High-pressure Raman and X-ray studies of barite, BaSO₄

Abstract

High-pressure Raman spectroscopic and X-ray diffraction experiments of barite, BaSO₄, were carried out in a diamond anvil cell up to 25 GPa at room temperature. On the basis of the changes in the diffraction patterns and the variation of lattice parameters with pressure, it is inferred that barite undergoes a phase transformation at 10 GPa. The phase transition accompanies the change in the force constant of vibrational modes in barite. Further compression beyond the phase transition causes the distortion of SO₄ tetrahedron as indicated by the splitting in the SO₄ stretching modes. Both X-ray and Raman data support that the phase transition in BaSO₄ is reversible. The compression data yield a bulk modulus of 63 ± 2 GPa for barite. Barite shows anisotropic compressibility along three crystallographic axes with c being the most compressible axis.

Keywords:

• Barite
• High pressure
• Phase transformation

We wish to thank S. Shieh for his help during the experiments at the Brookhaven National Laboratory. The assistance of staff in X17C beam line is also appreciated. This project was supported by the National Science Council (NSC-87-2116-M-006-012) and the Synchrotron Radiation Research Center, Taiwan.