## 3 Results and Discussion
### HIP-Treated Fullerite C\({}_{60}\) Study
The diffraction patterns of the fullerite sample at a temperature of 1270 K are qualitatively similar to the ones of the materials formed at the carbonization final stages and graphitization initial stages of various carbon-containing compounds [69; 70; 71; 72; 73]. Their diffraction patterns are also characterized by the presence of several wide diffuse lines. The diffuse band appearance at 41-47\({}^{\circ}\), corresponding to two-dimensional (10) and (11) graphene layer reflexes and (100) and (101) HOPG peaks, indicates the presence of a small amount of graphene layer fragments with various degrees of defectiveness in the system [69; 70]. A wide band in the region of 20-30\({}^{\circ}\) is characterized by a maximum, the position of which approximately corresponds to that of the (002) diffraction peak of graphite and MWCNTs. This indicates that a significant number of these two-dimensional ordered carbon clusters is a part of crystallites from packages of nanoscale graphene layers [69; 70]. However, it should be noted that the absence of three-dimensional (hkl) reflexes on the diffractograms indicates the absence of a three-dimensional ordering of graphene planes characteristic of graphite. The estimation of the average sizes of nanoparticles using the Warren-Scherrer equation [69; 74], which relates the average lateral dimensions \(L_{a}\) and the height (thickness) \(L_{c}\) of the graphene layers packaging with the width of the corresponding (10), (11) and (002) diffraction peaks, showed that the average values of the \(L_{a}\) and \(L_{c}\) parameters were in the range 2-4 nm. A similar sequence of changes in the fullerite structure can be traced on the basis of the temperature dependence of the Raman spectra shown in Figure 3. The C\({}_{60}\) Raman spectra change slightly with an increase in the temperature up to 1120 K. All the above-mentioned spectra preserve the pristine C\({}_{60}\) spectrum main features, even though they  
Figure 2: XRD patterns of the pristine and HIP-treated at different temperatures fullerite C\({}_{60}\). The vertical lines at the top indicate the HOPG diffraction peaks (002), (100) and (101). show a small broadening and a decrease in peak intensities over the entire spectral range except the 1200-1800 cm\({}^{-1}\) region where the wide band formation is observed. However, at temperatures above 1120 K, the Raman spectra change significantly, especially in the 1100-1700 cm\({}^{-1}\) region. In particular, the intensities of the all peaks decrease and a wide band in the 2600-3200 cm\({}^{-1}\) region appears. Moreover, one can see a very low-intensity peak at 96 cm\({}^{-1}\), strong decrease in intensity and red shift of the \"pentagonal pinch\" mode from 1468 cm\({}^{-1}\) to 1462 cm\({}^{-1}\). A new peak appearing in the Raman spectrum of C\({}_{60}\) at 96 cm\({}^{-1}\) and the red shift of the A\({}_{\rm g}\)(2) \"pentagonal pinch\" mode indicate the formation of dimers of the C\({}_{60}\) molecule in a fullerite during the HIP treatment. At the same time, according to the XRD data (Figure 2), the pristine fullerite fcc structure was partially preserved. The appearance of a low-energy peak (96 cm\({}^{-1}\)) is caused by a full-symmetric oscillation of the C\({}_{60}\) molecules in the dimer. The frequency of this oscillation is in good agreement with its theoretically predicted value [75], which is also confirmed experimentally [76; 77]. Moreover, the A\({}_{\rm g}\)(2) \"pentagonal pinch\" mode (1463 cm\({}^{-1}\)) is associated with the A\({}_{\rm g}\)(2) mode for the C\({}_{60}\) dimer [78]. Instead of narrow peaks H\({}_{\rm g}\)(6)-H\({}_{\rm g}\)(8) two very broad bands at 1350 cm\({}^{-1}\) and 1591 cm\({}^{-1}\) appear. The intensity of these bands grows with the increasing temperature up to 1270 K. As a result, all the pristine C\({}_{60}\) features in the Raman shift spectrum disappear, which indicates the complete destruction of the C\({}_{60}\) molecules.