Pressure- and temperature-induced transformations in crystalline polymers of C 60
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TATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS
Pressure and TemperatureInduced Transformations in Crystalline Polymers of C601 K. P. Meletova,* and G. A. Kourouklisb a
Institute of Solid State Physics, Russian Academy of Sciences, Chemogolovka, Moscow Region, 142432 Russia b Physics Division, School of Technology, Aristotle University of Thessaloniki GR54006, Thessaloniki, Greece Email: [email protected] Received June 23, 2011
Abstract—The great advantage of the C60 molecule is its potential for polymerization, due to which the mol ecule can be the building block of new all carbon materials. In addition, it contains, both sp2 and sp3 hybrid ized carbon atoms, which allows synthesizing new carbon materials with desired physicochemical properties using both types of carbon bonding. The one and twodimensional polymeric phases of C60 are prototype materials of this sort. Their properties, especially polymerization under pressure and room temperature via covalent bonding between molecules belonging to adjacent polymeric chains or polymeric layers, can be used for further development of new materials. The present review focuses on the study of the pressureinduced polymerization and thermodynamic stability of these materials and their recovered new phases by insitu highpressure Raman and Xray diffraction studies. The phonon spectra show that the fullerene molecular cage in the highpressure phases is preserved, while these polymers decompose under heat treatment into the initial fullerene C60 monomer. DOI: 10.1134/S1063776112080122
CONTENTS 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706 2. Pressureinduced transformations in the 2DT polymer . . . . . . . . . . . . . . . . . . . . . . . . . 708 3. Transformations of the 2DR polymer at high pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713
4. Pressure and photoinduced transformations in the linear polymer of C60 . . . . . . . . . . . . . . . . . . . .716 5. Thermal stability of fullerene polymers . . . . . . . . . . .719 6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .720 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .721
1. INTRODUCTION
due to the 30 unsaturated double C=C bonds in the molecular cage. Initiators of the polymerization pro cess have been identified as (i) visible light [2], (ii) alkali metal doping [3, 4], and (iii) highpres sure/hightemperature (HPHT) treatment of the pris tine C60 [5–7]. The important alterations in the struc tural features of the polymeric C60 are the decrease in the intermolecular distances and the deformation of the fullerene molecular cage, which results in lowering the symmetry of the parent C60 molecule [2]. The pho topolymerized C60 material mainly contains dimers on the surface of the samples due to the small penetration depth of the visible light; the material becomes insolu ble in commonly used solvents, but reverts to the initial monomer under heating for a short period of time a
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