Observation of a chemical reaction reversibly triggered by a structural phase transition

Two distinct radical species, (AsO₄)^4- and (AsO₃)^2-, created by irradiation in crystals of ND₄D₂AsO₄, undergo (taking into account the deuterons) the following chemical reaction: AsO₃D^- + OD^- ? AsO₄D^2-₂The effect occurs at the antiferroelectric-paraelectric phase transition of the compound. Its essential feature is that the reaction is completely reversible i.e. that it can be triggered by the phase transition, the direction of the reaction depending on the direction of passage of the Curie point. An analogy is presented with a biological process, namely the second step of the cooperative binding of oxygen on haemoglobin.