Crystal structure of C 60 following compression under 31.1 GPa in diamond anvil cell at room temperature J.H. Rhee, D. Singh, Y. Li, S.C. Sharma * Department of Physics, The University of Texas at Arlington, Box 19059, Arlington, TX 76019, USA Received 4 April 2003; accepted 8 May 2003 by A.H. MacDonald Abstract We have conducted X-ray diffraction experiments in order to examine modifications in the crystal structure of C 60 following compression under 31.1 GPa in a diamond anvil cell at room temperature. The material under ambient and 31.1 GPa is further characterized by laser Raman spectroscopy. The high pressure phase is identified as a mixture of body-centered orthorhombic ðImmmÞ; rhombohedral ðR  3mÞ; and an unidentified phase. q 2003 Elsevier Ltd. All rights reserved. PACS: 61.48.+c; 61.10.-i; 61.50.Ks Keywords: A. Fullerene; C. X.-ray diffraction; E. Raman Spectroscopy 1. Introduction The electronic and structural properties of fullerenes and carbon Nanotubes continue to be of significant interest. The electronic and vibrational properties of these materials under high pressure have been studied in some detail [1–3]. However, there are issues, related to the crystal structure of the high-pressure phases that need further investigation. The pressure – temperature (P – T) phase diagram of C 60 has been studied using quenched samples that are prepared by high- pressure high-temperature (HPHT) treatments and sub- sequently compressed under high pressures [3]. Since, the eventual structure of the material may depend on the synthesis route employed; it is of interest to investigate effects of pressure on samples synthesized by techniques that do not rely solely on the HPHT treatment. In the present work, we have compressed C 60 under 31.1 GPa in a diamond anvil cell at room temperature and studied its crystal structure and vibrational properties by using X-ray diffraction (XRD) and laser Raman spec- troscopy. Using high resolution Raman spectroscopy, we observe that the vibrational properties of the material under 31.1 GPa in a diamond anvil cell at room temperature are almost identical to the vibrational properties of the material recovered upon release of the pressure. This facilitates characterization of the crystal structure of the high pressure phase of the material without facing practical difficulties in conducting XRD measurements on a sample compressed in a diamond anvil cell. We identify the high-pressure (31.1 GPa) structure of C 60 by conducting X-ray diffraction measurements with a 300 mm diameter collimated X-ray beam incident on the recovered sample. 2. Experimental details C 60 powder of 99.9% purity and containing 1–10 mm particles was used in this work. The X-ray diffraction data were obtained by using a two-dimensional X-ray Diffract- ometer system with a 300 mm diameter collimated X-ray beam of wavelength ¼ 0.22897 nm from a Cr target and a cylindrical imaging plate. In transmission mode, complete Debye Sherrer rings were recorded, which were integrated to produce the conventional intensity vs 2u plots and structural details of the material by using standard data analysis software [4]. High resolution Raman spectra were measured by using 1.25 m, f/11 monochromator, 1200 and 0038-1098/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0038-1098(03)00430-7 Solid State Communications 127 (2003) 295–297 www.elsevier.com/locate/ssc * Corresponding author. Tel.: þ81-727-224-70; fax: þ 81-727- 236-37. E-mail address: sharma@uta.edu (S.C. Sharma).