Elastic modules of solid C-60: measurement and relationship with nanostructure

Elastic moduli of solid C-60 have been measured in single crystal of primar y fullerite and diverse metastable phases of polymerized acid amorphous C-6 0 synthesized under high-pressure high-temperature (HPHT) conditions within the wide range of pressure p = 5-13 cpa and temperature T = 500-1870 K. Sm all sizes and heterogeneity of HPHT samples admit application of the specif ic microacoustic technique. A focused ultrasonic beam and ultra-short probi ng pulses have been employed to measure sonic velocities and study elastic module within an area of 100-300 mu m in diameter. Ultrasonic measurements have revealed permanent increase of elastic module of HPHT phases when ther e is rise in pressure and temperature. The bulk elastic module K and shear module G are compared with those in diamond for three-dimensional (3D) poly merized C-60 Amorphous C-60 produced at the highest pressure p = 13 GPa and temperature T = 1600-1900 K possesses unique mechanical properties which i ncludes the highest value of the longitudinal sound velocity (c(L) = 26 km/ s) among substances now known and values of the bulk module (K approximate to 700-800 GPa) substantially greater than the bulk elastic module in diamo nd (K approximate to 440 similar to 490 GPa). Essential elastic heterogenei ty of the most HPHT stares has been shown including smooth distribution of elastic properties over a specimen for crystalline polymerized phases. Experimental results as well as model calculations developed on the base of the finding evidence that elastic properties correlate with state of fulle rene molecules, character and number of covalent bonds and nanostructure of the matter. Measuring elastic properties is one of the effective ways to g et information on nanostructure of solid C-60, to classify and identify its diverse phases. (C) 2000 Elsevier Science Ltd. All rights reserved.