Theory of order-disorder phase transitions of B-cations in AB'_1/2B''_1/2O₃ perovskites

Perovskite-like oxides AB'_1/2B''_1/2O₃ with two different cations in the B-sublattice may experience cation order-disorder phase transitions. In many cases the degree of cation ordering can be varied by suitable synthesis conditions or subsequent sample treatment, which has a fundamental impact on the physical properties of such compounds. Therefore, understanding the mechanism of cation order-disorder phase transition and estimation of the phase transition temperature is of paramount importance for tuning of properties of such double perovskites. In this work, based on the earlier proposed cation-anion elastic bonds model, a theory of order-disorder phase transitions of B-cations in AB'_1/2B''_1/2O₃ perovskites is presented, which allows reliable estimation of the phase transition temperatures and of the reduced lattice constants of such double perovskites.