Growth of BaxSr1-xSO4 nano-steps on barite (001) face

Abstract

Crystal growth has been promoted in the fluid cell of an Atomic Force Microscope (AFM) by passing Ba–Sr–SO4 aqueous solutions over barite (001) cleavage surfaces. Steps advance in structural continuity with the original barite (001) surfaces and two-dimensional nucleation occurs preferentially on the newly-formed terraces. The terraces are, on average, 7.5% lower than pure barite terraces. Since the ionic radius of Sr2+ is smaller that the ionic radius of Ba2+, the reduction of terrace height is consistent with an extensive incorporation of Sr2+ into the barite structure. Therefore, it can be considered that the newly-formed terraces have compositions corresponding to terms of the BaxSr1xSO4 solid solution. A non-linear dependence of step rate on [SrSO4] concentration in the solution (and therefore on supersaturation) has been found. The growth behaviour has been discussed by considering both the physicochemical properties of the BaxSr1xSO4 solid solution–aqueous solution (SS–AS) system and a kinetic-based step growth model.