Investigation of Room Temperature Formation of the Ultra‐Hard Nanocarbons Diamond and Lonsdaleite (original) (raw)
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Lonsdaleite: The diamond with optimized bond lengths and enhanced hardness
Cornell University - arXiv, 2021
Diamond is known as the hardest substance due to its ultra-strong tetrahedral sp 3 carbon bonding framework. The only weak link is its cubic cleavage planes between (111) buckled honeycomb layers. Compressing graphite single crystals and heating to moderate temperatures, we synthesized a bulk, pure, hexagonal diamond (lonsdaleite) with distorted carbon tetrahedrons that shorten the bond between its hexagonal (001) buckled honeycomb layers, thus strengthening their linkage. We observed direct transformation of graphite (100) to lonsdaleite (002) and graphite (002) to lonsdaleite (100). We find the bulk lonsdaleite has superior mechanical properties of Vicker hardnesses HV = 164±11 GPa and 124±13 GPa, measured on the surface corresponding to the original graphite (001) and (100) surfaces, respectively. Properties of lonsdaleite as the supreme material can be further enhanced by purifying the starting material graphite carbon and finetuning the high pressure-temperature synthesis conditions. Diamond possesses unmatched hardness and other extreme properties, and is regarded as an ideal material for applications ranging from super abrasives, heat sink, bio-sensor, quantum computation, to photonic devices 1,2. These supreme properties are originated from its unique building blocks of sp 3 carbon, bonded to each other with 1.54Å bond length and 109.5° bond angle that form perfect tetrahedrons. This single type of bonding extends infinitely in two dimensions to form buckled honeycomb carbon layers and the layers stack in the third dimension to form the (111) planes of cubic diamond crystals. Such structure, however, also has a weakness. The (111) linkage are relatively weak between layers, resulting in weak (111) cleavage planes that limit the strength of diamond. Selectively strengthening interlayer bonds relative to the intralayer bonds would lower the symmetry of cubic diamond to hexagonal. Hexagonal diamond was predicted decades ago 3 , and subsequently synthesized by dynamic explosion 4 and static compression 5. Natural hexagonal diamond was discovered in Canyon Diablo iron meteorite, and named lonsdaleite after pioneer woman crystallographer Kathleen Lonsdale 6. Although lonsdaleite was theoretically predicted to have superior mechanical properties than cubic diamond 7 , pure, bulk lonsdaleite has never been synthesized and its hardness has thus never been measured.
The researchers are now studying a variety of materials using the technique with the hope of preserving these high-pressure states in NDCs. "We are also looking into scaling up our high-pressure materials synthesis," reveals Qiaoshi Zeng. [48] KAIST researchers developed a three-dimensional (3-D) hierarchically porous nanostructured catalyst with carbon dioxide (CO2) to carbon monoxide (CO) conversion rate up to 3.96 times higher than that of conventional nanoporous gold catalysts. [47] The Lyding Group recently developed a technique that can be used to build carbonnanotube-based fibers by creating chemical crosslinks. [46] Swansea University scientists have reported a new approach to measuring the conductivity between identical carbon nanotubes which could be used to help improve the efficiency of electrical power cables in the future. [45]
Lonsdaleite Films with Nanometer Thickness
We investigate the properties of potentially the stiffest quasi-2-D films with lonsdaleite structure. Using a combination of ab initio and empirical potential approaches, we analyze the elastic properties of lonsdaleite films in both elastic and inelastic regimes and compare them with graphene and diamond films. We review possible fabrication methods of lonsdaleite films using the pure nanoscale "bottom-up" paradigm: by connecting carbon layers in multilayered graphene. We propose the realization of this method in two ways: by applying direct pressure and by using the recently proposed chemically induced phase transition. For both cases, we construct the phase diagrams depending on temperature, pressure, and film thickness. Finally, we consider the electronic properties of lonsdaleite films and establish the nonlinear dependence of the band gap on the films' thicknesses and their lower effective masses in comparison with bulk crystal. SECTION: Physical Processes in Nanomaterials and Nanostructures L onsdaleite is a carbon allotrope with a hexagonal lattice, often called hexagonal diamond due to its crystal structure.
Carbon mineralogy and crystal chemistry
2013
Here we focus on the essential characteristics of the three most common minerals of native carbon-graphite, diamond, and lonsdaleite-all of which play roles in Earth's subsurface carbon cycle. For more comprehensive reviews of the chemical and physical properties of these carbon polymorphs see Bragg et al.
Novel carbon diamond-like phases LA5, LA7 and LA8
In thiswork, the structure and properties of seven diamond-like carbon phases obtained by linking the graphene layers were calculated using DFT and PM3 methods. The LA5 (Cmca), LA7 (Cmcm), and LA8 (I41/amd) diamondlike phases were predicted and studied in this work for the first time. Values of the unit cell parameters of the predicted phases are: a = 4.337 Å, b = 5.024 Å, and c = 4.349 Å for LA5 phase; a = 4.942 Å, b = 4.808 Å, and c = 4.390 Å for LA7 phase; and a = 4.906 Å and c = 4.960 Å for LA8 phase. For these LA5, LA7, and LA8 phases, various structure characteristics, densities, cohesive energies, bulk moduli, electronic densities of states and X-ray patterns were calculated. The comparative analysis showed that the diamond-like phase properties depend on the extent of their structure deformation relative to the cubic diamond structure.
Diamond: Synthesis, Characterisation and Applications
Advanced Structured Materials, 2010
In this chapter we review some aspects of the synthesis and characterisation of chemical vapor deposited diamond. Chemical Vapor Deposited (CVD) diamond is arguably the first of the "new" carbon materials that has received extensive research attention due to its potential industrial applications. Intense research activities on CVD diamond that spanned over 30 years brought much progress in understanding and techniques on the synthesis and laboratory demonstration of applications. However, industrial scale applications are still elusive, mainly due to the many technical hurdles that must be overcome in order to fully benefit from the wonderful properties of diamond. Although CVD diamond has been superseded by fullerene in the 1990s, later carbon nanotubes and more recently the emergence of graphene, it is worth looking at this fascinating form of synthetic diamond which may yet make a comeback in years to come. Attention was given to the established techniques for the synthesis and characterisation of CVD diamond as well as issues related to the challenges of industrial applications of CVD diamond.
Formation of diamond from the liquid phase of carbon
Combustion, Explosion, and Shock Waves, 1993
Results are presented for synthesis of the diamond phase of carbon during detonation of the high-temperature explosive benzotrifuroxan (BTF)-C6N606. The detonation products of this nonhydrogenic explosive have a high temperature which initially falls in the region of thermodynamic stability of the liquid phase of carbon. A two-stage synthesis process is proposed: drops of liquid carbon with diameters O. 1-1.0 I~m are formed initially, and these drops subsequently crystallize into the diamond structure. The experimental results given here confirm this hypothesis.