High performance (BI,PB)2SR2CA2CU2Oy composites

Abstract

The present invention provides a (Bi,Pb)SCCO-2223 oxide superconductor composite which exhibits improved critical current density and critical current density retention in the presence of magnetic fields. Retention of critical current density in 0.1 T fields (77 K, ⊥ ab plane) of greater than 35% is disclosed. Significant improvements in oxide superconductor wire current carrying capacity in a magnetic field are obtained by subjecting the oxide superconductor composite to a post-processing heat treatment which reduces the amount of lead in the (Bi,Pb)SCCO-2223 phase and forms a lead-rich non-superconducting phase. The heat treatment is carried out under conditions which localize the lead-rich phase at high energy sites in the composite.

What is claimed is:  
     
         1 . A method of processing a (Bi,Pb)SCCO-2223 oxide superconductor composite after oxide superconductor phase formation, comprising: 
 providing a (Bi,Pb)SCCO-2223 oxide superconductor composite, said oxide superconductor composite comprising (Bi,Pb)SCCO-2223;    heating the oxide superconductor composite under conditions selected to reduce the lead content of the (Bi,Pb)SCCO-2223 oxide superconductor by about 5 percent to about 50 percent by weight and to localize the exsolved lead in a secondary phase at high energy sites of the composite.    
     
     
         2 . A method of processing a (Bi,Pb)SCCO-2223 oxide superconductor composite after oxide superconductor phase formation, comprising: 
 providing a (Bi,Pb)SCCO-2223 oxide superconductor composite, said oxide superconductor composite comprising (Bi,Pb)SCCO-2223;    heating the oxide superconductor composite under oxidizing conditions, said conditions sufficient to oxidize a portion of Pb 2 +present in (Bi,Pb)SCCO-2223 into Pb 4+  and to localize the Pb 4+  in a secondary phase at high energy sites of the composite.    
     
     
         3 . A method for improving intergranular electrical properties of a (Bi,M)SCCO-2223 oxide superconductor composite after oxide superconductor phase formation, comprising: 
 providing an oxide precursor to (Bi,M)SCCO-2223 oxide superconductor composite, where M is selected from the group consisting of Tl, Sb and Sn and is present in an amount up to its solubility limit in the oxide precursor;    processing the composite so as to convert the oxide precursor into (Bi,M)SCCO-2223;    heating the oxide superconductor composite under oxidizing conditions, said conditions sufficient to oxidize a portion of M 2+  present in (Bi,M)SCCO-2223 into M 4+  and to localize the M 4+  in a secondary phase at high energy sites of the composite    
     
     
         4 . The method of  claim 1 ,  2  or  3 , wherein the high energy site comprises one or more sites selected from the group consisting of high angle c-axis tilt boundaries, pores, interfaces between the superconducting and secondary phases and edge boundaries for the superconducting phase.  
     
     
         5 . The method of  claim 1 ,  2  or  3 , wherein the heating step is carried out under oxidizing conditions.  
     
     
         6 . The method of  claim 1 ,  2  or  3 , wherein the heat treatment is effective to provide a composite which exhibits a critical current retention at 0.1 T (77 K, ⊥ ab plane) in the range of about 15% to about 50%.  
     
     
         7 . The method of  claim 1 ,  2  or  3 , wherein the heat treatment is effective to provide a composite which exhibits a critical current retention at 0.1 T (77 K, ⊥ ab plane) in the range of about 20% to about 40%.  
     
     
         8 . The method of  claim 1  or  2 , wherein the (Bi,Pb)SCCO-2223 is processed to impart intergranular connectivity of the oxide grains before heat treatment of invention.  
     
     
         9 . The method of  claim 1 ,  2  or  3 , wherein the heat treatment comprises: 
 heating the wire at a temperature in the range of about 500° C. to about 800° C. at an oxygen pressure of about 0.03 atm to 100 atm O 2  for a time sufficient to provide a critical current retention at 0.1 T of at least 15% (77 K, ⊥ ab plane).  
 
     
     
         10 . The method of  claim 8 , wherein the temperature is in the range of 630° C. to 790° C. at an oxygen pressure of about 0.03 atm to 100 atm O 2 .  
     
     
         11 . The method of  claim 8 , wherein the temperature is in the range of 650° C. to 750° C. at an oxygen pressure of about 0.08 atm to 1.0 atm O 2 .  
     
     
         12 . The method of  claim 1  or  2 , wherein the lead-rich secondary phase comprises a hexagonal crystal structure characterized by an X-ray diffraction pattern comprising the following peaks (20(relative intensity)): 17.9(45), 32.3(100), 31.5(62), 44.8(42), and 55.5(45).  
     
     
         13 . The method of  claim 1  or  2 , wherein the (Bi,Pb)SCCO-2223 comprises lead in an amount in the range 3 wt % to about 8 wt % before heat treatment.  
     
     
         14 . The method of  claim 1  or  2 , wherein the (Bi,Pb)SCCO-2223 comprises lead in an amount in the range 4 wt % to about 6 wt % before-heat treatment.  
     
     
         15 . The method of  claim 1  or  2 , wherein the (Bi,Pb)SCCO-2223 comprises about 6.5 wt % lead.  
     
     
         16 . The method of  claim 3 , wherein the (Bi,M)SCCO-2223 comprises M in an amount of less than 10 wt %.  
     
     
         17 . The method of  claim 1  or  2 , wherein the heat treatment is carried out under conditions to reduce the lead content of (Bi,Pb)SCCO-2223 in an amount in the range of about 15 wt % to about 25 wt %.  
     
     
         18 . The method of  claim 1  or  2 , wherein the heat treatment comprises: 
 heating the oxide superconductor under conditions which are oxidizing to Pb +2  relative to a lead-rich phase stability curve.  
 
     
     
         19 . The method of  claim 1  or  2 , wherein a (Bi,Pb)SCCO-2223 is obtained by heating in the range of 800° C. to 850° C. for a first dwell time and heating in the range of 780° C. to 815° C. for a second dwell time under an oxygen partial pressure in the range of 0.01 to 1.0 atm.  
     
     
         20 . The method of  claim 1  or  2 , wherein a (Bi,Pb)SCCO-2223 is obtained by heating in the range of 825° C. to 830° C. for a first dwell time and heating in the range of 805° C. to 813° C. for a second dwell time under an oxygen partial pressure in the range of 0.01 to 1.0 atm.  
     
     
         21 . The method of  claim 18 , further comprising heating in the range of 780° C. to 790° C. for a third dwell time under an oxygen partial pressure in the range of 0.01 to 1.0 atm.  
     
     
         22 . The method of  claim 1 ,  2  or  3 , wherein the composite is in the form of a silver sheathed wire.  
     
     
         23 . The method of  claim 21 , wherein the composite is a multifilamentary silver sheathed wire.  
     
     
         24 . The method of  claim 1  or  2 , wherein the lead-rich secondary phase is formed in a relative fraction in the range of about 0.002 to 0.5.  
     
     
         25 . The method of  claim 1  or  2 , further comprising: 
 providing a(Bi,Pb)SCCO-2223 oxide superconductor composite comprising a noble metal.  
 
     
     
         26 . A method of preparing a (Bi,Pb)SCCO-2223 oxide superconductor composite, comprising: 
 modifying the lead content of a (Bi,Pb)SCCO-2223 superconducting phase during processing of a (Bi,Pb)SCCO-2223 oxide superconductor composite, such that the lead content of the (Bi,Pb)SCCO-2223 superconducting phase is in the range of 3% to 8% during formation of the (Bi,Pb)SCCO-2223 phase and such that the lead content of the (Bi,Pb)SCCO-2223 superconducting phase is reduced up to 25% during post formation processing of the oxide superconductor phase.    
     
     
         27 . A (Bi,Pb)SCCO-2223 oxide superconductor composite wire, comprising: 
 a (Bi,Pb)SCCO-2223 oxide superconductor filament substantially supported in a noble metal phase, wherein the filament comprises a lead-rich secondary phase,    the wire characterized in that when tested over a current carrying distance of 10 cm, the wire possess a J ret  at 0.1 T in the range of greater than 35% (77 K, ⊥ ab plane).    
     
     
         28 . A (Bi,Pb)SCCO-2223 oxide superconductor composite, comprising: 
 a (Bi,Pb)SCCO-2223 oxide superconductor phase supported in a noble metal phase,    the (Bi,Pb)SCCO-2223 oxide superconductor phase comprising a lead-rich secondary phase localized at high energy sites and a (Bi,Pb)SCCO-2223 phase.    
     
     
         29 . A (Bi,Pb)SCCO-2223 oxide superconductor composite, comprising: 
 a (Bi,Pb)SCCO-2223 oxide superconductor phase supported in a noble metal phase,    the (Bi,Pb)SCCO-2223 oxide superconductor phase comprising Bi:Pb:Sr:Ca:Cu in the nominal stoichiometry of 2.5(±0.05):0.4(±0.04):2.3(±0.06): 2.3(±0.04):3.0(±0.15).    
     
     
         30 . The composite of  claim 28 , further comprising: 
 a lead-rich secondary phase comprising Bi:Pb:Sr:Ca:Cu in the nominal stoichiometrv of 0.9(±0.09):1.1(±0.21):1.6(±0.06): 1.7(±0.08):1.0(±0.23).    
     
     
         31 . The composite of  claim 26  or  27 , wherein the (Bi,Pb)SCCO-2223 is lead deficient.  
     
     
         32 . The composite of  claim 26  or  27 , wherein (Bi,Pb)SCCO-2223 comprises lead from about 2 wt % to about 6.8 wt % lead.  
     
     
         33 . The oxide superconductor of  claim 30 , wherein the lead-deficient (Bi,Pb)SCCO-2223 phase, comprises lead about 4.75 to about 5.5 percent by weight.  
     
     
         34 . The oxide superconductor of  claim 30 , wherein the lead-deficient (Bi,Pb)SCCO-2223 phase, comprises lead about 3.4 to about 4.2 percent by weight.  
     
     
         35 . The composite of  claim 27 , wherein the composite is in the form of a wire and the oxide superconductor phase is in the form of a filament.  
     
     
         36 . A (Bi,M)SCCO-2223 oxide superconductor wire, comprising: 
 a (Bi,M)SCCO-2223 oxide superconductor filament supported in a noble metal phase, wherein M is selected from the group consisting of Pb, Tl, Sb, Sn, Te, Hg, Se, As and mixtures thereof,    the wire characterized in that when tested over a current carrying distance of 10 cm, the wire possess a J ret  at 0.1 T of greater than 35% (77 K, ⊥ ab plane).    
     
     
         37 . The oxide superconductor composite of  claim 27 , wherein the wire is characterized in that when tested over a current carrying distance of 10 cm, the wire possess a J ret  at 0.1 T in the range of greater than 25% (77 K, ⊥ ab plane).  
     
     
         38 . The oxide superconductor wire of  claim 27 , the wire characterized in that when tested over a current carrying distance of 10 cm, the wire possess a J ret  at 0.1 T of greater than 35%.  
     
     
         39 . The oxide superconductor composite of  claim 27 , wherein the wire is characterized in that when tested over a current carrying distance of 10 cm, the wire possess a J ret  at 0.1 T in the range of about 35% to about 50% (77 K, ⊥ ab plane).  
     
     
         40 . The composite of  claim 26 ,  27  or  33 , further characterized in that an increase in J ret  of the composite does not produce a proportional increase in J c  (self field or zero field) of the composite.  
     
     
         41 . The oxide superconductor composite of  claim 26  or  27 , wherein the lead rich secondary phase is present in a relative fraction in the range of about 0.01 to about 0.5.  
     
     
         42 . The oxide superconductor of  claim 27 , wherein the high energy site comprises one or more sites selected from the group consisting of high angle c-axis tilt boundaries, pores, interfaces between the superconducting and secondary phases and surface boundaries for the superconducting phase.  
     
     
         43 . The oxide superconductor composite of  claim 26  or  31 , wherein the wire comprises multiple filaments of (Bi.Pb)SCCO-2223 supported by the noble metal phase.  
     
     
         44 . The oxide superconductor composite of  claim 26  or  27 , wherein the lead-rich secondary phase comprises a hexagonal crystal structure characterized by an X-ray diffraction pattern comprising the following peaks (20(relative intensity)): 17.9(45), 32.3(100), 31.5(62), 44.8(42), and 55.5(45).  
     
     
         45 . The oxide superconductor composite of  claim 26  or  27 , wherein the lead-rich secondary phase has a diffraction pattern substantially that described in JCPDS card No. 44-0053.