ＲＥ１２３溶融凝固バルクの高臨界電流特性化に対する微量置換効果

Abstract

Effects of RE mixing and dilute impurity doping for the CuO chain on the critical current properties for RE123 melt-solidified bulks were investigated. Low level Lu or Tb mixing to the RE site of Y123 or Dy123 melt-solidified bulks showed high Jc characteristics compared to the undoped bulks. Especially in the a-growth region of Tb mixed bulks, Jc in the low magnetic field was largely improved up to ∼ 105 A cm-2 at 77 K. Through microstructural observation, X-ray diffraction and local compositional analysis, the formation of finely dispersed BaTbO3 precipitates was confirmed in the Dy123 matrix, suggesting that these precipitates acted as effective pinning centers. The addition of fine BaTbO3 powder was also effective for enhancement of Jc. Furthermore, Tb4O7 added Dy123 melt-solidified bulks exhibited remarkably improved Jc due to the generation of fine BaTbO3 precipitates with 0.1 ∼ 0.2 μm in size in the Dy123 matrix without decreasing Tc. This result means Tb4O7 is a more effective additive than CeO2, which slightly decreases Tc. On the other hand, effects of dilute impurity doping to the CuO chain of Y123 melt-solidified bulks on their flux pinning properties were also studied. All the Fe-, Co-, and Ga-doped samples maintained high Tc above 90 K and exhibited dramatically improved Jc characteristics accompanying huge second peaks in Jc-H curves. This result suggests that the introduction of local disorders in the CuO chain by dilute impurity doping is more excellent way to improve the critical current properties of the RE123 system than direct impurity substitution for Cu in the CuO2 plane, which always decreases Tc.