Practical Electron Microscopy and Database

In general, composite structures are essentially combinations of two or more structures. The incommensurate composite crystals are formed by two or more interpenetrating periodic structures (also called subsystems). The basic structures of these subsystems are mutually incommensurate. The interactions between the subsystems affect the periodicity of these subsystems, which make all subsystems modulated. The incommensurate composite structures therefore can be considered as the intergrowth of two or more incommensurately modulated structures.

The incommensurate composite structures consists of misfit layer structures, intergrowth compounds, Vernier structures and chimney-ladder structures [1 - 3]. For instance, the general formula A_1-pCr₂X_4-p (A =ˆ Ba, Sr, Eu, Pb, X = ˆS, Se) [1 - 3] represents an unusual average structure formed by the intergrowth of three different substructures that are mutually incommensurate along one direction.

[1] Hyde, B.G., Andersson, S., 1989. Inorganic Crystal Structures. Wiley, New York.
[2] Yamamoto, A., 1993. Crystallography of quasiperiodic crystals. Acta Cryst. A 52, 509 - 560.
[3] Yamamoto, A., 1996. Determination of composite crystal structures and superspace groups. Acta Cryst. A 49, 831 - 846.