Anomalous properties in ferroelectrics induced by atomic ordering.

Complex insulating perovskite alloys are of considerable technological interest because of their large dielectric and piezoelectric responses. Examples of such alloys include (Ba1-xSrx)TiO3, which has emerged as a leading candidate dielectric material for the memory-cell capacitors in dynamic random access memories; and Pb(Zr1-xTix)O3 (PZT), which is widely used in transducers and actuators. The rich variety of structural phases that these alloys can exhibit, and the challenge of relating their anomalous properties to the microscopic structure, make them attractive from a fundamental point of view. Theoretical investigations of modifications to the atomic ordering of these alloys suggest the existence of further unexpected structural properties and hold promise for the development of new functional materials with improved electromechanical properties. Here we report ab initio calculations that show that a certain class of atomic rearrangement should lead simultaneously to large electromechanical responses and to unusual structural phases in a given class of perovskite alloys. Our simulations also reveal the microscopic mechanism responsible for these anomalies.