Session S15 - Materials Theory and Simulation V.
FOCUS session, Wednesday afternoon, March 14
Room 211, Washington State Convention Center
We studied the structure and stability of solid CO^2 at pressures up to 110 GPa and temperatures up to 3000 K focussing on potential nonmolecular phases. Such phases display remarkable optical, electronic and elastic properties [1]. We used in situ high-P Raman spectroscopy and x-ray diffraction as structural probes. The high temperature experiments were performed by CO^2-laser heating. At pressures above 42 GPa and temperatures below 2000 K we generated a novel, monoclinic phase of CO^2 which appears, like CO^2-V [1], to be nonmolecular. There is, however, some indication that this phase is a 2-d network structure rather than a 3-d one like CO^2-V. We further show that CO^2 in the solid state breaks down to oxygen and diamond along a negative P-T reaction boundary crossing 2000 K around 60 GPa. The phase relations in the C-O system at high pressures appear to be similar to the C-S [2] rather than the Si-O system, although expanded to much larger scales both in P and T. Supported by NSF DMR-9972750