Pressure induced dimerisation of C70

Abstract

Solid CT0 has been subjected simultaneously to high pressures and temperatures (HPHT), with pressures upto 7.5 GPa and temperatures upto 750°C. X-ray diffraction measurements on the recovered samples indicate that the initial h.c.p. solid C70 transforms to a rhombohedral structure which recovers to an f.c.c. structure on annealing. The associated changes in the intra molecular vibrational modes have been probed through infrared (IR) and Raman measurements. The 1R measurements on these HPHT samples show splitting of some of the pristine modes and occurrence of several new modes. These sharp IR modes in the HPHT treated samples, which are seen to be different from that reported for photopolymerised C70, have been attributed to the formation of C70 dimers. 0 1997 Published by

Buckyballs under Pressure

“…Iwasa et al [45] observed a polymerized phase by both solubility studies, X-ray diffraction, and IR/UV/visible spectroscopy after treating either hcp or fcc C 70 for 1 h at 5 GPa at temperatures up to 800 C. As for C 60 , IR spectroscopy showed many new modes and the observed frequencies agreed well with the results of theoretical calculations for dimers. On heating at zero pressure these dimers reverted to pristine C 70 at 300 o C. The final structure after depolymerization was always fcc, irrespectively of the initial lattice structure, indicating that this is the most stable phase of C 70 at 300 o C. Similar results were found by Premila et al [46], using pressures up to 7.5 GPa at temperatures up to 750 K. They identify the structure of the new polymer as rhombohedral, probably consisting of an array of C 70 dimers. Finally, Blank and co-workers [47] carried out studies over a very wide range of pressure and temperature, 4-12.5 GPa and up to 1770 K. In this range they observed three different phases, a rhombohedral phase produced at ''low" temperatures, below 1000 K at 4 GPa or 700 K at 12.5 GPa, a tetragonal, very hard, three-dimensionally polymerized phase at high temperatures above 10 GPa, and a disordered, semi-graphitized, layered structure at very high temperatures at all pressures.…”

“…More recently, however, high-pressure-high temperature polymerization has indeed been observed [45][46][47]. Iwasa et al [45] observed a polymerized phase by both solubility studies, X-ray diffraction, and IR/UV/visible spectroscopy after treating either hcp or fcc C 70 for 1 h at 5 GPa at temperatures up to 800 C. As for C 60 , IR spectroscopy showed many new modes and the observed frequencies agreed well with the results of theoretical calculations for dimers.…”

A new fullerene network phase obtained from C70 at high-pressure and high-temperature

“…The extremely rich behavior of C 60 ‐based network phases just described, suggests the extension of such studies to other fullerenes and in particular to C 70 . However, initial studies have only produced disordered structures and the enthusiasm on C 70 fullerene networks had quickly dropped . The apparent inability of C 70 molecules to form ordered network structures under high pressure, in opposite to C 60 , seemed a natural consequence of their low reactivity and also of constraints on intermolecular bonding imposed by the uniaxial alignment of the low‐symmetric molecules in the solid.…”

Pressure Behaviour of Single Wall Carbon Nanotube Bundles and Fullerenes: A Raman Study

“…It was shown that the position and the shape of the radial breathing mode (%170 cm ± ±1 ) of SWNT depends on the exciting laser energy which can be explained in terms of a diameter-selective Raman scattering mechanism. We have earlier used Raman spectroscopy to explore the pressure and temperature induced orientational phase transitions in solid C 60 and solid C 70 [10,11], pressure induced amorphisation of solid C 70 [12] and pressure-temperature induced polymeric phases [13,14] of C 60 and C 70 . The main focus of this paper is to discuss our recent results on pressure effects on SWNT bundles probed using Raman spectroscopy upto a maximum pressure of 25.9 GPa in a diamond anvil cell [15].…”