Electrical Properties of Ceramics

Doping. The addition of small quantities of other materials to markedly affect the properties of the main component. Electrical properties of ceramics are particularly susceptible to modification in this way. 

The electrical properties of ceramic substrates perform an important task in the operation of electronic circuits. Depending on the applications, the electrical parameters may be advantageous or detrimental to circuit function. Of most interest are the resistivity, the breakdown voltage or dielectric strength, and the dielectric properties, including the dielectric constant and the loss tangent. 

The electrical properties of ceramic insulators are in no way impaired by the addition of PEG. Usually, as little as 1% PEG 20,000 is sufficient to plasticize the body adequately for extrusion. Spray-dried oxide ceramic material requires a PEG content of 4% on average, while for injection molding the additions may be considerably higher without adversely affecting the electrical properties. 

A. K. Sarkar and T. L. Peterson, Fabrication and electrical properties of ceramic superconductor/polymer composites, Polym. Eng. Sci. 52 305 (1992). 

Properties and Mature of Bonding. The metaUic carbides are interesting materials that combine the physical properties of ceramics (qv) with the electronic nature of metals. Thus they are hard and strong, but at the same time good conductors of heat and electricity. 

Grain boundaries have a significant effect upon the electrical properties of a polycrystalline solid, used to good effect in a number of devices, described below. In insulating materials, grain boundaries act so as to change the capacitance of the ceramic. This effect is often sensitive to water vapor or other gaseous components in the air because they can alter the capacitance when they are absorbed onto the ceramic. Measurement of the capacitance allows such materials to be used as a humidity or gas sensor. 

As we have mentioned, the piezoelectric properties of ceramics are generated by a poling process. Apparently, if a strong electric field in a direction other than the poling direction is applied, the piezoelectric property is altered or lost. The safe value of an ac field to avoid causing depoling, Ej, can be found in the product specifications. 

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. 

To improve, mechanical or electrical properties of Si3N4 ceramics different types of composite materials have been developed (Table 16). Among them Si3N4/TiN and Si3N4/SiC are the most extensively investigated. 

After 14 years on the faculty of Imperial College, Jacobs moved from London, England, to London, Ontario, where his research program focused on the optical and electrical properties of ionic crystals, as well as on the experimental and theoretical determination of thermodynamic and kinetic properties of crystal defects.213 Over the years his research interests have expanded to include several aspects of computer simulations of condensed matter.214 He has developed algorithms215 for molecular dynamics studies of non-ionic and ionic systems, and he has carried out simulations on systems as diverse as metals, solid ionic conductors, and ceramics. The simulation of the effects of radiation damage is a special interest. His recent interests include the study of perfect and imperfect crystals by means of quantum chemical methods. The corrosion of metals is being studied by both quantum chemical and molecular dynamics techniques. 

Only a few authors have reported results concerning the electrical properties of CNT-ceramic composites and most have been concerned with the influence... 

Huang, Q. and Gao, L., Manufacture and electrical properties of MWCNT/BaTi03 nanocomposite ceramics , J. Mater. Chem., 2004, 14, 2536-2541. 

Thermal Evaporation The easiest way of evaporating metal is by means of resistance evaporators known commonly as boats . Boats, made of sintered ceramics, are positioned side by side at a distance of approximately 10 cm across the web width (Fig. 8.1). Titanium boride TiB2 is used as an electrically conductive material with boron nitride BN (two-component evaporator) or BN and aluminum nitride AIN (three-component evaporator) as an insulating material [2]. By combination of conductive and insulating materials, the electrical properties of evaporators are adjusted. 

Figure 12. The conductivity of negatively doped SrTiOj as a function of oxygen partial pressure. Top model (D negative doping), Bottom experimental data from Ref.51. (Reprinted from G. M. Choi and H. L. Tuller, Defect Structure and Electrical Properties of Single-Crystal Bao.ojSro. TiOj. /. Am. Ceram. Soc. 71, 201-205. Copyright 1988 with permission from the American Ceramic Society.)...

Nadaud N., Nanot M., Boch P. Sintering and electrical properties of titania- and zirconia-containing In203-Sn02 (fTO) ceramics. J. Am. Ceram Soc. 1994 77 843-46. 

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