Superconducting cuprates copper oxide

A major scientific breakthrough in the area of material science involving copper occurred in late 1986 and early 1987 the discovery of the so-called high-temperature cuprate superconductors (see Superconductivity). These copper-oxide containing materials hold the record for the highest transition temperature (Tc, the temperature at which all resistance to electricity is lost), currently 133 K, which is sigiuficant... 

Those readers not familiar with superconductivity in organic materials may find the Tc values rather low. However, they are comparable to values for inorgaiuc metallic elements. Here is a list of some selected examples FcCNb) = 9.25 K, rc(Pb) = 7.20 K, rc(a-Hg) = 4.15 K, rc(Sn) = 3.72 K, Tc(Al) = 1.17 K, Tc(ri) = 0.40 K, etc. It is interesting to note that copper does not exhibit a superconducting transition. The highest known Tc values of any material correspond to the copper-oxide series with Tc 138 K as the absolute record for the thallium-doped mercury-cuprate compound. 

All the high Tc superconductors discovered so far, with one exception, contain weakly coupled copper oxide, Cu02, planes. The highest critical temperatures are found for cuprates containing a Group 2 metal (Ca, Ba, Sr) and a heavy metal such as Tl, Bi, or Hg. The structures of all the cuprate superconductors are based on, or related to, the perovskite structure. The one report (in 2000) of a non-cuprate high T superconductor is of surface superconductivity in Na WOs. The structure of NUxWOs is also based on the perovskite structure. 

An unusual feature of the cuprate superconductors is the anomalous suppression of superconductivity in La2 Ba Cu04 and related phases when the hole concentration X is near 1/8. A possible explanation is a dynamical modulation of spin and charge giving antiferromagnetic stripes of copper spins periodically separated from the domains of holes. Neutron-diffraction evidence has been presented in the case of Laj g Nd() Sr CuO (x = 0.12) which is a static analogue of the dynamical stripe model (Tranquada et al., 1995). It appears that spatial modulations of spin and charge density are related to the superconductivity in these oxides. 

The superconducting oxides include both perovskites and Ruddlesden-Popper compounds which have an orthorhombic arrangement of cubic cells, alternatively of the perovskite and sodium chloride structures. The common feature of all of these is the presence of copper as a major component. The first ceramic superconductor was a lanthanum-strontium substituted cuprate (Lai Sr Cu04 z), which is a perovskite, but subsequently the inter-oxide compound Y203 2BaO 3CuO, commonly referred to as a 123 compound, was shown to have superior performance. The speculation concerning the conduction mechanism is that this involves either Cu3+-Cu2+ positive hole... 

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