Atomistic simulation of the effects of calcium and strontium defects on the surface structure and stability of BaSO4

Abstract

BaSO₄ (baryte), SrSO₄ (celestine) and CaSO₄ (anhydrite) were studied using atomistic simulation techniques and their equilibrium morphologies determined from the calculated surface energies. Monolayer and bilayer growth of strontium sulfate or calcium sulfate on barium sulfate were modelled and the calculated surface energies used to determine the resulting morphologies. It was found that this overgrowth is energetically unfavourable in all cases. The average energy increase per strontium sulfate added was calculated to be very similar for most faces (0.5–0.6 eV). However, the energy increase per calcium sulfate unit added varied between 0.9 and 1.4 eV. The energies of a layer of SrSO₄ or CaSO₄ segregated in the bulk of the BaSO₄ crystal were also calculated. The structures of the surfaces found to be the most stable were studied in detail ({210} and {001} faces of BaSO₄ and SrSO₄, {001} and {010} faces of CaSO₄). The surface structure of the substrate and overgrowth of both strontium sulfate and calcium sulfate were studied in detail for the {210} and {001} faces of barium sulfate.