Order-Disorder Transition and Disordered Structures

Abstract

This chapter consists of two parts. The first part treats applications of Landau’s theory of symmetry and phase transitions as discussed in Chap. VII to a variety of order-disorder processes that have been mentioned in earlier chapters, namely: CsCl-type to bcc-type, CdCl₂-type to NaCl-type, incommensurate ordering in Sc_1-xS, and CdI₂-type to NiAs-type. The second part is a discussion of a few known ordered defect structures which provide examples of interesting solid- state ordering phenomena that are at this time not well understood. These structures include Ti_1-xO_1-x, Lu₃S₄, and the defect titanium and chromium sulfides and WO₂.₄₁. There are many other cases of ordered defect structures, however, these examples are sufficient to convey the point that there are some rather complicated structural effects accompanying the ordering of vacancies in transition metal compounds.