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Abstract
The aim of this paper is to contribute to a better understanding of the behaviour of mineral barite, BaSO4, at high pressures, particularly the recently reported phase transition at 27 GPa to a new structure type. For this purpose, we will focus on the evolution of its BaS cation array with pressure, which will additionally allow for a rational description of the structure. When the initial Pnma barite structure transforms into the also orthorhombic P212121 structure, no change in the coordination number of Ba or S atoms occurs ([SO4] tetrahedra and [BaO12] dodecahedra). However, the second coordination sphere presents an increase of neighbour atoms and a decrease of the Ba–S distances. This rearrangement of atoms is related to the Buerger's mechanism of the B1–B2 phase transition for the BaS cation array, confirming that cations (second neighbours) do not arrange in an arbitrary way.
Acknowledgements
Financial support from the Spanish Consolider Ingenio 2010 Program (Project No. CDS2007-00045) is acknowledged. The work was also supported by Spanish MICCIN under Project No. CTQ2009-14596-C02-01 as well as from Comunidad de Madrid and European Social Fund: S2009/PPQ-1551 4161893 (QUIMAPRES).