Superconductivity ceramic materials exhibiting

Superconductivity has been known since 1911, and superconducting systems based on various metal alloys (e.g., NbTi and Nb3Sn) are currently used as magnets and in electronics. These materials exhibit superconductivity only at temperatures below 23 K and require cooling by liquid helium. The discovery of ceramics that exhibit superconductivity at temperatures up to 120 K, the so-called high-temperature superconductors, has sparked a tremendous amount of scientific activity and commercial interest around the world. 

Research chemists found that they could modify the conducting properties of solids by doping them, a process commonly used to control the properties of semiconductors (see Section 3.13). In 1986, a record-high Ts of 35 K was observed, surprisingly not for a metal, but for a ceramic material (Section 14.24), a lanthanum-copper oxide doped with barium. Then early in 1987, a new record T, of 93 K was set with yttrium-barium-copper and a series of related oxides. In 1988, two more oxide series of bismuth-strontium-calcium-copper and thallium-barium-calcium-copper exhibited transition temperatures of 110 and 125 K, respectively. These temperatures can be reached by cooling the materials with liquid nitrogen, which costs only about 0.20 per liter. Suddenly, superconducting devices became economically viable. 

In addition to exhibiting superconductivity at temperatures, above the boiling point of liquid nitrogen (77 K), these ceramic materials can sustain very high currents, an important characteristic necessary for any large-scale application. More recent results have shown that materials containing thallium and calcium ions in place of the lanthanide ions super- J... 

Electrical and Electronic Applications. Silver neodecanoate [62804-19-7] has been used in the preparation of a capacitor-end termination composition (110), lead and stannous neodecanoate have been used in circuit-board fabrication (111), and stannous neodecanoate has been used to form patterned semiconductive tin oxide films (112). The silver salt has also been used in the preparation of ceramic superconductors (113). Neodecanoate salts of barium, copper, yttrium, and europium have been used to prepare superconducting films and patterned thin-fHm superconductors. To prepare these materials, the metal salts are deposited on a substrate, then decomposed by heat to give the thin film (114—116) or by a focused beam (electron, ion, or laser) to give the patterned thin film (117,118). The resulting films exhibit superconductivity above Hquid nitrogen temperatures. 

When cooled to very low temperatures, some materials lose all electrical resistance and exhibit superconductivity. Some alloys are superconductive when cooled in liquid helium (boiling point 4.2 K), but some ceramics are superconductive at higher temperatures and need only be cooled in liquid nitrogen (boiling point 77.3 K) to show this effect. 

Superconductors are materials that have the ability to conduct electricity without resistance below a critical temperature above absolute zero. The phenomenon of superconductivity was first seen in mercury at liquid helium temperatures. Great interest developed in this area in the late 1980s, when Muller and Bednorz discovered that even ceramic-like materials can exhibit superconductivity. C. W. Chu subsequently found yttrium barium copper oxide (YBCO) to be superconducting above liquid nitrogen temperatures. Indeed, various books are devoted to this subject. > In the following subsections we highlight representative force field applications that have aided the understanding of static and dynamic properties of superconductors. 

The correct stoichiometry, or composition, is necessary because for some materials they exhibit the required property only within a certain composition range. An example is the high-temperature superconductors whose structures we described in Chapter 7. For YBaiCusOet (YBCO), the value of the superconducting transition temperature depends on the value of x. When x is close to one the transition temperature is -90 K. When x = 0.3 the transition temperature is reduced to 30 K. The change in oxygen stoichiometry is associated with a change in the structure of the material. Many technologically important ceramics exist in different crystalline forms. Another... 

The observed disappearance of electrical resistance when mercury and a few other alloys were cooled at liquid He temperature, led to die term superconductors. Only in 1986 did an oxide exhibit superconductivity and at higher transition temperatures, T. The following year the ceramic oxide YB2Cu307. (or YBCO) was found to become superconductor at a temperature >77 K (the boiling point of nitrogen). The ease of its preparation and its study makes it an interesting material. 

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