Lead electro-optic properties

Lead lanthanum zirconate titanates (PLZT) containing 3-12 mol. % La and 5-30 mol. % Ti form a class of ceramics with important dielectric, piezoelectric and electro-optic properties. They may contain vacancies on B as well as A sites and have a remarkable facility for changing their polar states under the influence of applied fields. 

It follows from the preceding results that the electro-optical properties of molecules in degenerate electronic states should have unusual temperature dependence, which is absent in the case of nondegenerate states. Even for nondipolar degenerate electronic states (e.g., for states in which the reduced matrix elements of the dipole moment are zero) for certain relationships between the vibronic constant and the temperature, there may be a quadratic dependence of the Kerr effect on p, similar to that observed in the case of molecules that are simultaneously anisotropic polarizable and possess a proper dipole moment. The nonlinear dependence on p under consideration is due exclusively to the vibronic interaction that redetermines the vibronic spectrum and leads to different polarizability in different vibronic states. This dependence on p has to be distinguished from that which arises due to the nonzero value of the dipole moment in the initial ground electronic state (e.g., as in the case of the E term in molecules with D3h symmetry). The two sources of the... 

As for purely electro-optic polymers the electro-optic functionality can be achieved in a variety of different ways including guest/host systems, side-chain and main-chain polymers, crosslinked polymers and self-assembly approaches (36-38). In amorphous polymers, the NLO chromophores which have a permanent dipole moment are oriented with an electric field to induce electro-optic effects (39). Orientation of these dipoles leads not only to macroscopic electro-optic properties but also to birefringence (40). In the oriented gas model and for a poling field applied along the Z axis these two effects can be described by (39) ... 

Transparent ferroelectric single crystals are traditionally used for electro-optic applications. Since the optical transparency was first discovered in lead-lanthanum-zirconate-titanate (PLZT), ferroelectric ceramics have been investigated in great depth such that, today, their characteristics allow them to compete with single crystals for certain electro-optic applications. The electro-optic properties of PLZT compositions are intimately related to their ferroelectric properties. Variations in ferroelectric polarization with an electric field, such as in a hysteresis loop, also affect the optical properties of the material. 

Liquid crystals, polymers and liquid crystalline polymers are soft condensed matter systems of major technological and scientific interest. In liquid crystals the orientational order of the constituent molecules is associated with a reduced or absent translational order. This gives liquid crystalline systems a combination of fluidity (liquid-like properties) and anisotropic electro optic properties, similar to those of a crystal. Orientational order can be controlled easily by the application of external fields, leading to the spatial switching of bulk properties in response to external stimuli. This provides the basis for a wide range of technological applications, including displays, optical switches, adaptive optics for telescopes and many other electro-optical devices. 

Further work on the electro-optical properties of liquid crystals led to the above-mentioned invention of a novel liquid crystal display. This display also consists of a thin layer of a nematic liquid crystal which is situated between two electrodes. However, the molecules are now anchored at the two opposite electrodes in such way that their preferred direction is twisted within the layer. This distortion of the nematic phase can be changed by the applied voltage leading to a change of the optical properties. Almost all liquid crystal displays used today in watches and other devices are based on this simple and rather robust construction principle. 

EquaticHi (6.13) clearly reveals that if we can make a significantly large in the composite LC-polymer medium, then we may have Ypsflc YflC which means the polarizatiOTi-tilt ratio shows no improvement due to polymer stabilization. This COTidition is somewhat disadvantageous from the application point of views because the polarizati(Mi-tilt ratio determines the electro-optic response of the medium. Therefore, it is important to identify the possibilities, which can lead a to that critical value for which Ypsflc Yflc- Q e, however, notes that for PSFLCs, a does not change with polymer stabilizatimi (Archer et al. 2008). Therefore, it is expected that PSFLCs may show superior electro-optic properties compared to pure FLCs as a remains fixed. 

The recent work of Krigbaum on main-chain and Finkelmann, Ringsdorf, etc., on side-chain polymer liquid crystals has generated much interest in the potential of these systems for use in electro-optic devices. The combination of polymeric specific and monomeric liquid crystal specific properties leads to an interesting range of potential materials for new display devices. The majority of the research over the last five years has concentrated on synthesis and the establishment of the basic property-structure relationships. However in the last year or so papers have started appearing where the electro-optic properties of some of these materials have been examined." ... 

Colloidal crysfals can be viewed as the mesoscopic counterpart of atomic or molecular crystals. They have been used to explore diverse phenomena such as crystal growth [52-54] and glass transition [55,56], and have many interesting applications for sensors [57], in catalysis [58,59], advanced coatings [60], and for optical/electro-optical devices for information processing and storage [61,62]. In particular, their unusual optical properties, namely the diffraction of visible light and the existence of a photonic stop band, make them ideal candidates for the development of photonic materials [61,63-66]. They may lead to the fabrication... 

The calculation of the electro-optical parameters describing Raman intensities is not yet very advanced, because of the paucity of data. Nevertheless, some success was achieved in calculations of the intensity of infrared absorption. The results on trans and gauche bond-rotation in ethylene glycol146 could be taken as a model for carbohydrates. Indeed, similar electro-optical parameters (/aCH, /aOH, /aCC, and /aCO) were calculated. This leads to the expectation that calculations of the intensity of the vibrational spectra of carbohydrates may be accomplished in the near future. In addition, the delicate problem of accounting for molecular interactions in calculating infrared intensities could be approached as it was for v(CCC) and i CO) vibrations in acetone.149 This will allow interpretation of weak, as well as strong, i.r. bands, in order to determine the structural properties of molecules. 

The Pockel s effect [3] refers to an electro-optical process wherein the application of large electric fields onto crystals lacking a center of symmetry can lead to nonlinear polarization effects and optical rotation. Pockel cells can be used in place of photoelastic modulators and can achieve very high modulation frequencies but often have the undesirable property of a nonzero birefringence in the absence of an applied field. 

As is evident from a consideration of Figs. 7-9, each of these chromophores has exhibited electro-optic activity exceeding that of lithium niobate while at the same time exhibiting auxiliary properties of chemical stability (Td >300 °C) and solubility that permits preparation of device quality materials [183,210-212]. These materials also illustrate another major direction in the preparation of electro-optic materials namely, the development of bridging segments that lead to improved chemical stability, improved solubility in spin-casting solvents, improved compatibility with polymer host materials, and which inhibit unwanted intermolecular electrostatic interactions (we shall discuss such interactions... 

In their ferroelectric state, the electro-optically useful PLZT compositions have an almost cubic structure, with the polar c axis being typically only about 1% longer than the a axes. Consequently the optical properties are almost isotropic and this, in part, is why high transparency can be achieved in the ceramic form. When an electric field is applied to the ceramic, domain alignment, or a field-enforced transition to the ferroelectric state, leads to the development of macroscopic polarization and so to uniaxial optical properties, i.e. the optic axis... 

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