interplanar

Interplanar is an adjective used to describe relationships, measurements, or structures that occur between planes. It is widely applied in physics, chemistry, and geometry to distinguish what lies between two or more planes from what exists within a single plane (intraplanar).

In crystallography, interplanar spacing, denoted d, is the perpendicular distance between two parallel crystallographic planes. Planes are described by Miller indices (hkl), and each set of planes has a characteristic d-value that influences how the crystal diffracts radiation. Bragg's law, nλ = 2d sin θ, relates d to the angle of diffraction and the radiation wavelength, allowing determination of lattice parameters and crystal structure.

In geometry and materials science, the concept extends to angles between planes (dihedral angles) and to properties that depend on the separation of planes, such as layer spacing in graphite or the spacing in layered compounds. Interplanar measurements are essential for characterizing crystalline quality, strain, and phase identification using diffraction techniques.

Usage is technical and contextual; the term is almost exclusively encountered in scientific literature and discussions of crystalline structures, diffraction, and geometric relations between planes.