Anomalous properties in ferroelectrics induced by atomic ordering

Complex insulating perovskite alloys are of considerable technological inte rest because of their large dielectric and piezoelectric responses. Example s of such alloys include (Ba1-xSrx)TiO3, which has emerged as a leading can didate dielectric material for the memory-cell capacitors in dynamic random access memories(1); and Pb(Zr1-xTix)O-3 (PZT), which is widely used in tra nsducers and actuators(2). The rich variety of structural phases that these alloys can exhibit, and the challenge of relating their anomalous properti es to the microscopic structure, make them attractive from a fundamental po int of view. Theoretical investigations of modifications to the atomic orde ring of these alloys suggest the existence of further unexpected structural properties(3) and hold promise for the development of new functional mater ials with improved electromechanical properties. Here we report ab initio c alculations that show that a certain class of atomic rearrangement should l ead simultaneously to large electromechanical responses and to unusual stru ctural phases in a given class of perovskite alloys. Our simulations also r eveal the microscopic mechanism responsible for these anomalies.