Ceramic Capacitor Materials

Approximately 40% of the U.S. electronic ceramics industry is represented by ferroelectrics. Table 3 shows U.S. consumption of ceramic capacitors and piezoelectric materials (109). 

Table 3. U.S. Ceramic Capacitor and Ceramic Piezoelectric Material Consumption ...

Strontium Titanate. Strontium titanate [12060-59-2], SrTiO, is a ceramic dielectric material that is insoluble in water and has a specific gravity of 4.81. It is made from strontium carbonate and is used in the form of 0.5-mm thick disks as electrical capacitors in television sets, radios, and computers. 

Capacitors. Ceramic materials suitable for capacitor (charge storage) use are also dependent on the dielectric properties of the material. Frequently the goal of ceramic capacitors is to achieve maximum capacitance in minimum volume. The defining equation for capacitance is given by ... 

Barium titanate and BaTi03-based materials are most commonly used for ceramic capacitors with high dielectric permittivity. BaTi03 powder of extremely high quality (in respect of its purity, stoichiometry, particles morphology) is required for most of the modem applications. This characteristic may be considerably improved by the application of alkoxide precursors. Thus, it is of no surprise that synthesis of BaTi03 and BaTi03-based materials from metal alkoxides attracted considerable attention for several decades. The first works on... 

The compositions of most dielectric materials used for ceramic capacitors are based on ferroelectric barium titanate. As discussed in detail in Pragraph 1.3 the permittivity of ferroelectric perovskites shows marked changes with temperature, particularly close to the phase transition. From the device point of view a high dielectric permittivity with stable properties over a wide temperature range is required. There are various specifications which have to be fulfilled (e.g. X7R AC/C(T = 25°C) < 0.15 in a range between -55°C and 125°C). 

Ceramic capacitors are prepared with their chemical compositions placing them close to a ferroelectric-paraelectric phase boundary, where the dielectric permittivity is anomalously high. These materials are commonly based on BaTiOs which is similar in structure and properties to the piezoelectric ceramics. 

I. Bum, Ceramic capacitor dielectrics, in Engineered Materials Handbook, Vol. 4 Ceramics and Glasses, ASM International, 1991, pp. 1112-1118. 

Barium and strontium have been incorporated in new materials research. Barium titanate (BaTi03) is used in ceramic capacitors and, when incorporated in tin, makes a material harder than diamond. Crystals of barium titanate are also used in optical materials. Strontium titanate (SrTi03) has such a high refractive index that it sparkles like diamond and is used in less expensive jewelry. 

We thank W. W. Rhodes of AT T Bell Laboratories at Murray Hill, New Jersey for supporting our work in the relaxor materials. Subsequent work on the processing and reliability of multilayer ceramic capacitors was achieved through many useful collaboration and discussions with our colleagues at AT T Bell Laboratories Engineering Research Center at Princeton, New Jersey. 

Yonezawa, M., Low-firing multilayer capacitor materials, Am. Ceram. Soc. Bull., 62, 1375 (1983). 

Magnetic ceramics represent an important fraction of the magnetic industry in the US, an estimated 40% of the total hard magnetic materials market value is dominated by ferrites, and in spite of the continuous development of new materials, ferrite consumption is still growing. In soft material applications, ferrites participate with an estimated 20% of the market value. In 1990, the estimated world production was 159 500 metric tons of soft ferrites, and 431 100 metric tons of hard ferrites (Ruthner, 1989). In addition to the versatility of ferrites, there are two essential factors which explain this success the low electrical conductivity, and the low production cost. The market value of ferrites ( 3/kg) is very low compared with other electroceramics 33/kg for varistors, 330/kg for thermistors and 1100/kg for ceramic capacitors (Cantagrel, 1986). 

Freiman, S.W. and Pohanka, R.C. (1989) Review of mechanically related failures of ceramic capacitors and capacitor materials. /. Am. Ceram. Soc., T2.,... 

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