Fullerite C60 Research Articles

Landau theory of barocaloric plastic crystals

We present a minimal Landau theory of plastic-to-crystal phase transitions in which the key components are a multipole-moment order parameter that describes the orientational ordering of the constituent molecules, coupling between such order parameter and elastic strains, and thermal expansion. We illustrate the theory with the simplest non-trivial model in which the orientational ordering is described by a quadrupole moment, and use such model to calculate barocaloric effects in plastic crystals that are driven by hydrostatic pressure. The model captures characteristic features of plastic-to-crystal phase transitions, namely large changes in volume and entropy at the transition, as well as the linear dependence of the transition temperature with pressure. We identify temperature regions in the barocaloric response associated with the individual plastic and crystal phases, and those involving the phase transition. Our model is in overall agreement with previous experiments in powdered samples of fullerite C60, and predicts peak isothermal entropy changes of ∼90JK−1kg−1 and peak adiabatic temperature changes of ∼35K under 0.60 GPa at 265 K in fullerite single crystals.

Numerical study of the chiral effect in C60 fullerite

Numerical study of the chiral effect in C60 fullerite

Изменение размеров фуллеритов C60 при их осаждении на подложку твердого тела

Nano-sized films are of great interest for such important industries as mechanical engineering and instrument making. Nanofilms themselves can be constructed from various elements and compounds; however, one of the most promising components used to create nanofilms is C60 fullerene and its compounds. C60 fullerites are molecular crystals in the nodes of which C60 fullerenes are located. It was fullerite C60 that was taken as the basic element of the nanofilm, the deposition of which was simulated in this work. An iron Fe(100) crystal was modeled as the substrate on which the nanofilm was deposited. The temperatures, at which the deposition and formation of the "substrate-nanofilm" system were studied, were 300 K, 700 K, 1150 K. Since the research was carried out at the level of nano-sized objects, the modeling was carried out using the molecular dynamics methods in the LAMMPS software package. The main result of the study is that the influence of temperature and the process of the interaction of C60 fullerites with each other and with the substrate on the size of the C60 fullerites themselves after their deposition on the substrate has been established.

Characterization of Fine Structure and Mechanical Properties of the Disordered Carbon Materials Synthesized from C60 Fullerite under High Pressure

Characterization of Fine Structure and Mechanical Properties of the Disordered Carbon Materials Synthesized from C60 Fullerite under High Pressure

Superconductivity in the Doped Polymerized Fullerite Clathrate from First Principles

Superconductivity in the new polymerized C60 fullerite clathrate doped with simple metals is investigated through density functional theory methods. The phonon dispersion curves are systematically computed for the clathrate structures containing the guest dopants (Li, Na, K, Be, Mg, Ca, Al, Ga, Ge) in one of the two distinct cages, fullerene‐like C60 and sodalite‐like C24, exhibited by this structure. Only four of these structures, Li@C24, Na@C24, Ga@C24, and Be@C60, are dynamically stable in the harmonic approximation. They all show superconducting behavior, although their critical temperatures are predicted to be below 2 K.

Hydrogen sorption by nanostructures at low temperatures (Review article)

The features of hydrogen sorption by a wide range of nanostructures — fullerite C60, carbon nanotubes, graphene structures, nanodispersed carbon, including Pd-containing nanoclusters, ordered silicon-oxide-based nanostructures (the MCM-41 family) and silicon-oxide aerogel — have been reviewed. Special attention is given to the sorption characteristics of carbon nanostructures that have been exposed to various modifying treatments (oxidation, gamma-ray irradiation in gas atmosphere, action of pulsed high frequency gas discharge). Two mechanisms of physical low-temperature sorption of hydrogen have been revealed to predominate in such nanostructures in different temperature intervals. At the lowest temperatures (8–12 K), the sorption can actually proceed without thermal activation: it is realized through the tunnel motion of hydrogen molecules along the nanostructure surfaces. The periodic structure of the potential relief, allowed by the surface frame of carbon and silicon-oxide nanostructures, along the rather low interpit barriers are beneficial for the formation of low-dimensional (including quantum) hydrogen-molecule systems practically without thermally activated diffusion. In such nanostructures, the hydrogen diffusion coefficients are actually independent of temperature at 8–12 K. At higher temperatures (12–295 K), a thermally activated mechanism of hydrogen diffusion prevails. The periodic structure of fullerite C60 contains periodic interstitial cavities, separated by rather low potential barriers. Their sizes are sufficient to accommodate impurity hydrogen molecules and, thus, allow diffusion processes, which can also have a tunnel nature. It is shown that gamma-irradiation and high-frequency gas discharge processing increase markedly the quantity of hydrogen strongly bonded to carbon nanostructures.

On polyamorphism in heterophase matter

Structural and thermodynamic features of continuous and discontinuous polymorphic phase transformations in amorphous matter caused by the rearrangement of mesoscopic molecular associations are considered. Polyamorphism of fluids expanded mercury, and the orientationally-disordered fullerite C60, pure and doped by heavy rare gases, is summarized.

Proportional correlation between heat capacity and thermal expansion of atomic, molecular crystals and carbon nanostructures

Correlation between thermal expansions β(T) and heat capacity C(T) of atomic and molecular crystals, amorphous materials with a structural disorder, carbon nanomaterials (fullerite C60, bundles SWCNTs of single-walled carbon nanotubes) was analyzed. The influence of the contribution to the coefficient of linear thermal expansion αXe(T) of Xe atoms adsorbed on the SWCNTs bundles is considered. The proportional correlation was found between the contribution to the coefficient of linear thermal expansion αXe(T) and the normalized to the gas constant heat capacity C Xe(T)/R of Xe atoms adsorbed on the SWCNTs bundles. The proportional correlation (β/β*) ∼ (CV/R) with the parameter β* for the bulk thermal expansion coefficient for cryocrystals is proposed. In the case of atomic crystals such as Xe and Ar, the proportional correlation (β/β*) ∼ (CV/R) is observed in the temperature range from the lowest experimental to temperatures where CV/R ≈ 2.3. The correlation is not observed in the temperatures where 2.3 < C V/R < 3 (classical Dulong-Petit law). It was found that the universal proportional correlation is also observed for molecular crystals with linear symmetry, such as CO2, CO, and N2O if the normalized heat capacity below the values CV/R ≈ 3 ÷ 3.5. It indicates that the proportional correlation between thermal expansions (β/β*) and heat capacity (CV/R) is related not only to the translational, but also to the rotational degrees of freedom of the molecule in the crystal. In the case of the C0, molecular crystal with translational and rotational degrees of freedom and intramolecular vibrations, the discussed above correlation occurs below the values of normalized heat capacity CV/R ≈ 7.5. In strongly anisotropic systems, such as systems of compacted bundles of single-walled carbon nanotubes and SWCNTs bundles with adsorbed Xe atoms, this universal dependence appears in a limited temperature range that does not include the lowest temperatures. A qualitative explanation of the observed correlation is proposed.

Numerical Study of the Passage of Natural Gas Components through C60 Fullerite in the Low-Temperature Phase

The movement of natural gas components through a crystalline fragment of C60 fullerite in a simple cubic phase is numerically investigated. The methods of classical molecular physics, the Monte Carlo and Euler approaches, and a step-by-step numerical method of a high order of accuracy are used to study the effects arising from the passage of the particles through the C60 fullerite. The influence of the characteristics of incoming particles on the permeability of fullerite was analyzed using the results of the performed calculations. The application of the fast integral approach based on the smoothed spherical potential is discussed and compared with the Monte Carlo method.

Quantum effects in the low-temperature thermal expansion of fullerite C60 doped with a 4He impurity

The thermal expansion of fullerite C60 doped with a 4He impurity at T ∼2 K has been investigated by the method of low temperature precision dilatometry in the interval T = 2.2−24 K. The character and the derived values of the thermal expansion coefficients were strongly dependent on the concentration of the 4He impurity in fullerite. In the interval T = 2.2−5 K the thermal expansion of the 4Hex−C60 system is negative, which is attributed to the tunnel movement of the 4He atoms in the cavity system of the C60 crystal lattice and at the crystallite surface. The contribution of this process to the thermal expansion decreases as the impurity (4He) concentration increases and the probability of 4He tunneling between the crystal lattice cavities and the impurity-free areas of the grain surface diminishes. In the temperature interval T = 4.5−24 K the thermal expansion of the 4Hex−C60 system is influenced predominantly by the mutual transformations of different orientation glass modifications of fullerite. Owing to their tunnel character the transformations make a negative contribution to the process of thermal expansion entailing a hysteresis and other anomalies observed in this temperature interval. The intensity of the processes provoked by the tunneling-encouraged phase transformations of the orientational glasses of C60 increases with the 4He concentration in fullerite.

Quantitative Characterization of Oxygen-Containing Groups on the Surface of Carbon Materials: XPS and NEXAFS Study

The results of the comparative quantitative study of oxygen-containing groups adsorbed on the surface of carbonized sponge scaffold (CSS), highly oriented pyrolytic graphite (HOPG), fullerite C60 and multi-walled carbon nanotubes (MWCNTs) introduced into a high vacuum from the atmosphere without any pre-treatment of the surface are discussed. The studied materials are first tested by XRD and Raman spectroscopy, and then quantitatively characterized by XPS and NEXAFS. The research results showed the presence of carbon oxides and water-dissociation products on the surfaces of materials. It was shown that main source of oxygen content (~2%) on the surface of HOPG, MWCNTs, and C60 powder is water condensed from the atmosphere in the form of an adsorbed water molecule and hydroxyl group. On the CSS surface, oxygen atoms are present in the forms of carbon oxides (4–5%) and adsorbed water molecules and hydroxyl groups (5–6%). The high content of adsorbed water on the CSS surface is due to the strong roughness and high porosity of the surface.

Clathrate structure of polymerized fullerite C60

Investigations of clathrate structures have gained a new impetus with the recent discovery of room-temperature superconductivity in metal hydrides. Here we report the finding, through density functional theory calculations, of a clathrate phase in the fullerite C60 system. Intermolecular bonds of the type 5/5 2+3 cycloaddition are induced between each C60 molecule and its twelve nearest neighbors in the face centered cubic lattice. Remarkably, this bonding creates on octahedral sites new C60 cages, identical to the original ones, and on tetrahedral sites distorted sodalite-like cages. The resulting carbon clathrate has a Pm3¯ simple cubic structure with half of the original face centered lattice constant. Eighty percent of its atoms are sp3-hybridized, driving a narrow-gap semiconducting behavior, a moderate bulk modulus of 268 GPa and an estimated hardness of 21.6 GPa. This new phase is likely to be prepared by subjecting C60 to high pressure and high temperature conditions.

Short notes: Photoluminescence of C60 fullerite intercalated with nitrogen molecules wide range of temperatures

The optical properties of C60 single crystals, intercalated with nitrogen molecules, were investigated by the spectral-luminescence method in the temperature range 20–230 K. The saturation was carried out under a pressure of 30 atm at various temperatures from 200 to 550°C. For the C60 + N2 system, the presence of a temperature boundary of the adsorption crossover of about 420°C was established (transition from the diffusion mechanism of intercalation — physisorption, to chemical interaction — chemisorption). The temperature dependence of the integrated radiation intensity of a new nitrogen-containing substance based on C60 fullerite has been recorded for the first time. Quenching of photoluminescence at low temperatures was found. The observed new effect of low-temperature quenching of photoluminescence is explained by the appearance in the process of chemical interaction between the N2 impurity molecules and the C60 matrix of effective exciton trapping centers and nonradiative deactivation of electronic excitation.

Mixed (Sr1 − x Ca x )33Bi24Al48O141 fullerenoids: the defect structure analysed by (S)TEM techniques

Abstract (Sr1−x Ca x )33Bi24+δ Al48O141+3δ/2 fullerenoid solid solutions have been synthesized and the effect of partial substitution of Sr by Ca has been characterized by (scanning) transmission electron microscopy, applying different imaging methods. Most of the defects commonly observed in face centered cubic compounds, have also been observed in (Sr1−x Ca x )33Bi24+δ Al48O141+3δ/2. Based on purely geometrical and topological models, structural presentations for the coherent twin boundaries and stacking faults have been constructed on the basis of complex spherical “Al84O210” units. The results are compared to defects observed in the crystallite fullerite C60.

Модифицирование структурно-фазового состояния и механических свойств пленок Ti – C60 – Ti, имплантированных ионами бора

Changes in the structure, phase composition, and mechanical properties of Ti – C60 – Ti films implanted with B+ ions (E = 80 keV, D = 1 1016 ion/cm2) after annealing in vacuum at temperature 570 K (3 hours) were studied by the methods of atomic force microscopy, X-ray diffraction and nanoindentation. The films were obtained by resistive evaporation in vacuum. Layers of titanium and C60 fullerite were sequentially deposited onto a substrate of oxidized single-crystal silicon. It has been established that during the condensation of the fullerite layer (h = 250 nm) on the underlying titanium layer (h = 120 nm), and then the titanium layer (h = 150 nm) on the fullerite layer, intense diffusion of titanium into the fullerite layer occurs. Implantation of titanium-fullerite-titanium films with boron ions leads to mixing of titanium and fullerite layers, while the size of structural elements increases in comparison with non-implanted films from 40 nm to 80 nm. Auger electron spectroscopy revealed that ion implantation results in an increase in the atomic fraction of oxygen in the films and the formation of a new TixOyC60 phase, which leads to an increase in the nanohardness of the mixed layers. The implanted Ti – C60 – Ti films were annealed in vacuum at T= 570 K for t = 3 h. Thermal annealing results in recrystallization of the fullerite phase and intensive growth of a new TixOyC60 phase with improved mechanical properties.

Особенности зависимости рамановских спектров кластерных структур трехмерно-полимеризованного фуллерита от давления

We study the effect of high hydrostatic pressure on 3D polymerized fullerite C60. We do not observe further structural changes until 150 GPa after a formation of 3D C60 under hydrostatic pressure 28 GPa. It is experimentally shown that the obtained samples consist of different clusters formed by sp3 bonds with a different set of force constants, the values of which vary within 20% and exceed the diamond force constants by the factor of 1.3–1.5. The influence of the exposure of laser radiation on the process of 3D polymerization of C60 under pressure was found. Increasing of the exposure by the factor of 15 leads to a decrease in the bulk modulus of 3D C60 from 610 GPa to 504 GPa.

Features of dependence of Raman spectra of cluster structures of three-dimensionally polymerized fullerite on pressure

We study the effect of high hydrostatic pressure on 3D polymerized fullerite C60. We do not observe further structural changes until 150 GPa after a formation of 3D C60 under hydrostatic pressure 28 GPa. It is experimentally shown that the obtained samples consist of different clusters formed by sp3 bonds with a different set of force constants, the values of which vary within 20% and exceed the diamond force constants by the factor of 1.3-1.5. The influence of the exposure of laser radiation on the process of 3D polymerization of C60 under pressure was found. Increasing of the exposure by the factor of 15 leads to a decrease in the bulk modulus of 3D C60 from 610 GPa to 504 GPa. Keywords: bulk modulus, ultrahard fullerite, high pressures, Raman spectroscopy.

The Formation of Nanoscale Closed Graphene Surfaces during Fullerite C60 Hot Isostatic Pressing

The fullerite C60 modified by hot isostatic pressing (HIP) at 0.1 GPa in argon near and beyond its thermal stability region (920–1270 K temperature interval) was studied by X-ray diffractometry, Raman spectroscopy, ultra soft X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy. It was found that the C60 molecules merge into closed nanocapsules with a graphene surface during the thermal treatment. The conducted studies showed that using HIP treatment of the fullerite C60, it is possible to obtain a chemically resistant material with a high hardness and elasticity, as well as a density lower than that of the graphite. This new material, consisting of closed graphene nanocapsules 2–5 nm in size, formed by sp2 covalent bonds between carbon atoms is promising for various applications, and as a basis for the synthesis of new composite materials.

Fullerite C60 optical constants in the C 1s NEXAFS region

Using data on the absorption cross sections the refraction coefficient spectral dependence n(E) and the spectra of the remaining optical coefficients (reflection coefficient, phase shift, and atomic form factor) in the fullerite C60 C 1s near edge X-ray absorption fine structure (NEXAFS) region (280–350 eV) were determined. For the n(E) calculations the Kramers-Kronig integral relations (KKRs) were used. The KKR computations were performed using data on atomic carbon absorption cross sections in the 10–30000 eV range and on solid and gaseous C60 – in the 0–120 eV. Absorption cross section spectrum in the fullerite C60 C 1s NEXAFS region were measured.

Organic Non-Wettable Superhydrophobic Fullerite Films.

A long-standing quest in material science has been the development of non-wettable superhydrophobic films based on a single organic material, without the requirement of fluorination or silane treatment. Here, such films and coatings, which are developed using colloidal gels of fullerite C60 and C70 nanocrystals, are described. It is illustrated that despite the high surface energy of these van der Waals molecular crystals their gelation can create films having self-affine fractal surfaces with multiscale roughness. Water droplets on resulting surfaces of fullerite films bead like a pearl resting in a Fakir state with contact angle exceeding 150°. The films are extremely water repellent and non-wettable; when submerged in water they stay dry up to 3 h even at a water depth of two feet and exhibit the plastron effect. A series of experiments are presented to provide comprehensive inspection of water droplet dynamics on these films. These include rolling, bouncing, squeezing, freezing, melting, evaporating; along with acidic and alkaline tests. Non-wettable films of such materials are unique as fullerites get photosensitized instantaneously generating extremely high yields (≈100%) of singlet oxygen (1 O2 ) that can destroy viruses and bacteria; thereby enabling their use in rheology, water purification, and medicinal devices.