CAPACITOR DIELECTRIC AND PIEZOELECTRIC CERAMICS

advanced industrial materials that, by virtue of their poor electrical conductivity, are useful in the production of electrical storage or generating devices. Capacitors are devices that store electric energy in the form of an electric field generated in the space between two separated, oppositely charged electrodes. Their capacity to store energy makes them essential components in many electric circuits, and that capacity can be greatly increased by inserting a solid dielectric material into the space separating the electrodes. Dielectrics are materials that are poor conductors of electricity. The nonconducting properties of ceramics are well known, and some ceramics are made into extremely effective dielectrics. Indeed, more than 90 percent of all capacitors are produced with ceramic materials serving as the dielectric. Piezoelectrics are materials that generate a voltage when they are subjected to mechanical pressure; conversely, when subjected to an electromagnetic field, they exhibit a change in dimension. Many piezoelectric devices are made of the same ceramic materials as capacitor dielectrics. This article describes the properties of the most prominent dielectric and piezoelectric ceramics and surveys their practical applications. Additional reading Materials on capacitor dielectric and piezoelectric ceramics may be found in A.J. Moulson and J.M. Herbert, Electroceramics: Materials, Properties, Applications (1990); Larry L. Hench and J.K. West, Principles of Electronic Ceramics (1990); and the section titled Electrical/Electronic Applications for Advanced Ceramics, in Theodore J. Reinhart (ed.), Engineered Materials Handbook , vol. 4, Ceramics and Glasses, ed. by Samuel J. Schneider (1991), pp. 110566.A good introduction to ceramics in general is provided by David W. Richerson, Modern Ceramic Engineering: Properties, Processing, and Use in Design, 2nd ed., rev. and expanded (1992). The processing of both traditional and advanced ceramics is described in James S. Reed, Introduction to the Principles of Ceramic Processing (1988); I.J. McColm and N.J. Clark, Forming, Shaping, and Working of High Performance Ceramics (1988); George Y. Onoda, Jr., and Larry L. Hench, Ceramic Processing Before Firing (1978); and four sections of the Reinhart book cited above: Ceramic Powders and Processing, pp. 41122; Forming and Predensification, and Nontraditional Densification Processes, pp. 123241; Firing/Sintering: Densification, pp. 242312; and Final Shaping and Surface Finishing, pp. 313376. Thomas O. Mason