basalplane

The basal plane is a term used in crystallography to describe the plane perpendicular to the c-axis in hexagonal and related crystal systems. It is the plane that contains the a-axes, and in conventional hexagonal indexing it corresponds to the (0001) plane (with the opposite face denoted (0001) or (000-1) in some conventions). The basal plane is spanned by the two in-plane lattice vectors, a1 and a2, which meet at 120 degrees and define the crystal’s in-plane symmetry.

In hexagonal crystals, the c parameter describes height along the c-axis, while the parameter a describes in-plane spacing within the basal plane. The arrangement of atoms within the basal plane determines many surface and growth properties of the material. The distance between equivalent basal planes is related to the c lattice parameter, and the basal plane often serves as a reference for orientation in crystal anatomy and diffraction studies.

Basal planes are prominent in several materials. For example, graphite consists of layers of carbon atoms arranged in graphene sheets that lie within basal planes; these sheets are stacked along the c axis with van der Waals gaps between them. Other materials with a hexagonal structure—such as hexagonal boron nitride and wurtzite-structured compounds like ZnO and SiC—also feature well-defined basal planes that influence their mechanical, electronic, and optical properties.

In deformation and crystal plasticity, basal planes are important because they often serve as easy slip planes in hexagonal close-packed (hcp) metals. The primary slip system for many such metals is {0001}<11-20>, reflecting the high atomic density and favorable slip directions within the basal plane.