Order-disorder reactions in the ferroelectric perovskites Pb(Sc1/2Nb1/2)O3 and Pb(Sc1/2Ta1/2)O3. II. Relation between ordering and properties

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