Physical and mechanical properties of C₆₀ under high pressures and high temperatures

Abstract

The physical and mechanical properties of a C₆₀ fullerene sample have been investigated under high pressure–high temperature conditions using a designer Diamond Anvil Cell. Electrical resistance measurements show evidence of C₆₀ cage collapse at 20 GPa, which leads to the formation of an insulating phase at higher pressure. Energy dispersive X-ray diffraction (EDXD) data indicated that the characteristic fcc reflections gradually decrease in intensity and eventually disappear above 28 GPa. A C₆₀ sample was laser-heated at a pressure of 35 GPa to a temperature of 1910±100 K and, subsequently, decompressed to ambient conditions. The photoluminescence spectra and the Raman spectrum of the pressure–temperature-treated sample were measured at a low temperature of 80 K. Raman peak at 1322.3 cm⁻¹ with full-width half-maximum of 2.9 cm⁻¹ was observed from the sample, which is attributed to the hexagonal diamond phase in the sample. The room temperature photoluminescence spectra showed a symmetric emission band centered in the red spectral range with a peak at 690 nm. The structural analysis of the pressure–temperature-processed C₆₀ sample using EDXD method showed strong internal structure orientation and a phase close to hexagonal diamond. Mechanical properties such as hardness and Young’s modulus were measured by nanoindentation technique and the values were found to be 90±7 and 1215±50 GPa, respectively and these values are characteristic of sp³-bonded carbon materials.

Keywords:

• High pressures
• High temperatures
• Super-hard materials
• Fullerenes

Acknowledgements

The authors acknowledge support from the National Science Foundation (NSF)—Division of Materials Research (DMR) under Grant No. DMR-0203779. Robert Hamner acknowledges support from the NASA-Alabama Space Grant Consortium Research Experiences for Undergraduates (REU) site at UAB under DMR-0243640. We would also like to thank Dr. Samuel T. Weir of Lawrence Livermore National Laboratory for research collaboration in the fabrication of designer DAC.