A NEW MIXED PHASE CERAMIC SUPERCONDUCTOR BASED ON THE Y-BA-CU-O SYSTEM WITH ADDITION OF TELLURIUM

We fabricated a new type of superconducting ceramic satisfying the stoichiometric ratio of YTe(x)Ba4Cu6O(y) with x ranging from 0 to 0.8, using compounds CuTeO3, Y2O3, BaCO3, and CuO. The T(c) (R = 0) values of these superconductors are found to fall in the 89-94 K range. When x = 0.72, the critical current density J(c) is found to be enhanced about 7 times compared to that of the YBa4Cu6O(y) (or the common YBa2Cu3O7-delta) ceramic. The lower and upper limits of J(c) measured and estimated for the best sample reach values of 1250 Acm-2 and over 10(4) Acm-2, respectively. X-ray and SEM analyses indicate clearly that these new superconductors have crystal structures very much different from that of the well-known Y-123 specimen. In particular, we found that the nominal YBa4Cu6O(y) ceramic is made up of dominant structure YBa4Cu5O11-delta plus a small amount of the common 123 phase. The crystal lattice constants of this 145 new phase are roughly estimated to be: a = 5.240 angstrom, b = 5.827 angstrom, c = 11.507 angstrom. When T(e) is mixed in, the mechanical hardness of the resulting ceramic is much enhanced.