Semiconducting ceramics

Most oxide semiconductors are either doped to create extrinsic defects or are aimealed under conditions in which they become nonstoichiometric. 

If we use the subscript i to denote intrinsic carrier concentrations, we can write 

For every electron that is excited into the conduction band, a hole is produced in the valence band. 

In ceramics these depend upon their interaction with the lattice. Typical values are very small ( 0.1cm V s ) orders of magnitude lower than in Si and GaAs. 

The intrinsic conductivity of many pure oxide semiconductors is generally very low because of their large g compared to Si and GaAs. To illustrate this point we will compare the room temperature conductivities of CuiO, a semiconducting oxide g = 2.1 eV, and GaAs, a III-V semiconductor g= 1.4eV. 

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The equations generally developed include all forms of the conduction. Eor example, to determine the flux or conductivity of ions in a soHd electrolyte as compared to electrons in a semiconducting ceramic, two terms are of interest the number of charge carriers and the mobiUty. The effects of temperature, composition, and stmeture on each of these terms must also be considered. 

Semiconducting Ceramics. Most oxide semiconductors are either doped to create extrinsic defects or annealed under conditions in which they become non stoichiometric. Although the resulting defects have been carefully studied in many oxides, the precise nature of the conduction is not well understood. Mobihty values associated with the various charge transport mechanisms are often low and difficult to measure. In consequence, reported conductivities are often at variance because the effects of variable impurities and past thermal history may overwhelm the dopant effects. 

Strontium titanate 23 324, 25 21 gems cut from, 25 46 semiconducting ceramic, 5 599-600 semiconductor, 5 600 superconductivity in, 5 603 Strontium tribismuthide... 

Among nonmetaUic resistance thermometers, an important class is that of thermistors, or temperature-sensitive semiconducting ceramics (5). The variety of available sizes, shapes, and performance characteristics is very large. One manufacturer lists in the catalog a choice of characteristics ranging from 100 Q at 25°C to 1 M Q at 25°C. 

Zinc oxide is a semiconducting ceramic used to make varistors (variable resistors). Write a balanced equation for the hydrolysis of zinc ethoxide in the sol-gel method for making ZnO powders. 

The science of gas-sensors based on changes in electronic conductivity of a semiconducting ceramic is a complex matter depending upon a combination of surface chemistry and electron transport in mainly transition metal oxides. As is usual in exploiting electroceramics, the applications technology runs ahead of... 

The breakthrough came in 1986 when J.G. Bednorz and K.A. Muller [37] reported superconductivity with Tc = 35 K in the semiconducting ceramic,... 

Probably the most common solid electrode is platinum, although it dissolves anodically in some melts, for example in halides. The choice of gold and silver [86] is also frequently made. Graphite is very often used because it is cheap and can be obtained in a wide range of sizes and qualities. These electrodes can be used over long periods of time, and they have a wide electrochemical stability, both anodic and cathodic. Vanadium and molybdenum are also used in appropriate systems. Studies for the use of some inert anodes made of semiconducting ceramics have been made, especially for aluminum electrolysis [87],... 

A Partially Conductive and a Partially Semiconductive Ceramic.. 182 7.5 Materials Contrasts in the SFM Non-Contact Mode. 185... 

Kikkawa, H., B. O Regan and M.A. Anderson (1991). The photoelectrochemical properties of Nb-doped Ti02 semiconducting ceramic membrane. Journal of Electroanalytical Chemistry, 309(1-2), 91-101. 

There are two types of the barrier layer capacitors. In the surface capacitors thin insulat layers are present at the surface of semiconducting ceramics these surface layers determine dielectric properties, and are formed by using a reduction/reoxidation process. In the sect type, ihe so-calied intergranular capacitor, the insulating layers have been formed at the gr boundaries (see e.g. Wernicke, 1978). 

The aqueous corrosion of ceramics may involve a charge-transfer or electrochemical dissolution process. However, in many cases, dissolution or corrosion may take place with no charge transfer yet may be determined by one or more electrochemical factors such as absorbed surface charge or electronic band bending at the surface of narrow-band-gap semiconducting ceramics. The aqueous corrosion of ceramics is important in a number of areas. One of the most important is the stability of passive oxide films on metals. The stability of ceramics is a critical aspect in some aqueous photoelectrochemical applications (12), an example being the photoelectrolytic decomposition of water. Structural, nonoxide ceramics such as SiC or Si3N4 are unstable in both aqueous acid and alkaline environments the latter is virtually unstudied, however. 

For good response time and accuracy, the sensitive material should be porous and as thin as possible, and the ceramic temperature needs to be in the range of 600-1000 °C. These requirements are met by applying the semiconducting ceramics as porous thick-film layers on a heated A1203 substrate. 

The functional phase in thick-film resistors is a mixture of electrically conducting (or semiconducting) ceramic powders such as ruthenium dioxide (RUO2), bismuth ruthenate (Bi2Ru207), lead ruthenate (Pb2Ru206), and Ag-Pd-PdO mixtures for use in air-fired pastes and tantalum nitride (TaN) for nitrogen-fired pastes. The resistance of thick-film resistors is specified in terms of sheet resistance, which has units of ohms/square (Q/D). 

In most ceramics the electronic contribution to the overall thermal conductivity is negligible. However, it can be significant in electrically conducting and semiconducting ceramics such as SiC, TiC, and graphite. 

Azad A-M, Hammond M. Thermodynamically-driven reconstitution of semiconducting ceramic oxides. In Jackson MJ, Ahmed W, editors. Proceedings of the fourth international surface engineering congress and exposition, August 1-3, 2005. St. Paul, MN ASM International, Materials Park, OH 2006, p. 231-240. 2006. ISBN 0-87170-835-31. 

Space Charge Layers in Semiconducting Ceramic Materials 699... 

Some ceramics are semiconductors. Most of these are transition metal oxides, such as zinc oxide. Ceramicists are most interested in the electrical properties that show grain boundary effects. Semiconducting ceramics are also employed as gas sensors. When various gases are passed over a poly crystalline ceramic, its electrical resistance changes. With tuning to the possible gas mixtures, very inexpensive devices can be produced. 

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