Degenerate (identity) chemical reactions in ferro­elastic crystals

The presence of degenerate chemical reactions in crystals is discussed. They take place in some order–disorder phase transitions in crystals. The other category of identity (degenerate) chemical reactions in crystals includes a few examples of domain reorientations with simultaneous hopping of atoms/ions in some ferroelastic crystals. The product of the hopping maybe either identical with the reactant though in a different orientation or a conjugated enantiomorph. In these examples, the hopping atom is either situated in a special position or disordered about it in the paraelastic phase. The article also discusses the definition of identity (degenerate) chemical reactions which do not take into cosideration the reactions in which the reactant and the product are enantiomers or enantiomorphs.