Because of pressing global environmental challenges, focus has been placed on materials for efficient energy use, and this has triggered the search for nanostructural modification methods to improve performance. Achieving a high density of tunable-sized second-phase nanoparticles while ensuring the matrix remains intact is a long-sought goal. In this paper, we present an effective, scalable method to achieve this goal using metal organic deposition in a perovskite system REBa 2 Cu 3 O 7 (rare earth (RE)) that enhances the superconducting properties to surpass that of previous achievements. We present two industrially compatible routes to tune the nanoparticle size by controlling diffusion during the nanoparticle formation stage by selecting the second-phase material and modulating the precursor composition spatially. Combining these routes leads to an extremely high density (8 × 10 22 m − 3 ) of small nanoparticles (7 nm) that increase critical currents and reduce detrimental effects of thermal fluctuations at all magnetic field strengths and temperatures. This method can be directly applied to other perovskite materials where nanoparticle addition is beneficial.

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The critical current densities of polycrystalline bulk SmFeAsO 1−x F x prepared by the powder-in-tube (PIT) method and by a conventional solid-state reaction were investigated using the remnant magnetic moment method and Campbell's method. Two types of shielding current, corresponding to global and local critical current densities J c were observed using both measurement methods. The global and local J c were on the order of 10 7 A/m 2 and 10 10 A/m 2 at 5 K, respectively. The local J c decreased slightly with increasing magnetic field. The global J c was independent of the preparation method, while the local J c was larger for samples prepared by PIT than for those prepared by solid-state reaction.

Addition of BaHfO 3 (BHO) nano-rods as pinning centers into a GdBa 2 Cu 3 O y (GdBCO) coated conductor dramatically improves the critical current properties in high magnetic fields. This is partly ascribed to the strong flux pinning of these pinning centers. In this paper it is reported that this improvement is mainly caused by unexpected enhancement of the upper critical field, B c2 . The mechanism of the enhancement of B c2 is not yet clear, although the strain around the interface between the pinning center and the superconducting matrix or the interface itself may scatter electrons. This result suggests that the critical current property of REBa 2 Cu 3 O y (RE: rare earth elements, REBCO) coated conductors could be designed not only by tailoring the microstructure of pinning centers but also by controlling the intrinsic superconducting property. Especially, the selection of pinning material and its content that determines B c2 is expected to be a key problem for further improvement of the pinning performance at high magnetic fields.