Barium titanate-based dielectrics

Multilayer capacitors A critical step in the manufacture of multilayer capacitors is, of course, the barium titanate-based starting powders, and the various routes for producing these are described in Section 3.4. The multilayer capacitor structure (Fig. 5.11) enables the maximum capacitance available from a thin dielectric to be packed into the minimum space in a mechanically robust form. 

S. Wang, G O. Dayton Dielectric Properties of Fine-Grained Barium Titanate Based X7R Materials J. Am. Ceram. Soc. 82 (10), (1999), 2677-2682. 

In addition to the multilayered ceramic capacitors just described, many of the barium titanate-based compounds that exhibit high dielectric constants are used in single-layer tape-cast capacitor devices. Relaxor materials such as lead magnesium niobate (PMN), which are characterized by high dielectric constants, broad dielectric maxima, and low sintering temperatures, have been manufactured in thin sheets by tape casting. 

Barium titanate-sintered ceramics are developed with the objective of producing materials with special electrical properties, particularly a high dielectric constant. Barium titanate-based sintered ceramics are produced with... 

Historically, materials based on doped barium titanate were used to achieve dielectric constants as high as 2,000 to 10,000. The high dielectric constants result from ionic polarization and the stress enhancement of k associated with the fine-grain size of the material. The specific dielectric properties are obtained through compositional modifications, ie, the inclusion of various additives at different doping levels. For example, additions of strontium titanate to barium titanate shift the Curie point, the temperature at which the ferroelectric to paraelectric phase transition occurs and the maximum dielectric constant is typically observed, to lower temperature as shown in Figure 1 (2). 

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). 

A significant increase in permittivity of barium titanate dielectrics, required very small size capacitors, can be attained by utilizing the barrier phenomena whi are based on the formation of thin insulating layers in semiconducting BaTi< ceramics. These systems exhibit permittivity values of the order 10. ... 

Conducting polymers also can be utilized to form core-shell structures with high dielectric constant particles. Fang et al. used PANl to encapsulate barium titanate via in situ oxidative polymerization. They examined the influence of the fraction of BaTiOs particles on the ER behavior, and found that the PANl/ BaTiOs compo-sites-based ERFs exhibit a better ER effect than does pure PANl, which result might be due to the unique ferroelectric properties as well as the high dielectric constant of BaTiOs nanoparticles. 

Barium titanate (BaTiOs) is historically one of the most important ferroelectric ceramic materials its main use in modern applications is as a base composition for capacitors, due to its high dielectric constant [98]. 

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