Plesiotwinning: oriented crystal associations based on a large coincidence-site lattice

Abstract

AbstractOriented crystal associations with a low degree of restoration of lattice nodes are discussed and it is shown that they are based on a large coincidence-site lattice (CSL). In this type of associations the oriented crystals are related by symmetry or pseudo-symmetry elements expressed by high indices in the crystal lattice. The relative orientations of the crystals correspond to rotations belonging to non-crystallographic point groups. In spite of the low number of common lattice nodes, these associations are not uncommon, especially in layer compounds. Since this kind of associations does not enter either in the definition of twinning or in that of cell-twinning, we propose to introduce the definition ofplesiotwinning. It is suggested that plesiotwins may form when two or more crystals coalesce or exsolve. A plesiotwin orientation may require a minor adjustment of the relative orientations, whereas a more stable configuration, such as a parallel growth or to a twin, may require a larger, kinetically more hindered rotation.