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The addition of long-term Zr2O3-ball milled Gd2BaCuO5 particles to a standard (Nd,Eu,Gd)Ba2Cu3Oy superconductor led to a spontaneous formation of extremely small (20–50 nm) Zr-rich (Nd,Eu,Gd)–Ba–Cu–O particles during the melt-growth process. This pinning medium, approaching the interesting physical limit of point-like pins from the side of large normal ones, dramatically enhanced supercurrents up to 90 K, both in low and intermediate fields. As a result, levitation experiment could be performed with liquid oxygen as a coolant. The particle size effect resemblance with fast neutron irradiation of RE–Ba–Cu–O single crystals is discussed.

In melt-processed (Nd0.33Eu0.38Gd0.28)Ba2Cu3Oy (NEG-123) materials we found a new type of nanometer-scale pinning defects. Structural analysis was made with a dynamic force microscope and a scanning tunneling microscope (STM) that both showed the formation of a nanometer-scale lamellar structure. The high magnification STM showed that the nanolamellas are in fact rows (or planes) of aligned NEG-rich clusters 3–4 nm in size. This new pinning medium led to an increase of Birr at 77 K for the H∥ c axis up to 12 T (measured by a superconducting quantum interference device) or 15 T (measured by a vibrating sample magnetometer). A secondary peak as high as 70 kA/cm2 was observed at 4.5 T and decreased to 49 and 22 kA/cm2 at 7 and 10 T, respectively.

Many tentatives have been made these last years to increase the pinning properties of melt-textured YBaCuO by secondary phases additions. The results are more or less positive depending on the processing conditions and the reactivity of the dopant, especially its action on the size and shape of 211 particles. In this paper, the effect of BaSnO3 additions up to 30 mol% on the microstructure and the superconducting properties of MPMG-processed YBCO is investigated. At high temperatures, BaSnO3 reacts rapidly with the liquid phases to form few microns size inclusions of a stable Y-Ba-Sn-Cu-Pt-O phase. This phase is found to consume platinum and to favor 211 coarsening at high temperature. For 30% doping, the entire microstructure is strongly affected and for low levels of doping (2% and 5%), we could not evidence any improvement in the superconducting properties, compared to undoped samples. But when the doping level is increased up to 10%, one can locally find a high density of submicron size 211 inclusions and Tc enhancement is observed. In this case, we could obtain improved Jc(B) properties up to 110 000 A/cm2, at 77 K in zero field.

The peak effect in melt-processed (Sm1−xEux)Ba2Cu3O7−δ crystals was modified with varying initial Sm/Eu ratios and was investigated up to 9 T down to 4.2 K. The experiment unveiled a linearly-temperature-dependent magnetization peak Bp(T). The fitting yielded a slightly lower critical temperature than bulk transition temperature Tc at null field. The scaling analysis of normalized pinning force versus reduced field B/Birr, where Birr is the irreversible field, showed a low peak at 0.37 in (Sm0.75Eu0.25)Ba2Cu3O7−δ and at 0.5 in (Sm0.25Eu0.75)Ba2Cu3O7−δ. The presence of regular compositional modulation is evident in both cases with transmission electron microscopy, and fluctuation diminishes in the latter composition. The modulation of flux pinning was thus attributed to the controlled compositional fluctuation.

The superconductivity in (Pb/Cu)-“1222” cuprates, (Pb, Cu) (Sr, Ln) 2 (Ln, Ce) 2 Cu 2 O z (Ln=Sm, Eu, Gd, Dy and Ho), has been found to be strongly dependent on the oxygen content as well as on the species of Ln ion. While the samples with Ln=Sm, Eu, Gd and Dy prepared in O 2 at an ambient pressure exhibit superconductivity, those with Ln=Ho required post-annealing in O 2 of a high pressure to become superconductors. It was likely that the ionic radius of Ln 3+ and oxygen stoichiometry were strongly related to each other and both played important roles in the occurrence of superconductivity in the (Pb/Cu)-“1222” compounds.

We prepared (Nd, Eu, Gd)Ba2Cu3Oy samples with various Nd: Eu: Gd ratios in the rare earth site. It was found that the three elements contributed to flux pinning in different ways. Nd mainly enhanced flux pinning at low magnetic fields, Eu controlled the second peak position and the irreversibility field, while Gd slightly enhanced intermediate and high-field Jc values. Scaling analyses for the pinning force density as a function of the reduced field h=Ha/Hirr (where Hirr denote the irreversibility field) showed that the highest peak was achieved at h=0.56. This value is even higher than the theoretically predicted highest value of h=0.5. We also show that a maximum flux pinning can be achieved in the whole magnetic field when very fine secondary phase particles are dispersed in a superconducting (Nd, Eu, Gd)Ba2Cu3Oy matrix with an optimum Nd: Eu: Gd ratio.

We have succeeded in enhancing Jc values of bulk Gd–Ba–Cu–O by employing fine Gd2BaCuO5 (Gd211) powders as precursor material. The mean diameter of Gd211 particles dispersed in the GdBa2Cu3Oy matrix could be reduced to 0.3 μm when we used ball-milled Gd211 starting powders

We fabricated a c -axis oriented Nd–Ba–Cu–O bulk superconductor with 10 wt.% Ag 2 O addition using the top-seeded melt-growth technique in 1% O 2 –Ar atmosphere. The size of the sample was 30 mm in diameter and 10 mm in thickness. We measured the field dependence of the trapped field at various temperatures. The peak effect of the trapped field could be observed, showing that the field-induced pinning is active even in large dimensions. The peak value of the trapped field reached 1.1 T at liquid nitrogen temperature. A high trapped field value of 3.75 T was recorded at 50 K.

Vickers hardness properties of YBCO bulk superconductor have been investigated from 40 to 293 K in this study. Hardness increased up to 18, 000±2500 MPa with decreasing temperature. Furthermore, cracks caused by the indentation process were observed with SEM, and the increase in crack length with decreasing of temperature was obtained. Fracture toughness KIC at cryogenic temperatures was attempted to estimate with Vickers hardness and crack length.

Electric field ( E )–current ( J ) characteristics of the NdBa 2 Cu 3 O 7− δ (Nd-123) bulk superconductor have been investigated by measuring the third harmonic ac susceptibility. They were compared with E–J characteristics determined with the dc magnetization measurements and magnetic relaxation methods. The n value was estimated on the assumption that E follows the power law: E ∼ J n . We found that the sample, which has the larger secondary peak on the J c – B curve, exhibits the more remarkable peak structure on the magnetic field dependence of the n value.

For the cold seeded melt growth of RE–Ba–Cu–O, it is important to decompose the precursor completely without melting the Nd–Ba–Cu–O seed crystal. We have studied the variation of growth mode with the maximum holding temperature ( T max ) and the holding time for Y and Gd systems. Growth modes were changed by T max and classified into four groups. In the case of Gd system, the temperature window for single-domain growth was narrow compared with Y system. This is ascribed to the fact that the decomposition temperature of Gd system is close to that of Nd123 seed crystal.

Bulk (Sm0.5Eu0.5)Ba2Cu3O7−δ superconductors were grown isothermally and with a vertical thermal gradient of −5 °C/cm in air. The crystals grown at a large growth rate under the thermal gradient exhibited a high-Tc value of 95 K and a plateau in the Jc–B curve at 1–4 T at 77 K with postannealing in Ar. We found that the substitution of Ba by rare-earth (RE) elements could be suppressed with a large growth rate. The narrow range of RE–Ba solid solution was attributed to the fast crystallization rate of RE1+xBa2−xCu3O7−δ with low-x values.

(Pb,Cu) (Sr,Nd)2(Ho,Ce)2Cu2Oz (z≈8.64) was made superconducting by heating at 500°C in O2 at a pressure of 90 atm. This oxide had a transition temperature (Tc) around 10 K. Its structure parameters were refined by the Rietveld method using neutron powder diffraction data. This compound belongs to space group 14/mmm and has a tetragonal unit cell with lattice constants, a=0.382496(8) nm and c=2.89862(7) nm. Atoms in fluorite-type layers and CuO2 planes are firmly bound at their ideal positions, whereas a (Pb,Cu)O monolayer is highly disordered and defective. In addition, an apical oxygen site in a [CuO5] pyramid is about 13% deficient. Such lattice instability in this oxide is discussed in connection with structural defects in other copper oxides.

There are several melt processes which promote high Jc in bulk YBaCuO. A comparison of various melt processes was performed in this study. It was found that size control of the Y2BaCuO5 inclusions is the key to the improvement in Jc values.

The structural analysis of a superconducting (Pb/Cu)-1222 phase, (Pb 0.5 Cu 0.5 )(Sr 0.875 Eu 0.125 ) 2 (Eu 0.75 Ce 0.25 ) 2 Cu 2 O z ( z ≈9), is performed by Rietveld analysis using X-ray powder diffraction data. Pb, Cu and O atoms constituting the (Pb/Cu)O monolayer in this crystal are found to be displaced from their ideal crystallographic sites as previously reported for the (Pb/Cu)-1212 compound. In addition, (Pb, Cu)-1222 compounds with nominal compositions of (Pb, Cu)(Sr, R) 2 (R', Ce) 2 Cu 2 O z (R, R': rare-earth element) are synthesized and characterized. Nearly single-phase samples are successfully obtained for the compounds with R = R ′ = Pr , Sm , Eu , Gd , Dy , Y or Ho , and for those with a pair of rare-earth elements, ( R , R ′) = ( La , Eu ), ( Nd , Eu ), ( Nd , Dy ), ( Nd , Y ), ( Nd , Er ), ( Sm , Eu ) or ( Eu , Gd ). Superconductivity is observed for the samples with R = R ′ = Sm , Eu or Gd and also for those with ( R , R ′) = ( La , Eu ), ( Nd , Eu ), ( Sm , Eu ) or ( Eu , Gd ).

The synergism of combined high-dose etoposide with standard dose cisplatin (HD-EP) was evaluated in 20 patients who had relapsed after treatment of small cell lung cancer. Each patient was given etoposide at 500 mg/m2/day on days 1 to 3 and cisplatin at 80 mg/m2 (two patients given 120 mg/m2) on day 1; autologous bone marrow was not transplanted. Five patients were given recombinant human granulocyte colony-stimulating factor (rhG-CSF, 50 micrograms/m2) in an attempt to reduce HD-EP induced neutropenia. The overall response was 50% (9 of 18); one complete response (6%), eight partial responses (44%), seven no change (39%), and two progressions of disease (11%). Of the 18 evaluable patients, 12 had been treated with regimens of conventional doses of etoposide with conventional doses of cisplatin or carboplatin, and of these, five (42%) achieved a partial response. The median duration of response was 8.4 weeks (range, 5.3 to 17.7) and the median survival time was 20.3 weeks (range, 1.6 to 91). All of the patients developed severe myelosuppression; rhG-CSF did not shorten the period of the leukopenia. Mucositis and liver dysfunction were the major nonhematologic manifestations of toxicity. Two treatment-related deaths resulted from sepsis. These results suggest that the activities of high doses etoposide with standard doses of cisplatin are synergistic against small cell lung cancer.

From January 1978 to March 1984, a series of 159 patients with newly diagnosed small cell lung cancer (SCLC) was treated with combination chemotherapy with or without chest radiation at the Osaka Prefectural Habikino Hospital. By March 31, 1989, ten patients (6.3%) had survived for 5 years or more after the initial chemotherapy, including nine of 95 patients (9.5%) with limited disease and one of 64 patients (1.6%) with extensive disease. All these 5-year disease-free survivors, except for one patient whose response could not be assessed by chest radiograph because of radiation fibrosis, had a complete response. Nine of the 71 patients (12.7%) treated with combination regimens containing doxorubicin survived 5 years or more, and only one of the 88 (1.1%) treated with regimens without doxorubicin had long-term survival (P less than 0.01). The sex, performance status (PS), and chest radiation after systemic chemotherapy did not correlate statistically with long-term survival (P greater than 0.05). Three of the ten patients died free of SCLC. Two of the ten patients (20%) developed second malignancies and died. The remaining patient died of pneumonia. The Cox regression analysis identified the PS and doxorubicin-containing regimens as important factors indicating improved survival. Combination regimens containing doxorubicin have, therefore, been found to be very effective in improving survival and achieving long-term survival.

In development of a flywheel energy storage system, electric power loss reduction is expected by using superconducting bearings. However, for realization of superconducting bearing strong levitation force, rotation loss reduction and axial descent reduction are required. It is known with axial descent reduction technology that a preload method is effective, whereas by this method, the levitation force becomes quite small compared with the normal levitation. We confirmed the performance of the preload method by experiment using a YBCO superconducting electromagnet. The preload method is improved and a method, which does not change the rate of the force relaxation and makes the levitation force larger than the existing preload method is proposed.

A reduced oxygen atmosphere during melt processing turned out to be critical for the fabrication of NdBa2Cu3Oy (Nd123) superconductors possessing high superconducting transition temperature (Tc) with a sharp transition and large critical current density (Jc) at 77 K. In a dc magnetization measurement, Nd123 superconductors melt processed in flowing a mixture gas of 1% O2 in Ar exhibited the Tc of about 95 K and the transition width of 1.5 K with the applied field of 10 Oe. A four‐probe measurement showed the zero resistive transition Tc (R=0) of about 95 K. An anomalous peak effect in the magnetization hysteresis (M‐H) loops was commonly observed and lead to large magnetic Jc of 2×104 A/cm2 at 77 K and 2 T for the applied field H parallel to the c axis of a sample (H∥c). This achievement is attributable to a preferential formation of high Tc phase (x

We report on a new type of correlated nanometer-scale pinning structure observed in a melt-processed $({\mathrm{N}\mathrm{d}}_{0.33}{\mathrm{E}\mathrm{u}}_{0.38}{\mathrm{G}\mathrm{d}}_{0.28}){\mathrm{B}\mathrm{a}}_{2}{\mathrm{C}\mathrm{u}}_{3}{\mathrm{O}}_{y}$ (NEG-123). It consists of $\mathrm{N}\mathrm{E}\mathrm{G}/\mathrm{B}\mathrm{a}$-rich clusters in the stoichiometric NEG-123 matrix forming a lamellar array with a period of a few nanometers. These lamellas appear within regular twins, thus representing their fine substructure---sometimes straight, sometimes wavy. This new material structure correlates well with the significant enhancement of pinning at high fields, represented by irreversibility field above 14 T at 77 K ($B\ensuremath{\parallel}c$). We believe that the new pinning medium enables one to significantly broaden the limits for high-field applications.

We have studied the structures of subgrains in large-grain RE123 (RE=Y, Sm) bulk superconductors, and their influences on superconducting properties. It was found from polarized optical microscopic observations that subgrains were formed in the early stage of grain growth and elongated along the growth direction with increasing their misorientation angles. For isothermally grown samples, subgrains are likely to form under large undercooling. Based on a comparative study of misorientation angles calculated through micro-area x-ray pole figure measurements with the geometry of the second-phase particles, the possible mechanism of subgrain formation was concluded to be the accumulation of dislocations formed as a result of entrapment of RE211 inclusions during crystal growth.

High quality single domain (Sm0.5Eu0.5)Ba2Cu3O7−δ superconductors were grown in air in a thermal gradient. Enhanced superconducting properties were obtained by combining post-annealing in Ar, (Sm0.5Eu0.5)2BaO4 addition and Pt doping. We found that the substitution of Ba by rare earth (RE) elements could be suppressed with a large growth rate and (Sm0.5Eu0.5)2BaO4 addition. The crystals exhibited a high Tc value of 94 K with a sharp superconducting transition, and a well developed peak effect at 77 K. The Pt doping enhanced Jc in low fields and resulted in the disappearance of the minimum of magnetization loops. High pressure oxygenation suppressed the secondary peak, but the field dependence of the maximum pinning force was different from that based on oxygen deficient clusters.

The samples consisting of SmBa2Cu3Oy (Sm123) precursors with RE2BaCuO5(RE211, RE=Y, Gd and Sm) or Nd4Ba2Cu2O10 (Nd422) were melt-textured in a reduced oxygen atmosphere. We have studied the relationship between the size of RE211 particles and the critical current density (J c ). When Y211 and Gd211 were added to a starting material, the size of RE211 phase particles in the bulk sample was remarkably reduced. As a result, J c values of these samples were larger than those of Sml23/Sm211 sample. The large c-axis oriented bulk sample 32mm in diameter was successfully fabricated from Sml23-Gd211precursor with 20wt% Ag2O addition. The trapped magnetic field of this bulk reached l.0T at 77K.

We have studied the melt growth of Ag doped Gd-Ba-Cu-O (Gd123 + 40mol% Gd211 + xwt% Ag, x=0–10) bulks by using a cold-seeding method with Nd-Ba-Cu-O seed crystal. Growth temperatures of the Ag doped bulks decreased with increasing Ag contents. EPMA and magnetic measurements showed that Gd element diffused into the seed crystal and formed (Nd, Gd)123 composite at the interfacial region. The formation of the composite phase raised the growth temperature. For cold-seeding, therefore it is necessary to increase the growth temperature for the fabrication of large grain samples.

Cracking mechanisms and tensile strengths for the melt-processed RE-Ba-Cu-O (RE123+RE211, RE: Sm, Y) bulks fabricated by a top-seeded melt-growth method were investigated. Four kinds of cracking mechanisms were discussed; 1) inhomogeneity in composition; 2) thermal stress; 3) phase transition during oxygen annealing; 4) Lorentz force induced by magnetic field. The tensile strengths of RE-Ba-Cu-O (RE: Sm, Y) were less than 30MPa, and the tensile strength along the c-axis was the weakest, which is due to the presence of the cleavage plane. Y-Ba-Cu-O showed the tensile strength higher than that of Sm-Ba-Cu-O, which is presumably ascribed to the longer bond length of the Sm123.

Nano-sized centers for magnetic flux pinning were successfully introduced into a bulk superconductor GdBa2Cu3O7−δ (Gd123) by mixing ZrO2 nanoparticles with precursor prior the melt growth in air. Superconducting properties and structure of doped Gd123 were studied by magnetization and transmission electron microscopy, respectively. The critical current density (Jc) and critical temperature indicate that the optimum addition amount is 0.2–0.8% ZrO2 in molar ratio to Gd123 as composition. With 0.4 mol % ZrO2 addition, Jc was increased to 100,000 A/cm2 at 77 K under self-field. The normalized pinning force deduced from the magnetization as a function of applied magnetic field shows single peak. Thus, the nano-sized ZrO2 addition enhanced the normal core pinning under low magnetic field, B/Birr

The relationship between mechanical property and microstructure was investigated by uniaxial compressive measurements for the melt-processed YBa2Cu3O7-d (Y123) bulks fabricated by a top-seeded melt-growth method. Compressive elastic moduli were quite dependent on the crystal structure and the crystal orientation. For the applied stress perpendicular to c-axis, both tetragonal and orthorombic Y123 samples showed linear relationship in the stress strain curves and large elastic modulus values. For the applied stress parallel to c-axis, while tetragonal samples exhibited almost linear relationship in the stress-strain curves with large elastic modulus, the orthorombic samples showed small elastic modulus values in a low stress (

Grain enlargement of light rare earth (LRE)-Ba-Cu-O (LREBCO) bulk superconductors has been systematically investigated with the top-seeded melt growth (TSMG) method. The (001) cleavage surfaces of melt-processed NdBCO seed crystals were used for achieving c-axis oriented LREBCO single grains. For the Nd-Ba-Cu-O system, Ag addition was necessary to ensure a temperature margin for seeding since the peritectic decomposition temperature of NdBa2Cu3Oy (Ndl23) decreases with Ag addition, while the NdBCO seeds were effective for other LRE-Ba-Cu-O systems. Careful study on the seeded melt growth at various undercoolings (ΔT) enabled us to successfully fabricate large c-axis oriented NdBCO-Ag or SmBCO single grains in air. The growth rates R of SmBCO are faster than that of YBCO at the same ΔT.

We systematically investigated the peritectic decomposition temperatures (Tp) of (Sm1-xGdx)Ba2Cu3Oy ((Sm1-xGdx)123) solid solutions and superconducting properties (Tc and Jc-B) of the binary mixed (Sm1- xGdx)-Ba-Cu-O ((Sm1-xGdx)BCO) bulk superconductors melt-processed in 1%O2-Ar atmosphere. The melt process was performed with/without NdBCO seed crystals. The Tp of (Sm1-xGdx) 123 linearly decreases from 1023°C to 1003°C with increasing x, i.e. the amount of Gd substitution on Sm. While Tc (94-95K) of melt-textured (Sm1-xGdx) BCO is independent of x and Pt dopant, Jc values increase with Pt doping since the (Sm,Gd)2Ba1Cu1Oy((Sm,Gd)211) is refined. NdBCO seeds were effective in fabricating (Sm1-xGdx) BCO large single grains.

REBa2Cu3Oy (RE=Nd,Sm) bulk superconductors were fabricated by the oxygen — controlled- melt -growth (OCMG) method, using a reduced oxygen partial pressure during melt growth. We investigated the grain enlargement and the properties of OCMG-processed REBa2Cu3Oy superconductors fabricated in a tube furnace with temperature gradient. From observations with a polarized optical microscope, it was revealed that the largest grain size with this process was 10×10 mm The dc magnetization measurement showed the Tc values from 94 K to 95 K in both NdBa2Cu3Oy and SmBa2Cu3Oy. The magnetic Jc for Ndl23 and Sml23 samples were 2.1×l04 A/cm2 and 9.7×103 A/cm2 at 2 Tesla and 77 K, respectively.

NdBa2Cu3Oy (Nd123) single crystals were grown by the flux method in low oxygen atmospheres using ZrO2 and Nd2O3 crucibles. The effects of the oxygen partial pressure (P O2) and the crucible materials on the flux-grown Nd123 single crystals were investigated. High quality Nd123 single crystals with onset T c of 93–95 K could successfully be obtained in a low P O2 using both ZrO2 and Nd2O3 crucibles. The peak effect was commonly observed on the M-H loops and a large J c value (> 2 × 104 A/cm2, 2 T) at 77 K and for H//c was achieved for the Nd123 crystals grown in the ZrO2 crucible.

We have measured the fracture toughness and the hardness of oxygen-controlled-melt-growth (OCMG) processed Nd-Ba-Cu-O samples and a flux-grown NdlBa2Cu30y (Nd123) single crystal. Preferred fracture planes were perpendicular to the cleavage plane. An indentation method was employed to investigate a hardness and fracture toughness. The hardness of OCMG-processed Nd-Ba-Cu-O was lower than that of the single crystal, but the fracture toughness was increased by the presence of the Nd4Ba2Cu2Oy (Nd422) second phase particles. We also investigated the size effect of Nd422 particles on mechanical properties. We found that smaller Nd422 is more effective in increasing the hardness and the fracture toughness.

Critical current density J c of Nd1+xJBa2-xCu3Oy (Nd123) single crystals flux-grown under the Oxygen-Controlled-Melt-Growth (OCMG) process has been investigated using DC magnetization measurements. The superconducting transition temperature T c of a Nd123 single crystal flux-grown using a 0.1% O2 — Ar gas in a zirconia crucible was 94 K. Using a magneto-optical observation method, the sample was found to be free of weakly-linked regions. DC magnetization hysteresis curves exhibited an anomalous peak effect in the high temperature range. This behavior is attributable to a field-induced pinning by finely-distributed low T c phases in the high T c matrix. J c calculation using the extended Bean model resulted in high J c of about 4 × 104 A/cm2 under 2 T and over 1 × 104 A/cm2 under 4 T at 77 K.

We have reported the melting points of Nd-Ba-Cu-O samples, measured by differential thermal analysis (DTA). When Ag was doped into the sample, the melting points of NdBa2Cu3Oy (Nd123) were depressed to lower temperature, implying the solidification temperatures of Ndl23 can be suppressed. In this paper, we report the Ag doping effect on the solidification temperatures for the Ag-doped Nd-Ba-Cu-O system and the properties of the oxygen controlled melt growth (OCMG)-processed Nd-Ba-Cu-O + Ag composites.

The effects of the nominal batch composition on the NdBa2Cu3Oy (Nd123) single crystals grown by a flux method were investigated. The single crystals of Nd123 were prepared by the slow cooling at a rate of 1°C/h from 1100°C to 960°C with various nominal batch compositions. Thicker crystals along c-axis could be obtained for the batches with Ba-richer compositions. Although all Nd123 crystals were non-superconducting above 10 K in a SQUID magnetization measurement due to Al contamination from Al2O3 crucible, thicker crystals could be applied as good seed crystals for the fabrication of large textured YBa2Cu3Oy (Y123) bulks.

Phases and microstructures involved in melt processing of NdBa2Cu3Oy (Nd123) superconductors were investigated. Compared with the Y-Ba-Cu-O system, the following obvious differences could be found for the Nd-Ba-Cu-O system; (1) A major solid phase in the melt-quenched materials from 1300~1450°C in air was Nd4Ba2Cu2Oy (Nd422) rather than Nd2O3, and (2) for a Nd123 sample prepared by an oxygen-controlled-melt-growth (OCMG) process in 1% O2 in Ar, while the Nd123 matrix composition was close to x=0.0 in Nd1+xBa2−xCu3Oy, the Nd422 grains inside the Nd123 matrix showed a Ba-excess and a Nd-deficiency corresponding to z= 0.05–0.1 in Nd4−zB2+zCu3Oy. On the other hand, common to the melt-processed YBa2Cu3Oy(Y123), stacking faults, twin boundaries, and dislocations could be observed for the OCMG-processed Nd123.

The effect of the Pt-dopant on the RE2O3-BaCuO,-CuO system during melt processing was investigated for RE= Nd and Sm. Pt-doping was found to suppress the coarsening of the major second phases, Nd4Ba2Cu2O10 (Nd422) and Sm2BaCuO5 (Sm211) in the Nd- and Sm-system respectively. With the same melt processing condition, lwt%Pt-doping was more effective for refining Sm211 than for Nd422, but it was not so effctive compared to Y2BaCuO5 (Y211) in the equivalent Y-system. Although SmBaCuO samples with and without Pt-doping, melt-grown by an oxygen-controlled-melt-growth (OCMG) process, showed the same onset transition temperature (T e ) of 94.5K in a SQUID measurement, the superconducting transition of the Pt-doped sample was relatively broad, which may be related to the phase separation caused by formation of a Pt-compound detected by an electron probe microanalyzer (EPMA).

The irreversibility fields (B irr ) for the rare earth(RE)Ba2Cu3Oy (RE=Nd, Sm, Eu) superconductors melt-grown in various partial oxygen atmospheres were investigated using an AC susceptometer. The B irr was determined by the peak temperature on the imaginary part of AC susceptibility under given DC magnetic fields applied parallel to the c-axis (B//c). The B irr , of Nd123, Sm123, and Eu123 melt-grown in reduced oxygen atmospheres commonly shifted to a high field region at a given temperature compared with that of a MPMG-processed Y123. It was also found that the B arr scaled with (1 − t2)1.5, where t (≡T/Tc) is reduced temperature.

For SmBaCuO superconductors, an oxygen-controlled melt growth (OCMG) process was applied. Like NdBaCuO, SmBaCuO melt-grown in reduced oxygen atmospheres exhibited enhanced T c with a sharp superconducting transition and larger J c in a high field region at 77 K and for the applied field parallel to the c-axis of the samples (H//c). An anomalous peak effect on the magnetization hysteresis was also observed. The peak position and the irreversibility field shifted to a high field region as an oxygen partial pressure (PO2) is decreased. While the OCMG-processed SmBaCuO showed relatively large Sm2BaCuO5 (Sm211) compared with Y2BaCuO5 (Y211) in a MPMG-processed YBaCuO, it was possible to obtain fine acicular Sm211 at the partial melt stage through a proper processing route.

REBa2Cu3Oy superconductors with rare earth (RE) ions with large radii (RE: La, Nd, Sm, Eu) exhibit relatively low T c due to the presence of RE-Ba solid solution. We have found that this solid solution can be suppressed if these superconductors are melt processed in a reduced oxygen atmosphere. We have also found that critical current densities of these superconductors are higher than those of melt processed YBa2Cu3Oy with fine Y2BaCuO5 inclusions in a high field region. The irreversibility line was also shifted toward the higher H-T region. We believe that flux pinning in these superconductors is ascribable to a finely distributed RE(Ba1−x,REx)2Cu3Oy phase in a good superconductive matrix.

An estimation of an intragranular critical current density Jc for a large YBCO bulk sample prepared by the MPMG method was performed by a trapped field measurement using a Hall probe. A single-domained rectangular YBCO sample (10mm×10mm×lmm) was field-cooled in liquid nitrogen under the field of 4000G. After the applied field was turned off, the field distribution in the area of l0mm×10mm was mapped by scanning the Hall probe at the interval of 0.5mm. The trapped field distribution was compared with the distributions calculated by numerical analyses assuming square current loops inside the sample. First, assuming a field-independent Jc, the measured profile was in good agreement with the calculated profile except in the high field region near the center. Therefore, the intragranular Jc was estimated to be 2.6×104A/cm2 (77K, 0T). Second, using the Irie-Yamafuji model taking into account a field-dependent Jc, the measured profile was in better agreement with the calculated profile even in the high field region. The material parameters in the relationship of J c =αB-n were found to be α=1.4×104A/cm2 and n=0.20. Finally, it is found that a trapped field measurement using a Hall probe is applicable to a Jc estimation of a large superconductor without destroying the sample.

We have performed ultrahigh vacuum scanning tunneling microscopy measurements at room temperature on (Nd 0.33 Eu 0.38 Gd 0.28 )Ba 2 Cu 3 O y (NEG123) crystals grown by an oxygen controlled melt growth process. Two characteristic nanostructures, namely, modulation and island structures have been observed on a cleaved surface of the NEG123 with high J c and high irreversible field H irr higher than 10 T at 77 K. These structures may be associated with an element substitution and the good J c – B property.

Gd–Ba–Cu–O bulk superconductor was fabricated with a cold seeding method. We have optimized the conditions to grow a single domain. The critical current density of the central region of the bulk was lower than the outer region in a lower magnetic field. However, the secondary peak was more remarkable. Such results are correlated with spatial fluctuation in the volume fraction of 2 1 1 phase particles.

Recent studies have shown that large bulk YBCO superconductors with high Jc values can be fabricated, and various applications using such bulk YBCO samples are now under consideration. For most applications, we need to have a sample in which large currents can flow in a large area. In order to achieve this, the control of crystal growth is critical, since YBCO superconductors are very anisotropic in their crystal structures and superconducting properties. Recently, we have found that crystal orientation of YBCO can be controlled by applying different temperature gradients in two directions perpendicularly to each other.

Thick films of YBa2Cu3O7-δ (YBCO) have been fabricated on yittria stabilized zirconia (YSZ) by using the screen printing method. In order to substantially increase Jc, it is clear that a method has to be found by which the number of weak links such as second phases and high angle grain boundaries can be reduced. In this paper, we report a promising method employing a seed crystal of RBa2Cu3O7-δ (R= Gd, Sm and Nd) by which large area of YBCO crystal can be fabricated in the thick film.