Substructures and their application in crystal structure analysis

This paper presents various substructure definitions which are used mainly for crystal chemical discussions and for crystal structure analysis purposes. It is directed to the fact that a distinction has to be made between how the sub~tructures should occur in nature, and those substructures which are specified for crystal structure determinations and accomodated to the set of measured structure factors employed in analyzing the structure. For the first case the ideal substructure or, if the substructure is disturbed, the idealizedsubstructures are defined. The substructure definitions according to Buerger (1959) and Takeuchi (1972) specified for the second case are discussed. The underlying principles for the structure determination are pointed out, if a substructure is used.