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Tbe real structure of RBa,Cu,O,-, (R = Y, rare earth) at intermediate values of S (0 < S < 1) is characterized by an inbomogewous distribution of oxygen atoms in the basal (Cul-01) planes. At a microscopic level the sample can be considered as a multi-phase system, the relative weight of coexisting stable and unstable microphases being determined by the value of 6 and the history of the sample. Standard x-ray and neutron diffraction techniques fail in distinguishing co-existing microphases as the typical size of corresponding ordered domains (10-100 lattice constants) is below the detection limit of these techniques. In contrast, the phonon frequencies (in particular of the Raman-active modes involving vibrations of mainly one type of atoms) are sensitive to the local atomic-site coordiiaation which may differ signifienntly for the different microphasea Thus, Raman spectroscopy provides an opportunity to analyse the microphases in RBa,Cu30,-, and their mutual transformations with 6 andlor under different treatments.

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The rotational dynamics of C 60 fullerites has been examined by measuring the Raman-active intramolecular modes at various temperatures. The linewidth of the H g modes increases significantly upon heating from slightly below ͑sc phase͒ to room temperature ͑fcc phase͒, whereas the broadening of the A g line is much weaker. We analyze these results considering the appearance of rotational satellite bands of the H g vibrational lines above T c ϭ256 K. We also discuss small additional contributions that may arise from rotationvibrational interactions in both the fcc and sc phases of the C 60 fullerite. ͓S0163-1829͑99͒00743-2͔FIG. 3. The rotational Raman shift calculated using the data given in Fig. 4 of Ref. 12. PRB 60 13 353 BRIEF REPORTS