Ceramic superconducting materials

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. 

Nonliving matter, such as blood plasma, serum, hormone solutions, foodstuffs, pharmaceuticals (e.g., antibiotics), ceramics, superconducting materials, and materials of historical documents (e.g., archaeological wood)... 

The importance of materials science to U.S. competitiveness can hardly be overstated. Key materials science areas underlie virtually every facet of modem life. Semiconductors underpin our electronics industry. Optical fibers are essential for communications. Superconducting materials will probably affect many areas ceramics, composites, and thin films are having a big impact now in transportation, construction, manufacturing, and even in sports—tennis rackets are an example. 

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. 

Many ceramics are partially polymeric in structure. These include the new superconductive materials that exist as polymeric sheets connected by metal ions similar to many of the silicate sheets. 

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. 

By 1959, the theory of superconductivity was firmly established, and even though there have been modifications, it has stood the test of time. But only, apparently, insofar as it relates to the conventional, metallic, low-temperature superconducting materials. The new high-temperature superconductors, the ceramics, pose another set of questions and may require an entirely new theory. 

The new superconducting ceramics offer a way out, if they can be made in some workable form, probably a thin film, and so long as the circuits can be operated at around 80° K or higher. The oxides could then be used on the circuit chips themselves to connect transistors and other devices and to make connections between chips. There is also the possibility that the superconducting properties in the new materials can be manipulated by, say, moving oxygen in and out as needed, or that the ceramics will turn out for some reason to be more suitable than conventional superconducting materials for use in transistors. 

But let s return to Josephson junctions for a moment. Even though a computer made of these incredible instruments has not yet been built, the junctions themselves, as we have said, are in use, fabricated of conventional superconducting materials. They are also beginning to appear in devices run by the new superconducting ceramics. 

These "high-temperature" superconducting materials are very interesting. First, they are not metals. They are ceramics. A ceramic is a clay-like material. It often consists of sand, clay, brick, glass, or a stone-like material. 

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