Phase relations on the join Bi-2201–CuO have been determined as a function of P(O2). Most of the major changes that occur between P(O2) of 1 and 0.01 atm occur in the most oxidizing part of the range. Stoichiometric Bi-2201 occurs only at the most oxidizing conditions and in a narrow temperature range near the solidus. In the Bi-2201–CuO system, the ternary phase that forms has higher Bi:Sr and Cu:Sr than Bi-2201. That phase, Sr14Cu24Oy, and CuO occur in the subsolidus and the invariant point at which they coexist with liquid is a ternary eutectic. The liquid is more Sr-rich than the Bi-2201–CuO join. Decrease in P(O2) produces a change in the Bi- 2201 solid solution so that stoichiometric Bi-2201 does not occur. At P(O2) ≤0.5 atm, all Bi- 2201 solid solutions have Bi:Cu<2 but Bi:Sr near unity and Sr14Cu24Oy does not form. Small amounts of a phase believed to be Bi9Sr11Cu5Ox form under these conditions and the primary phase field of that phase crosses the pseudobinary join and minimum melting is at a ternary tributary reaction point. The liquid there is more Bi-rich than the join. Further decrease in P(O2) causes a continued freezing point depression and enlargement of the CuO primary phase field so that the compositions of multiply-saturated liquids move away from the CuO apex.

Previously we reported on a two-layer electrodeposition process of thallium oxide superconductors that showed transport critical current density above 106 A/cm2 at 77 K in zero field. In this article, we report our effort to convert an electrodeposited thick film of (Tl,Bi,Pb)2(Sr,Ba)2Ca1Cu2Ox to (Hg,Bi,Pb)2(Sr,Ba)2Ca1Cu2Ox by the cation-exchange process. We are also reporting magneto-optical imaging data on Tl oxide superconductor films, which are compared with YBCO. Magneto-optical imaging provides insight into the nature of current flow in the Tl oxide superconductor, and thus, will help us to improve the critical current density in bulk high-temperature superconductor wire or tape.

Oxide high-Tc superconducting wires and tapes with high critical current density (Jc) are essential to future electrical power applications. Recently, YBa2Cu3O7−x (YBCO) thin films grown on Ni-based alloy tapes have attracted intense interest because of their promise for these applications. To achieve high Jc, buffer layers are necessary for fabricating biaxially aligned YBCO thin films. In our studies, yttria-stabilized zirconia (YSZ) layers were deposited on Ni- based alloy substrates by ion-beam assisted deposition, and CeO2 buffer layers were subsequently deposited on the YSZ layer by pulsed laser deposition (PLD) or electron beam evaporation. In addition, MgO layers were deposited on Ni-based alloy substrates by inclined substrate deposition. Finally, biaxially textured YBCO thin films were deposited on these buffered metallic substrates by PLD under optimized conditions. The orientation and in-plane textures of YBCO and the buffer layers were characterized by X-ray diffraction Ø/2Øscans, ø- scans, and pole figure analysis. The superconductive transition features were examined by measuring inductive Tc and transport Jc.

In our previous work we have obtained YBCO thick films on silver alloy substrate via the peritectic solidification. To further develop grain-textured YBCO thin films for conductor development, in this study, we have used a sol gel approach to deposit YBCO thin films on two different substrates, namely, yttrium-stabilized zirconia (YSZ) and a silver alloy containing 10 % of palladium (Ag –10%Pd). We have found that the sol gel film on YSZ exhibits an epitaxial growth. This is confirmed by both x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD data also indicate that the YBCO film on Ag-10%Pd has a c-axis grain orientation. The details are reported on sol gel synthesis and XRD and HRTEM characterization of the YBCO thin films.

Creation of precipitates in bulk matrix to act as pinning centres is a prospective way to improve critical current density in high temperature superconductors. It is possible to generate such precipitates via partial decomposition of the supersaturated solid solution derived from a superconducting phase. To control this process one should go by a knowledge of stability field for these solutions. The objective of present work was determination of the homogeneity area of Bi2Sr2Ca1−xRxCu2O8+d and Bi2Sr2−xCaRxCu2O8+d (R = Nd, La). Semi-quantitative XRD analysis was used to evaluate phase composition of specimens quenched from various temperatures. It was found that solubility limits of Nd and La in Bi-2212 for cases of alkaline earth element substitution by rare earth elements with smaller ionic radii (substitution Ca by Nd; Sr by Nd and La) were the same (values of x are about 0.8). These limits are determined by fraction of Cu+ ions in lattice site attributed to Cu2+. In case of substitution of Ca by La stability area of 2212 was found to be much narrower (values of x about 0.3) compared to other substitutions. One ca n deduce this fact from the difference of Ca2+ and La3+ ionic radii.

Levitation force and magnetic field trapping are the most important properties of YBCO large grain materials. They are dependent on the pinning force exerting on the magnetic flux lines by various crystal defects in YBCO. In this paper, Ga-doped bulk YBCO samples were fabricated by SmBCO seeded melt-growth process. The levitation force and trapped field were enhanced by the introduce of nanometer scale week superconducting regions which are formed by the Ga partially substituting for Cu on the Cu-O chain.

Melt textured YBCO samples with and without 211 inclusions were irradiated by fast neutrons. The enhancement of the critical current density was studied as a function of the 211 content by means of SQUID magnetometry at temperatures from 5 to 77 K and magnetic fields from 0 to 8 T. The highest enhancement factor, found at 77 K and 1.5 T for a 211-free sample, is 27. The enhancement is less effective for samples with 211 inclusions. However, the critical current densities after irradiation show a similar temperature and field dependence in all samples. The role of the initial microstructure on the radiation effects is discussed.

Resistive superconducting (SC) transition, current-voltage characteristics, and X-ray diffraction (XRD) of YBaCuO ceramics have been studied after exposure to 18 MeV proton beam at 300 K. In the interval of 1013 −5×1014 cm−2 the irradiation induced oxygenation of weak intergrain contacts and grain alignment, anisotropy and broadening of SC-transition measured along and across the proton beam, and residual magnetization were found. The proton induced anisotropic texture is responsible for the critical current increase at 77 K and the resistivity decrease at 90–200 K. In a higher dose interval of 1013 −1015 cm−2 the SC-transition parameters degrade and the resistivity increases, depending on a texture degree, weak intergrain links become deoxygenated and no texture occurs. The magnetization (pinning) and the anisotropy of SC-transition can be due to localization of charges at the proton induced defects (mostly in oxygen sublattices).

Differential thermal analysis and thermogravimetric analysis (DTA/TGA) experiments have been completed in the BaF2-BaO-Y2O3-CuOx-H2O system at various oxygen pressures to determine the effect of adding solid BaF2and gaseous H2O (at pH2O = 2.5 kPa) on the eutectic melting in the system BaO-Y2O3-CuOx. We have investigated the eutectic melting temperature over the range of pO2 = 20 Pa to pO2 = 0.1 MPa under the following conditions: 1) without BaF2 or H2O; 2) with H2O only; 3) with BaF2 only; 4) with both BaF2 and H2O. Results indicate that without BaF2 or H2O, eutectic melting is depressed from 917°C at pO2 = 0.1 MPa to 838°C at pO2 = 1 kPa. At oxygen pressures below 1 kPa, down to pO2 = 20 Pa, no further lowering of eutectic melting temperature was observed. The topologies of the temperature vs. log pO2 curves for various combinations of BaF2 and H2O were similar to that for the experiments without BaF2 or H2O, but all curves were shifted to lower temperatures. For the experiments with addition of BaF2 only, H2O only, and BaF2 with H2O, the eutectic melting temperatures as a function of pO2 were lowered by, respectively, 5°C - 15°C, 15°C - 25°C and 20°C - 30°C. Application of results to the “BaF2ex-situ” method of processing Ba2YCu3Ox coated conductors is discussed.

Two special processing procedures based on freeze-drying synthesis have been developed in order to obtain fine (100nm) single phase LaSrCuO4−σ powders and dense ceramics. The rate of phase formation is strongly influenced by the composition of the salt precursor while the most crucial factors are heating rate and PO2 during decomposition. Studies of oxygen mobility in La2−xSrxCuO4−σ performed by dynamic-thermal O18-isotope exchange method revealed that all ceramic samples possess substantial catalytic activity in the isotope exchange reaction between oxygen molecules 32O2 and 36O2. Besides, substitution of La for Sr in La2−xSrxCuO4−σ (x =1) results in the decrease of oxygen release onset temperature from 460 to 380°C. Such a dependence correlates quite well with data on diffusion coefficients calculated for various x from the results of coulometric titration experiments. Samples with x=1 demonstrated also good catalytic activity in the reaction of CO oxidation.

Two novel complementary and non-destructive techniques for texture analysis of YBCO coated conductors are presented. Micro-Raman (μ-Raman) spectroscopy enables an easy analysis of the film homogeneity by determining the distribution of a- and c-oriented grains within the tape with a 1 μm spatial resolution and acquisition times of 5 min/spot. In addition, synchrotron x-ray diffraction analysis in transmission geometry and 2D detectors enables, with acquisition times of 100 ms, simultaneous observation of a- and c- crystallites and in-plane textures of substrates, buffers and superconducting layer. Thus, opening the field of this technique to in-situ analysis of epitaxial growth of coated conductors prepared by ex-situ processes. Results from these two techniques for stainless steel tapes buffered with IBAD-YSZ and coated with PLD-YBCO are analyzed.

Recent Progress of development for coated conductors by the LPE technique was reviewed. Double layered LPE films were applied to the growth on metal substrates. In both cases of MgO- and NiO- buffers, the constructions were succeeded to grow on Hastelloy and Ni tapes, respectively. In the case of the MgO-buffer, the problem, which is the melting back of the 1st LPE layer during dipping for the growth of the 2nd LPE layer, was found. The problem was solved by means of the selection of the materials for each LPE layer to introduce the difference in the growth temperature for the 1st and the 2nd layers. The lower growth temperature for the 1st LPE layer than that for 2nd one is effective to avoid the problem. On the other hand, the double layered LPE films on Ni tapes revealed Tc of 85K. Concerning the long tape processing, the high growth rate of 1≈ was confirmed even without rotation using the long tape apparatus.

We report on the new superconducting materials with the formula Ru1−xSr2GdCu2+xO8-z that have been synthesized under high-pressure oxygen conditions. By changing the ratio between Ru and Cu in the compound we were able to increase the temperature of the superconducting transition up to 72 K for x=0.3 and 0.4. Reentrant dependencies of the magnetization found at low temperatures are qualitatively explained assuming a quasi two-dimensional character of the superconducting regions. The magnetic characteristics of these compounds are discussed and compared to the existing data on RuSr2GdCu2O8 magnetic superconductor (Tcon=45K, TN=132 K).

We have succeeded in synthesizing RE-Ba-Cu-O (RE = Gd and Dy) bulk superconductors with excellent field trapping properties. Large c-axis oriented single-domain Gd-Ba-Cu-O bulk samples with Ag addition were melt-textured under controlled oxygen partial pressure of 1.0%. The Gd-Ba-Cu-O sample 50 mm in diameter could trap a high flux density of 2.4 T at 77 K. In addition, we measured the trapped field between two Gd-bulks in order to minimize the demagnetizing effect and found that it reached 3.3 T. The single-domain Dy-Ba-Cu-O/Ag bulk 48 mm in diameter was also fabricated in air and its trapped field was 1.9 T at 77 K.

We studied the origin of peak effect in the magnetic field dependence of Jc in NdBa2Cu3O7-σ single crystals. The single crystals were grown by the slow cooling method under various partial O2 pressures(PO2) (0.04∼1%) in Ar atmosphere. We found that the peak effect depends on PO2 and it disappears for the crystals grown under low PO2∼0.04%. This result demonstrates the important role of Nd/Ba substitution for the peak effect because it is known that the Nd/Ba substitution decreases with lowering PO2. We also investigated the role of oxygen vacancies in the peak effect for the crystals with different amount of Nd/Ba substitution. We found that the main cause of peak effect in fully oxygenated crystals is due to local low Tc regions caused by the Nd/Ba substitution rather than those by the oxygen vacancies.

The synthesis at high pressures ( ∼60 Kbar) and high temperatures (∼1100 °C) of the title new ruthenates has been achieved and the materials compared to the gadolinium analogue. The structure remains tetragonal (S.G. P4/mmm) and the cell parameters linearly decrease following the lanthanide contraction. Preliminary results concerning the complex magnetic properties of these materials, where superconductivity, antiferromagnetism and a superimposed ferromagnetic ordering coexist, are presented.

The influence of γ - irradiation on the structure of both superconducting and non-superconducting non-stoichiometric ceramics YBa 2 Cu 3 O 7−x by the neutron diffraction method has been investigated.

The results caused due to the γ-irradiation of a powder sample YBa2Cu3O6.98 in evacuated ampoule crystalline lattice distortion can manifest themselves when content of O atoms decreases up to (7-x ) 6,64. The O atoms move away from O(1) and O(4) position mainly during this process. The Meissner effect does not appear. The lattice parameters are changed in an irradiated non -stoichoimetric sample mainly due to arising radiation defects.

Melt textured YBa2Cu3O/Y2BaCuO5 were post processed by high oxygen pressure for different periods and temperatures. This process permits the control of the microstructure, in particular the growth and shape of the stacking faults and thereby the partial dislocation density. Analysis of the Jc(H,T) behavior allow to separate the contribution of Y2BaCuO5 interface from that of dislocations. It is shown that the in-plane partial dislocations act as point-like pinning centers increasing Jc up to 180% but this enhancement factor is counterbalanced by the effect of the stacking faults associated to the partial dislocations.

The enormous technological potential of high-temperature superconductors (HTS) was realized immediately following their discovery in 1986, yet these materials largely remain laboratory curiosities as scientists struggle to scale from coupons to long lengths of practical coated conductor. Although both vacuum and non-vacuum processes are being investigated for commercial production, low-throughput vacuum techniques were the first to succeed in producing the buffer and superconducting layers necessary for superconducting tape with high critical currents. However, vacuum processes are not only expensive but impractical when addressing the needs for rapid production of kilometer lengths of wire. The innovative Combustion Chemical Vapor Deposition (CCVD) method used with the Rolling Assisted Biaxially Textured Substrates (RABiTS™) technology has shown significant promise in fabricating the multi-layer structures necessary for successful HTS tape while overcoming many of the shortcomings of traditional vacuum techniques. The key advantage of the CCVD technology is its ability to deposit high quality thin films in the open atmosphere using inexpensive precursor chemicals in solution. As a result, continuous, production-line manufacturing is possible with significantly reduced capital requirements and operating costs when compared to competing vacuum-based technologies. The current status of development for production of long lengths of high-temperature superconductors using CCVD will be discussed.

Ultrathin superlattices of 123 superconducting cuprates have been fabricated by high oxygen pressure sputtering technique. The superlattices show high quality, with negligible step disorder, roughness and interdiffusion. The insulating PrBa2Cu3O7 (PBCO) layer thickness has been kept constant at 5 unit cells (u.c.) and the superconducting YBa2Cu3O7 (YBCO) layer thickness has been changed from 8 u.c. to 1 u.c. In these uncoupled multilayers the critical temperature (Tc0) changes from 44 (1 u.c. YBCO) to 80 K (8 u.c. YBCO). In the vortex liquid regime, at constant temperature, the angular dependence of the magnetoresistance scales down with the applied magnetic field values in all the temperature range. This behavior allows us to study the anisotropy and dimensionality behavior of the mixed state in ultrathin superlattices. A dimensional crossover 3D-2D is found in the anisotropy with the 1 u.c. YBCO superlattices following a pure 2D behavior.