon nitrides are also expected to be potential superhard materials [7,8,9,10,11,12,13,14,15]. Since the prediction of hexagonal β -C 3 N 4 with extraordinary hardness, extensive experimental, and theoretical investigations have been carried out to search for new C–N materials with novel properties.…”

“…In recent years, several different crystal structure prediction technique-based algorithms have been the most prevalent strategies to explore and predict new material structures. Using the swarm optimization technique, Li et al [13] found a novel low compressible and superhard bct -CN 2 phase. Zhang et al predicted that the stable CN is P 4 2 / m phase [11].…”