Electrooptical ferroelectrics

In the broad range of ceramic materials that are used for electrical and electronic apphcations, each category of material exhibits unique property characteristics which directiy reflect composition, processing, and microstmcture. Detailed treatment is given primarily to those property characteristics relating to insulation behavior and electrical conduction processes. Further details concerning the more specialized electrical behavior in ceramic materials, eg, polarization, dielectric, ferroelectric, piezoelectric, electrooptic, and magnetic phenomena, are covered in References 1—9. 

Many ceramic applications are high value and small volume, so energy expenditure is high. Ferroelectric magnets, electronic substrates, electrooptics, abrasives such as silicon carbide and diamond, are examples. Diamond is found naturally, and made synthetically by the General Electric Company at high pressure and temperature. Synthetic diamonds for abrasives require less energy to make than the value in Table 4 nevertheless, the market is carefully divided between natural and synthetic diamonds. 

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... 

Photopolymerization and Electrooptic Properties of Polymer Network/Ferroelectric Liquid-Crystal... 

LiNbOj is a widely used ferroelectric crystal with various applications in the nonlinear optics and integrated optics (10). Another attractive material for 10 devices is LiTaOs. Its electrooptic (EO) and nonlinear (NL) coefficients are comparable to those of LiNbOj, and its photorefractive damage threshold is more than an order of magnitude higher than that of LiNbOj in the visible range. 

Approximately ten years ago, it was first reported by Haertling and Land (jj that optical transparency was achieved in a ferroelectric ceramic material. This material was, in reality, not just one composition but consisted of a series of compositions in the lanthanum modified lead zirconate-lead titanate (PLZT) solid solution region. The multiplicity of compositions, each with different mechanical, electrical and electrooptic properties has led to a decade of study in defining the chemical and structural nature of these materials in understanding the phenomena underlying their optical and electrooptic properties and in evaluating the practicality of the large number of possible applications (2-12),... 

Electrooptic Properties, The electrooptic properties of the PLZT materials are intimately related to their ferroelectric properties. Consequently, varying the ferroelectric polarization with an electric field such as in a hysteresis loop, produces a change in the optical properties of the ceramic. In addition, the magnitude of the observed electrooptic effect is dependent on both the strength and direction of the electric field,... 

CERAMICS - CERAMIC PROCESSING] (Vol 5) - [CERAMICS - NONLINEAROPTICAL AND ELECTROOpTIC CERAMICS] (Vol 5) - [CERAMICS -OVERVIEW] (Vol 5) - [FERROELECTRICS] (Vol 10) - pTTANIUMCOMPOUNDS - INORGANIC] (Vol24) - [BARIUMCOMPOUNDS] (Vol 3) - [BARIUMCOMPOUNDS] (Vol 3) -boron oxide m prepn of [BORON COMPOUNDS - BORON OXIDES, BORIC ACID AND BORATES] (Vol 4)... 

The major trends in ferroelectric photonic and electronic devices are based on development of materials with nanoscale features. Piezoelectric, electrooptic, nonlinear optical properties of fe are largely determined by the arrangement of ferroelectric domains. A promising way is a modification of these basic properties by means of tailoring nanodomain and refractive index superlattices. 

Mixed-metal oxides constitute a significant proportion of electroceramics (e.g., ferroelectrics or superconductors). In addition, electrooptical ceramics such as Pb(LaZrTi)03(PLZT), PbNb2/3Mg1/303(PNM), and Bi4Ti3Ol2 received considerable attention. It may be pointed out that the low-temperature SG route appears to be more suitable for lead containing materials in view of the comparatively more volatile characteristic of lead oxide, which tends to disturb the desired stoichiometry of the multimetal oxide material involving lead, prepared by the MOCVD procedure. 

In contrast, the nonlinearities in bulk materials are due to the response of electrons not associated with individual sites, as it occurs in metals or semiconductors. In these materials, the nonlinear response is caused by effects of band structure or other mechanisms that are determined by the electronic response of the bulk medium. The first nonlinear materials that were applied successfully in the fabrication of passive and active photonic devices were in fact ferroelectric inorganic crystals, such as the potassium dihydrogen phosphate (KDP) crystal or the lithium niobate (LiNbO,) [20-22]. In the present, potassium dihydrogen phosphate crystal is broadly used as a laser frequency doubler, while the lithium niobate is the main material for optical electrooptic modulators that operate in the near-infrared spectral range. Another ferroelectric inorganic crystal, barium titanate (BaTiOj), is currently used in phase-conjugation applications [23]. 

Nematic materials are only one member of a large family of a variety of structurally different compounds forming liquid crystalline mesophases. Although only nematics have yet found really widespread use, mostly for display applications, some structurally highly diverse smectic phases also have unique electrooptical characteristics, for example ferroelectricity or antiferroelectricity, which can be modulated by selective fluorination [5, 51]. For 20 years intensive effort has been devoted to making practical use of these phenomena. 

We consider only conventional LCDs that use nematic liquid crystals as the electrooptic material. There are less common types of LCDs that use other types of liquid crystals, such as cholesteric and ferroelectric liquid crystals. 

The M M03 compounds crystallize with perovskite structures Figure 5.23), and exhibit ferroelectric and piezoelectric properties (see Section 13.9) which lead to uses in electrooptical and acoustic devices. 

Chemical and physical processing techniques for ferroelectric thin films have undergone explosive advancement in the past few years (see Ref. 1, for example). The use of PZT (PbZri- cTi c03) family ferroelectrics in the nonvolatile and dynamic random access memory applications present potentially large markets [2]. Other thin-film devices based on a wide variety of ferroelectrics have also been explored. These include multilayer thin-film capacitors [3], piezoelectric or electroacoustic transducer and piezoelectric actuators [4-6], piezoelectric ultrasonic micromotors [7], high-frequency surface acoustic devices [8,9], pyroelectric intrared (IR) detectors [10-12], ferroelectric/photoconduc-tive displays [13], electrooptic waveguide devices or optical modulators [14], and ferroelectric gate and metal/insulator/semiconductor transistor (MIST) devices [15,16]. 

On the other hand, it has been shown on LMWLCs that the well-known SmC, where the molecules are tilted with respect to the layer normal, is no longer the only possibility to obtain a fluid biaxial phase [63], As a consequence, a strict determination of the chiral smectic phase structure requires not only a careful analysis of the X-ray diagrams obtained on powder as well as on aligned samples, but also a study of the electrooptic response, which allows discrimination between the ferroelectric, the antiferro-electric, and the ferrielectric behavior. 

As there is no appropriate method to measure directly the rotational viscosity of ferroelectric liquid crystals, y is generally deduced from the electrooptic response time measurements [ 12,18,44]. The relationship between fio 9o and t is not straightforward and requires the use of a theoretical model for the optical transmission based on the bookshelf geometry briefly summarized in the following. 

Sasaki T, Ikeda T. 1995c. Photochemical control of properties of ferroelectric liquid crystals. 3. Photochemically induced reversible change in spontaneous polarization and electrooptic property. J Phys Chem 99 13013 13018. 

Haertling, G.H. (1991) Electrooptic ceramics and devices , in Engineered Materials Handbook Volume 4 Ceramics and Glasses, ASM International, p. 1124. Haertling and Land (1971) developed the PLZT system of transparent ferroelectric ceramics. 

Haertling, G.H. and Land, C.E. (1971) Hot-pressed (Pb,La)(Zr,Ti)03 ferroelectric ceramics for electrooptic applications, J. Am. Ceram. Soc. 54, 1. This is the original citation for transparent PLZT ceramics. Kaiser, P. (1973) Spectral losses of unclad fibers made from high-grade vitreous silica, Appl. Phys. Lett. 23, 45. Developed the MCVD process. 

Much of this early effort dealt with modulator technology that is considered too slow (1-100 kilohertz) for high-speed applications such as optical interconnection and memory read/write. This includes modulators based on electrooptic effects in ferroelectric liquid crystals (ELCs) and in a ceramic containing lead, lanthanum, zinc, and titanium (PLZT). These electrooptic materials are bonded in some fashion to Si circuits to create hybrid SPAs. 

Ferroelectric materials have numerous microelectronics applications, including capacitors (7,2), nonvolatile memory devices (2-4 electrooptic devices 1,4) and many others (5). The ferroelectrics described in this paper are Pb(ZrxTii x)03 (PZT), BaTi03, and YMn03. Here we investigate the use of a photochemical method for the direct deposition of these complex materials. 

Finally the three remaining Chapters 10-12 are devoted to optics and electrooptics of, respectively, nematic, cholesteric and smectic (ferroelectric and antiferro-electric) phases. In contrast to my earlier book published by WUey in 1983, only the most principal effects have been considered and the discussion of the underlying principles is much more detailed. 

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