Abstract

Condensed models of crystal structures based on the stacking of equal square-type layers corresponding to the three possible symmetries (plane groups p4m, p4g and p4) are studied in a general way for the regular stacking modes. The minimum set of standard sheets required to represent any structure based on each layer symmetry is derived by considering transparent sheets, either square or standard rectangular in shape. In the latter case four sheets are necessary for p4m and p4g patterns, and eight sheets for p4 patterns. An example of a p4g layer occurring in the CuAl2 and TISe structures is presented.