Secondly, polytypism is a form of polymorphism found in layered structures in which low energy alternate stacking configurations can be adopted by the translation of layers with no change to the intra-layer atomic coordination . In inorganic systems, different polytypes may display different functional properties, such as in (bilayer / multi-layer) graphene , or transition metal dichalcogenides . Thirdly, planar disorder refers to translational displacements between consecutive layers in the crystal which may, in principle, encompass a range of displacements, from well-defined to random. As displacements between layers become less random (a scenario defined as 'order-disorder' polytypism by Dornberger-Schiff ), geometric equivalence on a local scale is restored but the crystal's long-range symmetry is still disrupted .