Thermal and acoustic transport properties of hard carbon formed from C60 fullerene

We have measured the acoustic and thermal transport properties of hard carbon formed from C-60 fullerene over a wide temperature and frequency ranges. The thermal conductivity monotonously increases with temperature, without a pronounced saturation around 5-10 K, and with a linear temperature variation at higher temperatures, which can be related to the linear temperature variation of the sound velocity in the same temperature range. The ultrasonic attenuation increases with frequency with a clear change of slope around 30MHz. This is attributed to resonant scattering from strong acoustic fluctuations of domain size of about 70 mum, and is probably the origin of the boundary scattering regime in the thermal conductivity. (C) 2002 Elsevier Science B.V. All rights reserved.