ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Extensive studies on Pb-doped Bi-Ca-Cu-O superconductors have seldom produced a single-phase Bi-based superconductor from a magnetic point of view without the 80-K phase in it, even though zero-resistance has been commonly observed around and above 100 K. This is mainly because of the additional intergranular phases controlled by calcium and copper diffusion which appears to be extremely sensitive to even minute traces of impurities. Hence, recent reports on the observation of superconductivity above 130 K in Sb-doped Bi-based alloys is of interest. We have prepared a number of Bi-based superconducting compounds containing Pb and/or Sb using the computerized coprecipitation method (which gives powders of submicrometer size particles) as well as a solid-state diffusion technique. The role of excess Ca on the superconducting properties have also been studied. Effects of various short- and long-term heat treatment conditions have also been investigated. The final pelletized samples have been characterized by x-ray, electrical, and magnetic property measurements. In most cases, Tc (R=0) of a sample can be easily enhanced to 105–110 K by modifying the annealing conditions. However, we have not yet been able to verify the claims of Tc(R=0) over 130 K although a small portion with Tc(onset) over 130 K does appear sometimes. Samples without Sb have to be annealed in air over 60 h to reach high Tc(R=0) than 100 K while those with Sb substitution need a maximum of 24 h to achieve the higher Tc. ac susceptibility studies over four decades of field amplitudes (3 mOe–30 Oe) show, below the diamagnetic onset temperature at 110 K, a knee around 100 K, which is perhaps due to intergranular low-field penetration. In any case in these samples it is possible to completely suppress the 80-K phase. From dc magnetic data we find that in these Sb-doped samples Jc(transport) can be varied from 350 to 1500 A/cm2 at 4.2 K, and is weakly field dependent as compared to those without Sb-doping. Systematic studies will be presented.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.344680
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