Application of the static concentration waves theory to structural transitions in some oxides

This paper reviews some possibilities for predicting the possible structure s and solid state transitions for some oxides. It is well known that some s ystems (metal, oxygen) exist in many different stable phases while some oth ers present only a few phases and, finally, others have only one possible o xide. The vanadium-oxygen system is a very good example of the first possib ility (more than 15 phases VxOy are to be found in the Literature) while th e iron-oxygen system belongs to the second category; finally, only one stab le oxide, NiO, is to be found in the nickel-oxygen system. Predicting the s table (or metastable) structures, may help us to understand the transitions between different polymorphs of one composition or, also, the relations be tween the different oxides as reduction occurs. We will start by a review o f some recent results on two polymorphs of vanadium dioxide VO2 where the e xperimental evidence is well explained, using the Static Concentration Wave s (SCW) theory. We will then, as an other example, employ this theory to de duce the known structures of iron oxides (FeO, Fe3O4 and Fe2O3 polymorphs a lpha, beta, gamma). (C) 1999 Elsevier Science B.V. All rights reserved.