Relative stability of some possible phases of graphitic carbon nitride

Lowther, J. E.

doi:10.1103/physrevb.59.11683

Cited by 128 publications

(77 citation statements)

References 29 publications

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“…Bulk forms of MoS 2 , h-BN or WS 2 are indeed centrosymmetric, owing to an antiparallel stacking sequence, and thus not piezoelectric 7 . However sheets of g-C 3 N 4 are not stacked in the same manner to form a bulk material and piezoelectricity is retained; the stacking sequence here is analogous to that of graphite 15 . Therefore, it is clear that the regularly placed triangular holes are indeed responsible for the apparent piezoelectric coupling found in graphene nitride.…”

Section: Resultsmentioning

confidence: 99%

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Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets

et al. 2014

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Piezoelectricity is a unique property of materials that permits the conversion of mechanical stimuli into electrical and vice versa. On the basis of crystal symmetry considerations, pristine carbon nitride (C 3 N 4 ) in its various forms is non-piezoelectric. Here we find clear evidence via piezoresponse force microscopy and quantum mechanical calculations that both atomically thin and layered graphitic carbon nitride, or graphene nitride, nanosheets exhibit anomalous piezoelectricity. Insights from ab inito calculations indicate that the emergence of piezoelectricity in this material is due to the fact that a stable phase of graphene nitride nanosheet is riddled with regularly spaced triangular holes. These non-centrosymmetric pores, and the universal presence of flexoelectricity in all dielectrics, lead to the manifestation of the apparent and experimentally verified piezoelectric response. Quantitatively, an e 11 piezoelectric coefficient of 0.758 C m À 2 is predicted for C 3 N 4 superlattice, significantly larger than that of the commonly compared a-quartz.

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Section: Resultsmentioning

confidence: 99%

“…The preferred stacking method for g-C 3 N 4 is by using a repeat unit in the P 6m2 symmetry group (Fig. 1b) with 3.29 Å spacing between sheets 15 . The metastable structure of b-C 3 N 4 ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets

et al. 2014

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“…One basic unit of connectivity is the planar triazine (C 3 N 3 ) ring that may be interconnected via linking -N= bonds to form polytriazine imide (PTI) layers with C 3 N 4 stoichiometry 14,16,[18][19][20] . The polymeric TGCN material synthesized by Algara-Siller et al…”

Section: Structural Complexity Among Carbon Nitride Polymorphs Atmentioning

confidence: 99%

“…This structure was first proposed in the mid-1990's as "graphitic carbon nitride" ("g-C 3 N 4 ") by analogy with the structurally related graphite 15,16 . A nanocrystalline material with C 3 N 4 stoichiometry had been reported from chemical vapor deposition 17,18 and related models were studied theoretically 16,19,20 . Triazine-based carbon nitrides can also be exfoliated to produce layered materials analogous to few-layered graphene 21,22 .…”

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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“…[5][6][7][8][9][10] Interestingly, a comparison among the expected stabilities of all the possible phases suggests that under ambient conditions, four of the sp 2 bonded phases are more stable than the a-and b-C 3 N 4 phases. This last finding is in good agreement with the experimental results from either the bulk or thin film synthesis methods, since these have mainly demonstrated the formation of substoichiometric amorphous carbon nitride phases with a preferentially sp 2 hybridisation for both C and N atoms.…”

Section: Guest Editorialmentioning

confidence: 99%

Status of technology of carbon nitride films: Challenges and opportunties

Rodil¹

2006

Surface Engineering

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Amorphous carbon films have widespread applications in many domains such as protective coatings, optoelectronics or biomedicals owing to their high chemical stability, mechanical properties, tribological performance and resistance to corrosion. The addition of nitrogen into the amorphous carbon matrix multiplies the possible applications since it significantly reduces the stress, improves the thermal and chemical stability, enhances the elastic properties providing hardness and flexibility and modifies the electro-optical properties. However, for the development of industrially relevant materials and their optimisation, there is still a huge need of obtaining a complete understanding of the detailed bonding configuration of C and N atoms in the a-CN structure since their physical properties are strongly correlated to their local structure. The huge complexity in the different hybridisation states in a-CN makes it difficult to work out the actual local structure using a single characterisation technique (Fig. 1). Nevertheless, this information is essential for tailoring of their properties as required in the proposed applications, such as magnetic storage disks, head readers, field emission displays, sensors and protective coatings for biomedical devices.In addition to the research and applications of disordered carbon nitride films, it must be remembered that the research on carbon nitride compounds started y15 years ago with the theoretical prediction of a material that could be harder than diamond, b-C 3 N 4 with a similar crystalline structure to the well known Si 3 N 4 . Figure 2 shows the bonding configuration expected for the super hard phase. Based upon the semi-empirical equation deduced by Cohen, 1 which relates high bulk modulus with short bond lengths and low ionicity, Sung and Sung 2 realised that crystalline phases of covalently bonded carbon and nitrogen materials might be harder than diamond. Liu and Cohen 3 then used pseudopotential calculations to determine the possible crystalline structures and found two super hard covalent bonded phases (a and b) that were predicted to be metastable under ambient conditions. Following this work, a great number of groups have attempted to synthesise C 3 N 4 using a variety of techniques, all of them suitable for the formation of metastable phases, such as thin film deposition or high pressure-high temperature systems.Other hard crystalline structures have also been proposed. Teter and Hamley 4 studied five different structures with the same stoichiometry. Using ab initio molecular dynamics, they calculated the energy-volume (EV) curves for several possible phases of C 3 N 4 and also the elastic constants for the cubic phases. In particular, the pressure, enthalpy and bulk modulus at zero pressure were evaluated. More importantly, Teter also estimated the shear moduli since the critical structural parameter describing the hardness is the shear and not the bulk modulus. Among all the calculated shear moduli of the C 3 N 4 phases, none of them was higher than the ...

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Relative stability of some possible phases of graphitic carbon nitride

Cited by 128 publications

References 29 publications

Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets

Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets

Carbon nitride frameworks and dense crystalline polymorphs

Status of technology of carbon nitride films: Challenges and opportunties

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