Pressure-induced phase transitions in gypsum |
| |
| Authors: | Eugene Huang Ji-An Xu Jung-Fu Lin Jing-Zhu Hu |
| |
| Affiliation: | 1. Institute of Earth Sciences, Academia Sinica , P.O. Box 1-55, Nankang, ROC, Taipei;2. Dept. Geophysical Sciences , University of Chicago , Chicago, IL, 60637, USA;3. Geophysical Laboratory , Carnegie Institute of Washington , Washington, D.C., 20015, USA |
| |
| Abstract: | Abstract We report high-pressure Raman scattering spectroscopy and energy dispersive X-ray diffraction investigations on gypsum, CaSO4 · 2H2O, at room temperature in a diamond cell. With increasing pressure, measurements indicate that CaSO4 · 2H2O undergoes two stages of crystalline-state phase transitions at 5 and 9 GPa, and then converts to a disordered phase above 11 GPa. The structures of the three high-pressure phases of gypsum have not been determined yet. These phases are tentatively named as “post-gypsum-I” (PG-I), “post-gypsum-II” (PG-II) and “disordered” according to the sequence of their appearance with pressure. Gypsum shows anisotropic compressibility along three crystallographic axes with b > c > a below 5 GPa. The difference in the behavior of the two OH stretching modes in gypsum is attributed to the different reduction rate in the hydrogen bonding distances by the anisotropic axial compressibility. |
| |
| Keywords: | Gypsum disordered OH stretching modes anisotropic compressibility |
|
|
