Superconductive ceramics materials

Until 1986 many experiments were carried out using metals and alloys. However, in 1986 Georg Bednorz and Alex Muller, two researchers of the IBM laboratory in Ruschlikon near Zurich, published an article in the Zeitschrift fur Physik in which they announced that they had made a superconducting ceramic material. It turned out to be a compound made of barium, copper, lanthanum and oxygen, which became superconducting at 35 K. They were awarded the Nobel prize for this discovery. After this, superconductors developed rapidly, at least as far as critical temperature is concerned. 

Superconducting ceramic materials have some limitations as electrical conductors when compared with an ordinary conductor such as copper wire. What are some of fliese ... 

This extraordinary discovery of superconductivity in a ceramic material led to an explosion of research on other ceramic systems. The most notable... 

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

G. Bednorz and K. A. Miiller (Zurich) for their important breakthrough in the discovery of superconductivity in ceramic materials. 

The same type of experiment has been carried out on electrodes of different superconducting materials. As deducible from Figure 16, not all of these ceramic materials undergo severe degradation in the presence of water. 

Here again certain trends were observed, and the most influential factor was the crystal structure which the superconducting material adopted. The most fruitful system was the NaCl-type structure (also referred to as the B1 structure by metallurgists). Many of the important superconductors in this ceramic class are based on this common structure, or one derived from it. Other crystal structures of importance for these ceramic materials include the Pu2C3 and MoB2 (or ThSi2) prototypes. A plot of transition temperature versus the number of valence electrons for binary and ternary carbides shows a broad maximum at 5 electrons per atom, with a Tc maximum at 13 K. 

In the system Ba(Pb1.xBix)Os, the compound with x = 0.25 must be considered the first discovered ceramic material showing high-temperature superconductivity (7). Structure determinations have been carried out over the entire range of composition (8)-(ll) and the refined parameters are presented in Table 2. Superconductivity in this system exists only for values of x between 0.05 and 0.35. The value of the critical temperature increases with x, reaches a maximum value Tc 13K for x = 0.25, and then decreases. For x > 0.35, the material becomes a semiconductor. 

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. 

Can this model also be applied to ceramic superconductors After extensive correspondence and a literature search involving scanning tunneling electronmicroscopy and screw dislocations in crystals, I decided to drop this subject, mainly because it exceeds the level of this book. It can, however, be concluded that superconductivity in ceramic materials is based on a different mechanism. 

Clay is one of the most important building materials conceived by humanity. Without clay, little from our past would remain preserved. Without clay, we would have fewer beautiful works of art to enjoy we would not have useful electrical insulators and other modern-day appliances. Recently, high -temperature (90°K or -183°C) ceramic superconducting materials have been developed. Ceramic materials are used to make heat shields for space vehicles, such as the space shuttle. Clay is a material of the past and of the future. We will always be playing with clay. 

Routes to monomeric , mononuclear , monolanthanide alkoxides, enolates, siloxides and aryloxides - an expanded title which will put the scope of the article in a more concrete form. The synthesis of mononuclear alkoxides, in particularly homoleptic derivatives [1], was decisively stimulated by the discovery of high temperature superconducting ceramics based on YBa2Cu307<, where yttrium represents the lanthanide elements [2]. The support of volatile and highly soluble molecular precursors is a prerequisite for synthesizing thin films of these materials by means of MOCVD [3] and sol gel processes [4], respectively. More recently, lanthanide alkoxide reagents became established in... 

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... 

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