Simultaneous Cation-Substitution Effects on Superconducting Properties of Sm-Ba-Cu Oxide Superconductors

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Cation-stoichiometric is SmBa_2Cu_3O_<7-d>(Sm-123) samples were synthesized to exclude contribution of pinning at particles of cation-nonstoichiometric phases and second phases to peak effect of J_c The samples were annealed in different conditions and had various oxygen contents. From results of Raman scattering, powder x-ray diffractometry and Rietveld analysis, cation-stoichiometric Sm-123 samples were successfully obtained. A Sm-123 sample with oxygen content, 7-d,=6.84 exhibited peak effect and its J_c value at 77 K and 1 T was 10kA/cm^2. On the other hand, samples with 7-d=6.89 and 6.95 did not exhibit the peak effect Contrary to the previous reports, it was concluded that oxygen depleted regions would work for the pinning to exhibit the peak effect in Sm-123 superconductors.A novel transmission electron microscopy technique termed as large area high-resolution transmission electron microscopy(LA_HRTEM) was developed to identyfy unknown origin of the peak effect in Y-Ba-Cu-O supe … More rconducting bulks. A specimen fabrication method was also developed for energy dispersive x-ray analyses in LA-HRTEM observations. Superconducting bulks of Y-Ba-Cu-O were synthesized by a melt growth technique under varied oxygen partial pressure. Distributions of grain sizes for Y_2BaCuO-(Y-211) particles and inter-twin-boundary-distances were measured utilizing LA-HRTEM. Area of the interface between the Y-211 particles and the Y-123 matrix was found to be proportional to the J_c value at low magntic fields. On the other hand, the inter-twin-boundary-distance was inversely proportional to the J_c value at high magnetic fields. From these results, oxygen depleted regions in the vicinity of the twin boundaies would work for pinning to exhibit the peak effect, while contribution of the interface between Y-211 particles and Y-123 matrix to the pinning for the appearance of the peak effect was very limited. A heat treatment program was developed to appear the peak effect reversively and confirmed the validity of the guiding principle for designing mateirals. Less