Ceramics electrical resistivity values

Materials can be classified as conductors, semiconductors or insulators. Conductors typically have resistivity in the range 10 2-103 xQ cm, semiconductors approximately 106-10n iQ cm, and insulators about 1013-1018 (xQ cm. Table 1.5 compares the electrical resistivity of the elements and compounds at room temperature. Although the carbides and nitrides have somewhat higher resistivity than do the pure metals, they still have resistivity in the regime of metallic conductors. In comparison the ceramic materials have much higher values, and are typically insulators. 

The Seebeck coefficient a and figure of merit Z for B4C-B ceramics as a function of C content are given in Fig. 7 and Fig. 8, respectively. The a was always positive, and its absolute value increases with increasing carbon content except for B4C+5B. a (0.30 0.38 mV/K), whose maxima was observed at 20 at.% C (B4O sintered at 2250 °C, showed opposite tendency of electric resistivity (7X 10 6 X10" Qm), whose minimum was at B4C+8B sample fired at 2250°C. Though the figure of merit Z is evaluated from electrical resistivity, thermal conductivity and Seebeck coefficient, the Z values showed maximum of 2.4 X 10 K at B4C+8B composite fired at 2250 °C. Therefore, the electric resistivity affects more than the Seebeck coefficient. 

Electrical Resistivity The value of electrical resisdvity is a measure of the resistance of material to the flow of electrid. For example, plastics and ceramics typically have high resisdtdty, whereas metals ically have low resisdvity, and among the best conductors of electricity are silver and copper. 

The units for resistivity are ohm meter ( 2 m). Table 2.30 gives the values of electrical resistivity for various materials, indicating that metals typically have low resistivities (and correspondingly high electrical conductivities) and ceramics and polymers typically have high resistivities (and correspondingly low conductivities). 

The most famous study of doped ZnO for TE purpose was reported by Tsubota et who showed that in the Al -doped ZnO series, a ZT 0.3 at 1273 K is reached for air-prepared ceramics Zno.98Alo.02O. As shown in Figure 4.35, the Al " doping, expected to create donor levels (electrons) to the conduction band, strongly reduces the electrical resistivity p) as compared with ZnO. At RT, p decreases by more than 3 orders of magnitude, the semiconducting behaviour of ZnO being replaced by almost T independent p values. 

Yoon et al. [48] proposed a liquid junction free polymer membrane-based reference electrode system for blood analysis under flowing conditions. They used silicmi wafers as well as ceramic substrate to fabricate ion selective sensors with an integrated reference electrode. The silver chloride layer was coated with a membrane based on aromatic polyurethane (PU 40 membrane) with equimolar amounts of both cathodic and anodic lipophilic additives (TDMACl and KTpCIPB) to reduce the electrical resistance (see Chaps. 12 and 13). The ceramic-based sensors were fabricated by screen-printing methods. Both reference electrodes showed a rather stable potential in various electrolyte solutions with different pH values and different concentrations of clinically relevant ions, providing that the ionic strength of the solution is over 0.01 M. The integrated ISE cartridge based on the ceramic chip could be used continuously for a week. 

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