THE INFLUENCE OF PROCESSING PRESSURE ON THE FORMATION OF THE HIGH-T(C) 2223 PHASE IN BI-PR-SR-CA-CU-O SUPERCONDUCTORS

The effects of processing pressure on the superconducting critical tra nsition temperature, T(c), of Bi1.6Pb0.4Sr1.9Ca2.05Cu3.Ox were investi gated. Uniaxial cold- and hot-pressed samples prepared from mixed oxid e and chemically coprecipitated powders were studied. The uniaxial col d-pressed specimens were pressed at a low pressure of 34.5 MPa (5000 p .s.i.) and a high pressure of 138.7 MPa (20 120 p.s.i.) and sintered a t 845-degrees-C for times ranging from 24-200 h. The mixed oxide sampl es showed a 0.5 K increase in T(c) as the pressure was increased, whil e the chemically coprecipitated samples showed a 3.6 K increase in T(c ) with the same increase in pressure. The uniaxial hot-pressed specime ns were hot pressed at 845-degrees-C for 6 h in oxygen at a pressure o f 34.5 MPa (5000 p.s.i.) and post-annealed for 24-30 h in air at 845-d egrees-C. These samples, both mixed oxide and chemically coprecipitate d, showed an increase in T(c) of approximately 25 K from the hot-press ed state to the post-annealed state. The highest T(c) achieved by eith er of these processing methods was 108.4 K.