Verbesserung der mechanischen und hochfrequenten Eigenschaften von YBCO-Schichten mittels unterschiedlicher Defektarten
Verbesserung der mechanischen und hochfrequenten Eigenschaften von YBCO-Schichten mittels unterschiedlicher Defektarten
The impact of defects upon the mechanical and microwave properties of HTS films isexamined. lt is demonstrated that adequate microscopic defects (Y$_{2}$O$_{3}$ precipitates)can increase the mechanical stability and, thus, the critical thickness and, at the sametime, substantialiy reduce the microwa...
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Personal Name(s): | Einfeld, J. (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2000
|
Physical Description: |
III, 123 p. |
Document Type: |
Report Book |
Research Program: |
ohne Topic |
Series Title: |
Berichte des Forschungszentrums Jülich
3774 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
The impact of defects upon the mechanical and microwave properties of HTS films isexamined. lt is demonstrated that adequate microscopic defects (Y$_{2}$O$_{3}$ precipitates)can increase the mechanical stability and, thus, the critical thickness and, at the sametime, substantialiy reduce the microwave surface resistance of HTS films. Finally, theimpact of artificial defects upon the surface resistance is examined. All experimentalresults are explained in terms of classical theories. YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ films with different size and density of Y$_{2}$O$_{3}$ precipitates were grownan LaAlO$_{3}$ and sapphire bv variation of the energv of the ions during sputter deposition. lt is demonstrated that the temperature dependence of the microwave surfaceresistance R$_{s}$ does not depend on the type of substrate material but on the densityof the defects. Films grown at low ion energy (resulting in a low density of microscopic defects) show a characteristic shoulder in the R$_{s}$ (T) curve which shifts to higherterperature and decreases in size with increasing energy of the ions (i.e. increasing density of microscopic defects). Temperature dependence and reduction of the surfaceresistance with increasing density of defects are explained in terms of the two-fluidmodel with thermally excited quasiparticles characterised bv a Drude-shaped conductivityspectrum. Values for the scattering rates can be derived from the measurementsof the surface resistance, which agree with the classical Matthiessen rule. The impurityscattering rate increases with increasing defect density. The experimental data and thetheoretical model demonstrate, that the surface resistance can be reduced by up to afactor of two over a wide temperature range. The reduction of the surface resistance isaccompanied by an improvement of the rnechanical properties of the HTS films whichleads to an increased critical film thickness. Both properties, namely the increase of thecritical thickness and the reduction of the microwave surface resistance, demonstratethe potential of microscopic defects for the improvement of HTS films for applications. |