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The possibilities of single crystals synthesis in conditions of nonisotropic one-axis contraction were studied. As a result of the work the single crystals of the tetragonal polymerized phase of C60 without orientational domains were obtained. The crystal structure of this phase was resolved using single crystal x-ray diffraction data. A structural model of this phase proposed early was confirmed and refined to final R = 0.075. The structure is slightly disordered. It consists of a random combination of the P42/mmc layers (84%) and of the Immm layers (16%), along the c axis. [ABSTRACT FROM AUTHOR]

The dimerization of C[sub 60] fullerene under conditions of quasi-hydrostatic compression at temperatures above 293 K is investigated by IR spectroscopy, Raman scattering (RS) spectroscopy, and x-ray diffraction. The measured dimer (C[sub 60])[sub 2] content in the products of the polymerization of fullerite as a function of the pressure, temperature, and treatment time shows that dimerization occurs even at room temperature in the entire pressure range above ∼1.0 GPa. However, at least at temperatures above 400 K dimerization does not result in the formation of a dimer phase as a stable modification of the system, since the dimer is an intermediate product of the transformation. It is shown that increasing the holding time at 423 K decreases the content of the dimer fraction in the samples and results in the formation of linear (at 1.5 GPa) and two-dimensional (at 6.0 GPa) polymers, which are structure-forming elements of the orthorhombic and rhombohedral polymerized phases. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It is established by x-ray diffraction and Raman scattering that the polymerization of C[sub 60] fullerene at 1.5 GPa and 723 K leads to the formation of an orthorhombic phase that is different from the previously identified high-pressure orthorhombic phase. It is determined by a calculation of the optimal packing of linear C[sub 60] polymers by the method of atom-atom potentials that the energetically favorable structure of the orthorhombic phase belongs to the space group Pnnm and not the previously proposed group Immm. The computed value of the rotation angle of the polymer chains that corresponds to the minimum packing energy was equal to 61°. The mechanisms leading to the formation of the polymerized phases are discussed on the basis of the results obtained. [ABSTRACT FROM AUTHOR]

The kinetics of fullerene solid-phase dimerization proceeding through the 2 + 2 cycloaddition of C[sub 60] at a pressure of 1.5 GPa is investigated by vibrational spectroscopy in the temperature range 373-473 K. Kinetic curves for the formation of (C[sub 60])[sub 2] dimers are obtained using the analytical band at 796 cm[sup -1] in the IR spectra of the (C[sub 60])[sub 2] dimer molecule. Under the assumption that the pressure-induced dimerization of C[sub 60] is an irreversible second-order reaction, the reaction rate constants are determined at different temperatures. The activation energy and the preexponential factor are found to be equal to 134 ± 6 kJ/mol and (1.74 ± 0.24) × 10[sup 14] s[sup -1], respectively. [ABSTRACT FROM AUTHOR]

By adiabatic vacuum calorimetry the temperature dependence of heat capacity for crystalline dimer of fullerene C60 has been determined in the range 6–340 K at standard pressure. Between 46 and 56 K, a glass-like transition of the dimer, the nature of which is, probably, similar to that described for C60, has been found. The results were used to calculate the thermodynamic functions of the dimer: the heat capacity Cp∘(T), enthalpy H°(T)−H°(0), entropy S°(T)−S°(0) and Gibbs function G°(T)−H°(0) over the range from T→0 to 340 K. For T<60 K the fractal dimension D in the heat capacity function of the multifractal variant of the Debye’s theory of heat capacity was estimated and in the 20–45 K range D was found to be 1. That indicates a chain structure of the dimer. The heat capacities of the dimer have been compared to those of the initial fullerite C60. The standard entropy of formation of the crystalline dimer from graphite, at T=298.15 K and at standard pressure, and the entropies of transition of the initial fullerite C60 to the crystalline dimer have been calculated. [Copyright &y& Elsevier]