Magnetic and microstructure study of bulk (Sm 0.33 Eu 0.33 Gd 0.33 )Ba 2 Cu 3 O y with submicron Gd 2 BaCuO 5 second-pha
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We fabricated melt-processed (Sm0.33Eu0.33Gd0.33)Ba2Cu3Oy superconductors with fine Gd2BaCuO5 (Gd-211) particles and studied microstructure and magnetic properties as a function of the Gd-211 content and the initial particle size. Microstructure observation by scanning electron microscopy and transmission electron microscopy confirmed the presence of submicron secondary-phase particles and nanometer-sized RE1+xBa2−xCu3Oy (x > 0) clusters. At 77 K, the critical current densities of 107 and 83 kA/cm2 were achieved at 0 T (self-field) and 2.2 T, respectively (superconducting quantum interference device data).
I. INTRODUCTION
Bulk high-Tc superconductors such as REBa2Cu3Oy [RE: Y, Nd, Sm, Gd] are of increasing technological importance for engineering applications like flywheel energy storage systems, magnetic bearings, superconducting permanent magnets, current leads, and noncontact transport systems.1–5 Advances in processing technology have enabled preparation of high performance (Nd,Eu,Gd)Ba2Cu3Oy (NEG-123) materials in relatively large dimensions.6–8 Recent studies of the NEG-1239 showed a strong effect of the matrix chemical ratio variation on pinning performance, especially at high fields. The matrix chemical ratio manipulation enabled control of the position and height of the secondary peak.10 A strong pinning around 2 T at 77 K could be obtained by replacing Sm for Eu in the NEG-123 system. Dark-field transmission electron microscopy (TEM) showed a high density of RE1+xBa2−xCu3Oy (RE-123) clusters 3–10 nm in size dispersed in the 123 matrix.11 The cluster size and dispersion varied with the matrix chemical composition. In melt-textured RE-123 materials flux pinning at low fields can be improved by adding RE-211 secondary phase particle (SPP).12 Microstructure analyses made by TEM–energy dispersive x-ray (EDX) identified the smallest submicron SPP in NEG-123 and NSG-123 systems as Gd2BaCuO5 (Gd-211).11,13 We have studied various types of SPP (NEG-211, Eu-211, Gd-211 and
a) b)
e-mail: [email protected] Present address: Institute of Physics ASCR, Na Slovance 2, CZ-182 21 Praha 8, Czech Republic J. Mater. Res., Vol. 18, No. 5, May 2003
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EuGd-211), mostly in the NEG-123 and NSG-123 matrices and found that the smallest particles were regularly of Gd-21114 when combined with an optimum content of Pt and CeO2.15 Critical current density was improved by the refinement of Gd-211 up to 105 A/cm2 at 77 K for H//c-axis. These results motivated us to perform a systematic study of the role of different elements in the ternary light-rare-earth (LRE) system. In the present study, we prepared (Sm,Eu,Gd)Ba2Cu3Oy bulk superconductors with various contents of fine Gd-211 particles and studied the final microstructure and magnetic properties. We also studied the effect of the initial size of Gd-211 particles on the superconducting performance. II. EXPERIMENTAL
High-purity commercial powders of Sm2O3, Eu2O3, Gd2O3, BaCO3, and CuO were mixed in a nominal composition of (S
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