Abstract
First- and second-order Raman scattering from mesophase pitch was studied. In spite of the great complexity of this material, both spectra were found still to retain a common similarity to those of highly disordered graphites but also to exhibit several differences, which have been assumed to be caused by a higher degree of disorder in pitch. It has been established that the first-order 1600 cm −1 mode is narrowed almost by half and split into two components. Distortion of the perfect polycyclic conjugation of the pitch molecules resulting in significant variations in stress for their CC bonds and consequently in large variations in the in-plane stretching force constants was assumed to be the reason for this splitting. This conclusion is supported by similar spectral peculiarities observed in first- and second-order Raman scattering from donor and acceptor graphite intercalation compounds. During carbonization, mesophase pitch is converted into a carbonaceous material similar to any highly disordered graphite and their spectra become identical. Pitch carbonization was assumed to involve a kind of phase transition under which intermolecular interactions change from Van der Waals to covalent-like character. Correspondingly, the intensity ratio I 1600/ I 1350 versus heat-treatment temperature relationship was assumed to represent a curve of change of state during this transition.
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