The ordering of the trivalent and pentavalent cations in the perovskites Pb(Sc1/2Nb1/2)O3 and Pb(Sc1/2Ta1/2)O3 can be varied by suitable heat treatments. The degree as well as the kind of order strongly affects the character of the FE - PE phase transition. A spatially homogeneous disorder leads to a diffuse phase transition whereas a hybrid crystal with a nonhomogeneous disorder shows a sequence of two FE - PE transitions.
Stenger, C. G. F., & Burggraaf, A. J. (1980). Order-disorder reactions in the ferroelectric perovskites Pb(Sc1/2Nb1/2)O3 and Pb(Sc1/2Ta1/2)O3: II. Relation between ordering and properties. Physica Status Solidi A: Applied research, 61(2), 653-664. https://doi.org/10.1002/pssa.2210610240