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Optical ferroelectrics

The properties of zeotype host-guest composites described above - i e, spatial organization, protection and stabilization of guest species - will become more important as molecules exhibit further properties that are essential for their use as materials. The well-developed synthetic methods for molecular compounds allow the preparation of designed molecular entities that possess predictable properties. However, no such thoroughly elaborated synthetic methods are available for the construction of organized arrays of functional molecules in their solid structures [36]. This is cumbersome since often the arrangement of the molecules in their solid compounds is detrimental to the effects (e g. non-linear optical, ferroelectric, electro-optical) that are to be exploited in materials. For example, many structures of molecules in the solid state are centrosymmetric. Also, molecular... [Pg.655]

MAJOR PRODUCT APPLICATIONS thermistors, capacitors, optics, ferroelectric ceramics, filler for ferroelectric polymers, pyro and piezoelectric composites... [Pg.42]

Second-harmonic generation for nonlinear optics, ferroelectricity, and piezoelectricity are all properties that are dependent on the pre.sence, magnitude, and orientation of bulk polarity in crystals and films. Therefore, the issue of how to design a polar solid from basic principles remains a challenge that has immense potential relevance to materials science. Obviously, a polar solid is guaranteed if a pure enantiomer is used as a component of a compound. However, the presence of polarity does not in any way imply that optimal packing will occur and, further-... [Pg.889]

K. Schmitt, R.-P. Herr, M. Schadt, J. FUnfecfailling, R. Budieckcr. X. H. Own, and C Beoecke, Strongly non-linear optical ferroelectric liquid crystals for frequency doubling, Uq. Cryst 14 1735 (1993). [Pg.876]

Key words Mesomorphism, calixarenes, bowlic liquid crystals, nonlinear optics, ferroelectricity... [Pg.389]

Clark N A, Handschy M A and Lagerwall S T 1983 Ferroelectric liquid crystal electro-optics using the surface stabilized structure Molec. Cryst. Liq. Cryst. 94 213-34... [Pg.2571]

In the single-domain state, many ferroelectric crystals also exhibit high optical nonlinearity and this, coupled with the large standing optical anisotropies (birefringences) that are often available, makes the ferroelectrics interesting candidates for phase-matched optical second harmonic generation (SHG). [Pg.203]

Certain glass-ceramic materials also exhibit potentially useful electro-optic effects. These include glasses with microcrystaUites of Cd-sulfoselenides, which show a strong nonlinear response to an electric field (9), as well as glass-ceramics based on ferroelectric perovskite crystals such as niobates, titanates, or zkconates (10—12). Such crystals permit electric control of scattering and other optical properties. [Pg.320]

The main categories of electrical/optical ceramics are as follows phosphors for TV, radar and oscilloscope screens voltage-dependent and thermally sensitive resistors dielectrics, including ferroelectrics piezoelectric materials, again including ferroelectrics pyroelectric ceramics electro-optic ceramics and magnetic ceramics. [Pg.271]

Tantalum and niobium are added, in the form of carbides, to cemented carbide compositions used in the production of cutting tools. Pure oxides are widely used in the optical industiy as additives and deposits, and in organic synthesis processes as catalysts and promoters [12, 13]. Binary and more complex oxide compounds based on tantalum and niobium form a huge family of ferroelectric materials that have high Curie temperatures, high dielectric permittivity, and piezoelectric, pyroelectric and non-linear optical properties [14-17]. Compounds of this class are used in the production of energy transformers, quantum electronics, piezoelectrics, acoustics, and so on. Two of... [Pg.1]

Since niobates and tantalates belong to the octahedral ferroelectric family, fluorine-oxygen substitution has a particular importance in managing ferroelectric properties. Thus, the variation in the Curie temperature of such compounds with the fluorine-oxygen substitution rate depends strongly on the crystalline network, the ferroelectric type and the mutual orientation of the spontaneous polarization vector, metal displacement direction and covalent bond orientation [47]. Hence, complex tantalum and niobium fluoride compounds seem to have potential also as new materials for modem electronic and optical applications. [Pg.9]

Crystals with one of the ten polar point-group symmetries (Ci, C2, Cs, C2V, C4, C4V, C3, C3v, C(, Cgv) are called polar crystals. They display spontaneous polarization and form a family of ferroelectric materials. The main properties of ferroelectric materials include relatively high dielectric permittivity, ferroelectric-paraelectric phase transition that occurs at a certain temperature called the Curie temperature, piezoelectric effect, pyroelectric effect, nonlinear optic property - the ability to multiply frequencies, ferroelectric hysteresis loop, and electrostrictive, electro-optic and other properties [16, 388],... [Pg.217]

Ferroelectric materials are capable of being polarized in the presence of an electric field. They may exhibit considerable anomalies in one or more of their physical properties, including piezoelectric and pyroelectric coefficients, dielectric constant, and optoelectronic constant. In the latter case, the transmission of light through the material is affected by the electric field, which produces changes in refractive index and optical absorption coefficient. Varying the applied field changes the phase modulation. [Pg.398]

The semiconducting properties of the compounds of the SbSI type (see Table XXVIII) were predicted by Mooser and Pearson in 1958 228). They were first confirmed for SbSI, for which photoconductivity was found in 1960 243). The breakthrough was the observation of fer-roelectricity in this material 117) and other SbSI type compounds 244 see Table XXIX), in addition to phase transitions 184), nonlinear optical behavior 156), piezoelectric behavior 44), and electromechanical 183) and other properties. These photoconductors exhibit abnormally large temperature-coefficients for their band gaps they are strongly piezoelectric. Some are ferroelectric (see Table XXIX). They have anomalous electrooptic and optomechanical properties, namely, elongation or contraction under illumination. As already mentioned, these fields cannot be treated in any detail in this review for those interested in ferroelectricity, review articles 224, 352) are mentioned. The heat capacity of SbSI has been measured from - 180 to -l- 40°C and, from these data, the excess entropy of the ferro-paraelectric transition... [Pg.410]

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). [Pg.17]


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See also in sourсe #XX -- [ Pg.2 , Pg.549 ]

See also in sourсe #XX -- [ Pg.2 , Pg.549 , Pg.604 , Pg.608 ]




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