|Crystal structures which are periodically
ordered in 3 dimensions are ordered structures (regular crystalline solids).
Statically-statistically disordered structures show periodic ordering
in dimensions less than 3, i.e. in 2, 1, or 0 dimensions. This phenomenon
is also called stacking disorder of structurally invariant Periodic Building
In this sense we exclude chemical disorder, e.g. different cation on a particular site, and dynamic disorder, e.g. rotational disorder of template molecules. We also exclude structural disorder within cavities of zeolite frameworks.
Consequently, disordered structures are built from periodic 0-, 1-, or 2-dimensional PerBU’s, which are built from smaller units composed of a limited number of T-atoms by applying simple operation(s) to the smaller unit, e.g. translation, rotation.
The relative orientation of neighboring PerBU’s can be described by stacking modes between the parallel aligned PerBU’s . The stacking mode contains the symmetry elements which relates The PerBU’s to each other including lateral translation components given in fraction of the basis vectors of the invariant PerBU.
Crystal structures built from PerBU’s are called end-member structures if periodic ordering is achieved in all three dimensions. Disordered structures are those where the stacking sequence of the PerBU deviates from periodic ordering up to statistic stacking sequences. All structures built from the same PerBU, ordered end-member structures and disordered intermediates belong to the same family of structure types.
|The disorder families are described using the following types of illustrations.|
skeletal drawing of the PerBU
- top and side views
drawing of the possible stacking modes for
|drawing of the intermediate structure (when feasible) and of the simplest end members, showing the stacking sequence of the PerBU|
|In some cases, a table of the stacking sequence mode and space group of each end member is given.|