Ceramics with Metal-Like Conductivity

Transition metals have partially filled d orbitals. 

Remember that Q (ohm ) is S (siemens). Some ceramics, for example TiO and VO, show metallic- 

The 2p orbitals from the oxygen atoms form a filled valence band. The bands formed by the 4s and 4p orbitals on the Ti are at a 

FIGURE 30.6 Energy bands of a transition metai oxide (a) d band empty (b) metallic oxide with d band partially filled. 

FIGURE 30.5 The structure of TiO. (a) The (100) plane, (b) The (200) plane. Both show the absence of alternate ions along 110 directions. The resultant superlattice has a monoclinic unit cell as indicated by the shaded region. 

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Fillers play an important role in powder coating of polyamide to form articles with a metal-like look (e.g., handles, mountings for radiators and pipes). For a material to be powder coated, it must withstand the stoving temperatures (170°C or more). It must also be electrically conductive, be chargeable and its reactive groups must be able to link with the coating system. Fillers such as metal and metal coated ceramic spheres and carbon fibers are added to polyamide for its strength and paintability. 

The electrochemical cell, as shown schematically in Fig. 1, consists of gas-tight ceramic electrolyse in the form of tubes, discs, planar substrates, or thick films which is sandwiched by precious metal like platinum or silver as electrodes. Both electrodes are in close contact with two separate gas compartments. Such cells often modified by other electrode materials like electric conducting oxides (chromites, manganites) are commonly used as gas sensors, fuel cells, and electrolysis cells. Yttria-stabilized zirconia (YSZ Zro.84To.i6< i.92) as oxide ionic conductor is widely used as an electrolyte. 

Detector elements 11 are formed on a ceramic substrate 1. Each detector element includes a photosensitive zone 9, an output terminal 4 and a common terminal S. The detector elements are arranged in an array protruding from a common metal line 3, which is connected to a terminal pad 6. The terminal electrodes and the common metal line are formed on a comb-like patterned photo-conductive layer 2. An aperture plate 7 of silicon or ZnS having apertures 8 formed therein by an anisotropic etching method is prepared. The purpose of the aperture plate is to restrict the field of view of the photosensitive zones. An auxiliary electrode 30 is formed on the aperture plate. When the aperture plate is assembled with the substrate using an adhesive, the auxiliary electrode is pressed against the common metal line and the common terminal, which together reduce the electrical resistance. 

Titanium diboride is an advanced ceramic material with properties similar to those of metals such as high thermal and electrical conductivity. The other distinguishing features of this material are its excellent oxidation resistance and chemical corrosion resistance at elevated temperatures. It can be used as an abrasive and oxidation protection coating as well as the electrode material in aluminium refining. In addition, like other borides it can also be used as a neutron absorber. 

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