| Summary: | A high critical-current density was observed in the material (Tl 0.5Pb0.5)Sr2Ca2Cu3O 9. Based on magnetic-hysteresis measurements, this single (insulating) Tl-O layer material has a Jc value of 1.24×10 5 A/cm2 when measured at a temperature of 77 K and a field of 1 T. This value of Jc is comparable to that measured here for YBa2Cu3O7 (1.04×105 A/cm 2), having single-conducting Cu-O chains, but considerably greater than the value for the material Tl2Ba2Ca 2Cu3O10 with double (insulating) Tl-O layers in which no hysteresis was observed under these same conditions. Our results from specific heat measurements indicate that the (Tl0.5Pb 0.5)Sr2Ca2Cu3O9 compound has a three-dimensional character due to the enhancement of the superconducting coupling along the c axis between the Cu-O planes and thus results in an increase in Jc compared to the two-dimensional Bi- and Tl-2212 and 2223 [e.g., (Bi or Tl)2(Sr or Ba)2CaCu2O 8 and (Bi or Tl)2(Sr or Ba)2Ca 2Cu3O10, respectively] compounds. We believe that the high Jc is associated with an increase in the irreversibility field, rather than an increase in pinning centers.
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