bicristal

A bicristal, or bicrystal, is a solid material that consists of two crystalline grains of the same substance joined along a planar grain boundary. The two grains may have different orientations, creating a misorientation at the boundary that influences the material’s properties. Boundaries are often categorized by the misorientation angle and the boundary plane, with common types including low-angle, high-angle, tilt, twist, and mixed boundaries.

Bicrystals are typically produced by taking a single crystal, cutting it along a chosen plane, and rejoining the pieces with a controlled relative orientation. They can also be formed by epitaxial growth on a substrate designed to impose two crystal orientations, often followed by annealing to consolidate the boundary.

The grain boundary in a bicrystal affects several material properties, such as diffusion, mechanical strength, electrical and thermal conductivity, and corrosion resistance. Boundary energy and mobility determine how the boundary reacts to temperature and stress. Some boundaries have lower energy and are more stable, while others may migrate or change with time.

Applications and significance: bicrystals are valuable in fundamental research to study boundary physics and to understand how grain boundaries influence macroscopic behavior. They are used in metals, ceramics, and semiconductors to investigate diffusion across boundaries, dislocation behavior, and transport phenomena. In engineering, concepts from bicrystal studies support grain-boundary engineering aimed at improving material performance.

Examples include copper and silicon bicrystals, with other studied materials such as nickel, SrTiO3, and GaAs. See also: grain boundary, polycrystal, epitaxy.