Amit Goyal – författare

The MRS Symposium Proceeding series is an internationally recognised reference suitable for researchers and practitioners.

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.

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.

Included in this volume are papers on biaxial and triaxial crystallographic texturing, epitaxial growth on biaxially textured substrates, melt-processing of YBCO, and basic information about HTS materials concerning phase diagrams, measurement of physical properties, characterization, and effects of various defects including grain boundaries on supercurrent transmission. Proceedings of the symposium held at the 104th Annual Meeting of The American Ceramic Society, April 28-May1, 2002 in Missouri; Ceramic Transactions, Volume 140.

The number of ceramic materials with a perovskite type structure is large and of considerable technological importance due to their rich crystal chemistry and structure-property relationships. Applications include multilayer capacitators, piezoelectric transducers, PTC thermistors, electrooptical modulators, optical switches, dielectric resonators, thick film resistors, electronic sensors, electrorestrictive actuators, magnetic bubble memory devices, laser host materials, ferromagnetic materials, refractory electrodes, second harmonic generators, batteries, ceramic electrodes, thermoelectric devices, and high temperature superconductors.This volume contains papers on the research and development of new perovskite materials for various applications including doping of existing perovskite materials as well as processing for improved properties.

This comprehensive volume is a good summary of the latest developments in high-temperature superconductor (HTS) research and an excellent resource for researchers and managers working in this field. The book is divided into three chapters: coated conductors; BSCCO-based conductors, MgB2 , and other HTS materials; and control of microstructure. Papers include topics such as long-length flexible wires and tapes, melt-textured YBCO materials, processing of HTS materials, the current status and potential for YBCO-based coated conductors, BSCCO-based conductors, and MgB2 based wires. Proceedings of the symposium held at the 105th Annual Meeting of The American Ceramic Society, April 27-30, in Nashville, Tennessee; Ceramic Transactions, Volume 149.

The MRS Symposium Proceeding series is an internationally recognised reference suitable for researchers and practitioners.