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Fragment of p,T diagram of C60 with experimental points at 1.5 GPa. A represents the existence range of atomic carbon materials. M corresponds to the monomeric state. Mp corresponds to the range of O and T polymerized phases of C60. 2 represents the suggested triple point (fcc-O-T). Figure 2. Evolution of the XRD patterns as a function of temperature (1000 s of treatment).
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The high-pressure states of C60 fullerene corresponding to the 1.5 GPa isobaric section of its p,T diagram in the 293−1073 K temperature range were investigated by X-ray diffraction and IR and Raman spectroscopies. It was shown that increasing the treatment temperature of C60 at quasihydrostatic pressure changes the nature of the polymerization pro...
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Context 1
... XRD Study. Figure 2 presents the evolution of the XRD patterns of the samples obtained at 1.5 GPa when temperature changes. In the low-temperature region (298-423 K), the patterns of samples treated for as long as 1000 s mainly keep cubic characteristics except some asymmetric broadening and a slight shift of the peaks toward greater angles (Figure 2). ...
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... XRD Study. Figure 2 presents the evolution of the XRD patterns of the samples obtained at 1.5 GPa when temperature changes. In the low-temperature region (298-423 K), the patterns of samples treated for as long as 1000 s mainly keep cubic characteristics except some asymmetric broadening and a slight shift of the peaks toward greater angles (Figure 2). However, a prolonged heating for 10 000 s leads to more pronounced changes: (1) cubic peaks (111) and (220) begin to split into two lines, and (2) a new diffuse peak appears at 12°- 13° (2 Θ). ...
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... unit cell parameters of this phase [a ) 9.086(4) Å, b ) 9.807(7) Å, c ) 14.73(1) Å] are in agreement with previous determinations. [9][10][11] The treatment for a long time (10 000 s) at 723 K as well as the treatment for a short time (1000 s) at 773 K lead to the formation of a mixture of phase O with another phase indexed as tetragonal (T) [a ) 9.083(5) Å, c ) 15.00(2) Å] (some reflections are marked T in Figure 2). This phase is identical with the tetragonal one reported before as forming at higher pressure. ...
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The high-pressure states of C-60 fullerene corresponding to the 1.5 GPa isobaric section of its p,T diagram in the 293-1073 K temperature range were investigated by X-ray diffraction and IR and Raman spectroscopies. It was shown that increasing the treatment temperature of C-60 at quasihydrostatic pressure changes the nature of the polymerization p...
Citations
... Further analysis indicates that the thermally cycled C 60 powder has a wider full width at half maximum (FWHM) of its main peak in the X-ray diffraction (XRD) spectrum. Moreover, a new feature at 11.4 degrees is present, as shown in Supplementary Fig. 7a, b, which is related to the formation of fullerene dimers and different fullerene derivatives at a certain fraction in the powder 37 . We also utilized the matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectroscopy technique to investigate the change in molecular weights of the powders. ...
Thermally evaporated C60 is a near-ubiquitous electron transport layer in state-of-the-art p–i–n perovskite-based solar cells. As perovskite photovoltaic technologies are moving toward industrialization, batch-to-batch reproducibility of device performances becomes crucial. Here, we show that commercial as-received (99.75% pure) C60 source materials may coalesce during repeated thermal evaporation processes, jeopardizing such reproducibility. We find that the coalescence is due to oxygen present in the initial source powder and leads to the formation of deep states within the perovskite bandgap, resulting in a systematic decrease in solar cell performance. However, further purification (through sublimation) of the C60 to 99.95% before evaporation is found to hinder coalescence, with the associated solar cell performances being fully reproducible after repeated processing. We verify the universality of this behavior on perovskite/silicon tandem solar cells by demonstrating their open-circuit voltages and fill factors to remain at 1950 mV and 81% respectively, over eight repeated processes using the same sublimed C60 source material. Notably, one of these cells achieved a certified power conversion efficiency of 30.9%. These findings provide insights crucial for the advancement of perovskite photovoltaic technologies towards scaled production with high process yield.
A review has been presented on the structural and mechanical properties of hard carbon phases synthesized from fullerite C60 under pressure. The density and nanostructure have been recognized as the key parameters defining the mechanical properties of hard carbon phases. By suggesting a version of the transitional high-pressure diagram of C60 (developed up to 20 GPa), the three areas of the formation of hard carbon phases have been highlighted. The corresponding phases of superhard carbon are (1) disordered sp2-type atomic structures at moderate pressures and high temperatures (> 1100 K), (2) three-dimensionally polymerized C60 structures at moderate temperatures and high pressures (> 8 GPa), and (3) sp3-based amorphous and nanocomposite phases at high pressures and temperatures. First region can be in turn separated into 2 subparts with different peculiarities of sp2 structures and properties: low pressure part (0.1–2 GPa) and high-pressure part (2–8 GPa). Temperature can be recognized as a factor responsible for the formation of nanostructures by the partial destruction of molecular phases, whereas pressure is a factor responsible for stimulating the formation of rigid polymerized structures consisting of covalently bonded C60 molecules, whereas the combination of both factors leads to the formation of atomic-based phases with dominating sp3 bonding.
We present a detailed study of transformations between the orthorhombic and
tetragonal polymeric states of C60. The transformations are
characterised by Raman spectroscopy and X-ray diffraction. We show that the
transformation from the orthorhombic (O) phase to the tetragonal (T) phase
is very fast and our results indicate that the transformation goes via an
intermediate dimer (D) state in a two-stage process, O↦D and, D↦T
transformations, where the second process is slower than the first. On the
other hand, the transformation from the tetragonal to the orthorhombic phase
is significantly slower, indicating a high-energy threshold to break the
polymer bonds at the temperatures used. The results also support earlier
suggestions that the tetragonal phase contains disordered dimers that can be
viewed as lattice defects in the formation of higher polymers.
A brief review of structural, electrotransport, optical, elastic, and mechanical properties of carbon phases synthesized under pressure by heating fullerite C60 and carbynoid materials is given. A large variety of carbon modifications with a variable bonding type, a variable mean coordination number, a variable molecular or atomic structural type, a variable characteristic dimensionality (from zero-to three-dimensional structures), a variable degree of covalence, etc., were prepared. Emphasis in the review is given to the elucidation of the interplay between the structural and topological characteristics of carbon phases and their key electronic and mechanical properties. A version of the kinetic phase diagram of fullerite C60 transformations on heating under pressure is also suggested. This version is modified with respect to the interpretations known in the literature.
Powder X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and molecular dynamics have been employed
to investigate structural transformations in hexagonal and cubic modifications of fullerite C60 after the action of high pressure (4 GPa) within the temperature range 20–1450°C. It has been found that fullerene molecules
polymerize to afford polymer structures only in the case of face-centered cubic samples. Under the effect of high pressure
and temperature, fullerite C60 with a hexagonal close-packed structure is initially transformed into the cubic modification and, then, forms polymerized
structures, which, during an increase in the treatment temperature, become less stable and ordered than the same polymerized
structures obtained directly from cubic fullerite C60. X-ray photoelectron spectroscopy measurements suggest deformation of the cages of fullerene molecules in the polymerized
structures.
We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 single-crystals treated at high-pressure and high-temperature. This allowed us to obtain structural information on the C60 dimer state which can be considered as an intermediate state in the polymerization process. In the 1-6 GPa pressure range the crystals are primarily formed of dimers with additional minor fractions of monomers, 1D and 2D polymers, as shown by the analysis of the Raman spectra. The dimers are disordered within an average cubic lattice derived from that of the monomer. Single-crystal diffraction patterns reveal a characteristic diffuse scattering intensity distribution which has been simulated by calculating the diffuse scattering produced by dimer and trimer model structures. Satisfactory agreement is obtained for random positional and orientational disorder of the C60-C60 dimers although a small concentration of similarly disordered trimers is likely. In a first approximation the dimer/trimer disorder can be considered as random but various inter-dimer correlations are probably present, as discussed.
