Critical current densities and the structural quality of 3- and 4 - μ m -thick superconducting YBa 2 Cu 3 O 7 layers synthesized using the ex situ process

• Published in: Journal of applied physics 2007-09, Vol.102 (5), p.053902-053902-6
• Main Authors: Solovyov, Vyacheslav F., Wiesmann, Harold J., Suenaga, Masaki
• Format: Article
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.2773997

In this work, we used quantitative x-ray diffraction measurements and optical metallography to investigate the relationship between structural quality and critical current densities J c for 3- and 4 - μ m -thick YBa 2 Cu 3 O 7 (YBCO) films grown on CeO 2 -buffered Ni-W substrates by the BaF 2 process. The J c of the films was shown to be approximately: (1) proportional to the intensity of the YBCO (006) diffraction line, and (2) inversely proportional to the average grain size of the c -axis oriented YBCO as determined from optical micrographs of polished surface of the films. We conclude that to achieve J c s well above 10 6   A / cm 2 in self-field and at 77 K, it is critical to suppress the formation of randomly oriented YBCO grains while maintaining high crystallographic quality of the c -axis oriented part of the film. The quality of the c -axis oriented YBCO was found to be strongly dependent on the YBCO grains size-e.g., the grains, which are smaller than 10   μ m , are required for high J c films. The fine-grain high J c films can be synthesized under processing conditions that promote a high rate of nucleation of c -axis oriented YBCO.