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We prepared filamentary 0.1 at% Zr-doped (Nd 0.33 Eu 0.38 Gd 0.28 )Ba 2 Cu 3 O x superconductors by solution spinning and partial melting in flowing 0.1% O 2 + Ar gas. The transport critical-current density ( J c ) was measured at 77 K in applied magnetic fields up to 14 T by rotating the sample along a direction perpendicular to the filament length. Anisotropic behavior of the field dependence of J c was detected by applying a field of more than 4 T. The J c values for the Zr-doped sample were higher than those for the undoped sample on the application of fields of up to 11 T. The J c values measured at the optimized angle for the doped sample were more than 10 5 A/cm 2 at 77 K by applying fields of up to 6 T. Transmission electron microscopy (TEM) of the sample was performed using an ultra high-voltage TEM to clarify the pinning centers. Intergrowth of 124 phase and stacking faults in the oriented 123 matrix were observed both for the doped and undoped samples. Zr doping resulted in the fluctuation of the structure with a short disorder range of 10–30 nm. A modulated structure and fine twin planes crossing each other were partly observed for the doped sample. The presence of such small-scale disorder could improve flux pinning in the middle field region.

In order to study the effect of matrix composition in the filamentary (Nd, Eu, Gd)Ba 2 Cu 3 O y ((Nd, Eu, Gd)123) superconductors on critical current density, we prepared three samples with various rare-earth ratios: (Nd 0.33 Eu 0.38 Gd 0.28 )123 (sample A), (Nd 0.33 Eu 0.33 Gd 0.33 )123 (sample B), (Nd 0.33 Eu 0.08 Gd 0.58 )123 (sample C). The filamentary precursor was prepared by a solution-spinning method and partially melted in flowing 0.1%O 2 + Ar and 1%O 2 + Ar. The samples had well aligned texture along the filamentary diameter as well as the length except sample C processed in flowing 1%O 2 + Ar. The T c value for the samples processed in flowing 0.1%O 2 + Ar is higher than that for 1%O 2 + Ar. The high J c value more than 10 4 A/cm 2 at 77 K and self-field is attained for samples A and B. The field dependence of J c for the samples was measured at 77 K up to 14 T by changing the angle along the filament diameter. The anisotropic behavior of the J c -B curve was detected. The J c values and irreversibility field for the samples processed in flowing 0.1%O 2 + Ar are higher than those for 1%O 2 + Ar. By optimizing the angle for the samples, the highest J c value of 3400 A/cm 2 at 14 T was attained for sample A.

We have prepared fine filamentary EuBa 2 Cu 3 O x superconductors by solution spinning and melt processing to fabricate the high- T c superconducting wire with high-critical current density ( J c ) at 77 K and high-magnetic fields. The filamentary precursor was partially melted in flowing 0.1% O 2 + Ar and then oxygenated. The samples in diameter of 55 μm had well aligned texture along the filament diameter as well as the length. The T c value of the sample was 90 K. The transport J c for the samples was measured at 77 K in applied magnetic fields up to 14 T by rotating the sample in a direction of the filament diameter. Anisotropic behaviour of the field dependence of J c along the filament diameter was detected. The sample rotated the optimized angle exhibited the highest J c value of 11,000 A/cm 2 at 77 K and 14 T. The transmission electron microscopic image for the filamentary EuBa 2 Cu 3 O x superconductors was observed by using ultra high-voltage transmission electron microscope to clarify the pinning center. Intergrowth of 124-phase and nano-scale particle in the orientated 123 matrix were observed. The presence of such small-scale disorders could improve flux pinning at high fields.

We prepared precursor filamentary Ho 1 Ba 2 Cu 3 O x superconductors by a solution spinning. The filamentary precursor was partially melted in flowing O 2 under various heating conditions. The J c value of the sample was strongly dependent on the flowing O 2 rate. A J c value of 10 4 A/cm 2 at 77 K and self-field was attained for the sample melted in flowing O 2 rate of 0.25 l/min. The J c was measured at 77 K in applied magnetic fields up to 14 T by rotating the sample along the direction perpendicular to the filament length. Anisotropic behavior of the field dependence of J c was detected. A J c value of 100 A/cm 2 at 77 K is maintained by applying the field of 14 T for the sample without rotating. By rotating the angle from the optimized angle to 90°, the J c value decreased drastically and disappeared by applying the field more than 9 T.

We have studied a fabrication of filamentary ternary RE123 superconductors by changing the RE element for pinning enhancement. In this paper, the J c of the filamentary (Eu, Gd, Ho)123 superconductors prepared by solution spinning and partial melting under various atmospheres was examined. As the oxygen partial pressure decreased, the optimum melting temperature decreased. The T c of the samples melted in flowing 0.1%O 2 + Ar and 1%O 2 + Ar was around 92 K and the T c for the samples melted in flowing 20%O 2 + Ar was low such as 83 K. The transport J c values for the samples were measured at 77 K in applied magnetic fields up to 14 T by rotating the sample in a direction of the filament diameter. Anisotropic behavior of the field dependence of J c along the filament diameter was detected. The highest J c value of 4100 A/cm 2 at 77 K and 14 T was detected for the sample melted in flowing 0.1%O 2 + Ar. By the rotating the angle for 90°, the superconductivity at 77 K was disappeared by applying the field more than 8 T.

This paper describes the preparation of filamentary potassium-doped C 60 superconductors prepared by the suspension spinning method. Commercial C 60 powder was suspended in mixed poly(vinyl alcohol) solution of dimethyl sulfoxide and hexamethylphosphoric triamide (sample A). The viscous suspension was extruded as a filament into a precipitating medium of methyl alcohol and coiled on a drum. The filamentary sample was also prepared by the suspension spinning by using polyacrylonitrile solution of N , N -dimethylformamide (sample B). The samples were pyrolyzed to remove volatile components. Doping of potassium for the samples was prepared as following: At first, powder samples of nominal composition K 6 C 60 was prepared by reaction of C 60 with excess potassium. The K 6 C 60 powder and filamentary sample with stoichiometric ratio of K 3 C 60 were placed in Pyrex glass tubes and vacuum-sealed and heated at 250 °C for 36 h. SQUID measurement shows the superconductivity of sample B with T c =18 K. On the other hand, the superconductivity more than 2 K was not detected for sample A.

The filamentary Sm123 precursor was prepared by a solution spinning method. The precursor was partially melted in flowing 0.1%O 2 + Ar and 1%O 2 + Ar. The transport J c value for the filamentary Sm123 superconductors was examined at 77 K in applied magnetic fields up to 10 T. The J c value higher than 10 4 A/cm 2 was maintained up to 4 T for the samples melted in flowing 1%O 2 + Ar. The J c value gradually decreased with increasing applied magnetic fields from 4 to 6 T and the superconductivity rapidly deteriorated by applying the fields above 8 T. On the contrary, the J c values drastically decreased for the samples melted in flowing 0.1%O 2 + Ar by applying the fields higher than 1 T, and the superconductivity at 77 K was disappeared around 4 T.

The transport J c at 77 K for filamentary (Gd,Dy,Ho)–Ba–Cu–O superconductors prepared by solution spinning and partial melting was measured in magnetic fields up to 10 T. The partial melting of the filamentary sample was examined in flowing 0.1% O 2 + Ar, 1% O 2 + Ar and 20% O 2 + Ar. The field dependence of J c for the sample partially melted in flowing 1% O 2 + Ar was superior to that for the other samples. The J c maintained around 10 4 A/cm 2 by applying the field up to 6 T and then decreased drastically.

Partial melting of filamentary (Nd 0.33 Eu 0.08 Gd 0.58 )Ba 2 Cu 3 O y superconductors in flowing 0.1% O 2 + Ar (sample A) and 1% O 2 + Ar (sample B) under various heating conditions was examined to obtain high transport J c . The T c values for sample A and sample B were 92.3 and 84.6 K, and maximum J c values at 77 K and self-fields were 19,000 and 350 A/cm 2 , respectively. Sample A had well-aligned texture along the filament diameter as well as filament length. The field dependence of J c for sample A was measured at 77 K and magnetic fields up to 10 T by changing the angle along the filament diameter. An angular dependence of the J c along the filament diameter was detected. By optimizing the angle, the sample showed J c value of 420 A/cm 2 at 77 K and 8 T.

In order to reduce thermal inputs through many measuring copper leads, we intended to fabricate a measuring leads unit using very fine YBa 2 Cu 3 O 7 filaments. The long YBa 2 Cu 3 O 7 filaments were prepared by a textile fiber spinning method for the oxide precursor. The 60 filaments with a size of 100 μm in diameter and 60 mm in length were attached onto three fiber-reinforced polymers, and were covered with epoxy resin. Both ends of the YBa 2 Cu 3 O 7 filament were soldered with pin connectors through copper leads with 0.1 mm in diameter. The YBa 2 Cu 3 O 7 measuring leads unit of 60 terminals was cooled by a pulse tube cryocooler. The newly developed YBa 2 Cu 3 O 7 measuring leads unit demonstrates the extremely small heat loads of 1/10 in comparison with conventional copper measuring leads.

We studied partial melting in filamentary Eu–Ba–Cu–O superconductors prepared by a solution spinning method. The precursor filaments were oxygen-controlled- melt-growth processed under various oxygen atmospheres in order to obtain a high Jc value. The superconducting properties of the Eu123 filament were strongly dependent on the heating condition and the atmosphere. The filamentary samples partial-melted in flowing 0.1% O 2 + Ar and 1% O 2 + Ar exhibited well aligned texture along the filament diameter as well as the direction of filament length and a dense microstructure without pores. Samples prepared in flowing 0.1% O 2 + Ar and 1% O 2 + Ar showed the Tc value of around 90 K, in contrast to the Tc value of 78 K for sample prepared in flowing 20% O 2 + Ar . The sample partial-melted in flowing 0.1% O 2 + Ar represented high Jc value more than 104 A/cm2 at 77 K and self-field over a wide partial melting temperature range of 1020–1040 °C and the excellent reproducibility.

The suspension spinning of commercially available MgB 2 powder was examined to fabricate a long superconducting MgB 2 wire. The MgB 2 powder was suspended in a mixed poly(vinyl alcohol) solution of dimethylsulfoxide and hexamethylphosphoric triamide. The viscous suspension solution was extruded as a filament into a precipitating medium of methyl alcohol and coiled on a drum. The as-drawn filaments were pressed and pyrolyzed to remove volatile components. The filaments were then cold pressed, enveloped by an iron sheet with a pellet of mixed powder of Mg and B, and vacuum sealed in a fused quartz tube and sintered. The effect of the J c on the starting materials and sintering conditions of the filamentary MgB 2 superconductors was examined. The J c of the sample was strongly dependent on the staring materials. The optimum sintering condition was sample to sample. The maximum J c value of more than 10 4 A/cm 2 at 4.2 K and self-field was attained.

The precursor Y1Ba2Cu3Ox (Y123) filaments were prepared by solution spinning through aqueous poly(vinyl alcohol) solution containing mixed Y, Ba and Cu acetates. The as-drawn filaments were heated to remove volatile components and to generate a superconducting phase. The filamentary superconductors were passed through Ag paste and sintered. By controlling the heating condition, the composite with excellent connection between the filaments and metallic Ag matrix was obtained. The overall transport critical current density (Je) of more than 2000 A/cm2 at 77 K and 0 T was achieved for the composite with partially melted Y123 filaments. Although the Je value decreased by applying a low magnetic field less than 0.1 T, the superconductivity of the composite maintained at 10 T at 77 K.

The preparation of filamentary (Nd, Gd)-123 superconductors was examined by changing starting composition and heating condition of melt processing in flowing 1% O 2 +Ar. High J c value of more than 2.4×10 4 A/cm 2 at 77 K and zero field and the high reproducibility were obtained for the filamentary (Nd 0.5 Gd 0.5 )-123 sample. The field dependence of J c for the sample was measured and J c value of more than 1×10 2 A/cm 2 at 77 K and 8 T was detected to the sample.

The precursor filament of Gd123 superconductors was prepared by solution spinning through a homogeneous aqueous solution of the metallic acetates. The precursor sample was partially melted in flowing 1% O 2 +Ar under various heating conditions. The maximum J c value of 2.1×10 4 A/cm 2 at 77 K and zero field was attained for filamentary Gd 1.18 Ba 2.12 Cu 3.09 O y superconductors. The sample had well aligned texture. The field dependence of J c for the sample was investigated. An angle dependence of J c along the filament diameter was detected. The J c value above 1×10 3 A/cm 2 was obtained at 77 K and 10 T.

The filamentary (Nd 0.333 Eu 0.333 Gd 0.333 ) 1.18 Ba 2.12 Cu 3.09 O x superconductors were prepared by solution spinning method and partially melted in flowing 1% O 2 +Ar and then oxygenated by a two-step process. The filamentary sample had a dense and well-aligned texture along the diameter as well as the length. The J c of the sample was measured at 77 K in fields up to 10 T. Anisotropic behavior of the J c – B curve along the filament diameter was detected. High J c value of more than 3500 A/cm 2 at 77 K and 10 T was achieved by applying the field in a direction normal to the c -axis of the sample.

The filamentary (Nd, Sm, Eu, Gd)–Ba–Cu–O (LRE123) precursor was prepared by the solution spinning method, through a homogeneous aqueous solution containing mixed acetates of Nd, Sm, Eu, Gd, Ba, and Cu, poly(vinyl alcohol) and organic acids. The filamentary sample was partially melted at 980°C in flowing 0.1% O 2 +Ar and oxygenated under various conditions. The transport critical current density ( J c ) for the samples was examined in magnetic fields up to 10 T at 77 K. The highest J c value of more than 1×10 4 A/cm 2 at 77 K and 9 T was achieved for the filamentary Nd 0.295 Sm 0.295 Eu 0.295 Gd 0.295 Ba 2.12 Cu 3.09 O x superconductors by controlling the oxygenation conditions.

Filamentary Nd123 superconductors were produced by solution spinning and oxygen controlled melt growth process. A transport critical current density, J c for the filamentary Nd123 sample prepared with various conditions was examined in magnetic fields up to 10 T at 77 K. Currents were passed along the fiber axis and were always normal to the applied magnetic field. The filamentary Nd123 superconductor exhibited J c values larger than the filamentary Y123 superconductor in high fields. An anomalous peak effect was not observed for the J c – H curve of the Nd123 samples and J c values were strongly dependent on the composition of the precursor and oxygenation condition. By controlling the melt growth process and post-annealing condition, high J c values exceeding 10 4 A/cm 2 at 77 K and 0 T and >10 3 A/cm 2 at 10 T were achieved for the filamentary Nd 1.18 Ba 2.12 Cu 3.09 O x superconductor prepared in flowing 1%O 2 +Ar.

The fabrication of superconducting Hg(Ba 0.5 Sr 0.5 ) 2 (Cu 0.9 Re 0.1 ) 2 O x (HgS1212) filament by solution spinning is reported. The precursor (Ba 0.5 Sr 0.5 ) 2 Ca(Cu 0.9 Re 0.1 ) 2 O x filament with a diameter of 300 μm was heated to remove volatile components and to react in a controlled Hg atmosphere. The filament was nearly single phase of Hg 1 Ba 2 Ca 1 Cu 2 O x (Hg1212) with T c of 93 K. The maximum transport critical current density ( J c ) of 2300 A/cm 2 at 77 K and 0 T was attained for the filament reacted at 880°C for 4 h. The texture of the reacted filament was dependent on the vaporizing material.

Partial melting of solution-spun (Y, Ho) 1 Ba 2 Cu 3 O x filament is examined in order to enhance the reproducibility of the high J c of the filament. The precursor filament was prepared by solution spinning through a homogeneous aqueous solution containing mixed acetates of Y, Ho, Ba and Cu, polyvinyl alcohol and organic acids. The substitution of Ho lowered the optimum partial-melted temperature to 1010°C. A high J cT value of more than 10 4 A/cm 2 at 77 K, 0 T that was reproducible appeared for the partially melted filament by applying a cooling rate of 40°C/h without the temperature gradient and without additional oxygenation. A maximum J cT value of 78 000 A/cm 2 at 77 K, 0 T was attained for the Y 0.75 Ho 0.25 Ba 2 Cu 3 O x filament. The micr microstructure presented in the filament is discussed as compared with the melt-textured bulk 123 superconductor.

Platinum coating of partially melted Y 1 Ba 2 Cu 3 O X filament produced by solution spinning is examined in order to enhance the J c of the filament. The filament was prepared by solution spinning through a homogeneous aqueous solution containing mixed acetates of Y, Ba and Cu, polyvinyl alcohol and organic acids. The heated filaments are dip-coated in aquious solution of Pt chlorate. By controlling the melt-growth process of the filament, dense and highly oriented textures are produced and a maximum transport J CT of 36 000 A/cm 2 at 77 K and 0 T is achieved. The fiber axis of the filament appears to coincide with the direction perpendicular to the c -axis of the orthorhombic phase in the superconducting layer. The J CT of the filament is strongly dependent on the degree of crystal orientation.

Zone melting was used to enhance the Jc of suspension spun Bi2Sr2Ca1Cu2Ox filaments. By controlling the directional solidification of the molten zone, highly orientated textures were produced and a transport critical current density of more than 2 × 104 A/cm2 at 77 K, 0 T was achieved.

Long precursor filaments are prepared by dry spinning with a starting homogeneous aqueous PVA solution containing Y, Ba and Cu acetates. By controlling the spinning process and partial-melting, a high J c value of more than 10 5 A/cm 2 at 77 K and 0 T was obtained. The filament with high J c does not always have a texture well aligned to the direction of the fiber axis. The field dependence of the transport J c of the filament at 77 K is small if the grain boundary is clean.

The Y1Ba2Cu4O8 superconducting filament has successfully been prepared by dry-spinning through a homogeneous aqueous solution containing Y, Ba and Cu acetates, polyvinyl alcohol and other organic acids. After removing volatile components, the 124 filament is obtained by heating at 780 °C for 3 h. A decomposition of the 124 filament is investigated for introducing fine flux-pinning centers into the 123 filament. A high transport JQ value of 1900 A/cm2 at 77 K and at O T is attained for the 123 filament through the decomposition of the 124 filament.

The filamentary monolithic RE123 (RE=Nd, Sm, Eu, Gd) precursor was prepared by a solution spinning method. The precursor was partially melted under various conditions and then oxygenated. The influence of field dependence of Jc on the initial different RE element in the filamentary RE123 superconductors was examined. The high Jc values were attained for Nd123 and Eu123 samples partially melted in flowing 0.1% O 2 + Ar and for Sm123 and Gd123 samples partially melted in flowing 1% O 2 + Ar . The field dependence of Jc for Eu123 sample was superior to that for the other samples.

The filamentary precursor (Nd 0.33 , Eu 0.33 , Gd 0.33 ) 1.18 Ba 2.12 Cu 3.09 O was prepared by a solution spinning method, and partially melted in flowing 0.1%O 2 +Ar, and then oxygenated by two-steps process. A high J c value of 2.5×10 4 A/cm 2 at 77 K and 0 T was obtained by controlling the heating conditions. The J c value of the sample oxygenated under various conditions was measured at 77 K in fields up to 9 T. The field dependence of J c was strongly dependent on the oxygenating conditions, and a high J c value of about 1.0×10 4 A/cm 2 at 77 K and 5 T was maintained.

We have synthesize the filamentary LRE (LRE=Nd, Sm, Eu, Gd)123 superconductors by solution spinning and melt growth process in flowing 1%O2+Ar (OCMG). The effect of heating condition for oxygenation on the field dependence of Jc at 77K of the filamentary (Nd, Sm, Eu, Gd)123 superconductors was examined. High Jc value of 6100 A/c2 at 77 K and 9 T was measured by controlling the heating condition. The Tc of the sample was 95 K with ΔTc=1.5K. The pinning properties of the sample were examined by extended analysis of volume pinning force and its found that Δκ-point pinning was dominant in this case.

Long precursor Ba 2 Ca 2 Cu 3 Re 0.2 O z filaments were spun by solution spinning method and reacted in a fused evacuated quartz tube with a pellet of Hg 1 Ba 1.8 Ca 2 Cu 3 Re 0.2 (BaF 2 0.2 O y . A partial meltong of filamentary specimens at a melting temperature ranging from 910° C and 930° C was examined. The J c of the specimens was enhanced by post-annealing up to 350° C in O 2 flow. By controling the heating condition, a maximum J c value of 1×10 4 A/cm 2 at 77 k and 0 T was observed.

Partial melting of fine solution-spun Y 1 Ba 2 Cu 3 O x filament is examined to enhance the Jc and to obtain a highly textured microstructure. The precursor filament with 110 μm in diameter was prepared by dry spinning with a starting homogeneous aqueous solution of Y, Ba and Cu acetates. By controlling solidified condition, a high Jc of more than 1x10 4 A/cm 2 at 77K and O T was attained for the filament of 20 μm in diameter. A well-aligned texture in the fine filament needs higher cooling rate for the following 123 crystal growth such as 75°C/h than that for a thick filament of 250 μm in diameter. A window of the optimum heating condition becomes very narrow as compared with the thick filament.

The pyrolytic processing of the precursor filament produced by solution spinning through a homogeneous aqueous solution containing PVA and Y, Ba and Cu acetates was studied. The thermal change of structure of the Cu(II) complex was examined using ESR and the effect of pyrolysis conditions on the microstructure and appeared phase was measured. The complex was eliminated by heating at more than 300°C and turned out to metallic Cu and metastable tetragonal phases, following to CuO and the metastable phase by heating up to 500°C.

We make a comparison between suspension spinning and solution spinning for the preparation of an oxide superconducting long filament. A high J c value of more than 10 4 A/cm 2 at 77 K, 0 T was attained for the melt-processed filaments after suspension spinning and solution spinning methods. While many kinds of high- T c superconducting filaments can be prepared by suspension spinning method, only a Y-Ba-Cu-O superconducting filament is successfully fabricated by solution spinning. However, the solution method can produce more uniform and finer materials than that for the suspension spinning method and introduce an effective flux pinning at 77 K.

The magnetization properties of the solution-spun YBaCuO filament are investigated. The filaments have been prepared by dry-spinning through a homogeneous aqueous solution containing mixed acetates of Y, Ba and Cu, polyvinyl alcohol and organic acids. After removing volatile components, the filament is sintered or is partial-melted. Significantly improved flux pinning has been achieved in the solution-spun filament. By adding a excess CuO and partial melting result in a enhancement of magnetic Jc and improvement of the field dependence on the Jc at both temperature of 4.4 K and 77 K. Thus, the solution spinning is able to introduce a effective fine flux pinning into the superconducting phase such as a elemental level.

We have studied the preparation of high Tc oxide superconducting filament using a low cost textile fiber spinning technology: The viscous precursor to a Y-Ba-Cu oxide was extruded as a filament, dried and subjected to heat treatment to remove volatile components and to generate oxide in the layered perovskite phase. The Jc of the high Tc Y-Ba-Cu-O system superconducting filament produced by suspension spinning was studied by changing the spinning condition. The high Jc at 77 K of 230 A/cm2 and 680 A/cm2 was observed for the filaments produced by aqueous spinning system and nonaqueous spinning system, respectively.