Session EC08 - Ferroelectrics I: Theoretical Modeling of Ferroelectrics.
FOCUS session, Monday morning, March 22
Room 364W, GWCC
\defßs\scriptscriptstyle It has recently been shown that single-crystal solid solution ferroelectric crystals can have dramatically improved electromechanical properties compared to conventional transducer materials. This discovery has stimulated research aimed at understanding the atomic structures of these materials and identifying parameters controlling the growth of large crystals. We have investigated the equilibrium crystal structure of PMN type relaxors with the stoichiometry Pb(B^ßs 2+_ßs 1/3B^ßs 5+_ßs 2/3)O_3 (where B^ßs 2+=Mg or Zn and B^ßs 5+=Nb), using the ab-initio projector mixed-basis technique(D. Singh, H. Krakauer, C. Haas, and A. Liu, PRB 46), 13065 (1992). Although the overall composition of the cation sites must maintain a 2:1 B^ßs 5+:B^ßs 2+ ratio for charge neutrality, experimental evidence has shown that apparently 1:1 ordered domains exist. Using supercell calculations, we have modeled 1:1 ordering using compositionally homogeneous and heterogeneous structures. The atomic positions in each compositional structure are relaxed using calculated forces and total energies. Results of these simulations will be presented to identify the likely local atomic order in these materials.