Directed assembly of controlled-misorientation bicrystals.

Grain boundaries play a vital role in determining materials behaviour, and the nature of these intercrystalline interfaces is dictated by chemical composition, processing history, and geometry (misorientation and inclination). The interrelation among these variables and material properties may be systematically studied in bicrystals. Conventional bicrystal fabrication offers control over these variables, but its ability to mimic grain boundaries in polycrystalline materials is ambiguous. Here we describe a novel solid-state process for rapidly generating intercrystalline interfaces with controlled geometry and chemistry, applicable to a broad range of materials. A fine-grained polycrystalline layer, contacted by two appropriately misoriented single-crystal seeds, is consumed by an epitaxial solid-state transformation until the directed growth fronts impinge. The seed misorientations establish the geometry of the resulting intercrystalline boundaries, and the composition of the sacrificial polycrystalline layer establishes the chemistry of the boundaries and their adjacent grains. Results from a challenging model system, titanium-doped sapphire, illustrate the viability of the directed assembly technique for preparing high-quality bicrystals in both twist and tilt configurations.