High-pressure study of the behavior of mineral barite by x-ray diffraction

In this paper, we report the angle-dispersive x-ray diffraction data of barite, BaSO(4), measured in a diamond-anvil cell up to a pressure of 48 GPa, using three different fluid pressure-transmitting media (methanol-ethanol mixture, silicone oil, and He). Our results show that BaSO(4) exhibits a phase transition at pressures that range from 15 to 27 GPa, depending on the pressure media used. This indicates that nonhydrostatic stresses have a crucial role in the high-pressure behavior of this compound. The new high-pressure (HP) phase has been solved and refined from powder data, having an orthorhombic P2(1)2(1)2(1) structure. The pressure dependence of the structural parameters of both room- and HP phases of BaSO(4) is also discussed in light of our theoretical first-principles total-energy calculations. Finally, a comparison between the different equations of state obtained in our experiments is reported.