In situ electrical conductivity and Raman study of C60 tetragonal polymer at high pressures up to 30 GPa

Theory predicts that tetragonal polymeric C-60 will undergo a phase transition into a metallic phase at pressures around 20 GPa. Raman and structural experiments at high pressures confirmed formation of a new phase above 20 GPa although the question about its electrical properties was still open. We report on the first simultaneous in situ study of vibrational and electrical properties of two-dimensional (2D) tetragonal C-60 polymer at pressures up to 30 GPa in a diamond anvil cell (DAC) specially designed for this purpose. Our results reveal an anomaly in Raman spectra and a drop in electrical resistance of the sample at 20-25 GPa. We tentatively associate this anomalous behaviour with a phase transition into the conductive phase although its metallic character is yet to be proven. At high pressures the Raman spectra exhibit a high degree of disorder. Upon pressure release the order was partially restored and, more importantly, a significant amount of the initial 2D polymeric phase was recovered. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim