Ceramic materials electrooptical

G. H. Haerfling, "Piezoelectric and Electrooptic Ceramics," in R. C. Buchanan, ed.. Ceramic Materials forElectronics, Marcel Dekker, Inc., New York, 1986. 

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. 

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),... 

This chapter deals with the synthesis and general properties of homo- and heterometallic alkoxides that are or might be used in chemical routes to electrooptical ceramic materials. Some considerations concerning structure, reactivity, and tailoring of their properties are also given. Emphasis is given to the most recent results. 

Along with the multilayered ceramic capacitors, there are many other categories of electronic ceramic materials that are active by nature— that is, they perform a function other than that of a simple insulator in the electronic circuitry. Some are conductors or semiconductors, while others act as resistors, sensors, electrooptics, or magnetic components. In this section we will describe some of the electronic devices that depend upon tape casting as a forming technique. 

A special class of materials that is also ferroelectric are electrooptic ceramics. Materials such as lanthanum-modified lead zirconate titanate (PLZT) produce excellent electrooptic devices. These polycrystalline ceramics exhibit voltage-variable behavior—that is, they can be switched from optically transparent to opaque by the application of voltage. Most of these devices, which are used for shutters, modulators, and displays, are processed by hot pressing to full density. Experiments in many laboratories are being carried out to tape-cast these materials into thin sheets. The main problem encountered to date has been the ability to sinter to full density. The use of nanosized powders has helped in this regard. The ability to tape-cast large sheets could open a wide variety of applications for these materials. 

Nonlinear optical and electrooptic ceramics. Electronic properties and material stmcture. 

These lead-based materials (PZT, PLZT, PMN) form a class of ceramics with either important dielectric, relaxor, pie2oelectric, or electrooptic properties, and are thus used for appHcations ia actuator and sensor devices. Resistive properties of these materials ia film form mirror the conduction processes ia the bulk material. Common problems associated with their use are low dielectric breakdown, iacreased aging, and electrode iajection, decreasiag the resistivity and degrading the properties. 

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,... 

Ferroelectncs - [CERAMCS-ELECTRONIC PROPERTIES AND MATERIAL STRUCTURE] (Vol 5) -barium compounds as [BARIUM COMPOUNDS] (Vol 3) -ceramics as [CERAMICS - NONLINEAROPTICAL AND ELECTROOPTIC CERAMICS] (Vol 5) -m infrared technology [INFRARED TECPINOLOGY AND RAMAN SPECTROSCOPY - INFRARED TECHNOLOGY] (Vol 14) -niobium compounds as [NIOBIUM AND NIOBIUM COMPOUNDS] (Vol 17)... 

Kerr coefficient -for electrooptic materials [CERAMICS - NONLINEAROPTICAL AND ELECTKOOPTIC CERAMICS] (Vol 5)... 

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 addition to the use of heterometal alkoxides, metal alkoxides are often associated with more easily available precursors such as acetates for the SG route to multicomponent oxides. A number of such alkoxide acetate precursors [e.g., MNb2(/i-OAc)2(/i-OR)4(OR)6 (M = Cd or Mg), PbZr3(/t4-0)(/i-0Ac)2(/i-OR)5(OR)5, and Gd2Zr6(/i4-O)2(pi-OAc)6(/t-OR)l0(OR)i0 (with R = i-Pr)] were characterized (564) by X-ray crystallography. Their hydrolytic studies indicate their potential use as precursors for the synthesis of electrooptical materials, for example, Pb(ScNb)03 (PSN), and dielectric ceramics, for example, [PbMg1/3Nb2/303] (PNM). 

G.H. Haertling, Electrooptic ceramics and devices, in Engineered Materials Handbook, Vol. 4 Ceramics and Glasses, ASM International, 1991, pp. 1124—1130. 

Traditional ceramics are quite common, from sanitary ware to fine chinas and porcelains to glass products. Currently ceramics are being considered for uses that a few decades ago were inconceivable applications ranging from ceramic engines to optical communications, electrooptic applications to laser materials, and substrates in electronic circuits to electrodes in photoelectrochemical devices. Some of the recent applications for which ceramics are used and/or are prime candidates are listed in Table 1.1. 

If an electrooptic ceramic is noncentrosymmetric then 5n is proportional to E. Examples of such materials include... 

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, especially polyciystalhne ceramics, are utihzed in various devices such as high-permittivity dielectrics, ferroelectric memories, pyroelectric sensors, piezoelectric transducers, electrooptic devices, and PTC (positive temperature coefficient of resistivity) components. 

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