Superconductivity doping-induced

Doping-induced superconductivity in MOMs has been demonstrated, e.g., for Ceo, where CSjRb),C6o reaches Tg values as high as 33 K (Tanigaki et al, 1991). 

Doped fullerites are called fullerides. The doping process proceeds by intercalating electroactive atoms or molecules into the crystal lattice in a very similar way as it is well known for the conducting polymers. Sofar only strong donors like alkali metals or earth alkali metals were found to dope the fullerites if the latter are exposed to the vapor of the metal. Doping induced conductivity has been observed for various metals and various fullerenes but metallic behavior and superconductivity was found sofar only for Ceo- Table 1 compiles a selected number of doped systems together with some of their transport properties. 

As a result, superconductivity is induced by donor doping and (Ndi jcCejc)2Cu04 is one of the rare examples of an -type conducting superconductor, which distinguishes it from other high-7c superconductors [5]. 

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],... 

In some organic conductors there is also magnetic field-induced superconductivity—for example, in /-(BETS TeCh at 17 T and 0.1 K [37], A new superconductor of picene (27) "doped" with alkali metals is reported to have TC = 18K [38]. Ca-intercalated graphite CaCf, superconducts below TC = 11.5K [39],... 

Pulsed laser ablation has been developed in many fields for the fabrication of thin films of oxide materials, in particular high Tc cuprate superconductors. In these materials, the increase of the carrier concentration can be obtained in many cases by chemical doping (cationic or anionic), in order to induce superconductivity. 

Figure 4d shows the equivalent x-0.158 material, prepared by copreclpltatlon. In this sample, the large, smooth, dark areas are replaced by 5-10 pm chunks. These contain Y, Ba, Cu, and traces of Ca, and Sr, as In the composite sample, but they also contain a trace of bismuth. The presence of B1 may Induce the Y-123 phase to adopt the tetragonal structure seen In the x-ray pattern of this siaterlal. This behavior has been observed In Y-123 that has been doped with iron (3-6) as little as a 2% substitution of iron for copper in Y-123 can lead to an orthorhomblc-to-tetragonal transformation, without loss of superconductivity. The Region B particles are also present In the coprecipitated sample and have a similar Y-Bl-Ba composition (with traces of Ca and Cu) to those seen In the composite material. 

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