Hybrid twinning – a cooperative type of oriented crystal association

Abstract

AbstractThe reticular theory of twinning is extended to include the contribution of different, coexisting sublattices that consist of quasi-restored nodes (cooperative sublattices) and are characterized by a specific superposition index. The overall degree of quasi-restoration of the twin lattice is a function of the superposition index of the cooperative sublattices, and is expressed by a new parameter, calledeffective twin index, which is the generalization of the classical twin index. Twins where the effective twin index is lower than the classical twin index are termedhybrid twins. Several twins (e.g. twins of pyrite and of forsterite) that could not so far be explained by the reticular theory because of their too high twin index are interpreted as hybrid twins. The effect of hybrid twins on diffraction patterns is discussed.