ChemInform Abstract: Effect of Hot-Pressing on the Bi-Pb-Sr-Ca-Cu-O System.

Abstract

Uniaxial hot-pressing has been used to improve the relative density and preferred gain orientation of the nearly pure (Bi, Pb)2Sr2Ca2Cu3O10-y (2223) phase in the Bi-Pb-Sr-Ca-Cu-O system. Samples were prepared by freeze-drying, calcining, and hot-pressing the powders at 650° to 840°C at 50 and 200 MPa for 2 h. The hot-pressed samples showed a high degree of grain alignment and increased density up to 99% of theoretical. At 200 MPa, the 2223 phase was partially destroyed during hot-pressing, probably because of the weak bonding between the Bi─O2 layers. However, the 2223 phase and superconductivity were recovered with subsequent annealing. The critical current density (Jc) was improved 10-fold over that of sintered samples through this technique, with the highest Jc being 2100 A°Cm−2 at 77.3 K and zero field. The hot-pressed samples also showed significant improvements in the Jc as a function of applied magnetic field. The Jc of a hot-pressed and postannealed sample at 0.2 T and 77.3 K was 2 orders of magnitude greater than that of a sintered sample.