Second-Generation HTS Conductors (Paperback, Softcover reprint of hardcover 1st ed. 2005)

Thediscoveryofhightemperaturesuperconductors(HTS)in 1986bytwoIBM scientists led to an unprecedented explosion of research and development efforts world-wide because of the signi?cant potential for practical applications offered by these materials. However, the early euphoria created by the exciting prospects was dampenedby the dauntingtask of fabricating these materials into useful forms with acceptablesuperconductingproperties. Progresstowardsthisgoalhasbeen hindered by many intrinsic materials problems, such as weak-links, ?ux-creep, and poor - chanicalproperties. TheearlieststudiesofcriticalcurrentdensityJ inHTSmaterialsrevealedthatfor c apolycrystallinematerialcontainingadistributionofgrainboundariesismuchlower than that for a single crystal. High angle grain boundariesact as Josephson coupled weak-links leading to a signi?cant ?eld-dependent suppression of the supercurrent acrosstheboundary. Forcleanstoichiometricboundaries, thegrainboundarycritical currentdensity dependsprimarilyonthe grainboundarymisorientation. The dep- denceof J (gb)onmisorientationanglehasbeendeterminedYBa O Cu (YBCO) c 2 3 7 in boundary types which can be formed in epitaxial ?lms on bicrystal substrates. Theseinclude 001]tilt, 100]tilt, and 100]twistboundaries. Ineachcasehighangle boundarieswerefoundtobeweak-linked. Theseexperimentshavealsobeenextended to arti?cially fabricated 001] tilt bicrystals in Tl Ba CaCu O, Tl Ba Ca Cu O, 2 2 2 8 2 2 2 3 x TlBa Ca Cu O (Tl-1223) and Nd Ce CuO . In each case it was found that, 2 2 3 x 1. 85 0. 15 4 as in YBCO, J depends strongly on grain boundary misorientation angle. Data on c currenttransmissionacrossarti?ciallyfabricatedgrainboundariesinBi-2212also- dicate that most large angle 001] tilt and 001] twist boundaries are weak links. It is likely that the variation in J with grain boundary misorientation is similar in all c high-T superconductors. Hence, thelow J observedinrandomlyorientedpolycr- c c tallineHTScanbeunderstoodonthebasisthatthepopulationoflowangleboundaries issmallandthatfrequenthighangleboundariesimpedelong-rangecurrent?ow. - ingconventionalprocessingtechniques, threeHTSmaterialsweresuccessfullyfab- catedinpolycrystallineformwithmodestJ 's. ThesearetheBi-2223powder-in-tube c conductors, theTl-1223spray-pyrolyzed?lmsandtheBi-2212melt-processedthick ?lms. Thesethreetypesofconductorscomprisedthe First-GenerationHTScond- torsorwires.