Superconducting cuprates preparation

Use of the combustion method in an atmosphere of air or oxygen to prepare complex metal oxides seems obvious. In the last three to four years, a variety of oxides have been prepared using nitrate mixtures with a fuel such as glycine or urea. It seems that almost any ternary or quaternary oxide can be prepared by this method. All the superconducting cuprates have been prepared by this method, although the resulting products in fine particulate form have to be heated to an appropriate high temperature in a desired atmosphere to obtain the final cuprate [18], Table 2 lists typical materials prepared by the combustion method. 

Several other novel strategies have been employed for the synthesis of superconducting cuprates some of them were mentioned earlier while discussing the various methods. Especially noteworthy are the use of the combustion method and the alkali-flux method for cuprate synthesis. Superconducting infinite-layered cuprates seem to be possible only when prepared under high pressures because of bonding (structural) considerations [87, 88]. In Table 7 we list the various cuprate superconductors along with their properties and the preferred methods of synthesis. 

Concerning the cuprates it is now clear that a nonrigid basic electron spectrum must be used. Doping creates not only carriers but prepares the whole background (incorporating also structural changes) for the appearance of superconductivity. Under corresponding approaches there are ones which take as the basis a narrow defect (bipolaron) band above the itinerant band [23,40-48], or stripe-induced minibands [11,42],... 

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