Carbon nitride and other speculative superhard materials

Sung, Chien-Min; Sung, Michael

doi:10.1016/0254-0584(95)01607-v

Cited by 313 publications

(82 citation statements)

References 17 publications

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“…GPa and is comparable to the known superhard materials c-BN (48 GPa) [81], γ-B28 (50 GPa) [82], and B6O (45 GPa) [3]. Accordingly, it is conceivable that the Cmcm-HfB4 may be a superhard material.…”

Section: C11+c22+c33+2(c12+c13+c23)>0 C11+c22-2c12>0 C11+c33-2c13>0supporting

confidence: 56%

Crystal Structure and Physical Properties of HfB4 via First-Principles Calculations

Zhang

Gao

Zhao

et al. 2017

Preprint

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By using the particle swarm optimization algorithm for crystal structure prediction, we reveal a newly orthorhombic Cmcm structure of HfB4, which is more energetically superior to the previously proposed YB4-, ReP4-, FeB4-, CrB4-, and MnB4-type structures in the considered pressure range. The phonon dispersion and elastic constants calculations confirm that the new phase is dynamically and mechanically stable. The calculated large shear modulus (240 GPa) and high hardness (45.7 GPa) imply that the predicted Cmcm-HfB4 is a potential superhard material. Meanwhile, the directional dependences of the Young's modulus, bulk modulus, and shear modulus for HfB4 are systematically investigated. Further analyses of the density of states and electronic localization function indicate that the strong B-B and B-Hf covalent bonds greatly contribute to its high hardness and stability.

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Section: C11+c22+c33+2(c12+c13+c23)>0 C11+c22-2c12>0 C11+c33-2c13>0supporting

confidence: 56%

Crystal Structure and Physical Properties of HfB4 via First-Principles Calculations

Zhang

Gao

Zhao

et al. 2017

Preprint

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“…This material is harder than stishovite and boron oxide and much harder than alumina 3,10 . Polycrystalline cubic boron nitride and sintered diamond are approximately two-times softer than their corresponding single crystal equivalents 3,7 . This suggests that the cotunnite-type TiO 2 is among the hardest known polycrystalline materials.…”

mentioning

confidence: 98%

The hardest known oxide

Dubrovinsky

Dubrovinskaia

Swamy

et al. 2001

Nature

330

237

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“…Between 11-47 GPa (using PBEsol) the α-C 3 N 4 structure with P 31c symmetry analogous to the ceramic phase α-Si 3 N 4 is predicted to be stable. This is one of the polymorphs considered by Cohen, Sung and others to constitute a likely ultra-low compressibility, superhard material 16,[25][26][27][28] . The α-C 3 N 4 structure contains sp 3 bonded 4-coordinated C atoms and sp 2 bonded three-fold coordinated N atoms characteristic of other low-enthalpy structures at high pressures.…”

Section: Structures Found In the High Pressure Searchesmentioning

confidence: 99%

“…Interest in dense carbon nitride polymorphs based on sp 3 bonded C atoms began with predictions from density functional theory (DFT) calculations of superhard properties 16,[25][26][27][28] . First investigations began by considering known structures such as those of Si 3 N 4 ceramic phases, and more recently using structure searching methods 29 .…”

Section: Introductionmentioning

confidence: 99%

Carbon nitride frameworks and dense crystalline polymorphs

et al. 2016

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We used ab initio random structure searching (AIRSS) to investigate polymorphism in C3N4 carbon nitride as a function of pressure. Our calculations reveal new framework structures, including a particularly stable chiral polymorph of space group P 43212 containing mixed sp 2 and sp 3 -bonding, that we have produced experimentally and recovered to ambient conditions. As pressure is increased a sequence of structures with fully sp 3 -bonded C atoms and three-fold coordinated N atoms is predicted, culminating in a dense P nma phase above 250 GPa. Beyond 650 GPa we find that C3N4 becomes unstable to decomposition into diamond and pyrite-structured CN2.

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Carbon nitride and other speculative superhard materials

Cited by 313 publications

References 17 publications

Crystal Structure and Physical Properties of HfB4 via First-Principles Calculations

Crystal Structure and Physical Properties of HfB4 via First-Principles Calculations

The hardest known oxide

Carbon nitride frameworks and dense crystalline polymorphs

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