Phase Of C60 Research Articles

Occurrence of natural fullerene C60 from the iridium-rich Cretaceous-Paleogene (K-Pg) boundary layers of the Um-Sohryngkew river section, Meghalaya, India

The presence of fullerene C60 in the iridium-rich Cretaceous-Palaeogene (K-Pg) boundary layer from the Um-Sohryngkew river section of Meghalaya is reported here for the first time. Different analytical methods, including transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared (FT-IR), and X-ray diffraction(XRD) techniques, have been used to characterize the presence of toluene-insoluble high-pressure phase of fullerene C60 in the acid resistant carbonaceous matter extracted from the Um-Sohryngkew river section, Meghalaya, India. Strong absorption peaks at wavenumbers 1427, 1181, 574, and 525 cm−1, which are indicative of pristine fullerene C60, can be seen in the FTIR spectroscopic study. The Raman spectrum also independently confirms the presence of fullerene, by exhibiting the characteristics peaks of pristine fullerene C60. The XRD technique provides further, independent validation of fullerenes, and the XRD pattern demonstrates fullerene presence. Fullerenes, high-pressure fullerene, the amorphous phase of C60, and iridium all coexist and offer conclusive proof of impact at the Cretaceous-Palaeogene (K-Pg) boundary extinction event.

Microstructure Evaluation, Quantitative Phase Analysis, Strengthening Mechanism and Influence of Hybrid Reinforcements (β-SiCp, Bi and Sb) on the Collective Mechanical Properties of the AZ91 Magnesium Matrix

Gravitational melt-stir casting produced hybrid nano-reinforcements (β-SiCp) and micro-reinforcements (Bi and Sb) of AZ91 composites. SiCp-diffused discontinuous β-Mg17Al12 precipitation with a vital factor of SiC was exhibited at the grain boundary region, formulated Mg3Si throughout the composite and changed the present Mg0.97Zn0.03 phases. The creation of Mg2Si (cubic) and SiC (rhombohedral axes) enhanced the microhardness by 18.60% in a 0.5 wt.% SiCp/AZ91 matrix. The microhardness of 1 wt.% SiCp/AZ91 was slightly reduced after Mg0.97Zn0.03 (hexagonal) reduction. The best ultimate tensile value obtained was about 169.33 MPa (increased by 40.10%) in a 0.5 wt.% SiCp/AZ91 matrix. Microelements Bi and Sb developed Mg3Bi2, Mg3Sb2 and monoclinic C60 phases. The best peak yield strength of 82.75 MPa (increased by 19.85%) was obtained with the addition of 0.5 wt.% SiCp/1 wt.% Bi/0.4 wt.% Sb. The mismatch of the coefficient of thermal expansion of segregated particles and the AZ91 matrix, the shear transfer effect and the Orowan effect, combined with the quantitative value of phase existence, improved the compressive strengths of the composites with 0.5 wt.% β-SiCp, 1 wt.% β-SiCp and 0.5 wt.% SiCp/1 wt.% Bi/0.4 wt.% Sb by 2.68%, 6.23% and 8.38%, respectively. Notably, the Charpy impact strengths of 0.5 wt.% and 1 wt.% β-SiCp-added AZ91 composites were enhanced by 236% (2.89 J) and 192% (2.35 J), respectively. The addition of Bi and Sb with SiCp resulted in the formation of a massive phase of brittle Al6Mn. Al–Mn-based phases (developed huge voids and cavities) remarkably reduced impact values by 80% (0.98 J). The discussion covers the quantitative analyses of X-ray diffraction, optical microscopy and scanning electron microscopy results and fracture surfaces.

Nanoindentation of pure and gas-saturated fullerite C60 crystals: Elastic-to-plastic transition, hardness, elastic modulus

Elastic-plastic transition at nanoindentation of (111) plane of pure C60 fullerite single crystals was studied. The onset of plastic deformation in the contact was noted due to the plateau formation in the initial part of loading curve. The estimated stress of plasticity beginning was found to be on the order of the theoretical shear stress required for homogeneous dislocation nucleation in the ideal crystal lattice of C60. The empirical values of elastic modulus E ∼ 13.5 GPa, hardness of the ideal crystal lattice H ∼ 1.4 GPa, and hardness at different indentation loads were obtained. The hardness vs load dependence was found consistent with the model of geometrically necessary dislocations. The loading diagrams shape and the dependencies of contact pressure vs indentation depth were strongly affected by gaseous interstitial impurities (hydrogen, oxygen, nitrogen) in C60 crystal; transition stress was essentially less and plateaus formation was observed at elevated indentation loads and depths as compared with pure fullerite crystal. For crystals, saturated with hydrogen, the enhanced value of elastic modulus (∼ 20.4 GPa) and hardness (∼ 1.1 GPa) were obtained. The results acquired at room temperature for C60 with face-centered cubic lattice are important for the description of the physical-mechanical properties of simple cubic lattice phase of C60 below 260 K (S. V. Lubenets, L. S. Fomenko, V. D. Natsik, and A. V. Rusakova, Fiz. Nizk. Temp. 45, 3 (2019) [Low Temp. Phys. 45, 1 (2019)]).

Three-dimensional fcc C60 polymer

A face-centered cubic (fcc) polymerized C60 phase has been synthesized at 9.5 GPa and 550 °C. The observed short lattice constant, 13.19 Å, indicates that a three-dimensional (3D) polymer with adjacent C60 molecules covalently bonded was obtained. Possible polymerized structures, with each molecule adopting one of the two standard orientations, have been investigated through density functional theory (DFT). It was found that intermolecular bonds, 56/56 2 + 2 cycloaddition, are formed between molecules with different orientations but no bonds are formed between molecules with the same orientation. The computed bulk moduli for these structures gave values ranging from 88 to 132 GPa. Although the distances between neighboring molecules and the volume per molecule from the models are close to the experimental values, the relaxed structures displayed symmetries lower than cubic, suggesting that the experimental fcc structure is likely disordered or frustrated.

Recent progress on high-pressure and high-temperature studies of fullerenes and related materials

Polymerization of fullerenes is an interesting topic that has been studied for almost three decades. A rich polymeric phase diagram of C60 has been drawn under a variety of pressure P and temperature T conditions. Knowledge of the targeted preparation and structural control of fullerene polymers has become increasingly important because of their utility in producing novel fullerene-based architectures with unusual properties and potential applications. This paper focuses on the polymeric phases of fullerenes and their derivatives under high P and/or high T. First, the polymerization behavior and the various polymeric phases of C60 and C70 under such conditions are briefly reviewed. A summary of the polymerization process of intercalated fullerenes is then presented, and a synthetic strategy for novel structural and functional fullerene polymers is proposed. Finally, on the basis of the results of recent research, a proposal is made for further studies of endohedral fullerenes at high P.

Clean and dry route of synthesis of C60/polyvinylpyrrolidone composite using supercritical carbon dioxide

In the present investigation, we have studied polymerization of (a) vinylpyrrolidone (VP) and (b) VP with C60 molecule applying various supercritical conditions with 2,2-azobisisobutyronitrile (AIBN) as a catalyst. Products hence obtained are polyvinylpyrrolidone (PVP) and fullerene-polyvinylpyrrolidone (C60/PVP) polymers. With polymerization reaction, the yield of corresponding C60–PVP polymers was significantly affected under applied concentrations of AIBN (304.5–1218.0 × 10−3 mol/dL) supercritical pressure (1200–1800 psi), temperature (C60 90 ± 1°) and time (3–6 h). The concentration of VP ranged 7.04–12.59 × 10−3 mol/dL. The samples of the synthesized C60/PVP polymer with lowest (24.8%) and highest (45.0%) yields were characterized using UV–Vis, FT-IR, 1H NMR, laser-induced breakdown spectra, scanning electron microscopy and simultaneous TG–DTA–DSC. The morphology of the C60/PVP polymers was confirmed by scanning electron micrographs which indicates the existence of separated C60 phases with heterogeneous morphology in corresponding C60/PVP polymers in all the cases. Simultaneous TG–DTA–DSC revealed enhanced thermal stability of C60/PVP.

Phase Transitions in a Mixture of Amorphous C60 and C70 Fullerene Phases at High Temperatures and Pressures

Phase transitions in two types of amorphous fullerene phases (C60–C70 (50/50) mixtures and an amorpous C70 fullerene phase) are studied via neutron diffraction at pressures of 2–8 GPa and temperatures of 200–1100°C. Fullerenes are amorphized by grinding in a ball mill and sintered under quasi-hydrostatic pressure in a toroidal-type chamber. Diffraction studies are performed ex situ. It is shown that the amorphous phase of fullerenes retains its structure at temperatures of 200–500°C, and amorphous graphite is formed at 800–1100°C with a subsequent transition to crystalline graphite. This process is slow in a mixture of fullerenes, compared to C70 fullerene. According to neutron diffraction data, the amorphous graphite formed from amorphous fullerene phases has anisotropy that is much weaker in a fullerene mixture.

Catalytic 3D polymerization of C60

ABSTRACTThe present study addresses the problems of catalytic synthesis of C60-based 3D polymers in the presence of carbon disulfide CS2. It is shown that CS2 lowers the pressure of fullerite 3D polymerization at room temperature. In particular, the pressure at which the 3D ultrahard fullerite C60 phase is formed decreases from 18 GPa to 7 GPa. The catalyst plays no significant role at room temperature and low pressures up to 6 GPa. When the C60 + CS2 is heated to 1200 K, the pressure of the 3D C60 polymerization is further reduced to 2–4 GPa. Based on the TEM data, we propose a 3D polymer structure based on C60 obtained by the catalytic synthesis.

Bonding Frustration in the 9.5 GPa fcc Polymeric C60

We argue that the face‐centered cubic (fcc) polymeric C60 phase obtained at 9.5 GPa can be mapped onto the classical frustrated Ising fcc antiferromagnet. Extensive density functional theory (DFT) calculations show that at 9.5 GPa 56/65 2+2 cycloaddition polymeric bonds are formed between neighboring molecules having different standard orientations but do not form when they have the same standard orientation. These “antiferromagnetic” bonds cannot be fully satisfied in the fcc lattice of the polymeric phase, resulting in a frustrated structure. By analyzing the ground state configurations of the frustrated Ising fcc antiferromagnet, a picture of the polymeric frustrated structure was obtained.

Computational modelling and simulation of polycrystalline coherent inelastic neutron scattering

Inelastic neutron scattering is an experimental technique widely used to investigate the vibrational characteristics of materials in condensed matter research. While coherent inelastic neutron scattering is typically restricted to single-crystal samples, analysis of the complex datasets obtained on polycrystalline samples remains challenging, even for the simplest of structures. However, given the common availability of high performance computing platforms, it is becoming feasible to apply computationally intensive calculation methods that sample millions of q-points to the simulation of polycrystalline models of increasing complexity, a technique referred to as poly-CINS analysis. This approach allows the interpretation of experimental results by comparison and fitting against theoretical models. This paper describes a new high-performance implementation of the Scatter code, a modelling package developed for the General Utility Lattice Program (Gulp) for heterogenous CPU-GPU computing architectures. It provides the ability to generate theoretical poly-CINS data sets from semi-empirical and ab-initio models. We present the computational framework behind its implementation, applying an example of a semi-empirical model for the dynamics of a large unit-cell system, namely the two (low and ambient temperature) phases of solid C60 to illustrate the methodology and its scalability characteristics.

Transformation-deformation bands in C60 after the treatment in a shear diamond anvil cell

The C60 fullerene has been investigated by high-resolution transmission electron microscopy and electron energy loss spectroscopy in a shear diamond anvil cell after applying pressure and shear deformation treatment of fcc phase. Shear transformation-deformation bands are revealed consisting of shear-strain-induced nanocrystals of linearly polymerized fullerene and polytypes, the triclinic, monoclinic, and hcp C60, fragments of amorphous structures, and voids. Consequently, after pressure release, the plastic strain retains five high pressure phases, which is potentially important for their engineering applications. Localized shear deformation initially seems contradictory because high pressure phases of C60 are stronger than the initial low pressure phase. However, this was explained by transformation-induced plasticity during localized phase transformations. It occurs due to a combination of applied stresses and internal stresses from a volume reduction during phase transformations. Localized phase transformations and plastic shear deformation promote each other, which produce positive mechanochemical feedback and cascading transformation-deformation processes. Since the plastic shear in a band is much larger than is expected based on the torsion angle, five phase transformations occur in the same region with no transformation outside the band. The results demonstrate that transformation kinetics cannot be analyzed in terms of prescribed shear, and methods to measure local shear should be developed.

Materials science in the time domain using Bragg coherent diffraction imaging

Materials are generally classified by a phase diagram which displays their properties as a function of external state variables, typically temperature and pressure. A new dimension that is relatively unexplored is time: a rich variety of new materials can become accessible in the transient period following laser excitation from the ground state. The timescale of nanoseconds to femtoseconds, is ripe for investigation using x-ray free-electron laser (XFEL) methods. There is no shortage of materials suitable for time-resolved materials-science exploration. Oxides alone represent most of the minerals making up the Earth’s crust, catalysts, ferroelectrics, corrosion products and electronically ordered materials such as superconductors, to name a few. Some of the elements have metastable phase diagrams with predicted new phases. There are some examples known already: an oxide ‘hidden phase’ living only nanoseconds and an electronically ordered excited phase of fullerene C60, lasting only femtoseconds. In a completely general way, optically excited states of materials can be probed with Bragg coherent diffraction imaging, both below the damage threshold and in the destructive regime. Prospective methods for carrying out such XFEL experiments are discussed.

Hybridization-Induced Carrier Localization at the C60 /ZnO Interface.

Electronic coupling and ground-state charge transfer at the C60 /ZnO hybrid interface is shown to localize carriers in the C60 phase. This effect, revealed by resonant X-ray photoemission, arises from interfacial hybridization between C60 and ZnO. Such localization at carrier-selective electrodes and interlayers may lead to severely reduced carrier harvesting efficiencies and increased recombination rates in organic electronic devices.

On the additivity of scattering phases in collisions of electrons on endohedrals

SynopsisIt is demonstrated that an inner atom, either Ne or Ar, qualitatively affects the electron scattering phases upon an endohedral, in spite of the fact that the fullerene consists of 60 carbon atoms, while the atom staffed inside is only one. Calculations are performed in the one-electron Hartree-Fock (HF) and random phase approximation with exchange (RPAE) for the inner atom while the fullerenes shell is substituted by static potential without and with the polarization potential. The total endohedral scattering phase is a sum of atomic, Ne or Ar, and fullerenes C60 phases, contrary to the intuitive assumption that the total phases on C60 and Ne@C60 or Ar@C60 has to be the same.

On the behavior of scattering phases in collisions of electrons with multiatomic objects

We have studied the energy dependence of several first scattering phases with multiatomic object. As concrete examples representing the general trends endohedrals Ne@C60 and Ar@C60 are considered. It appeared that the presence of an inner atom, either Ne or Ar, qualitatively affects the scattering phases, in spite of the fact that the fullerene consists of 60 carbon atoms, while the atom staffed inside is only one. Calculations are performed in the one-electron Hartree-Fock (HF) and random phase approximation with exchange (RPAE) for the inner atom while the fullerenes shell is substituted by static potential without and with the polarization potential. It appeared that the total endohedral scattering phase is simply a sum of atomic, Ne or Ar, and fullerenes C60 phases, contrary to the intuitive assumption that the total phases on C60 and Ne@C60 or Ar@C60 has to be the same.

Hybrid disordered blends formed from fullerene porous layers and zinc oxide grown by atomic layer deposition

Thermally evaporated fullerene C60 porous films served as templates for a hybrid (molecular-inorganic) disordered blend formation. C60 films were covered with zinc oxide (ZnO) grown by atomic layer deposition. ZnO filled every pore in the C60 layer which led to the formation of C60–ZnO films with separate and distinguishable phases of C60 and ZnO constituents. Morphological, structural, optical, and electrical properties of the so-obtained films were investigated. Deposition of ZnO polycrystalline films on C60 porous layers resulted in the formation of ZnO with additional structural defects, compared to the films grown on planar substrates, which affected the electrical transport in the ZnO–C60 layers.

C60 chain phases on ZnPc/Ag(111) surfaces: Supramolecular organization driven by competing interactions.

Serpentine chain C60 phases were observed in scanning tunneling microscopy (STM) images of C60 layers on zinc phthalocyanine (ZnPc) or pentacene covered Ag(111) and Au(111) surfaces. This low-density, quasi-one-dimensional organization contrasts starkly with the close-packed hexagonal phases observed for C60 layers on bare metal substrates. STM was employed to perform a detailed investigation of these chain structures for C60/ZnPc/Ag(111) heterolayers. Motivated by the similarity of these chain phases, and the chain and stripe organization occurring in dipole-fluid systems, we investigated a model based on competing van der Waals attractions and electrostatic repulsions between C60 molecules as an explanation for the driving force behind these monolayer phases. Density functional theory (DFT) calculations revealed significant charge transfer to C60 from the Ag(111) substrate, through the intervening ZnPc layer, inducing electrostatic interactions between C60 molecules. Molecular dynamics simulations performed with attractive van der Waals interactions plus repulsive dipole-dipole interactions reproduced the C60 chain phases with dipole magnitudes consistent with DFT calculations.

Explaining fullerene dispersion by using micellar solutions.

An effective computational strategy to describe the dispersion of C60 by surfactants is presented. The influence of parameters such as surfactant concentration and molecular length on the final morphology of the system is explored to explain the experimental results and to understand the incorporation of C60 inside micelles. Both neutral and charged amphiphilic molecules are simulated. The long-discussed problem of the location of fullerenes in micelles is addressed and C60 is found in the hydrocarbon-chain region of the micelles. If the available hydrophobic space increases, C60 is localized in the inner part of the micellar core. Short, charged amphiphilic stabilizers are more efficient at dispersing fullerenes monomolecularly. Two different phases of C60 are observed as the C60/surfactant ratio varies. In the first, aggregates of C60 are entrapped inside the micelles, whereas, in the second, colloidal nanoC60 is formed with surfactants adsorbed on the surface.

Synthesis of ultrahard fullerite with a catalytic 3D polymerization reaction of C60

3D polymerization of C60 realizes under conditions of large plastic deformation at pressure 6–7GPa and room temperature in the presence of CS2. The phase of 3D-polymerized C60 is identical to ultrahard fullerite synthesized from pure C60 at 18GPa pressure: in both cases, the samples plough diamond during the rotation of the sample in a shear diamond anvil cell, bulk module is 585GPa, and a sequence of phase transitions preceding to ultrahard phase is also the same in both cases (in the presence of CS2, the phase transitions take place at lower pressures than in pure C60). Raman and transmission microscope studies confirm the structure equivalence of samples of both types. The absence of sulfur in the structure of ultrahard fullerite synthesized in the presence of CS2 proves the catalysis role of CS2 in the 3D polymerization of C60.

Pressure-induced transformation and superhard phase in fullerenes: The effect of solvent intercalation

We studied the behavior of solvated and desolvated C60 crystals under pressure by in situ Raman spectroscopy. The pressure-induced bonding change and structural transformation of C60s are similar in the two samples, both undergoing deformation and amorphization. Nevertheless, the high pressure phases of solvated C60 can indent diamond anvils while that of desolvated C60s cannot. Further experiments suggest that the solvents in the solvated C60 act as both spacers and bridges by forming covalent bonds with neighbors in 3D network at high pressure, and thus, a fraction of fullerenes may preserve the periodic arrangement in spite of their amorphization.