The orientation and morphology of platinum precipitates in sapphire

The orientation relationship, crystallography and structure of heterointerfaces influence their energy, and collectively these interface properties can exert a profound effect on a wide range of multiphase-material properties. In this study, stable interfaces were identified and relative interfacial energies were determined in a model oxide-metal system from measurements of the shapes of Pt inclusions in a sapphire matrix. Platinum precipitates were formed in sapphire via ion implantation followed by thermal annealing in air. The morphology of precipitates with a high-symmetry orientation relationship was determined after annealing at 1600 °C for 100 h, processing conditions anticipated to result in equilibrium morphology if shape changes are only diffusion limited. The precipitates were found to have both faceted and rough interfaces. The facets coincided with low-index planes of sapphire. All sapphire facets that appear in the Wulff shape of undoped sapphire at 1600 °C were observed, but additional facets also appeared. Lack of complete convergence on an equilibrium shape is believed to be due to the absence of ledge-producing defects in some particles, and the inability to overcome the nucleation energy barriers required to form ledges.