A superconducting joint technology used for high-temperature superconductors (HTS) is the key for enabling persistent operation of HTS magnets. In the present work, we have succeeded in developing a superconducting joint between REBCO-coated conductors (CCs) using a joint strap with a microcrystalline GdBCO precursor intermediate layer. Heat treatment and oxygen annealing, with a total processing time of less than 1 d, grows a biaxially-textured intermediate layer to connect the GdBCO layers in the CCs. Microstructure observation of a part of the joint cross-section with SEM and TEM showed that the intermediate layer and the GdBCO layers in the conductors were atomically connected. An electron backscatter diffraction result showed that both the c- and a-axis misorientations among the GdBCO layers of the joined conductor and the GdBCO layer of the joint strap were about less than 5°. This intermediate grown superconducting joint gives a critical current of >100 A at 77 K in a self-field. A critical current of a joint at 4.2 K in a self-field is seven times higher than that at 77 K. The persistent field decay of a small double pancake coil, terminated with this joint, showed a joint resistance in the range of <3 × 10−12 Ω to <5 × 10−13 Ω at 77 K in a self-field over three days, with an operating current of ∼10 A (∼14% of the calculated coil critical current). The results show a promising prospect of the joint to be used for persistent magnets such as NMR and MRI.

A strategy for producing highly ductile electrodeposited bulk nanocrystalline metals with face-centered cubic structures was developed in a NiW alloy model system. Bulk nanocrystalline NiW alloys with similar grain size (2030 nm), and varying crystallographic orientations were produced. The electrodeposited alloys showed tensile elongation ranging between 0 and 13%. Scanning ion microscopy reveled that all electrodeposited alloys had similar meso-scale structures that are typical of electrodeposited metals. This indicated the variation of ductility and fracture surfaces was not caused by cluster structures filled with nano-grains. The tensile behavior of the bulk nanocrystalline NiW alloys could be explained by considering the effects of growth processes during electrodeposition on the presence of hydrogen and defects. Our discussion surrounding NiW alloys outlines the conditions necessary to obtain the high tensile ductility. Our findings are in good agreement with those for other electrodeposited nanocrystalline face-centered cubic metals. We also provide guidelines for selecting electrodeposition conditions to produce bulk nanocrystalline metals with face-centered cubic structures and high tensile ductility.

Threading dislocations have been studied by means of etch pit method using molten KOH+Na 2 O 2 solution, cathodoluminescence and transmission electron microscopy. We focus on the geometrical features of etch pits and their correlation with the recombination behavior at the dislocations. Four types of etch pits can be recognized after etching according to their sizes and depths, among which the middle-sized etch pits correspond to dislocations with the strongest non-radiative recombination. TEM observation has confirmed that dislocation beneath the large-sized etch pit is a mixed-type dislocation having both c-and a-component.

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.

Correlations between the structural properties and nonradiative recombination (NRR) behaviors of threading dislocations in freestanding hydride-vapor-phase-epitaxy (HVPE) GaN substrates were investigated using cathodoluminescence (CL), the etch pit method, transmission electron...