PHOTO- AND PRESSURE-INDUCED TRANSFORMATIONS IN THE LINEAR ORTHORHOMBIC POLYMER OF C₆₀
Meletov K.P., Davydov V.A., Arvanitidis J., Christofilos D., Andrikopoulos K.S., Kourouklis A.

Received: April 17, 2008

PACS: 61.48.-c, 62.50.-p, 64.70.K-, 78.30.Na, 78.55.Kz

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Stability of the linear orthorhombic polymer of C₆₀ under pressure and laser irradiation is studied by Raman scattering and X-ray diffraction measurements. The Raman spectrum at ambient pressure remains unchanged, in the time scale of the experiment, up to the intensity 3200 W/cm² of the 514.5 nm line of an Ar⁺ laser, but irreversible changes are observed at higher intensities. The Raman spectra recorded at increased pressure show similar irreversible changes even at the laser intensity as low as 470 W/cm². The X-ray diffraction and Raman measurements of the pressure-treated samples, performed after pressure release, show that the nonirradiated material does not exhibit any changes in the crystal structure and phonon spectra. This behavior indicates a pressure-enhanced photo-induced transformation to a new polymeric phase characterized by a Raman spectrum that differs from those of the other known polymeric phases of C₆₀. The Raman spectra of the photo-transformed linear orthorhombic polymer of C₆₀ were measured at the pressure up to 29 GPa. The pressure dependence of the Raman mode frequencies show singularities near 4 GPa and 15 GPa, respectively related to a reversible phase transition and an irreversible transformation to a metastable disordered phase. The diffuse Raman spectrum of the disordered phase does not exhibit essential changes with an increase in pressure up to 29 GPa. The high-pressure phase transforms to a mixture of pristine and dimerized C₆₀, after pressure release and exposure to ambient conditions for 30 hours.