Dielectrics Barium titanate, BaTiO

Barium titanate, BaTiOs, is a ferroelectric material (see Chapter 9) widely used in capacitors because of its high dielectric constant. It was initially prepared by heating barium carbonate and titanium dioxide at high temperature. 

The relative permittivity values normally encountered in crystals are rather small (Table 11.1). Some crystals, however, exhibit relative permittivity values many orders of magnitude higher than those in normal dielectrics. For example, one crystallographic polymorph of barium titanate, BaTiOs. has a relative permittivity, e, of the order of 20 000 (more values are given in Table 11.2.). By analogy... 

Cho, S. D., Lee, J. Y, and Paik, K. W., Effect of particle size on dielectric constant and leakage current of epoxy/barium titanate (BaTiOs) composite films for embedded capacities, in International Conference on Electronic Materials and Packaging, 2001, pp. 63-68. 

Electronic ceramics include barium titanate (BaTiOs), zinc oxide (ZnO), lead zirconate titanate [Pb(ZrJ ii ()03], aluminum nitride (AIN), and HTSCs. They are used in applications as diverse as capacitor dielectrics, varistors. 

Barium titanate (BaTiOs) was the first ceramic in which ferroelectric behavior was observed and is probably the most extensively investigated of all ferroelectrics. Its discovery made available ks up to two orders of magnitude greater than had been known before. This property was very soon utilized in capacitors and BaTiOs remains the basic capacitor dielectric in use today (although not in its pure form). There are several reasons why BaTiOs has been so widely studied ... 

NaKC4H40e 4H2O), monopotassium dihydrophosphate (KH2PO4), or barium titanate (BaTiOs). At sufficiently high temperatures ferroelectrics show normal dielectric behavior. However, below a certain critical temperamre (so called. Curie temperature), even a small electric field causes a large polarization, which is preserved even if the external field is switched off. This means that below the Curie point ferroelectric materials show spontaneous polarization. The phase transition at the Curie temperature is related to the change of the lattice symmetry of the sample. 

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]. 

Barium carbonate also reacts with titania to form barium titanate [12047-27-7] BaTiO, a ferroelectric material with a very high dielectric constant (see Ferroelectrics). Barium titanate is best manufactured as a single-phase composition by a soHd-state sintering technique. The asymmetrical perovskite stmcture of the titanate develops a potential difference when compressed in specific crystallographic directions, and vice versa. This material is most widely used for its strong piezoelectric characteristics in transducers for ultrasonic technical appHcations such as the emulsification of Hquids, mixing of powders and paints, and homogenization of milk, or in sonar devices (see Piezoelectrics Ultrasonics). 

Barium titanate is usually produced by the soHd-state reaction of barium carbonate and titanium dioxide. Dielectric and pie2oelectric properties of BaTiO can be affected by stoichiometry, micro stmcture, and additive ions that can enter into soHd solution. In the perovskite lattice, substitutions of Pb ", Sr ", Ca ", and Cd " can be made for part of the barium ions, maintaining the ferroelectric characteristics. Similarly, the TP" ion can partially be replaced with Sn +, Zr +, Ce +, and Th +. The possibihties for forming solution alloys in all these stmctures offer a range of compositions, which present a... 

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. 

The information about nanocrystalline ferroic powders fabricated by various chemical synthesis technologies is reported in Table 5.2. Their possible applications are also listed. Powders of the same ferroics for two different applications might be obtained by different techniques since the requirements of size distribution, morphology, agglomeration and impurity composition are determined by different technological conditions. For example, barium titanate is a dielectric with high dielectric constant and it is widely used in multilayer ceramic capacitors, whereas semiconducting properties of rare-earth doped BaTiOs are important for thermistors. 

Titanates are double oxides of the form MeTiOa or Me2Ti04. Barium titanate BaTiOa and its solid solution crystals with other titanates are especially well-known. BaTiOs crystallizes in the perovskite structure. Its technical importance results from its ferroelectric and associated piezoelectric properties, its high dielectric constant at room temperature, and the interesting semiconducting properties which it exhibits when doped [13]. The remarkable temperature dependence of the electrical resistance of such doped material (the temperature coefficient can be metal-like) is used to advantage in control and circuit devices. 

Qrmposite samples of PMMA/BaTIOi were prepared by polymerization of MMA in which fine partides of BaTiO were dispersed [931-33]. Samples with 0 to about 60 vol% BaTiOt were successfully obtained without any considerable gradient of ceramic powder concentration. Further enrichment of the composite with barium titanate led to a sharp rise in porosity of the material. This is a known property of mixtures of solid dielectrics (109]. 

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