Recently, an improvement in the flux pinning performance of REBa2Cu3O7-δ (REBCO) bulk was achieved employing high energy ultrasonic irradiation (up to 300 W and 60 min) prior to the infiltration-growth process. Here, we demonstrate that a higher ultrasonic power and shorter duration treatment (450 W for 30 min) of the RE 2BaCuO5 (RE211, RE= Y, Gd) powder produces individual, nanometer-sized and surface damaged RE211 particles (RE211Ultra). We study the growth of YBCO and GdBCO systems via the top-seeded melt-growth method, with the addition of 30 mol% of RE211Ultra, which were pre-treated by high-energy ultrasonication and compared with the conventional method. Isothermal growth experiments clarified that the addition of RE211Ultra particles enables faster and more effective crystal growth via an improved peritectic reaction due to their size in the nanometer range and presence of sharp edges, which are crucial for growing large, single grain bulks of REBCO. Microstructural investigations by scanning electron microscopy indicated the presence of two differently sized RE211 inclusions within the bulk GdBCO and YBCO superconductors. All samples showed an onset of superconductivity at 1/492 K or above. Utilizing the effective growth temperature window and the addition of RE211Ultra, single grain bulks of GdBCO and YBCO were fabricated by the slow-cooling method. The field dependent critical current density (J c) of the bulk samples using RE211Ultra were found to exhibit superior performance over the standard GdBCO/YBCO samples due to significant changes of sample growth and of their microstructures. Here, we discuss various factors affecting the addition of RE211Ultra on the development of the microstructure, growth of bulk, single grain materials and further, the superconducting properties of different REBCO superconductors.
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