c-axis

In crystallography, a c-axis is a line used to describe the orderly arrangement of atoms within a crystal. It is typically the vertical axis in a crystal's coordinate system. The lengths of these axes, known as lattice constants, and the angles between them determine which of the seven crystal systems a solid belongs to. Atoms within a crystal's unit cell are positioned relative to these crystallographic axes, and planes within the crystal are also described using them. The c-axis, along with other axes like 'a' and 'b', helps define the crystal's structure, such as in the hexagonal system where three equal axes lie in a plane perpendicular to a fourth, different-length c-axis.12