Synchrotron Infrared and X-ray Diffraction Studies of Gypsum at High Pressure

Liu, Zhenxian¹, Hexiong Yang², Ho-kwang Mao¹, and Russel J.Hemley¹

¹Geophysical Laboratory, CIW

²Florida International University

zxliu@bnl.gov

NSLS-U2 (DAC) and NSLS-X17C (DAC)

We have performed high-pressure far-infrared (IR) and x-ray diffraction studies on gypsum (CaSiO₄∙H₂O) up to 25 GPa at U2A and X17C beamlines, National Synchrotron Light source. High-pressure IR spectra show that frequencies of all IR active lattice modes bellow 400 cm^-1 increase with pressure except the H₂O translational lattice mode. A phase transition starts from 5 GPa and completes about 6 GPa based on the peak splits and discontinuity of frequencies. X-ray diffraction confirmed this phase transition based on the different diffraction patterns. Moreover, a second phase transition follows up immediately after the first phase transition. This transformation is attributed to the impact of both pressure and synchrotron diffraction. The structure of the high pressure phase has P3₁21 space group with chemical formula CaSiO₄∙0.8H₂O and is quenchable.