Mechanical and Electrical Characteristics of Oxide Superconductor Thin Films

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YBa_2Cu_3O_<7-x> (YBCO) superconducting thin film was prepared on an [111] oriented Ag film by an off-axis rf magnetron-sputtering. The [111] oriented Ag film was prepared on the (001) single-crystal natural mica substrate at the substrate temperature 200ﾟC in the argon atmosphere. The YBCO film grew with not only the strong orientation for caxis but also three-symmetrical orientation for a and b axs on the mica/Ag substrate without post-annealing. The full width at half maximum intensity of the 003 omega-rocking curve of the YBCO film was 1.52ﾟ. The optimal substrate temperature was 620ﾟC,when the partial pressure of oxygen was 1.0*10^<-2>Torr.Tc (onset) and Tc (zero) of the films were 84K and 77K respectively, according to the AC magnetic susceptibility measurements. The Jc of the film was measured by the conventional four-probe method, and Jc (J//ab) value was 1.4*10^<-1>A/cm^2 at 77K in a liquid nitrogen bath. The YBCO film showed the thickness dependence of Tc's mainly because of … More the large lattice mismatch of Ag (111) to YBCO (001). The Ag layr was found to play an important role that it became a current-path when the current value exceeded the critical current of the YBCO layr. This effect made the conductor stable. The relationships between the Jc at 77K and the strain of the YBCO films were measured to reveal the mechanical stability of the YBCO conductor, assuming the application of the conductor to the micro superconducting-coil. The Jc value of the YBCO film didn't change even when the tensile strain of 1*10^<-2> was applied. In case of compression, the Jc value increased with the increasing of strain, corresponded to the maximum, about 150% value of the Jc (strain=0), at-0.8*10^<-2>, then drastically decreased. These result ensure that the conductor can be applied to the micro-coil if the maximum strain is less than 1*10^<-2>. The stability of the Jc was also checked by dipping and taking out the film in the liquid nitrogen bath repeatedly. The surface roughness of the film increased with the repetition time due to the large thermal shrinkage and expansion of the Ag film during dipping and taking out processes, however, the Jc value was kept at the constant value even after 7 times repetition. Less