Diamond-like Phases Research Articles

Ab initio calculations of the formation polymerized fullerite from endohedral clusters Li@C24

First-principle calculations of a new endohedral cluster Li@C24 proved its stability at room temperature. In the case of bulk compression of fullerite Li@C24, polymerization leading to the formation of a diamond-like LiC24 structure occurs at a pressure of 0.18 GPa. This pressure is an order of magnitude lower than the pressure at which diamond-like CA4 phase can form from clusters C24.

Stability, elastic properties and deformation behavior of graphene-based diamond-like phases

Abstract The stability, elastic moduli and deformation behavior of graphene-based diamond-like phases are examined by molecular dynamics simulations. Three important criteria are considered to study stability of the structure within applied methods. Molecular dynamics simulations are performed to derive stiffness and compliance coefficients, and stress-strain curves under hydrostatic compression of diamond-like phases. The analysis of elastic properties (Poisson’s ratio, Young’s modulus and shear modulus) is carried out. Analytical calculations are used. From the obtained stability criteria, it is found that only two graphene-based diamond-like phases, LA3 and LA6, instead of eight known, can be considered stable in molecular dynamics approach. Young’s modulus, measured in linear elastic regime, of stable phases orientationally dependent: values in different directions can differ two times. Analysis of the variability of shear modulus showed that for LA6 values are much higher than for LA3. Again, shear modulus are orientation-dependent for some directions. In non-elastic regime, stable diamond-like phases can be stretched until 0.012 and compressed until 0.1. The main mechanisms of non-elastic deformation is stretching of the covalent bonds and valent angles.

Structure and morphology of composite coating of chromium with diamond nanoparticles on sintered steels

Electrochemical chromium coatings modified with diamond nanoparticles (ND) were deposited on sintered steel materials obtained from iron powder and ultrafine graphite powder. The diamond nanoparticles were produced by detonation synthesis. Their average size is 6 nm. The sintered steel consisted of 0.2, 0.4, 0.6 and 0.8%C (added in the form of graphite) by weight. The produced composite coatings consisting of Cr + ND were compact, tightly adhering to the substrate, with thickness of about 25–35 μm. The surface morphology and microstructure of the coatings were investigated by SEM and EDS analyzes. The main objective of the study was to explore the presence of ND in the coating by the X-ray photoelectron spectroscopy and the impact of the ND concentration in the electrolyte on the presence of the diamond nanoparticles in the coating. The spectra of the C1s photoelectronic line were obtained, the sp3/sp2 ratio and the sp3 + sp2 sum were determined electronically on the surface of the coatings (depth 10 nm). The Cr2p photoelectronic line spectra were also obtained. The coatings were deposited from electrolytes with ND concentrations of 10, 25 and 40 g/l. A diamond-like phase has been found in coatings obtained at concentrations of diamond nanoparticles in the electrolyte of 25 and 40 g/l. The sp3/sp2 ratio with a value equal to or greater than 1.2 is an indication of the presence of a diamond-like phase in the coatings and the ratio depends on the concentration of ND in the electrolyte.

A superhard orthorhombic carbon with all six-membered-ring in sp3 bonding networks

We identify by first-principles calculations a new diamond-like carbon phase with a 16-atom orthorhombic primitive cell in Pbcn (D2h14) symmetry. This new carbon allotrope consists of all sp3 six-membered rings like as the reported BC8, BC12 and R16 carbon, while energetically more stable than these carbon phases. Its dynamical stability has been confirmed by phonon mode analysis and molecular dynamics simulations. The calculated bulk modulus (435 GPa) and Vickers hardness (93 GPa) are comparable to that of diamond, showing as a superhard carbon material. Electronic band calculations reveal that it is an insulator with an indirect band gap of 4.35 eV. Simulated X-ray diffraction spectrum presents a complicated pattern, showing an amorphous form of diamond, reflecting its structural complexity stemming from its multiple bond lengths and bond angles, but matches well with the diffractions peaks found in the diamond-rich coatings on stainless steel substrate. These findings lay a foundation for further study of this new diamond-like carbon allotrope and its outstanding properties.

Elastic properties of diamond-like phases based on carbon nanotubes

Eight diamond-like structures (tubulanes) of different morphology based on carbon nanotubes are studied by the combination of molecular dynamics simulation and analytical calculations. Molecular dynamics is used for the structure relaxation, stability analysis, and calculation of the stiffness and compliance coefficients of stable tubulanes. Six stable tubulanes which can be elastically deformed are distinguished among the considered structures. Engineering elastic constants such as Young's modulus, Poisson's ratio, shear modulus, and bulk modulus are found by analytical methods. Two of the studied structures, TA6 and TB, are found to be partial auxetics having negative Poisson's ratio with the minimum values of −0.01 and −0.8, respectively. The maximum Young's modulus for tubulanes TA6, TA8, and TB is found to be >1 TPa. In combination with hardness close to that of diamond, considered phases with their outstanding mechanical properties can be potentially used as protective coatings.

Synthesis of Microcrystals of Heavy-Boron-Doped Diamond and BC3-Heterodiamonds at High Pressures and Temperatures

The results of the synthesis and analysis of diamond crystals with heavy boron doping (about 2%), which were obtained from mixtures of gas black with m-carborane at 8 GPa and 1873 K, are presented. A high boron concentration in the diamond lattice was confirmed by x-ray data and the characteristic Raman scattering spectra, which correspond to diamond with metallic conductivity. Thermobaric treatment of the diamond-like dl-BC3 phase (1100 K, 25 GPa) results in the formation of BC3-heteronanodiamond.

Evidence of diamond-like carbon phase formation due to 80 keV Xe+ ion impact on pencil-lead graphitic systems with oblique angle incidence

We report on the effect of 80 keV Xe+ ion irradiation on the commercially available, sectioned 10B pencil-graphite specimens subjected to normal and oblique angle incidence of ions (θi = 0°–70°) and considering a fixed ion fluence of . The pristine and irradiated samples were characterized by powder x-ray diffraction, atomic force microscopy and Raman spectroscopy studies. Unlike pristine graphite and normal incidence cases, several ripple patterns can be visualized in the atomic force micrographs of the specimens irradiated with an oblique angle incidence. Moreover, apart from conventional G-band located at , a distinct diamond-like carbon (DLC) phase has been witnessed at in the Raman spectra of the graphitic specimens subjected to ion impact and for values of 50° and 70°. The formation of the DLC phase along with surface ripple formation would find numerous scopes while dealing with properties such as surface transport, field emission and mechanically hard coating in miniaturized devices.

Modeling of synthesis pathways for diamond-like polycyclobutane phases

Modeling of synthesis pathways for diamond-like polycyclobutane phases

Anneal-hardening behaviour of Cr C, Cr Ni C and Cr Ni Fe C alloy deposits

Abstract Cr C, Cr Ni C and Cr Fe Ni C deposits were successfully prepared from Cr3+-based plating baths with suitable amounts of complex agents and metal salts. The Cr-based alloy deposits could be hardened after rapid thermal annealing (RTA) at 500 °C for a few seconds. The highest hardness of 1800 Hv could be detected from the Cr C deposit after RTA at 500 °C for 15 s. The hardening mechanism of annealed Cr-based alloy deposits is attributed to the precipitation of crystalline diamond-like phases. The diamond-like phase in a membrane shape was observed in the annealed-hardened Cr C alloy deposits, while nano-sized membranes and particles were found in annealed-hardened Cr Ni C and Cr Ni Fe C deposits, respectively.

Diamond-like phase formed of carbon C24 clusters

The crystalline structure and some properties of the cubic diamond-like CA6 phase have been calculated by the density-functional theory method in the generalized gradient approximation. As a result of calculations, it was found that the density, cohesive energy, bulk modulus, hardness and band gap width of this phase are 2.824 g/cm3, 7.59 eV/atom, 351 GPa, and 71 GPa, respectively. The phase structure of CA6 should be stable at room temperature.

Ab initiocalculations of carbon and boron nitride allotropes and their structural phase transitions using periodic coupled cluster theory

We present an ab-initio study of boron nitride as well as carbon allotropes. Their relative thermodynamic stabilities and structural phase transitions from low- to high-density phases are investigated. Pressure-temperature phase diagrams are calculated and compared to experimental findings. The calculations are performed using quantum chemical wavefunction based as well as density functional theories. Our findings reveal that predicted energy differences often depend significantly on the choice of the employed method. Comparison between calculated and experimental results allows for benchmarking the accuracy of various levels of theory. The produced results show that quantum chemical wavefunction based theories allow for achieving systematically improvable estimates. We find that on the level of coupled cluster theories the low- and high-density phases of boron nitride become thermodynamically degenerate at 0 K. This is in agreement with recent experimental findings, indicating that cubic boron nitride is not the thermodynamically stable allotrope at ambient conditions. Furthermore we employ the calculated results to assess transition probabilities from graphitic low-density to diamond-like high-density phases in an approximate manner. We conclude that the stacking order of the parent graphitic material is crucial for the possible formation of meta-stable wurtzite boron nitride and hexagonal carbon diamond also known as lonsdaleite.

Size-dependent phase morphologies in LiFePO4 battery particles

Lithium iron phosphate (LiFePO4) is the prototypical two-phase battery material whose complex patterns of lithium ion intercalation provide a testing ground for theories of electrochemical thermodynamics. Using a depth-averaged (a-b plane) phase-field model of coherent phase separation driven by Faradaic reactions, we reconcile conflicting experimental observations of diamond-like phase patterns in micron-sized platelets with observations of surface-controlled patterns in nanoparticles. Elastic analysis predicts this morphological transition for particles whose a-axis dimension exceeds twice the bulk elastic stripe period. We also simulate a rich variety of non-equilibrium patterns, influenced by size-dependent spinodal points and electro-autocatalytic control of thermodynamic stability.

Formation of Diamond-Like Phases from Hexagonal and Tetragonal Graphene Layers

Structural mutual transformations of graphites and diamond-like phases are studied theoretically using the density functional theory. It is established that the phase transitions of hexagonal graphene to diamond- like phases should occur at uniaxial stresses of ~66–71 GPa, while some diamond-like phases can be obtained from tetragonal graphene at much lower pressures of ~40–52 GPa.

Modeling of Phase Transitions of Graphites to Diamond-Like Phases

The method of the density functional theory is used to study structural transformations between graphites and diamond-like phases. The calculations have been carried out in two approximations: a local density approximation and a generalized gradient approximation. It is found that the phase transitions of hexagonal graphene layers to a cubic diamond and diamond-like phases must occur at uniaxial compressions of ~57–71 GPa, whereas some diamond-like phases can be obtained from tetragonal graphene layers at significantly lower pressures of 32–52 GPa. The X-ray diffraction patterns have been calculated for the phase transition of graphite I41/amd to tetragonal LA10 phase that takes place at the minimum pressure that can be used for experimental identification of these compounds.

Deformation Behavior of Three-Dimensional Carbon Structures Under Hydrostatic Compression

The paper presents the results of numerical simulation aimed at studying the deformation behavior of carbon structures containing carbon atoms with various coordination numbers and, consequently, various electronic configurations and properties. Namely, the method of molecular dynamics was used to study the deformation behavior of two different structures of crumpled graphene (sp2-material formed by graphene flakes bonded by Van der Waals forces) and carbon diamond-like phases (rigid sp3-structures) under hydrostatic compression. Stress-strain curves have been obtained, structural features have been shown to affect mechanical properties of three-dimensional carbon structures.

Моделирование фазовых переходов графитов в алмазоподобные фазы

AbstractThe method of the density functional theory is used to study structural transformations between graphites and diamond-like phases. The calculations have been carried out in two approximations: a local density approximation and a generalized gradient approximation. It is found that the phase transitions of hexagonal graphene layers to a cubic diamond and diamond-like phases must occur at uniaxial compressions of ~57–71 GPa, whereas some diamond-like phases can be obtained from tetragonal graphene layers at significantly lower pressures of 32–52 GPa. The X-ray diffraction patterns have been calculated for the phase transition of graphite I 4_1/ amd to tetragonal LA 10 phase that takes place at the minimum pressure that can be used for experimental identification of these compounds.

Synthesis, Characterization of Elastic and Electrical Properties of Diamond-like BCx Nano-Phases Synthesized under High and Low Pressures

ABSTRACTThis paper presents experimental results on the synthesis of boron rich diamond-like carbon phases (BCx) obtained by high pressure sintering (s-BCx) and pulsed laser deposition (PLD-BCx). It has been shown that sintering of a mixture of a powder of micro-diamonds with a powder of boron in the toroid type high pressure device leads to the creation of s-BCx phase with a low resistivity, and high elastic moduli. The PLD-BCx film found to be rigid with the resistivity as low as that of best conductive boron–doped diamond films. It indicates that the presence of B atoms in a laser plasma leads to the formation of sp3 bonds in the material in the process of chemical sputtering. The combination of unique characteristics can be achieved by changing the ratio B/C.

Влияние высокодозной имплантации углерода на фазовый состав, морфологию и автоэмиссионные свойства кристаллов кремния

AbstractThe study of high-dose carbon-ion implantation without post-process annealing reveals significant modification of the morphology, surface-layer phase composition, and field-emission properties of silicon wafers. The effect of the electrical conductivity type on the evolution of the silicon-crystal surface morphology, upon a variation in the irradiation dose, and a high content of diamond-like phases in the region of microprotrusions at the maximum dose regardless of the electrical conductivity type are found. It is demonstrated that the high-dose implantation of carbon in silicon wafers with a pre-structured surface increases the maximum density of field-emission currents by more than two orders of magnitude.

Deformation behavior of diamond-like phases: Molecular dynamics simulation

The variations of the structure and properties of the diamond-like materials is now of high interest because diamond-like carbon phases has a wide range of commercial applications, especially as the protective coatings with its unusual mechanical properties and strength close to the strength of the diamond. Here the deformation behavior of the stable diamond-like phases is carefully analyzed by molecular dynamics simulation. Five stable structures (A3, A7, A8, A9 and B) based on the fullerene-like molecules are considered. The structural transformations during hydrostatic tension and compression are investigated to understand the deformation mechanisms. Deformation at hydrostatic tension can be divided into three regimes depending on the deformation mechanism. It is found that diamond-like structures can be hydrostatically compressed until the diamond densities, but most of them are losing crystalline order and transform to the amorphous state. Thermal fluctuations decrease the critical strain values at hydrostatic tension but have almost no effect on critical compression strain.

Thermoelectric generator based on composites obtained by sintering of detonation nanodiamonds

A model of a thermoelectric generator is proposed, in which composite materials obtained by sintering diamond nanoparticles are used as the main component. To increase the useful conversion of heat into electric current, it is proposed to use the effect of electron drag by ballistic phonons. To reduce the ineffective heat spread, it is proposed to use the effect of thermal resistance of the boundaries between the graphite-like and diamond-like phases of the composite.An experimental confirmation of the existence of an optimal volume ratio between graphite-like and diamond-like phases of the composite is predicted and obtained.The highest achieved value of thermoelectric coefficient in the actual structure is 80 µV K−1 (which means 20 times increase compared to that of composites not of the optimal structure), with a thermal conductivity of 50 W m−1 K−1. These results were obtained with constant electrical conductivity. The combined influence of these two effects in case of the ideal composite structure should result in an increase of the thermoelectric efficiency parameter by three orders of magnitude.