The special features of formation of carbon nanostructures, their classification and site on the state diagram of carbon

Abstract

The peculiarities of possible formation of low-temperature carbon structures (fullerite F, crystalline carbyne CC, nanotubes crystals NTC) in the area of graphite G realization in the state diagram P-T have been described in the present paper. In addition, the regions of existence of high-temperature structures (molecular carbyne C, graphene Gr, molecules of nanotubes NT, fullerene molecules Fn, pent- and sixatomic cyclic molecules) in the area of gaseous carbon have been marked. In response to changing state of carbon atoms the hypothetic areas of these structures formation have been indicated on the P-T diagram. The temperature levels I … IV of existence of different carbon structures have been marked off. Discussion has been presented concerning the possibility of formation not only of single-layered or single-wall nanotubes (SWNT) and fullerenes Fn, but of multi-layered or multi-wall nanotubes (MWNT) and fullerenes (so-called onion) as well. Their location has been shown on the P-T diagram. The results of statistical theory of phase transformations in carbon crystals as: diamond→← fullerite (D→← F), fullerite→← graphite (F→← G), graphite→← carbyne (G→← C) have been presented. The overall formula for Gibbs thermodynamic potential has been given and it defines the dependence on temperature, pressure, order parameters, energetic constants. The equilibrium values of order parameters have been evaluated as a function of temperature and external all-round pressure. The plots of temperature dependence of thermodynamic potential ϕi (T) have been constructed for different pressures for the examined phases i = D,F,G,C, the state diagram of carbon has been plotted by the intersection points of the ϕi(T) curves. The qualitative correspondence between experimental and design diagram of carbon state has been received.