We report on detailed investigations of the thermal and acoustical properties on hard fullerene-based carbons. The novel materials were obtained from pressuretemperature treatment of C60 and C70 and are known for a unique combination of their diamond-like hardness and amorphous carbon-like electrical conductivity. Xray diffraction and high-resolution transmission electron microscopy investigations have revealed that nanocrystalline and amorphous phases co-exist in samples of both kind of hard fullerene-based carbons, i.e. C60 and C70. The materials possess an unusual, linear or close-to-linear temperature dependence of the thermal conductivity above 20 K. Between 0.1 K and 10 K the thermal conductivity of C60 is characterized by a monotonous increase versus temperature (power law T1.4), without a well defined plateau around 5-10 K. Sound velocity decreases linearly from 4 K up to 100 K. Both linear regimes are characteristic of disordered structures, and can be analysed by the phonon-fracton hopping model developed for fractal and amorphous structures. The obtained data are compared with thermal conductivity in diamond, graphite and glassy carbon and are consistent with the structure of a disordered or amorphous-like solid formed by polymerisation and partially transformed fullerene clusters.

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