The pressure dependence of the structure of solid C70at ambient temperature has been measured to 25 GPa by energy-dispersive X-ray diffraction. The face-centred cubic structure transforms irreversibly to a rhombohedral phase at 0.35 GPa. Crystalline C70is stable to 18 GPa when a phase change to amorphous carbon occurs. C70has a slightly smaller compressibility than C60- The temperature dependence of the structure at ambient pressure has also been investigated by neutron diffraction. A transition to a rhombohedral phase occurs near 280 K with the f.c.c. structure coexisting at least to 200 K. The crystallographic symmetry of the lowest-temperature phase appears to be lower than rhombohedral. On warming, the rhombohedral phase is stable to 350 K. Strong static and dynamic disorder dominates the crystal chemistry of solid C70.
ASJC Scopus subject areas
- Physics and Astronomy(all)