Second-Generation Hts Conductors

ISBN-13: 9781441954787 / Angielski / Miękka / 2010 / 347 str.

Amit Goyal

Opis

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.

Spis treści

Methods to Produce Biaxially Textured Substrates.- IBAD Template Films for HTS Coated Conductors.- Epitaxial Superconductors on Rolling-Assisted-Biaxially-Textured-Substrates (RABiTS).- Inclined Substrate Deposition.- ISD by Thermal Evaporation.- Methods of YBa2Cu3O7?? Deposition and Related Issues.- Pulsed Laser Deposition of YBa2Cu2O7?? for Coated Conductor Applications: Current Status and Cost Issues.- Methods of HTS Deposition: Thermal Evaporation.- Sputtering of Y1Ba2Cu3O7??.- Pulsed Electron-Beam Deposition of High Temperature Superconducting Films for Coated Conductor Applications.- BaF2 Post-Deposition Reaction Process for Thick YBCO Films.- Issues and Progress Related to the Continuous Ex-Situ BaF2 Processing of Long-Length YBCO Coated Conductors.- Solution Deposition of Yba2Cu3O7?? Coated Conductors.- Non-Fluorine Based Bulk Solution Techniques to Grow Superconducting YBa2Cu3O7?? Films.- Jet Vapor Deposition for Continuous, Lowcost Manufacture of High Temperature Superconducting Tape.- Processing of Long-Length Tapes of High-Tempera Ture Superconductors by Combustion Chemical Vapor Deposition.- MOCVD Growth of YBCO Films for Coated Conductor Applications.- LPE Processing for Coated Conductor.- Deposition of Other HTS Materials.- Ex-Situ Processing of Ti-Containing Films.- Epitaxy of Hg-Based High-Tc Superconducting Thin Films.