On the crystallography of precipitation

A general approach for investigating the crystallography of precipitation is developed from a systematic analysis of interfacial structures. The central hypothesis in this approach is that a habit plane or major facet developed in a precipitation reaction is the physical realization of a singular interface. The common characteristics in the structures of any singular interfaces are periodicity and singularity. Similar to the division between small and large angle grain boundaries, the distinction between the 3D primary and 2D secondary preferred state has been specially emphasized for correct descriptions of the interfacial defects. Twelve types of singular interfaces have been classified according to their characteristic features. The relationship between this microstructural description and the macroscopic parameters used to characterize discrete singular interfaces is established in the framework of the model lattices, i.e. the O-lattice/CSL/DSCL. The macroscopic parameters can be identified in reciprocal space according to three Deltag parallelism rules, where Deltag is a difference vector linking correlated reciprocal lattice vectors in the two lattices. These rules can consistently account for the crystallography of precipitation, with either rational or irrational orientation relationship and habit planes, observed in a broad variety of systems. Other major models in the literature have been reviewed and their connections with the present approach have been discussed. (C) 2004 Elsevier Ltd. All rights reserved.