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Ni–Cr alloys have been focused on as a new promising material for the reinforcement of DI-BSCCO wire. In addition to Ni–Cr alloy lamination, the thinner Type H wire and pretension have been employed. The fabricated Type H wires laminated with 35- $\mu\text{m} $ -thick Ni–Cr alloys have shown no degradation in $I_c$ properties and surpassed all the Type HT wires laminated with the thicker stainless-steel tapes in the tensile strength and double bending diameter. It was demonstrated that the wire could tolerate the practical extent of tensile load up to 10 000 cycles. The in-field $I_c$ performance has hardly been compromised with the moderate pretension. These results, along with the smaller cross-sectional size, have led to the compatibility between high $J_e$ and high mechanical strength. The Type HT wire with the thinner Type H wire and 30- $\mu\text{m}$ -thick Ni–Cr tapes are currently developed.

In this study, we extensively used electron backscatter diffraction orientation imaging microscopy to visualize the grain structure in the flat-rolled (Bi,Pb)2Sr2Ca2Cu3O x (Bi-2223) tapes. The thermomechanical process made the grains’ c-axes oriented normal to the tape surface. The 24% difference in critical current density J c was caused by the ∼5° difference in the degree of out-of-plane texture. Although the in-plane orientations are not controlled, the Bi-2223 grains can form the domains, each of which consists of the grains with similar in-plane orientation. Controlling the domain formation could be the next protocol to raise the J c of Bi-2223 tapes.

The thermal conductivity, κ ( T ), of the Bi2223/Ag tape reinforced by metal tapes (stainless steel (SS) or copper-based alloy (CA)) from both side was evaluated along the length ( l ) and width ( w ) directions. κ ( T ) along the l -direction was measured directly using a single tape and that along the w -direction was estimated from the κ ( T ) measured for a stacked bundle which consists of several sandwiched Bi2223/Ag tapes. We analyzed the obtained κ ( T ) curves using an equivalent heat current circuit, and found that the heat transports along both directions were nearly the same and that the route of heat-flow depended on the species of the reinforcing metal. The absolute values of κ ( T ) at 77 K along the l - and w - directions for the Bi2223/Ag-SS tape were 174 and 140 W m −1 K −1 and those for the Bi2223/Ag-CA tape were 206 and 206 W m −1 K −1 , respectively, the values of which were approximately 30–40% and 10–15% smaller than those of the standard Bi2223/Ag tape.

Sumitomo Electric has been developing the silver-sheathed Bi2223 multi-filamentary wires since the discovery of Bi-based superconductors. DI-BSCCO (Dynamically-Innovative BSCCO) is the high performance wires produced with the controlled-overpressure (CT-OP) sintering technique. The recent R&D activities have enabled to produce the 1000 m-long wires with I c of 200 A and the maximum I c reached 250 A at 77 K by short sample. Besides, the fine control of the carrier density with the non-stoichiometric oxygen enhanced the in-field I c performances at lower temperature. At a magnetic field of 3 T applied normal to wire surface, the I c of 280 A at 30 K, and 420 A at 20 K were successfully achieved. To meet the growing needs for various high temperature superconducting applications, Type HT wire with high mechanical strength and Type G wire with low thermal conductivity have been developed.

Recently, we have updated the highest J c and I c at 77 K, self-field, for our R&D short length tapes and I c × L at 77 K, self-field, for our kilometer-length manufacturing product. For our short length R&D tapes, we have updated the I c to 236 A. The highest J c has reached 663 A/mm 2 . Furthermore, we have broken our own world record performance of I c × L with the production of a 4.2 mm wide, 2084 m long Bi wire that carries an average current of 176 A. This has resulted in a new record—high wire performance of 367 k Am.

Electrical and mechanical characteristics of Type HT tape, which is standard 4.2 mm wide DI-BSCCO tape reinforced with metallic tapes, have been evaluated. Longitudinal distributions of critical current and n-index in kilometer long Type HT tape has proved uniform from end to end just like the original insert tape, which is Type H tape. Type HT-CA reinforced with 50 mum thick heat-resistant copper alloy is highly balanced tape with high mechanical properties and low splice resistance. Type HT-SS reinforced with 20 mum thick stainless steel has the best mechanical properties, which has been demonstrated under the actual environment in high field magnet, namely the hoop stress load test energizing a one-turn coil in external high magnetic field and liquid helium.

We report the NdBa2Cu3Oy (Nd123)-Ba3Cu5Oz(035) pseudo-binary section in the Nd2O3-BaO-CuO system under the oxygen partial pressure pO2 = 0.01 atm. We performed thermogravitational and differential thermal analysis (TG-DTA) and powder x-ray diffraction (XRD) measurements for quenched samples. We also performed high-temperature XRD for the determination of equilibrium solid phases at elevated temperatures. In situ observation of the primary solid phases with laser scanning microscopy was also performed for an accurate determination of the liquidus line. In comparison with the Nd123-035 pseudo-binary phase diagram in air, the liquidus line under pO2 = 0.01 atm shifts to a lower temperature.

Nd1+xBa2-xCu3Oy (Nd123ss) single crystals were isothermally grown under controlled oxygen partial pressure of 1% O2 at various growth temperatures (Tg) from 1000 to 1020 °C with a flux method. The flux composition of 20 mol% NdBa2Cu3Oy (Nd123) and 80 mol% Ba3Cu5O8 (035) was employed. Nd123ss single crystals grown at Tg≥1010 °C exhibited a transition temperature Tc≈95 K with transition width ≈1 K, the peak field (Bpk)≈2-3 T and the irreversibility field (Birr) at 77 K much higher than the experimental limit of 7 T. As the growth temperature is lowered, both the Bpk and Birr were reduced, which can be explained in terms of the chemical fluctuation which can occur at lower Tg.

In order to explain the effect of uniaxial strain on the critical current of DI-BSCCO-Bi2223 tapes, we employed a springboard sample holder that can smoothly and continuously apply both tensile and compressive strains to tape samples. Over a narrow tensile strain region, the critical current in the tapes decreased linearly with increasing strain and returned reversibly with decreasing strain. When compressive strain was applied, the critical current first increased and then reached a weak maximum. Thereafter, it decreased monotonically with further increases in compressive strain. At room temperature, the local strain exerted on BSCCO filaments was measured by means of a quantum beam diffraction technique. Over the whole tensile strain region up to 0.2% and the small compressive strain range, the local strain changed linearly with applied strain. When the compressive strain was applied beyond the relaxation strain, the local strain (measured by diffraction) versus the applied strain (measured using a strain gauge) deviated from linearity, which is characteristic of strain relaxation and the onset of BSCCO filament fracture. Thus, the strain at the maximum critical current corresponds to a crossover point in strain, above which the critical current decreased linearly and reversibly with increasing applied strain, and below which the critical current decreased due to the BSCCO filament fracture. In this paper, we clearly characterize the reversible range terminated by both compressive and tensile strains, in which filaments do not fracture. Our analysis of the compressive regime beyond the relaxation strain suggests that although BSCCO filament fracture is the primary factor that leads to a decrease in critical current, the critical current in those regions of filaments that are not fractured increases linearly and reversibly with decreasing applied strain at compressive strains well beyond the reversible region for the tape.

We investigated the superconducting properties of Nd1+xBa2-xCu3O7-δ with x=0.0, 0.1, 0.2, 0.3, and 0.4 as a function of the oxygen content. The temperature variation of the oxygen content was studied by means of both TG-DTA and an iodometric titration technique. The amount of oxygen absorbed during oxygenation decreases with increasing x. We have also studied the effect of the oxygen content on the superconducting properties for the samples with various x. It was found that the optimum annealing temperature for the highest T c is higher for larger x.

Excellent high tolerance on the yield stress and critical current of BSCCO-Bi2223 tapes was realized by the pretensioned lamination technique. The yield stress at room temperature and the stress to 95% Ic retention exceeded 430 and 510 MPa, respectively. In order to make clear the potential of this technique, the influence of thickness of lamination sheet and degree of pretension was investigated in detail. The observed yield stress at which the macroscopic yielding starts due to the fracture of BSCCO filaments has been successfully evaluated by calculation as a function of stainless steel sheet thickness and pretension, which is useful as engineering data. The relaxation stress at which the local strain starts to relax due to filament fracture was expressed as a unique function of the thermal residual strain exerted on BSCCO filaments together with the residual strain induced by the pretension treatment. The force free stress at which the local stress exerted BSCCO filaments becomes zero was proportional in magnitude to the residual strain exerted on BSCCO filaments. The stress to 95% Ic retention was elucidated to give a good indication, at which the critical current decreases abruptly due to the fracture of BSCCO filaments.

A remarkable improvement in the strain dependence of critical current and the mechanical properties of DI-BSCCO-Bi2223 tapes was achieved by means of the pretensioned lamination technique. In order to elucidate the origin of this high performance, the local strain exerted on BSCCO filaments was investigated by means of the synchrotron radiation technique. The relaxation strain Ar was expressed by the sum of thermal strain and tensile strain in the fracture of BSCCO filaments. It was concluded that the central parameter when considering the improvement of strain induced properties is the force free strain exerted on BSCCO filaments together with their own strength.

To improve the mechanical properties of silver-sheathed BSCCO wire, the laminated BSCCO wires with stainless steel were made under some experimental conditions. The dependence of the stainless steel thickness and the dependence of the pre-tension of stainless steel tapes on the laminated BSCCO were investigated by mechanical tests (tensile test at 77 K and RT and double-bending test at RT) using short samples. Due to the difference of the coefficient of thermal expansion (CTE) and the relaxation to equilibrium after removing the total pre-tension of no laminated BSCCO (insert tape) and stainless steel tapes, the residual axial compressive strain applies to an insert tape after the lamination process. A high compressive strain up to the compressive yield of the silver-alloy is so useful for improvement of the mechanical properties of BSCCO wire. Measurement results were approximately the same as the simple model calculated from the residual strain applied to an insert tape by the difference of CTE and pre-tension. The stainless-steel-laminated BSCCO wire 'Type HT-SS' has been able to be achieved over 500 MPa at 77 K by increasing stainless steel thickness and the residual axial compression for an insert tape. The developed tough DI-BSCCO has a higher hoop force to compare with YBCO-coated conductor using Hastelloy substrates under the same circumstances such as magnetic field, winding diameter and transport current.

High Ic in DI-BSCCO has been demonstrated even in high temperature up to 90K and parallel magnetic field up to 200 mT. This performance is advantageous especially to power cables cooled with pressurized liquid nitrogen, where current and temperature fluctuates in real operation. Recent development has updated the highest Jc at 77K, self-field to 630 A/mm2 in a R&D tape. The evaluation by a scanning magnetic microscope has demonstrated the highest Jc of 900 A/mm2 at the midst of a tape which has Ic of 200 A. This property promises innovative Ic more than 300 A in future DI-BSCCO.