Ferroelectricity in Silver Perovskite Oxides

There are two silver perovskite oxides: AgNbO3 and AgTaO3. AgNbO3 has a noncentrosymmetric group of Pmc21 at room temperature with a ferri-electric ordering of polarization. Such a ferri-electric state with small polarization can be changed into a ferroelectric state with very large polarization by a high electric field or by a chemical modification. The induced ferroelectric phase shows promising electromechanical response for applications in piezoelectric devices. In contrast, AgTaO3 is a quantum paraelectric, but ferroelectricity also can be induced through chemical substitution. The findings of good ferroelectric and piezoelectric performance in the silver perovskites are hoped to trigger further theoretical and experimental investigations on these systems.Comment: 30 pages, 41 figures; Ferroelectrics - Material Aspects, Mickael Lallart (Ed.), ISBN: 978-953-307-332-3, InTech, Rijeka, Croatia. 2011, pp.413-44

Role of Ca off-Centering in Tuning Ferroelectric Phase Transitions in Ba(Zr,Ti)O3System

We here report the substitution effects of the smaller Ca for the bulky Ba in the (Ba1-xCax)(Ti-1-yZry)O3 perovskite oxides for two systems (Ba1-xCax)TiO3 with y=0 and (Ba1-xCax)(Ti0.9Zr0.1)O3 with y=0.1. Ca off-centering was found to play a critical role in stabilizing the ferroelectric phase and tuning the polarization states in both systems. It was demonstrated that the atomic displacement due to Ca off-centering in the bulky Ba-sites in the perovskite structure provides an effective approach to compensate for the reduction of ferroelectricity due to chemical pressure, which allows to keep the Curie point nearly constant in the (Ba1-xCax)TiO3 system and increase the Curie point in the (Ba1-xCax)( Ti0.9Zr0.1)O3 system. It was commonly observed that the Ca off-centering effects lead to the shift of the rhombohedral–orthorhombic and orthorhombic–tetragonal phase transitions toward lower temperatures and the ferroelectric stability of the tetragonal phase, resulting in the occurrence of quantum phase transitions with interesting physical phenomena at low temperatures in the (Ba1-xCax)TiO3 system and remarkable enhancement of electromechanical coupling effects around room temperature in the (Ba1-xCax)(Ti0.9Zr0.1)O3 systems over a wide range of Ca-concentrations. These findings may be of great interest for the design of green piezoelectric materials

Pb(Mg1/3Nb2/3)O3 (PMN) Relaxor: Dipole Glass or Nano-Domain Ferroelectric?

Combining our comprehensive investigations of polarization evolution, soft-mode by Raman scattering and microstructure by TEM, and the results reported in the literatures, we show that prototypical relaxor Pb(Mg1/3Nb2/3)O3 (PMN) is essentially ferroelectric for T<Tc~225 K. Its anomalous dielectric behavior over a broad temperature range results from the reorientation of domains in the crystal. A physic picture of the structure evolution in relaxor is also revealed. It is found that nanometric ferroelectric domains (gennerally called as polar nano-region (PNR)) interact cooperatively to form micrometric domain. Such multiscale inhomogeneities of domain structure in addition to the well-known inhomogeneities of chemical composition and local symmetry are considered to play a crucial role in producing the enigmatic phenomena in relaxor system.Comment: 16 pages, 10 figures; http://www.intechopen.com/books/advances-in-ferroelectrics/pb-mg1-3nb2-3-o3-pmn-relaxor-dipole-glass-or-nano-domain-ferroelectric

catena-Poly[[[aqua­pyridine­zinc(II)]-μ2-3,3′-(p-phenyl­ene)diacrylato] pyridine solvate]

The title compound, {[Zn(C12H8O4)(C5H5N)(H2O)]·C5H5N}n, has been prepared by hydro­thermal reaction. The ZnII atom is six-coordinated by four carboxyl­ate O atoms of two p-phenylenediacrylate (ppda2−) ligands, one N atom of a pyridine mol­ecule and one O atom of a water mol­ecule in a distorted octa­hedral environment. The carboxyl­ate groups of the ppda2− anions are in a bridging–chelating mode, in which two O atoms chelate one Zn2+ ion. These connections result in an extended chain structure. Parallel packing of the chains forms a two-dimensional network with inter­molecular edge-to-face inter­actions. Further linkages between the layers through O—H⋯O hydrogen-bonding inter­actions result in a three-dimensional supra­molecular architecture with one-dimensional recta­nglar channels