Disordered Polytypes
A good example of disorder in a SiC crystal is shown in this topograph. Extensive streaking along the 314l diffraction row is caused by a disordered layer measuring 180 µm. Diffuse scattering results from a non ordered crystallographic repeat along the c axis.
A defect band can be seen in the central 5270 reflection often indicating the presence of disordered layers. In this case the total crystal thickness is 1200 µm and the model is 6H+1DD+6H+1DD+6H.
Of the sample 78% contain a region of varying disorder.