Phase Separation at the Nanoscale: Structural Properties of BaO Segregates on MgO-Based Nanoparticles

Composite BaO/MgO nanoparticles have been prepared by chemical vapor synthesis and subsequent annealing in controlled gas atmospheres. High resolution transmission electron microscopy and X-ray diffraction reveal that a part of the obtained nanoparticles can be characterized as support particles with hemispherical BaO phases. The structural and energetic properties of BaO units dissolved inside the MgO host and adsorbed on MgO(100) were investigated by density functional theory (DFT) calculations. Moreover, ab initio thermodynamics was used to explore the shape of BaO and MgO particles in a water environment as a function of temperature. The calculations suggest that the spherical shapes of the segregates result from the growth process and become thermodynamically stabilized by surface hydroxylation.