Superconductors metal oxide

Superconductors (Metals, oxides, organic charge transfer salt)... 

In a sense, a superconductor is an insulator that has been doped (contains random defects in the metal oxide lattice). Some of the defects observed via neutron diffraction experiments include metal site substitutions or vacancies, and oxygen vacancies or interstituals (atomic locations between normal atom positions). Neutron diffraction experiments have been an indispensable tool for probing the presence of vacancies, substitutions, or interstituals because of the approximately equal scattering power of all atoms. 

One of the most exciting properties of some materials is superconductivity. Some complex metal oxides have the ability to conduct electricity free of any resistance, and thus free of power loss. Many materials are superconducting at very low temperatures (close to absolute zero), but recent work has moved the so-called transition temperature (where superconducting properties appear) to higher and higher values. There are still no superconductors that can operate at room temperature, but this goal is actively pursued. As more current is passed through... 

Metalorganic superconductors, 23 851 Metal oxide catalyst formaldehyde manufacture, 12 115-117 Metal oxide catalysts, 10 81 Metal oxide electrodes, silylating agents and, 22 700... 

Lai.85Ba0.i5CuO4) lost its resistance at a Tc = 30-35 K. The observation of superconductivity in a metal oxide at temperatures higher than those of metals themselves triggered a change in emphasis in superconductivity research towards this type of material. In 1987 two research groups, at the University of Houston and the University of Alabama, reported that the oxide of formula YBa2Cu307 x (commonly known as T-2-3 superconductor , from the stoichiometric ratios Y Ba Cu of 1 2 3) displayed a Tc of 92 K. 

A continuous process based on hydrodynamic cavitation can be employed to prepare a wide variety of metal oxides in grain sizes of 1 -10 nm, such as iron oxide, bismuth molybdate, perovskites, platinum-loaded zeolite, and other ceramics and superconductors [170]. The method uses a microfluidiser for mechanically generating hydrodynamic cavitation and the internal pressure of the liquid media is elevated from ambient pressure to between 1000 to 25 000 psi. 

Gloom for Oxide Superconductors Dismayed at the progress through the years, even with the most promising room-temperature metallic, binary oxides, many scientists abandoned the search for new high temperature oxide superconductors. Also, it should be mentioned that a deep-rooted prejudice had developed which claimed that the BCS theory had imposed a maximum transition temperature limit of 25 K for all superconducting materials, and that this temperature had already been achieved in certain alloys of niobium. Some scientists, however, were steadfast in their determination to break this barrier, optimistic in their outlook, and they continued their search for this unusual phenomenon in other metallic oxide systems. 

A determined search for superconductivity in metallic oxides was initiated in mid-summer of 1983 at the IBM, Zurich Research Laboratories in Riischliken, Switzerland. This research effort was an extension of previous work (145) on oxides, namely, Sr1.xCaxTiOs, which exhibited some unusual structural and ferro-electric transitions (see Section 2.2a). During the summer of 1983, the superconductivity research was focussed on copper-oxide compounds. Muller had projected the need for mixed Cu2+/Cu3+ valence states, Jahn-Teller interactions (associated with Cu2+ ions), and the presence of room temperature metallic conductivity to generate good superconductor candidates. These researchers then became aware of the publication by Michel, Er-Rakho, and Raveau (146) entitled ... 

Soft metallic elements such as Al, In, Pb, Hg, Sn, Zn, Tl, Ga, Cd, V and Nb are type I superconductors. Alloys and chemical compounds such as Nb3Sn, V3Ga, and lZa3In, and some transition elements, are type II superconductors. Type II substances generally have a higher Tc than do type I superconductors. The recently discovered transition metal oxide superconductors have generated intense interest because they are type II superconductors with very high transition temperatures. Table 13.1 summarizes Tc for selected superconductors. 

It is clear that no organic compound with a polymer chain of conjugation has been found to be superconducting. It is equally clear that all known superconductors are metal, compound alloy, or metal-oxide of some kind (including ceramics ). This fact suggests that the quasi-free electrons do play an important role in superconductivity. Thus, the key to the superconductivity mechanism should lie in a combination of Covalon-conduction and quasi-free electrons. 

Kremer, R.K., Kim, J.S., Simon, A., in Bussmann-Holder, A., Keller, H., editors. High Tc Superconductors and Related Transition Metal Oxides. Berlin Springer 2007, p. 213. 

Strongly correlated electron systems including high-Tc superconductors were discussed in talks by S. Ovchinnikov (Theory for transition metal oxides), G. Petrakovskii (Magnetism of 2D spin systems),... 

---