High Tc superconducting ceramic

The re arch in catalysis is still one of the driving forces for interface science. One can certainly add to the topics of interface physics the whole new field of interface problems that is about to spring out of the new high Tc superconducting ceramics, i.e. the fundamental problem of the matching of the superconducting carriers wave-functions with the normal state metal or semiconductor electron states, the super-conductor-superconductor interfaces and so on, as well as the wide open discovery field for devices and applications. 

Raman spectroscopy has played a significant role in the characterization of electrical conductors, some of which have become superconductors. There are three general classes of compounds that have been investigated using Raman spectroscopy. These are the high- Tc superconducting ceramics the low-7 ... 

The discovery of the new high Tc, superconducting ceramics has generated excitement among physicists and material scientists alike. It is important to recognize that these materials are very similar to other advanced ceramics in that they are prepared from oxide powders which are pressed and sintered. They are polycrystalline materials whose electrical, magnetic, and mechanical properties will be critically dependent on their... 

Oligomerization becomes more and more important as the N-Z difference increases, that is, as the oxidation state Mz+ decreases. Divalent metals give insoluble polymeric alkoxides [Af(OR)2]n (Af2+ = Fe, Co, Ni, Cu,. ..). This was a real drawback for the sol-gel synthesis of high-Tc superconducting ceramics, such as YBa2Cu307-e. Bulky ligands, such as 2-(2-ethoxy-ethoxy)ethoxide had then to be used to prevent oligomerization and obtain soluble copper oxide molecular precursors [11]. 

After more than ten years of extensive experimental and theoretical studies of the phenomenon of the high Tc superconductivity (HTSC) [1], we still do not know a microscopic mechanism responsible for this phenomenon. Numerous theories of pairing, which lead to high Tc values, are based on models [2-9] and cannot connect a specific chemical composition of HTSC ceramics with the value of the transition temperature Tc. For creating a quantitative theory of the HTSC phenomenon further comparative studies of the electronic structure and their relative properties of SC and non-SC ceramics are needed. In this paper, we confine ourselves to calculations of the electronic structure of the SC yttrium ceramics. 

The second main part of a PLD system is the vacuum chamber. The author s group developed a large-area PLD process for the double-sided deposition of high-Tc superconducting thin films (see for example [8,10]). As substrate heater an arrangement of KANTHAL wire in ceramic tubes is used... 

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. 

In the second example BCS theory relates the appearance of a superconducting state to the breakdown of electromagnetic gauge symmetry by interaction with regular ionic lattice phonons and the creation of bosonic excitations. This theory cannot be extended to deal with high Tc ceramic superconductors and it correlates poorly with normal-state properties, such as the Hall effect, of known superconductors. It is therefore natural to look for alternative models that apply to all forms of superconductivity. 

Superconductivity is the absence of resistance to dc conduction this occurs only below a critical temperature Tc, a critical magnetic field (which is a function of T and current density j), and a critical current density j, which is a function of T and H. For alloys, does not exceed 23 -24 K (by contrast, some of the recently discovered ceramic high-Tc cuprate superconductors, such as HgBa2Ca2Cu30j , have Tc values as high as 140 K and can have comparable y c values), Designers of superconducting solenoid magnets... 

The processing of high Tc ceramic superconductors by traditional ceramic techniques is reviewed. All high Tc ceramic superconductors are layered Cu-0 compounds that are closely related to each other. In each, Cu-0 coordination polyhedra are typical of Cu+2 compounds. A critical step in processing these compounds is the intercalation of oxygen which changes the coordination polyhedra at a few atomic sites and causes a dramatic effect on the superconducting properties. 

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