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PbZr 1-x Ti x O 3 (PZT) and Pb(Mg 1/3 Nb 2/3 ) 1-x Ti x O 3 (PMN-xPT) are complex lead-oxide perovskites that display exceptional piezoelectric properties for pseudorhombohedral compositions near a tetragonal phase boundary. In PZT these compositions are ferroelectrics, but in PMN-xPT they are relaxors because the dielectric permittivity is frequency dependent and exhibits non-Arrhenius behavior. We show that the nanoscale structure unique to PMN-xPT and other lead-oxide perovskite relaxors is absent in PZT and correlates with a greater than 100% enhancement of the longitudinal piezoelectric coefficient in PMN-xPT relative to that in PZT. By comparing dielectric, structural, lattice dynamical, and piezoelectric measurements on PZT and PMN-xPT, two nearly identical compounds that represent weak and strong random electric field limits, we show that quenched (static) random fields establish the relaxor phase and identify the order parameter.lead zirconate titanate | piezoelectricity | short-range order | soft modes | neutron scattering T he remarkable electromechanical properties of lead-oxide perovskite (ABO 3 ) relaxors such as Pb(Mg 1/3 Nb 2/3 ) 1-x Ti x O 3 (PMN-xPT) and Pb(Zn 1/3 Nb 2/3 ) 1-x Ti x O 3 (PZN-xPT) have inspired numerous attempts to understand the piezoelectricity in terms of the structural phase diagram, which contains a steep morphotropic phase boundary (MPB) separating pseudorhombohedral and tetragonal states over a narrow compositional range where the piezoelectricity is maximal (1-5). These materials exhibit very low strain-electric field hysteresis, extremely large dielectric constants, and record-setting piezoelectric coefficients at room temperature that form an unusually appealing set of properties with the potential to revolutionize a myriad of important technological applications spanning medical diagnostic sonography, military sonar, energy harvesting, and high-precision actuators (6-8). Many researchers have argued that quenched random electric fields (REFs) play a central role in establishing the relaxor phase, in part because the B sites of all known leadoxide perovskite relaxors are occupied by random mixtures of heterovalent cations (9-13). However, there is ample theoretical work that suggests relaxor behavior can occur in the absence of REFs (14-16). In fact it has not been proven conclusively that REFs are essential to the relaxor state or that they play any role in the ultrahigh piezoelectricity. These basic questions persist in the face of decades of research mainly because there exists no rigorous definition of what a relaxor is, i.e., there is no precise mathematical formulation of the relaxor-order parameter. To date, any material for which the real part of the dielectric permittivity e′ðω; TÞ exhibits a broad peak at a temperature T max that depends strongly (and in some cases only weakly) on the measuring frequency, ω, is classified as a relaxor. This definition has been applied equally to PMN and PZN, which possess strong REFs, as well as to specific compositions of K(T...

Neutron diffraction data obtained on single crystals of PbZr(1-x)Ti(x)O3 with x=0.325 and x=0.460, which lie on the pseudorhombohedral side of the morphotropic phase boundary, suggest a coexistence of rhombohedral (R3m/R3c) and monoclinic (Cm) domains and that monoclinic order is enhanced by Ti substitution. A monoclinic phase with a doubled unit cell (Cc) is ruled out as the ground state.

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Supramolecular self-assembly offers an efficient pathway for creating macroscopically chiral structures in biology and materials science. Here, a new peptide consisting of an N-(9-fluorenylmethoxycarbonyl) headgroup connected to an aromatic phenylalanine-tryptophan dipeptide and terminated with zwitterionic lysine (Fmoc-FWK) and its cationic form (Fmoc-FWK-NH2) were designed for self-assembly into chiral structures. It was found that the Fmoc-FWK peptide self-assembled into left-handed helical nanoribbons at pH 11.2-11.8, whereas it formed nanofibers at pH 5 and 12 and large flat ribbons composed of many nanofibers in the pH range of 6-11. However, only nanofibers were observed in the cases of Fmoc-FWK-NH2 at different values. A series of structural characterizations based on CD, FTIR, UV-vis and fluorescence spectroscopy reveal that the electrostatic and aromatic interactions and the associated hydrogen bonding direct the self-assembly into various structures. The enhanced π-π stacking and hydrogen bonding were found in the helical nanoribbons. This difference in intermolecular interactions should be derived from the ionization of carboxyl and amino groups from lysine residues at different pH values. Furthermore, we performed molecular dynamics simulations to gain insight into the assembly mechanisms. The results imply that a relatively rigid molecular conformation and the strong intramolecular aromatic interaction between Trp and Fmoc groups favor chiral self-assembly. This study is the first attempt to design a Fmoc-tripeptide for the fabrication of helical structures with macroscopic chirality, which provides a successful example and allows us to create new peptide-based chiral assembly systems.