Analysis of electrostatic stability and ordering in quaternary perovskite solid solutions

There are three distinct classes of perovskite structured metal oxides, defined by the charge states of the cations: A(I)B(V)O(3), A(II)B(IV)O(3), and A(III)B(III)O(3). We investigated the stability of cubic quaternary solid solutions ABO(3)-A'B'O-3 using a model of point-charge lattices. The mixing enthalpies were calculated and compared for the three possible types of combinations of the compounds, both for the random alloys and the ground-state-ordered configurations. The mixing enthalpy of the (I,V)O-3-(III,III)O-3 alloy is always larger than the other alloys. We found that, different from homovalent alloys, for these heterovalent alloys a lattice constant mismatch between the constituent compounds could contribute to stabilize the alloy. At low temperatures, the alloys present a tendency to spontaneous ordering, forming superlattices consisting of alternated layers of ABO(3) and A'B'O-3 along the [110] direction.