Heat capacity and raman scattering in C/sub 70/ crystal

Summary form only given. Successive structural phase transitions in C/sub 70/ crystal were studied by heat capacity and Raman scattering. Single crystals were prepared by the usual evaporation method from C/sub 70/ powder with purity of more than 98% using benzene as solvent. Heat capacity was measured between 4.2 and 375 K by means of the ac calorimetry. We observed two anomalies at 62 K and around 255 K in the heat capacity. The latter is assigned as an orientational ordering transition in the C/sub 70/ molecular rotation along the long axis. Above 255 K the C/sub 70/ molecules in crystal can rotate freely and rapidly along the long axis. The jumping motion occurs between the symmetry equivalent orientations below 255 K when the temperature is lowered. The 62-K anomaly probably comes from the freezing of the jumping motion. Raman spectra of C/sub 70/ crystal were measured in the temperature region 18-340 K. When compared with C/sub 60/ crystal, many Raman lines were observed. Two weak peaks at 1090 and 1435 cm/sup -1/ appear below about 150 K, but no anomaly at this temperature was found in the heat capacity.