Ferroelectric system properties

Therefore we propose here an alternative route to inspect the local dielectric and polarization properties using non-destructive and non-invasive methods based on scanning force microscopy (sfm). Simultaneously, these techniques offer a high resolution in real space being extended down to the atomic scale when inspecting ferroelectric systems under ultra-high... 

As the polarization is not confined to a fixed direction in a monoclinic phase, its unconstrained rotation can explain the highly valued properties of ferroelectric systems near the MPB [25]. A relationship between the polarization rotation and a strong enhancement of the electromechanical response in perovskite ferroelectrics was demonstrated by Fu and Cohen [32], from a first principles study of the internal... 

The rate dependencies of the ferroelectric material properties are also reflected in the dynamics after fatigue. Initially, most of the domain system will be switched almost instantaneously [235], and only a small amount of polarization will creep for longer time periods [194]. A highly retarded stretched exponential relaxation was observed after bipolar fatigue treatment [235], and these observations correlated well with the thermally activated domain dynamics. If the overall materials response was represented in a rate-dependent constitutive material law 236], however, then a growing defect cluster size would retard the domain dynamics considerably. Hard and soft material behaviors were also representable as different barrier heights to a thermally activated domain wall motion, as demonstrated by the theoretical studies of Belov and Kreher [236]. 

Recently, ferroelectric properties have been found in chiral columnar systems [27] and also discoid cholesteric and discoid-blue phases have been found [17]. H. Bock describes chiral ferroelectric systems in Chapter 10. 

Typical property of a ferroelectric system, the hysteresis loop, shows marked dependence on the pressure (Fig. 29). Observations of the hysteresis loops have shown that the spontaneous polarization abruptly increases at the Sm A-Sm C transition point when T decreases at p = const (Fig. 30a) or when p increases at T = const (Fig. 30b). That is accompanied by an increase of the tilt angle (Fig. 30c). 

There is often a wide range of crystalline soHd solubiUty between end-member compositions. Additionally the ferroelectric and antiferroelectric Curie temperatures and consequent properties appear to mutate continuously with fractional cation substitution. Thus the perovskite system has a variety of extremely usehil properties. Other oxygen octahedra stmcture ferroelectrics such as lithium niobate [12031 -63-9] LiNbO, lithium tantalate [12031 -66-2] LiTaO, the tungsten bron2e stmctures, bismuth oxide layer stmctures, pyrochlore stmctures, and order—disorder-type ferroelectrics are well discussed elsewhere (4,12,22,23). 

Potassium Phosphates. The K2O—P20 —H2O system parallels the sodium system in many respects. In addition to the three simple phosphate salts obtained by successive replacement of the protons of phosphoric acid by potassium ions, the system contains a number of crystalline hydrates and double salts (Table 7). Monopotassium phosphate (MKP), known only as the anhydrous salt, is the least soluble of the potassium orthophosphates. Monopotassium phosphate has been studied extensively owing to its piezoelectric and ferroelectric properties (see Ferroelectrics). At ordinary temperatures, KH2PO4 is so far above its Curie point as to give piezoelectric effects in which the emf is proportional to the distorting force. There is virtually no hysteresis. 

PZN-PT, and YBa2Cug02 g. For the preparation of PZT thin films, the most frequently used precursors have been lead acetate and 2irconium and titanium alkoxides, especially the propoxides. Short-chain alcohols, such as methanol and propanol, have been used most often as solvents, although there have been several successful investigations of the preparation of PZT films from the methoxyethanol solvent system. The use of acetic acid as a solvent and chemical modifier has also been reported. Whereas PZT thin films with exceUent ferroelectric properties have been prepared by sol-gel deposition, there has been relatively Httle effort directed toward understanding solution chemistry effects on thin-film properties. 

In other cases, if the fluorination process leads to cardinal changes in the crystal structure of the initial oxide compounds, new compounds with polar structures can be obtained. A demonstrative example of such materials are compounds that belongs to the system Na5(W3 xNbx)09..xF5+x and that have chiolite-type structures, when neither pure fluoride nor oxide display any ferroelectric properties [393 - 395]. 

To produce novel LC phase behavior and properties, a variety of polymer/LC composites have been developed. These include systems which employ liquid crystal polymers (5), phase separation of LC droplets in polymer dispersed liquid crystals (PDLCs) (4), incorporating both nematic (5,6) and ferroelectric liquid crystals (6-10). Polymer/LC gels have also been studied which are formed by the polymerization of small amounts of monomer solutes in a liquid crystalline solvent (11). The polymer/LC gel systems are of particular interest, rendering bistable chiral nematic devices (12) and polymer stabilized ferroelectric liquid crystals (PSFLCs) (1,13), which combine fast electro-optic response (14) with the increased mechanical stabilization imparted by the polymer (75). 

The introduction of a polymer network into an FLC dramatically changes phase and electro-optic behavior. Upon addition of monomer to the FLC, the phase transitions decrease and after polymerization return to values close to that observed in the neat FLC. The phase behavior is similar for the amorphous monomers, HDD A and PPDA. The electro-optic properties, on the other hand, are highly dependent on the monomer used to form the polymer/FLC composite. The ferroelectric polarization decreases for both HDDA and PPDA/FLC systems, but the values for each show extremely different temperature dependence. Further evidence illustrating the different effects of each of the two polymers is found upon examining the polarization as both the temperature and LC phase of polymerization are changed. In PPDA systems the polarization remains fairly independent of the polymerization temperature. On the other hand, the polarization increases steadily as the polymerization temperature of HDDA systems is increased in the ordered LC phases. 

Orthopedic devices, 3 721-735 joint replacement, 3 727-735 Orthopedic marrow needles, 3 743-744 Orthophosphate (PO4), in soil, 11 112 Orthophosphates, 18 830-841 20 637 magnesium, 18 839 manufacture of, 18 853-855 Orthophosphate salts, 18 836 Orthophosphoric acid, 18 815, 817-826 condensation of, 18 826 properties of, 18 817-819 solubility of boron halides in, 4 140t orf/zo-phthalic resins, 20 101, 113 formulation of, 20 102 Orthorhombic crystal system, 8 114t Orthorhombic phosphorus pentoxide, 19 49 Orthorhombic structure, of ferroelectric crystals, 11 95, 96 Orthorhombic symmetry, 8 114t Orthosilicate monomers, in silicate glasses, 22 453... 

More than 80 years ago ferroelectricity was first discovered in the rather complex compound Rochelle salt. It was long beheved to be a rather exceptional property since no other system with reversible polarization was discovered... 

In order to understand these extreme changes in physical and chemical properties of hydrogen-bonded systems, first attempts to model their dynamics were related to rather simple structures, as exhibited by the KDP family or squaric acid and its analogues. The isotope effects on their ferro- or anti-ferroelectric transition temperatures are listed in Table 1 together with the corresponding isotope exponent. 

In addition, many of the ferroelectric solids are mixed ions systems, or alloys, for which local disorder influences the properties. The effect of disorder is most pronounced in the relaxor ferroelectrics, which show glassy ferroelectric behavior with diffuse phase transition [1]. In this chapter we focus on the effect of local disorder on the ferroelectric solids including the relaxor ferroelectrics. As the means of studying the local structure and dynamics we rely mainly on neutron scattering methods coupled with the real-space pair-density function (PDF) analysis. 

Obviously, chirality is an essential property in molecular chemistry, and knots are exciting systems in this context. With a touch of fantasy, it could be conceived that some of the chemical processes for which chirality is essential (enan-tioselection of substrates, asymmetric induction and catalysis, cholesteric phases, and ferroelectric liquid crystals molecular materials for non linear optics...) could one day use enantiomerically pure knots. 

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