Pressure-induced structural transformation of CaC2

The high pressure structural changes of calcium carbide CaC2 have been investigated with Raman spectroscopy and synchrotron X-ray diffraction (XRD) techniques in a diamond anvil cell at room temperature. At ambient conditions, two forms of CaC2 co-exist. Above 4.9 GPa, monoclinic CaC2-.. diminished indicating the structural phase transition from CaC2-pi to CaC2-.. At about 7.0 GPa, both XRD patterns and Raman spectra confirmed that CaC2-. transforms into a metallic Cmcm structure which contains polymeric carbon chains. Along with the phase transition, the isolated C-2 dumbbells are polymerized into zigzag chains resulting in a large volume collapse with 22.4%. Above 30.0 GPa, the XRD patterns of CaC2 become featureless and remain featureless upon decompression, suggesting an irreversible amorphization of CaC2. Published by AIP Publishing.