Superhard superstrong carbon clathrate

Abstract

Carbon clathrate is a kind of typical carbon allotrope that has an open framework composed of various types of cages, displaying intriguing electronic and mechanical properties. This paper proposes a superhard superstrong carbon clathrate via first-principle calculations. This carbon clathrate, called C 60 clathrate, contains 60 carbon atoms buckled through sp 3-hybridized bonds in a cubic unit cell with symmetry of Im-3m, and possesses the network topology of commonly called binodal net. C 60 clathrate is energetically more stable than fullerene C 60 at ambient pressure, and it is more favorable than graphite at a pressure above 50.1 GPa. C 60 clathrate can be constructed by small C 24 cage and flat C 18 drum. It shows a high density of 3.34 g/cm 3 , which is the densest carbon clathrate to date. The estimated Vickers hardness and tensile strength of C 60 clathrate are comparable with those of diamond, reaching remarkably high values of 91.6 and 90.7 GPa, respectively. The estimated Vickers hardness, tensile strength, and shear strength of C 60 clathrate reach remarkably high values of 82.8, 90.7, and 76.4 GPa, respectively, indicating its superhard and superstrong characteristic. Band structure calculations indicate that C 60 clathrate is semiconductive with a direct band gap of 2.26 eV. C 60 clathrate can be potentially used in photovoltaic devices.

Topological carbon materials: A new perspective

“…Besides the graphene networks or carbon foams 52,[132][133][134][135][136][137][138][139][140][141][142][143] , other 3D carbon allotropes that have been proposed previously include the Mackay crystals [144][145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163] .…”

Clathrate Structure of Fullerite C60

“…An important consequence of having each molecule bonded to its neighbors via the double 5/5 2+3 cycloadditions, is that the resulting fcc polymeric structure has its octahedral interstitial sites enclosed by truncated icosahedron cages (identical to the original C 60 molecular cages) and its tetrahedral interstitial sites enclosed by distorted truncated octahedron cages. These truncated octahedron cages, with 24 atoms arranged in 8 hexagons and 6 rhombi, are a distorted version of the sodalite-type cages displayed by numerous clathrates [9][10][11][12][13]. The original C 60 molecular cages are strongly deformed and their double hexagonal rings, lying perpendicular to the cubic axes, are now perfectly planar.…”

“…Clathrates are open-framework structures with facesharing polyhedral cages that can contain guest species, atoms or molecules [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Hydrates are an important group of clathrate structures, being the focus of intense investigations on the possibility of greenhouse gases storage [1].…”

“…Carbon has exceptional flexibility as shown by the profusion of allotropes with distinct physical and chemical properties [3,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Despite the large number of geometries carbon constructs may adopt, no carbon clathrate has been synthesized so far, in contrast to other group IV elements.…”

“…Despite the large number of geometries carbon constructs may adopt, no carbon clathrate has been synthesized so far, in contrast to other group IV elements. There have been several theoretical studies discussing the stability of different carbon clathrates, such as C 46 , C 34 and C 24 , whose construction is based on polyhedral cages and arrangements exhibited by clathrates of other chemical elements [13][14][15][16]. A significant step towards the synthesis of carbon clathrates has been done recently with the high-pressure synthesis of mixed carbon-boron clathrates, where metal atoms, strontium or lanthanum, are trapped inside ordered sodalite-like cages formed by carbon and boron [9,10].…”