Internal Friction and Sound Wave Velocities in Pure C₆₀ Fullerite

Abstract

The temperature dependence of the attenuation and sound wave velocity of compacted pure C,, fullerite is measured in the temperature interval from 100 to 300 K at a frequency of about 5 MHz. Two internal friction peaks are observed at 250 and 215 K. The conclusion is made that the internal friction peak at 250 K is connected with the structural phase transition and the peak a t 215 K is due to the relaxation by reorientation of C 6 , molecules in the stress field of ultrasonic waves. The magnitudes of the elastic moduli of C,, fullerite are determined by sound velocity measurements. The results are compared with theoretical estimations of the elastic moduli and experimental data of other authors.

Band-Like Charge Transport in C60 Single Crystals

“…(1). A longitudinal sound velocity of c l % 3 Â 10 5 cm/s has been used [22]. Interestingly not only the value of the mobility exhibits a discontinuity around 255 K due to the phase transition.…”

Integral and Local Elastic Properties of C60 Single Crystals

“…To grow such crystals the modified growth technique from the vapor phase [1] was applied. We used microcrystalline C 60 powders of 99.95% purity.…”

“…Besides the elastic stiffness matrix can serve as a good experimental test of the validity of theories describing the intermolecular interaction in solid C 60 . Although there were some measurements of elastic constants for compacted C 60 specimens [1] and polycrystalline C 60 films [2] and of the Young modulus for small C 60 single crystals [3,4], the full-scale elastic stiffness matrix of solid C 60 was not determined. The present paper is devoted to the experimental evaluation of the elastic stiffness matrix of solid C 60 by acoustic techniques.…”

Experimental Research of Gruneisen Parameter of Fullerite C60 Single Crystal Near Structural Phase Transition at 260 K Using Photoacoustic Technique

“…For illumination of sample the He-Ne laser (1) was used, which radiation (with wavelength of 0.63 microns and power of 25 mW) were modulated on intensity on frequency 32 Hz by the mechanical chopper (2). After splitting by beam splitter (3) part of optical radiation by optical fiber (4) moved to sample fixed on low-temperature photoacoustic cell (6), placed in cryostat with liquid nitrogen (5).…”

“…One of the semiconductor materials of new generation is fullerite C 60 . There are numerous researches of physical properties of this sample, including phase transition at 260 K [1][2][3][4][5]8]. However, in our opinion, anharmonism of crystal lattice of fullerite C 60 is investigated insufficiently.…”