Ceramic materials dielectric properties

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 ... 

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. 

Xie, Y., Yin, S., Hashimoto, T., Kimura.H. and Sato, T. (2009) Microwave-hydrothermal synthesis of nano-sized Sn2+-doped BaTi03 powdersand dielectric properties of corresponding ceramics obtained byspark plasma sintering method. Journal of Materials Science, 44, 4834—4839. 

Many of the fundamental relationships and concepts governing the electrical properties of materials have been introduced in the previous section. In this section, we elaborate upon those topics that are more prevalent or technologically relevant in ceramics and glasses than in metals, such as electrical insulation and superconductivity, and introduce some topics that were omitted in Section 6.1.1, such as dielectric properties. 

Dielectrics, optics and magnetism (properties of certain ceramic materials)... 

There are other promising ceramic fibres, e.g. boron carbide and boron nitride. Boron nitride fibre has the same density (2.2 g cm-3) as carbon fibre, but has a greater oxidation resistance and excellent dielectric properties. Boron carbide fibre is a very light and strong material. 

Dielectric Constant The dielectric constant of material represents its ability to reduce the electric force between two charges separated in space. This property is useful in process control for polymers, ceramic materials, and semiconductors. Dielectric constants are measured with respect to vacuum (1.0) typical values range from 2 (benzene) to 33 (methanol) to 80 (water). The value for water is higher than that for most plastics. A measuring cell is made of glass or some other insulating material and is usually doughnut-shaped, with the cylinders coated with metal, which constitute the plates of the capacitor. 

In conclusion, it has been demonstrated that the pyroelectric properties of polar materials can be compared relatively simply through the measurement of a few key physical parameters (pyroelectric,dielectric and thermal coefficients) and the judicious use of appropriate figures-of-merit. It is essential that the dielectric properties are measured in the frequency range appropriate for device use, and this is typically in the range of a few to 100 Hz. The properties of many pyroelectric ceramics and thin films have been compared and it has been shown that good pyroelectric properties can be obtained from this films manufactured at relatively low temperatures, a fact that bodes well for their future applications in fully-integrated arrays. 

The origin of this relaxation is in heterogeneity of the ceramic, in which anisotropically shaped grains exhibit strong variation in their piezoelectric and dielectric properties in different directions. As discussed in [17], in such heterogeneous materials Maxwell-Wagner like processes may lead to a behavior shown in Figure 13.6. 

Basantakumar Sharma and Sarma H. N. K., A Mansingh, Ferroelectric and dielectric properties of sol-gel processed barium titanate ceramics and thin film. J. Materials Science. 34(1999) pp. 1385-1388. 

Barium titanate (BaTiOj), a perovskite-type electro-ceramic material, has been extensively studied and utilized due to its dielectric and ferroelectric properties. The wide applications of barium titanates include multiplayer capacitors in electronic circuits, nonlinear resistors, thermal switches, passive memory storage devices, and transducers. In addition, barium titanate can be used for chemical sensors due to its surface sensivity to gas adsorption. 

Several kinds of dielectric materials have been widely investigated to improve their properties and to meet the requisites of high dielectric constant (K), low dielectric loss (Qf), and low TCF. Based on these requisites, complex perovskite compound, A(B,B )03, was extensively studied from the viewpoint of the compositional and structural dependence on their microwave dielectric properties. Among them, much attention has been paid to lead-based ceramics with complex perovskite structures because of their superior dielectric properties required for microwave devices. 

Most of the search for improved microwave materials has been mainly empirical, and it is necessary that the intrinsic properties of materials be known to control and design the dielectric properties of materials. Recently there have been reports on the intrinsic properties of materials by the IR reflectivity spectra and calculation of theoretical polarizability. However, there are discrepancies between the intrinsic properties obtained from these methods and the measured properties due to grain, grain boundary, and pores. Therefore the effects of porosity on the dielectric properties should be considered to evaluate the intrinsic dielectric properties and to predict the dielectric properties of ceramics with pores. 

The ferroelectric Pb(Mgy3Nb2/3)03 (PMN) ceramic has been the snbject of extensive investigations due to its high dielectric coefficient and high electrostrictive coefficient, which renders it suitable for use in capacitors and electrostrictive actuators. However, the successful exploitation of this material is limited by the difficulty of producing a single-phase material with the perovskite structnre. Conventional solid state synthesis techniques invariably resnlt in the formation of one or more pyrochlore phases, which exhibit poor dielectric properties. 

Rao, Y., Ogitani, S., Kohl, P, and Wong, C.P., High dielectric constant polymer-ceramic composite for embedded capacitor application, in Proceedings of the International Symposium on Advanced Packing Materials Processes, Properties, and Interfaces, IEEE, Piscataway, NJ, 2000. 

The mechanisms by which microwave energy is absorbed by the entire processing system (the microwave applicator, the specimens, and the thermal insulation) are crucial to understand the microwave processing of ceramic materials. The microwave energy absorbed per unit time per unit volume, pabs (the powder density), can be related to dielectric properties of the material and to the applied electromagnetic field " ... 

This section deals solely with the response of ceramics to the application of a constant electric field and the nature and magnitude of the steady-state current that results. As discussed below, the ratio of this current to the applied electric field is proportional to a material property known as conductivity, which is the the focus of this section. The displacement currents or non-steady-state response of solids which gives rise to capacitive properties is dealt with separately in Chaps. 14 and 15 which treat the linear and nonlinear dielectric properties, respectively. 

X. Wei and X. Yao, Nonlinear dielectric properties of barium strontium titanate ceramics, Materials Science and Engineering, B, 99, 74-78(2003),... 

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