Ana Smontara

Structural (XRD and HRTEM) investigations of fullerite C60 and C70 samples

Abstract Since the carbon states on the basis of C 60 and C 70 exhibit very interesting physical properties such as hardness exceeding diamond, we focused our investigations on the comparison of structures of the C 60 and C 70 hard phases synthesized at high pressure and high temperatures. X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM) investigations have revealed that two states (amorphous and nanocrystalline) co-exist in samples of both kinds of fullerites. The difference between the diffraction patterns of C 60 and C 70 has been ascribed mainly to the grade of disorder. The XRD and HRTEM results have been correlated with the transport properties (electrical and thermal conductivity) of the samples.

Transport properties of fullerite samples

We have studied the transport properties of hard C 60 and hard C 70 fullerites. The samples from pristine C 60 and C 70 powder were synthesised at high pressure and high temperatures. Their electrical resistivity at room temperature is 35μ Qm and 85 μΩm, respectively, and is weakly dependent on temperature. X-ray diffraction show lack of the long range crystalline order. The room temperature value of the thermal conductivity is 2Wm -1 K -1 for both samples. Thermal conductivity of hard C 70 fullerite increases with temperature and becomes almost temperature independent in the temperature range 10 K-30 K. Contrary, thermal conductivity of hard C 60 fullerite increases with temperature in whole investigated temperature range, which is a consequence of the competing influences of the higher conductivity of crystalline regions and of the thermal resistance which arises at the junctions between amorphous and crystalline regions.