ABSTRACT
Each phase will be characterized by the separation between the ordered planar boundaries. If planar boundaries are introduced into a crystal in an ordered way a new and longer unit cell will result. Instead of using defects confined to one or a few atom sites, some systems utilize planar faults or defects to change the composition. A planar fault in a crystal is created by schematically cutting the crystal into two and rejoining the pieces. The chapter provides a brief overview of some of the more important of Point defects and planar defects and the compounds that they are particularly associated with. In systems which contain point defect clusters isolated point defects have been replaced by aggregates of point defects with a well-defined structure. The chapter explains instances of considerable structural complexity occurring within fairly narrow stoichiometry ranges, in which, for the systems involved, any non-stoichiometric composition can be accommodated by an ordered structure.
