Raman spectroscopy at simultaneous pressure and temperature: Phase relations and lattice dynamics of CaCo sub 3
- Pacific Northwest Lab., Richland, WA (United States)
- Washington Univ., Seattle, WA (United States). Mineral Physics Group
Raman spectra of oriented single crystals of calcite were measured at simultaneous high pressures and temperatures up to 40 kbar and 350{degrees}C. The fluorescence frequency shift of Sm:YAG was utilized for accurate pressure determination at elevated temperature, which exhibits negligible temperature shift in this temperature range. With increasing pressure the calcite-CaCO{sub 3}(II) and CaCO{sub 3}(II)-CaCO{sub 3}(III) transformations are observed at 14.5 and 18.5 kbar, respectively, and CaCO{sub 3}(III) remains the stable phase beyond 40 kbar. At elevated temperature and pressure, the width of the CaCO{sub 3}(II) stability field decreases and, at temperatures greater than 200{degrees}C, CaCO{sub 3}(III) transforms to aragonite. The CaCO{sub 3}(III)-aragonite phase boundary is insensitive to pressure over the 20 to 40 kbar interval. Calcite-CaCO{sub 3}(II) phase transition is first order and reversible, the CaCO{sub 3}(II)-CaCO{sub 3}(III) transition exhibits kinetic irreversibility, and the CaCo{sub 3}(III)-aragonite transition is sluggish and irreversible. Lattice dynamical calculations along T to F direction in calcite indicate an unstable phonon mode. The atomic displacements associated with this mode are consistent with those required for a continuous, displacive calcite-CaCO{sub 3}(II) phase transition. 29 refs., 3 figs.
- Research Organization:
- Pacific Northwest Lab., Richland, WA (United States)
- Sponsoring Organization:
- DOE; USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 6186582
- Report Number(s):
- PNL-SA-19964; CONF-9110228--3; ON: DE92002246
- Country of Publication:
- United States
- Language:
- English
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