Comparative NMR study of new carbon forms Original Research Article

A comparative 13C-NMR study of several new phases of pressure/temperature-treated C60, a bundle of carbon nanotubes, graphite and diamond was carried out in the 4–300 K temperature range. It was found that face-centered cubic and rhombohedral high-pressure phases of C60 reveal very unusual NMR lines at 110 and 70 ppm, respectively, shifted from that of pristine C60 (143 ppm). These lines disappear in a hard carbon phase prepared by compression of C60 at more severe conditions. Comparison with NMR spectra of pristine C60, diamond and graphite showed that the fullerenes acquire some partial sp3 character when they are pressure-treated at 3–4.6 GPa and various temperatures (720 °C). However they are apparently not transformed into four-fold-coordinated diamond-like carbon clusters. NMR spectra of carbon nanotubes exhibited an anomalous shift which may be attributed to their cylindrical geometry.