Electrical and optical properties of tetragonal polymeric C60 under high pressure

C60 having unique icosahedral truncated structure is known to form polymer or dimer between fullerene cages under high pressure and temperature. In this work the electrical and optical properties of 2-dimensional tetragonal polymeric C60 were studied under high uniaxial pressure, p, to investigate the phase transformation.
The electrical resistance value, R, decreased from 10¹⁰ to 5×10⁵ Ω as a result of pressure cycling (with ramp pressure increase in each cycle) to a maximum pressure of 32 GPa by using a diamond anvil cell (DAC). A substantial drop in R after decompression (~10¹⁰ Ω) was reached in a cycle with a ramp pressure of 22 GPa that we consider as a cross-over/phase transition p. A subsequent p-cycling to 32 GPa resulted in further (20 times!) drop in the R of the recovered sample and exhibited anomalies in R vs p behavior.
The results of Raman measured after decompression showed that the ratio of the 2-dimensional T-phase to 1-dimensional O-phase decreased as increasing the cycling p. Raman-mapping of the recovered material showed Raman spectra inhomogeneities across the sample stemming from a non-hydrostatic pressure distribution in the DAC and the relationship between shear and normal stress.