Compositional Inversion Symmetry Breaking in Ferroelectric Perovskites

Cubic perovskite compounds of the form $\left(A_{1/3}{A}_{1/3}^{\prime }{A}_{1/3}^{\prime \prime }\right)B{\mathrm{O}}_3$ and $A\left(B_{1/3}{B}_{1/3}^{\prime }{B}_{1/3}^{\prime \prime }\right){\mathrm{O}}_3$, in which the differentiated cations form an alternating series of monolayers, are studied using first-principles methods. Such compounds are representative of a possible new class of materials in which ferroelectricity is perturbed by compositional breaking of inversion symmetry. For isovalent substitution the ferroelectric double-well potential becomes asymmetric, so that minority domains may no longer survive. The symmetry breaking is enormously stronger for heterovalent substitution; here the double-well behavior is destroyed. Tuning between these behaviors may allow for the optimization of desired materials properties.