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

This paper reviews some possibilities for predicting the possible structures and solid state transitions for some oxides. It is well known that some systems (metal, oxygen) exist in many different stable phases while some others present only a few phases and, finally, others have only one possible oxide. The vanadium–oxygen system is a very good example of the first possibility (more than 15 phases V x O y are to be found in the literature) while the iron–oxygen system belongs to the second category; finally, only one stable oxide, NiO, is to be found in the nickel–oxygen system. Predicting the stable (or metastable) structures, may help us to understand the transitions between different polymorphs of one composition or, also, the relations between the different oxides as reduction occurs. We will start by a review of some recent results on two polymorphs of vanadium dioxide VO 2 where the experimental evidence is well explained, using the Static Concentration Waves (SCW) theory. We will then, as an other example, employ this theory to deduce the known structures of iron oxides (FeO, Fe 3O 4 and Fe 2O 3 polymorphs α, β, γ).