三浦 正志

Abstract Given their excellent superconducting properties, REBa₂Cu₃O_y (REBCO)-coated conductors (CCs) are anticipated to be utilized in a variety of magnet applications. To further increase the critical current density J _c of these materials to levels needed for commercial applications, this study employs reel-to-reel (RTR) pulsed laser deposition (PLD) to fabricate REBCO+BaHfO₃ (BHO) CCs. PLD creates BHO nanorods, which serve as flux-pinning defects. The material is subjected to O²⁺ irradiation to introduce more defects. The irradiation-induced defects serve as flux-pinning centers to the REBCO+BHO-nanorod CCs, increasing J _c along the c axis and over a wide range of magnetic-field angles compared with conventional REBCO+BHO-nanorod CCs. Both nanorods and irradiation-induced defects are demonstrated to be effective pinning centers in this material.

Abstract The addition of artificial pinning centers has led to an impressive increase in the critical current density (J_c) of superconductors, enabling record-breaking all-superconducting magnets and other applications. The J_c of superconductors has reached ~0.2–0.3 J_d, where J_d is the depairing current density, and the numerical factor depends on the pinning optimization. By modifying λ and/or ξ, the penetration depth and coherence length, respectively, we can increase J_d. For (Y_0.77Gd_0.23)Ba₂Cu₃O_y ((Y,Gd)123), we can achieve this by controlling the carrier density, which is related to λ and ξ. We can also tune λ and ξ by controlling the chemical pressure in Fe-based superconductors, i.e., BaFe₂(As_1−xP_x)₂ films. The variation in λ and ξ leads to an intrinsic improvement in J_c via J_d, allowing extremely high values of J_c of 130 MA/cm² and 8.0 MA/cm² at 4.2 K, consistent with an enhancement in J_d of a factor of 2 for both incoherent nanoparticle-doped (Y,Gd)123 coated conductors (CCs) and BaFe₂(As_1−xP_x)₂ films, showing that this new material design is useful for achieving high critical current densities in a wide array of superconductors. The remarkably high vortex-pinning force in combination with this thermodynamic and pinning optimization route for the (Y,Gd)123 CCs reached ~3.17 TN/m³ at 4.2 K and 18 T (H||c), the highest values ever reported for any superconductor.

A new metal organic deposition (MOD) process using precursor solution containing metal trifluoroacetates was developed to improve in-field performance. In this process, the pinning centers of BaMO3 (M: metal elements such as Zr and Hf) materials could be made to be finer by reducing the once coating thickness in the coating and calcination step. This is referred to as the ultrathin once coating (UTOC)-MOD process. This process improves the in-field performance. The UTOC-MOD process also has the advantage of uniformity of 2-dimensional J(c)-distribution, which was determined using a scanning hall-probe microscopy analysis. Improvement of the J e uniformity was also confirmed based on scribed tapes. A smaller dispersion of the filament-critical current values in the UTOC-MOD tape was determined based on a comparison with the results for obtained by a conventional process. With respect to the mechanical strength, it was established that the dispersion of the delamination strength, which was evaluated using stud-pull equipment, was suppressed. Microstructural analysis revealed that, the UTOC films were pore-free, although large pores are present in the films when conventional MOD is utilized. This difference in the microstructure can he attributed to the aforementioned improvement in the uniformity of the UTOC-MOD films.

(Y0.77Gd0.23)Ba2Cu3O y [(Y,Gd)BCO] films were grown on CeO2 buffered R-plane sapphire (R-Al2O3) substrates using trifluoroacetate metal organic deposition (TFA-MOD). Annealing of the CeO2 buffered R-Al2O3 substrates was performed to control the crystallinity and surface morphology of the CeO2 buffer layer. The annealing treatment led to a significant improvement in the crystallinity and surface morphology of the CeO2 buffer layer. A (Y,Gd)BCO film grown on the CeO2 buffer layer with high crystallinity and an atomically flat surface exhibited high self-field (at 77 K) and in-field (at 20 K, 9 T, μ0 H∥c) critical current densities (J c). Annealing of the CeO2 buffer layer thus enabled enhancement of not only the self-field J c for the (Y,Gd)BCO film but also the in-field J c.

Because of pressing global environmental challenges, focus has been placed on materials for efficient energy use, and this has triggered the search for nanostructural modification methods to improve performance. Achieving a high density of tunable-sized second-phase nanoparticles while ensuring the matrix remains intact is a long-sought goal. In this paper, we present an effective, scalable method to achieve this goal using metal organic deposition in a perovskite system REBa2Cu3O7 (rare earth (RE)) that enhances the superconducting properties to surpass that of previous achievements. We present two industrially compatible routes to tune the nanoparticle size by controlling diffusion during the nanoparticle formation stage by selecting the second-phase material and modulating the precursor composition spatially. Combining these routes leads to an extremely high density (8 x 10(22) m(-3)) of small nanoparticles (7 nm) that increase critical currents and reduce detrimental effects of thermal fluctuations at all magnetic field strengths and temperatures. This method can be directly applied to other perovskite materials where nanoparticle addition is beneficial.

<p>This paper reviews our study on in-field superconducting properties and thermally activated vortex motion (creep) in BaFe₂(As_1-xP_x)₂ (Ba122:P) thin films with BaZrO₃ nanoparticles fabricated on a MgO single crystal using pulsed laser deposition (PLD). We demonstrated that introducing controlled uniformly dispersed BaZrO₃ nanoparticles into Ba122:P films significantly improves its in-field superconducting properties without degrading crystallinity, critical temperature and self-field critical current density (J_c). The nanoparticles doped Ba122:P films show an increase in J_c at all magnetic-field orientations and significantly reduced vortex creep, indicating that nanocomposite films could be a promising candidate for in-field applications.</p>

We fabricated Y0.77Gd0.23Ba2Cu3Oy [(Y,Gd)BCO] and BaZrO3 (BZO) nanoparticle doped (Y, Gd)BCO ((Y, Gd) BCO+BZO) films on CeO2 buffered metallic substrates [= coated conductor (CC)] by using trifluoroacetate metal organic deposition (TFA-MOD). In this paper, in order to investigate the influence of grain-boundary angles of CeO2 buffer layer (Delta phi(CeO2)) on crystallinity and superconducting properties of (Y, Gd) BCO, the TFA-MOD films are fabricated on metallic substrates with various Delta phi(CeO2). The Delta phi of the superconducting layer decreases with decreasing Delta phi(CeO2) in both CCs. The self-field critical current density (J(c)(s.f.)) of (Y,Gd)BCO+BZO CC with Delta phi(CeO2) = 2.0 degrees is 5.8 MA/cm(2) at 77 K, which is 1.5 times higher than that of CCs with Delta phi(CeO2) = 4.0 degrees. Moreover, the (Y, Gd)BCO+BZO CC with Delta phi(CeO2) = 2.0 degrees showed the minimum critical current density (J(c,min)) of 0.81 MA/cm(2) at 77 K and 3 T. Thus, the improvement of the grain boundaries by using the improved buffer layer has an important role in the improvement of J(c) in TFA-MOD REBa2Cu3Oy CCs.

A wide range of coating thicknesses was utilized in the trifluoroacetate metal-organic decomposition process for (Y, ;Gd) Ba2Cu3O7-delta (YGdBCO) coated conductor including BaZrO3 (BZO) particles with a thin once-coated thickness(d(once)), which was developed for improving the critical current density in a magnetic field (J(c) (B)). The value of J(c) (B) increased as donce decreased to 30 nm, and a sample fabricated with d(once) = 30 nm exhibited high values of J(c) (B) of 0.27 and 1.60 MA/cm(2) at 77 and 65 K, respectively, at 3 T (B//c). However, the value of J(c) (B) of a sample with d(once) = 17 nm was almost the same as or slightly lower than that of the sample with d(once) = 30 nm. This tendency was explained by the change in the size of the BZO particles in the YGdBCO superconducting films. Additionally, the Cu elemental peak and the valleys of other elements were observed at the same position and at certain intervals in the elemental concentration line profiles along the depth direction of the precursors, fabricated under different donce conditions from 170 to 30 nm. However, the peaks and valleys were extremely suppressed, and the wave structure was barely observed in the sample with d(once) = 17 nm. The refining of BZO particles by reducing donce could be explained by the limited diffusion due to the existence of the concentration valleys/peaks. Moreover, the effect of the diffusion barrier due to the valleys/peaks might become weaker in the sample with d(once) = 17 nm.

Superconductors are excellent testbeds for studying vortices, topological excitations that also appear in superfluids, liquid crystals and Bose-Einstein condensates. Vortex motion can be disruptive; it can cause phase transitions(1), glitches in pulsars(2), and losses in superconducting microwave circuits(3), and it limits the current-carrying capacity of superconductors(4). Understanding vortex dynamics is fundamentally and technologically important, and the competition between thermal energy and energy barriers defined by material disorder is not completely understood. Specifically, early measurements of thermally activated vortex motion (creep) in iron-based superconductors unveiled fast rates (S) comparable to measurements of YBa2Cu3O7-delta (refs 5-10). This was puzzling because S is thought to somehow correlate with the Ginzburg number (Gi), and Gi is significantly lower in most iron-based superconductors than in YBa2Cu3O7-delta. Here, we report very slow creep in BaFe2(As0.67P0.33)(2) films, and propose the existence of a universal minimum realizable S similar to Gi(1/2)(T/T-c) (T-c is the superconducting transition temperature) that has been achieved in our films and few other materials, and is violated by none. This limitation provides new clues about designing materials with slow creep and the interplay between material parameters and vortex dynamics.

We show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO3 nanoparticles. (Y-0.77 Gd-0.23)Ba2Cu3Oy films were grown on metal substrates with different concentration of BaZrO3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO3 concentration, the nanoparticle size remains constant but the twin -boundary density increases. Up to the highest nanoparticle concentration (n similar to 1.3 x 10(22)/m(3)), the irreversibility field (H-irr) continues to increase with no sign of saturation up to 60T, although the vortices vastly outnumber pinning centers. We find extremely high H-irr namely H-irr = 30T (H parallel to 45 degrees) and 24T (H parallel to c) at 65 K and 58T (H parallel to 45 degrees) and 45T (H parallel to c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged.

We studied the anisotropy and superconducting properties of BaFe 2(As1-xPx )2 films with various phosphorus contents x (=0.19-0:45) fabricated on MgO by pulsed laser deposition. We demonstrated that the x =0:28 film with optimal critical temperature (T c,zero = 26:5 K) has the lowest anisotropy of upper critical field (γH = 1:54), as well as the highest irreversibility field. This is different from the case of cuprate superconductors, and preferable for application. Moreover, the minimum angular dependence of the critical current density for the x = 0:28 film at 1 T and 10 K is over 1.0MA/cm2, indicating that this film could be a promising candidate for in-field application. © 2013 The Japan Society of Applied Physics.

We studied the effect of systematically-controlled size (22-83 nm) and density (0.1-13 × 1021 m-3) of strong pinning random BaMO3 (M=Zr, Nb, Sn) nanoparticles (NPs) by engineering of their inclusion in (Y0.77Gd0.23)Ba2Cu 3Oy ((Y,Gd)BCO) coated conductors. The critical current density (Jc) gradually increases from that of pure (Y,Gd)BCO to that of 3 wt% BZO with increasing density of NPs for H ∥ c and H ∥ 45°. Moreover, at low/intermediate fields the films with higher densities of isotropic pinning centers show nearly isotropic angular dependence at both 77 and 65 K, indicating that a high density of spherical nanoparticles effectively pins vortices over a broad angular range. We find that the enhancement of J c depends mainly on the density of the NPs and not on their size. The vortex melting transition (characterized by the critical exponent (s) of the resistive transition) changes, particularly at H ∥ 45° in films with higher densities of NPs. This change is reflected in a decrease of s to a value very close to that observed for H ∥ c, similar to that of a Bose-glass. Thus, the density and morphology of the pinning centers are important factors determining not only Jc but also the character of the solid-liquid transition. © 2013 IOP Publishing Ltd.

Superconducting BaFe2(As0.6P0.4)(2) (Ba122:P) thin films were fabricated on MgO(100) substrates by a pulsed laser deposition (PLD) method using a second-harmonic Nd:YAG (yttrium aluminum garnet) laser. Structural investigation by means of x-ray diffraction confirmed both c-axis orientation and in-plane alignment, or epitaxial growth on the substrate. The film exhibited T-c(onset) = 26.5 K and T-c(zero) = 24.0 K. High J(c) values of 3.5 MA cm(-2) at 4.2 K in the self-field and over 1 MA cm(-2) at 10 K under 1 T were also obtained. Fabrication of Ba122: P film by Nd: YAG PLD seems to be a promising approach for preparing superconducting tapes, since a high-T-c and high-J(c) film can be relatively easily obtained.

Magnetic relaxation measurements in YBa2Cu3O7-delta (YBCO) films at intermediate and high temperatures show that the collective vortex creep based on the elastic motion of the vortex lattice has a crossover to fast creep that significantly reduces the superconducting critical current density (J(c)). This crossover occurs at temperatures much lower than the irreversibility field line. We study the influence of different kinds of crystalline defects, such as nanorods, twin boundaries, and nanoparticles, on the high-temperature vortex phase diagram of YBCO films. We found that the magnetization relaxation data is a fundamental tool to understand the pinning at high temperatures. The results indicate that high J(c) values are directly associated with small creep rates. Based on the analysis of the depinning temperature in films with columnar defects, our results indicate that the size of the defects is the relevant parameter that determines thermal depinning at high temperatures. Also, the extension of the collective creep regime depends on the density of the pinning centers.

We study the vortex dynamics of NaxCa1-xFe2As2 single crystals with x = 0.5 (underdoped) and x = 0.75 (optimally doped), having T-c approximate to 19.4 and 33.4 K, respectively, by performing magnetization measurements of the critical current density J(c) and flux creep rate S. We find that the J(c) versus temperature, T, dependence is consistent with delta T-c pinning, indicating strong pinning associated with randomly distributed defects larger than the coherence length xi. The temperature dependence of S shows a crossover between glassy (elastic) and plastic creep regimes. The boundary T-cr(H) between both creep regimes coincides with the upper limit of the regime of strong pinning by nanoparticles. The glassy exponent mu in the optimally doped crystal is consistent with the thermal collective creep theory previously applied to cuprate superconductors, but in the underdoped sample the plateau in S(T) indicates that mu approximate to 3-3.3, a value larger than the existing theoretical predictions. We discuss the quantum creep contributions in both samples.

We study the correlation between crystalline structure and superconducting properties in Na-doped Ca1-xNaxFe2As2 single crystals for three chemical compositions (x = 0.5, 0.6, 0.75). We find the maximum superconducting transition temperature T-c similar to 33.4 K at x similar to 0.75. The Na substitution causes the decrease of the a-b crystallographic axes and the increase of the c axis in the tetragonal phase. The single crystals show perfect diamagnetism, indicating full superconducting volume. The anisotropy ratio for the upper critical field near the superconducting transition temperature is gamma = 1.85 +/- 0.05, independently of the Na content. A narrow vortex liquid phase was detected in the sample with highest T-c (x = 0.75), consistent with the expectations based on a Lindemann criterion. The analysis of the critical currents shows no evidence of correlated pinning and indicates that the pinning arises from a combination of several mechanisms. At low fields, pinning by random nanoparticles dominates. At higher fields, a small and field independent J(c) in the optimally doped crystal may originate in the simultaneous presence of sparse large nanoparticles and a much denser distribution of smaller particles, with the sparse pins producing a caging effect that constrains the volume of the vortex bundle associated with the denser and weaker defects.

The improvement of critical current density properties of REBCO coated conductors for applications in superconducting power devices is desired. It is known that the critical current density J(c) of REBCO thin films made by the TFA-MOD method in a magnetic field is greatly improved by the introduction of BZO-nanoparticles of a non-superconducting phase as artificial pinning centers. In addition, the field angle anisotropy can also be reduced by isotropic flux pinning interactions of nanoparticles. However, a detailed report on the mechanism of flux pinning with a quantitative investigation in such coated conductors has not been given. In this study, the field angle dependence of the critical current density is measured for TFA-MOD-processed YGdBCO coated conductor with a superconducting layer of 0.65 mu m thick, and the results are theoretically analysed to clarify the flux pinning mechanism.

We study the field (H) and temperature (T) dependence of the critical current density (J(c)) and irreversibility field (H-irr) at different field orientations in Y0.77Gd0.23Ba2Cu3Oy with randomly distributed BaZrO3 nanoparticles (YGdBCO + BZO) and YBa2Cu3Oy (YBCO) films. Both MOD films have large RE2Cu2O5 (225) nanoparticles (similar to 80 nm in diameter) and a high density of twin boundaries (TB). In addition, YGdBCO + BZO films have a high density of BZO nanoparticles (similar to 25 nm in diameter). At high temperatures (T &gt; 40 K), the superconducting properties, such as J(c), H-irr, and flux creep rates, are greatly affected by the BZO nanoparticles, while at low temperatures the superconducting properties of both the YBCO and YGdBCO + BZO films show similar field and temperature dependencies. In particular, while the J(c) of YBCO films follow a power-law dependence (proportional to H-alpha) at all measured T, this dependence is only followed at low T for YGdBCO + BZO films. As a function of T, the YGdBCO + BZO film shows J(c) (T, 0.01T) similar to [1 -(T/T-c)(2)](n) with n similar to 1.24 +/- 0.05, which points to "delta T-c pinning." We analyze the role of different types of defects in the different temperature regimes and find that the strong pinning of the BZO nanoparticles yields a higher H-irr and improved J(c) along the c axis and at intermediate orientations at high T. The mixed pinning landscapes due to the presence of disorder of various dimensionalities have an important role in the improvement of in-field properties.

To clarify the growth mechanism of faceted REBa(2)Cu(3)O(7-delta) (RE123, RE = Sm, Y) crystals, the growth process of the crystals was observed in situ by using a high temperature microscope. The growth rate of each faceted interface of a crystal growing from the liquid + 211 phases under an undercooling was obtained from the relationship between the position of each interface and growth time. It was observed that some of the faceted interfaces of a growing crystal stopped growing after a period of time, while other interfaces continued to grow with a growth rate approximated by a function of the undercooling. The above stoppage of the growth was observed in situ for the first time, and this fact could give powerful support to the mechanism for a similar phenomenon in REBCO films which were fabricated by the trifluoroacetates metal organic deposition method: growing microstructures of RE123 crystals in the film were revealed by transmission electron microscopy (TEM) for quenched specimens. Some very thin a-axis grains were formed by a change in c-axis growth rate. Furthermore, we showed the above growth and stop phenomena of faceted interfaces of REBCO crystal grains using numerical simulations. (C) 2010 Elsevier B.V. All rights reserved.

The flux pinning properties in a magnetic field of various directions are investigated for trifluoroacetates-metal organic deposition (TFA-MOD) processed Y(1-x)Gd(x)Ba(2)Cu(3)O(y) (YGdBCO)-coated conductors with the superconducting layer of 0.5 mu m thick with artificial BaZrO(3) (BZO)-nanoparticles. It is found that the critical current density is enhanced in a wide range of field angle except around the direction parallel to the a - b plane, resulting in low field-angle anistropy. The enhancement off, in the wide range of field angle is attributed to the isotropic pinning of nanoparticles. The decrease in the critical current density in the field direction parallel to the a b plane is considered to be caused by limitation of growth of stacking faults by distributed BZO nanoparticles. The observed results were theoretically explained by the flux creep-flow model and the above speculation of the pinning mechanism was confirmed. (c) 2010 Elsevier B.V. All rights reserved.

Tin-compounds were doped into YBa2Cu3O7-delta (YBCO) films as pinning centers to enhance J(c) in magnetic fields. YBCO films were grown by a metal organic deposition process using tri-fluoroacetates starting solutions. Tin-acetylacetonate salts were then dissolved into the starting solution as pinning centers. J(c) of the YBCO films with tin-acetylacetonates were enhanced in all magnetic field angles. Transmission electron microscopy (TEM) and TEM-EDS (Energy Dispersive X-ray Spectroscopy) observations revealed the existence of tin-compound particles with the size of about 30 nm in the YBCO film. These nano particles were distributed randomly in the film and were considered to act as 3-dimentional pinning centers. (C) 2010 Elsevier B.V. All rights reserved.

We investigated the joining of two REBCO (REBa(2)Cu(3)O(7-x), RE = Y, Gd) coated conductors using the diffusion joint process. REBCO coated conductors with stabilizing silver layer were joined by various joining conditions. Two pieces of the silver layer of tapes were overlapped in a face to face manner. Then, the pieces were pressurized and heat-treated at about 623-673 K under a pressure using some weights in oxygen atmosphere. Finally, the joint resistivity was obtained as low as about 10 n Omega cm(2) by 10 MPa for YBCO tape. The joint resistivity of the GdBCO tape was 50-60 n Omega cm(2), which was higher than YBCO, but improved to 37 n Omega cm(2) at 10 MPa by improving the joining conditions. Influences of joining conditions such as pressure and evenness of specimens and holders were investigated on joint adhesion and resistivity. (c) 2010 Published by Elsevier B.V.

A Y1-XSmxBa2Cu3Oy (YSmBCO) superconductive layer containing BaZrO3 (BZO) particles was fabricated on a Hastelloy substrate with a CeO2/Gd2Zr2O7 buffer layer by trifluoroacetates-metal organic deposition. The nanostructures of the layer were characterized by transmission electron microscopy and found to be comparatively dense and predominantly composed of c-axis oriented grains. Some BaCeO3 regions formed at the interface between the YSmBCO and the CeO2 layers. BZO particles and the (Y,Sm)(2)Cu2O5 (225) phase were formed in the YSmBCO. The average sizes of the BZO and the 225 phase particles were 20 and 150 nm, respectively, with random orientation. The BZO particles were found to be homogeneously distributed within the YSmBCO layer, which should enhance its superconducting behavior in high magnetic fields.

Higher irreversibility fields (H(irr)) increase the upper bound for applications of superconductors and could expand market penetration. We present the studies in pulsed field (up to 65 T) of superconducting films on flexible metal substrates. We investigate the effect of disorder on H(irr) at different field orientations for YBa(2)Cu(3)O(y) and BaZrO(3)-nanoparticle-dispersed Y(0.77)Gd(0.33)Ba(2)Cu(3)O(y) (YGdBCO+BZO). We find that H(irr) is higher for YGdBCO+BZO along the c-axis and at intermediate orientations. The vortex melting transition is investigated using the resistive transition&apos;s critical exponent. The behavior can be explained by the mixed pinning landscape from randomly distributed BZO nanoparticles and c-axis correlated disorder.

For investigation of the flux pinning properties of nanoparticles in TFA-MOD processed Y1-xGdxBa2Cu3Oy (YGdBCO) coated conductors, the critical current density was compared in various directions of the magnetic field for YGdBCO+BaZrO3 (BZO) and YGdBCO coated conductors with the superconducting layer of 0.5 mu m thickness. It was found that J(c) for theta = 0 degrees (B//c) is larger but J(c) for theta = 90 degrees (B//ab) is smaller in YGdBCO+BZO than in YGdBCO. The increase in the normal field is attributed to the pinning of nanoparticles, while the decrease in the parallel field is considered to be caused by limitation of extension of stacking faults by distributed BZO nanoparticles. In addition, the n-value (E proportional to J(n)) decreases by introduction of BZO nanoparticles for theta = 90 degrees, while it is unchanged for theta = 0 degrees. These results are well described by a theoretical model of flux creep and flow.

We studied the effects of uniaxial constant pressures by using some weights on the properties of the diffusion joints using Ag stability layers of REBa2Cu3O7-X (REBCO, RE=Y, Gd) coated conductors. Two tapes were stuck in a face to face manner with Ag surfaces in contact, and were pressed uniaxially during the joining under a constant pressure at 673K in a pure oxygen atmosphere. The Ag area at the joint was 6x5 mm(2) for YBCO coated conductors produced by modified metal-organic deposition (MOD) process using precursor solution of trifluoroacetates (TFA) for Y and Ba and F-free salt for Cu. A very low resistance of about 10 n Omega cm(2) across the joint was achieved by the diffusion joining under the pressure of 10 MPa. The relations between the joint resistance, the joint structure and the joint pressure were investigated.

A high critical current density J(c) with a nearly isotropic angular dependence at 77.3 K was recently obtained by the introduction of nanoparticles to (Y, RE) Ba2Cu3Oy (RE123, RE = Sm, Gd)-coated conductors prepared by trifluoroacetate metal-organic deposition (TFA-MOD). The flux pinning properties were evaluated on the basis of detailed measurements of the upper critical field, the irreversibility field and the critical current density of the TFA-MOD RE123-coated conductor. We found that strong random pinning by the BaZrO3 nanoparticles and weak c-axis correlated pinning by twin boundaries functioned cooperatively in nanoparticles introduced to (Y, Gd)123-coated conductors prepared by TFA-MOD. The coexistence of two different pinning centers played an important role in the nearly isotropic angular dependence of Jc.

We developed a new fabrication technique which we call the &apos;in-plume growth (IPG)&apos; technique. A REBa2Cu3Oy layered film for a coated conductor (REBCO CC) is grown in the plume using a pulsed-laser deposition (PLD) method with a short distance between the target and the substrate (d(T-S)) to increase the production rate. In general, the critical current density (J(c)) of PLD-REBCO CCs using an RTR system decreases as d(T-S) decreases since the amount of the dead layer increases and the composition of the REBCO layer becomes off-stoichiometric. In this work, we fabricated high-J(c) GdBa2Cu3Oy (GdBCO) CCs using the IPG technique by varying the target composition and the tape moving speed to control the composition of the REBCO layer and to suppress the formation of a-axis-oriented grains. As a result, the IPG-GdBCO CCs, which were fabricated at 2 m h(-1) (deposition area = 1-turn x 6.5 cm = 6.5 cm(2), laser power = 300 mJ, f = four-plumes x 30 Hz), showed the following characteristics: I-c = 312 A cm(-1) width (J(c) = 2.6 MA cm(-2)) with 1.2 mu m in thickness and 1 m length. The production speed and the J(c) value are 3.0 and 1.8 times higher, respectively, compared to those deposited under standard conditions without using the IPG technique. This result indicates that the PLD-REBCO CCs could be more competitive for production of CCs for practical electric power applications in the near future.

Grains of BaZrO3 (BZO) in REBa2Cu3Oy (REBCO) films exhibit microstructural differences, depending on whether they were deposited by pulsed-laser deposition (PLD) or metal-organic deposition (MOD). In order to understand the origins of these differences, we examined the formation mechanism of BZO nanoparticles in the MOD process with detailed observations of the quenched films by transmission electron microscopy. The BZO nanoparticle was found to form in the precursor during the temperature ramp prior to the formation of the Y1-xSmxBa2Cu3Oy (YSmBCO) crystals. The YSmBCO grew layer by layer while entrapping the BZO particles, which resulted in random dispersion of the BZO particles in the YSmBCO layer. Consequently, uniformly dispersed BZO nanoparticles were formed in the YSmBCO matrix derived from the TFA-MOD process. These findings indicate that a key factor in achieving fine dispersion of BZO nanoparticles in the superconducting matrix is strongly related to nucleation of the BZO phase crystals in the precursor before growth of the YSmBCO layer, which is unique to the MOD process. In subsequent testing, YSmBCO-coated conductors with uniformly dispersed and densely concentrated BZO nanoparticles showed striking isotropic magnetic-field angular dependence of critical currents.

On the research and development of a reel-to-reel TFA-MOD (Metal Organic Deposition using Trifluoroacetates) process, a present status is reviewed and its future strategy is addressed. As a base of the study, the 90 m long tape with uniform I(c) distribution of the 300 A/cm-width level was obtained on the CeO(2) buffered IBAD-Gd(2)Zr(2)O(7)/Hastelloy C276 substrate. The tape has the 56 m region with the end-to-end I(c) value of 250 A, which corresponds to maximum product of I(c) x L of 14.000 Am. Based on the results, several directions on R&D have been studied such as "higher I(c)", "higher I(c)-B", "higher production rate both in coating/calcinations and crystallization steps" and lower cost buffer/substrate". Then, an extremely high I(c) value of 735 A/cm-width was achieved in a short tape by the compositional control (e.g. Ba-deficient), in the starting solutions. On the efforts for achieving higher I(c)-B properties, high I(c) values of 115 and 35 A/cm-width under the magnetic fields of I and 3 T were obtained by the RE mixture of Y and Gd in REBCO, addition of Zr and a growth rate control process. On the other hand, the production rate for the coating/calcinations process was improved by development of new starting solutions, which uses F-free Y salt instead of TFA salt of Y. The high J(c) value of 1.9 MA/cm(2) was confirmed using the precursor films fabricated at a high traveling rate of 10 m/h. Concerning a higher rate in the crystallization step, the multi-turning system with a vertical gas flow system was developed. The validity of the concept was confirmed using 2-turn parts of the furnace. The high I(c) value of 250 A/cm-width was realized in the 5 m tape crystallized with a traveling rate of 3 m/h, which is equivalent to 15 m/h for usage of entire area of the furnace of 10-turns. Furthermore. in order to achieve the lower cost, the architecture of the coated conductor with a low cost buffer/substrate system has been developed. An IBAD buffered substrate using IBAD-MgO layer (CeO(2)/LMO/IBAD-MgO/Hastelloy C276) was developed and a high production rate of 24 m/h was realized for IBAD-MgO layer using a small ion gun system with the area of 6 x 22 cm(2). The grain texturing of the substrate was reached the Delta phi value of 4 degrees in the CeO(2) layer. This substrate was applied to the above mentioned multi-turning crystallization furnace for TFA-MOD process. Then. a 5 m long tape with 260 A/cm-width (@77 K. s.f.) was achieved. According to the TFA-MOD process in the above achievements, the prospects of each issue for the future stage were independently confirmed. Consequently, R&D combining the above-mentioned achievements for longer tapes are expected in the next Stage. (C) 2009 Elsevier B.V. All rights reserved.

GdBa2Cu3Oy(GdBCO) films were fabricated on pulsed laser deposition (PLD)-CeO2/ion-beam-assisted deposition (IBAD)-Gd2Zr2O7/HasteIloy C276 metal substrate tapes using the continuous in-plume PLD method. The control of the target composition is important to improve the critical current density (J(c)) property, especially in the case of a short target-substrate distance. As a result, the critical current (I-c) value of 320 A/cm-W and the J(c) value of 3.2 MA/cm(2) were obtained by using the target composition of Gd:Ba:Cu = 1:23.4 (GdBa2Cu3.4Oy) in a short sample. It was also found that a high growth rate for the GdBCO film could be realized by crystal growth in the plume (in-plume) for the target. A twice higher growth rate was achieved by the in-plume PLD technique comparing with that in the conventional condition in which crystal growth takes place near the plume edge. In addition, in order to improve the 1, values in the external magnetic fields, we introduced the artificial pinning centers using a 5 mol%BaZrO3 doped GdBa2Cu3.4Oy target by the in-plume method. The BaZrO3 nanorods were effectively introduced by in-plume PLD and the obtained sample showed improved I-c-B-theta properties due to enhanced B parallel to c; the minimum I-c value of 25.6 A/cm-W at 3 T in the 1.6 mu m thick film. (C) 2009 Elsevier B.V. All rights reserved.

YBa(2)Cu(3)O(7-y) (YBCO) long tapes derived from the metal-organic deposition (MOD) method using the starting solution containing trifluoroacetate (TFA) have been developed with high critical currents (I(c)) over 200 A/cm-width. However, high speed production of YBCO films is simultaneously necessary to satisfy the requirements of electric power device applications in terms of cost and the amounts of the tapes. In this work, we developed a new TFA-MOD starting solution using F-free salt of Y, TEA salt of Ba and Cu-Octylate for application to the coating/calcination process and discussed several issues by using the Multi-turn (MT) Reel-to-Reel (RTR) system calcination furnace for the purpose of high throughput without degradation of the properties. The coating system was improved for uniform deposition qualities in both longitudinal and transversal directions. YBCO films using the new starting solution at the traveling rate of 10 m/h in coating/calcination by the MT-RTR calcination furnace showed the values of the critical current density of 1.6 MA/cm(2) as thick as 1.5 mu m at 77 K under the self fields after firing at the high heating rate in the crystallization. (C) 2009 Elsevier B.V. All rights reserved.

YBa2Cu3O7-delta (YBCO) films were grown by using precursor films with barium concentration gradient in film thickness by an advanced metal organic deposition process using trifluoroacetates (TFA-MOD). We have reported previously that a lot of non-reacted particles such as Y- and Cu-oxides were remained for the YBCO film surface grown by the precursors using a starting solution with barium-poor (cation ratio as Y:Ba:Cu = 1:1.53). Then, the barium concentration was increased in the film surface to complete the reaction among these Y and Cu residues and Ba and to increase the Y123 growth thickness for realizing higher J(c) performance. Transmission electron microscopy (TEM) observation showed the increase of film thickness of YBCO grown by the precursors with barium concentration gradient in film thickness, indicating that the reaction between these Y and Cu-oxides and Ba proceeded to form Y 123 phase. Consequently, higher J(c) was obtained for the YBCO film by the precursors mentioned above than that of the YBCO film by the precursors with a constant concentration. Effects of barium concentration gradient in the precursors on the superconducting properties and microstructures in the YBCO film were discussed. (C) 2009 Elsevier B.V. All rights reserved

YBa(2)Cu(3)O(y) (YBCO) films grown by starting solutions with Ba-poor (Y:Ba:Cu = 1: 1.53, Ba/Y = 1.5) have been reported to perform higher J(c) than that for YBCO films with stoichiometric one due to smaller and less pores in YBCO films by metal organic deposition (MOD) using tri-fluoroacetates (TFA). However, we have reported that a lot of non-reacted particles such as Y and Cu oxides were remained for the YBCO film surface grown by the precursors using Ba-poor solution. In this study, influences of YBCO growth rate on microstructures of the YBCO film were discussed to control microstructures of these second phase particles. As a result, microstructures of the YBCO film depended strongly on the YBCO growth rate, residues of Y and Cu oxides were dispersed randomly throughout the YBCO film grown at higher growth rate. Consequently, it was succeeded to control the segregated phases as seen in the previous YBCO film with Ba/Y = 1.5 at the film surface into the YBCO film. J(c) of the YBCO film grown at higher rate was a value almost equal to that grown at previous growth rate. (C) 2009 Elsevier B.V. All rights reserved.

We have developed a new starting solution consisting of non-fluorine (F-free) yttrium salt, barium trifluoroacetate and copper octylate with focusing on a high-speed production of YBa(2)Cu(3)O(7-y) (YBCO) coated conductors by the trifluoroacetate-metal-organic deposition (TFA-MOD) method. High critical current density (J(c)) was recognized in the YBCO films fabricated on CeO(2) buffered ion-beam assisted deposition (IBAD)-Gd(2)Zr(2)O(7)/Hastelloy substrates from the new starting solution at a wide range of the heating rates in the calcination process (2 -&gt; 25 degrees C/min, 2.3 -&gt; 2.4 MA/cm(2)). Additionally, any degradation of J(c) performance (higher than 2 MA/cm(2) at 77 K, self-fields) up to about 0.4 mu m per single coating was not observed in the YBCO films fabricated from the new starting solution at the heating rate of 5 degrees C/min in the calcination process. The relationship between fluorine contents in the single coating film and J(c) performance of the YBCO films suggested that the fluorine content in the single coating film determines the quality (bulk density, uniformity, etc.) of the precursor film. (C) 2009 Elsevier B.V. All rights reserved.

YBa2Cu3Oy (YBCO) coated conductors were fabricated by trifluoroacetates (TFA)-metal organic deposition (MOD) previously using a single reel-to-reel (RTR) crystallization furnace with a gas flow system parallel to the tape surface which could realize only a low production rate. In this study, we developed a new muiti-turn (MT) RTR furnace with a vertical gas flow system to increase the production rate of the crystallization step and attained the Uniform reaction in the tapes of the multi-turn system. We fabricated YBCO films with different conditions partial pressure of water vapor, the total pressure and the gas flow volume using the MT-RTR furnace with the vertical gas now system, in order to investigate the influence of the processing parameters on the growth rate and the superconducting properties of the YBCO films. It was found that the growth rate of the YBCO phase film increased under the conditions of the high gas flow rate, the low total pressure and the high water vapor partial pressure. As a result, 21 times higher J(c) value was attained at 17 times faster growth rate than that without controlling the processing parameters in the crystallization step. This is thought to be due to the suppression of coarsening Of Y2Cu2O5 and CuO particles in the precursor film. Consequently, the high I-c,I-end-to-end value of 250 A was achieved in a 5 m long tape fabricated at the production rate of 3 m/h using the only two lanes of the entire MT-RTR crystallization furnace with 10 lanes. (C) 2009 Published by Elsevier B.V.

YBCO films grown by the starting solution with Ba-poor (cation ratio as Y : Ba : Cu = 1 : 1.5 : 3) have been reported to have higher than that for YBCO films with stoichiometric composition due to smaller and less pores in TFA-MOD YBCO. In this study, Ba concentration in the Ba-poor YBCO films was controlled in film thickness direction, and influences of the Ba concentration gradient on microstructures and properties were investigated to realize higher Precursor films with Ba-poor composition and with Ba-rich composition in the thickening direction were prepared and then the films were crystallized. Increasing the Ba concentration in thickening direction led to higher than that of Ba-poor YBCO. Cross sectional TEM observations showed that the effective YBCO thickness increased for YBCO film with higher Ba concentration in comparison to the previous Ba-poor YBCO film.

Progresses in the development of the TFA-MOD process for the coated conductors in Japan are reviewed. In the fundamental approaches, some important advantages of Ba-poor starting solution were found such as for obtaining higher Jc, shorter reaction time and wider process temperature window. The high Ic value of 735 A/cm-w@77 K was attained. Additionally, introduction of artificial pinning centers by Sm-substitution and Zr-addition to the Ba-poor films was successfully investigated. The films showed a high minimum Ic value of 42 A/cm-w at 77 K, 1 T. Furthermore, isotropic Ic properties in the angular dependence of applied magnetic fields was realized by the uniform distribution of nanoprticles of Zr-compound. On the other hand, two different process of MOD including batch and reel-to-reel (RTR) types have been developed as an engineering process for low cost and long tape production with high superconducting performances at a high rate. In the batch type, long tape synthesis process could be developed by the optimization of the growth conditions in a large furnace. A 500 m long tape was heat-treated and a high Ic value of 310 A/cm-w in a 250 m tape was confirmed. Concerning the RTR type, a high production rate system was developed after confirmation of the ability of the continuous process in a 90 m long tape. A multi-turn with a vertical gas flow system was developed for this purpose. This system was applied to the fabrication of superconducting films on the lower cost buffer layers including a high deposition rate IBAD-MgO layer. Currently, a 5 m long tape with 250 A/cm-w was obtained at the production rate of 3 m/h using a part of the multi-turn system, which is equivalent to 15 m/h in the entire use of the furnace.

Artificial pinning centers ( APC) for TFA-MOD Y1-x Sm-x Ba2Cu3Oy (YSmBCO) coated conductors were introduced to enhance J(c) under the magnetic fields and to improve the magnetic field angular dependence of J(c). The coated conductors showed high J(c) and isotropic J(c)-B-theta properties with the ratio(J(c,min)/J(c,max)) of 0.91 (77 K, B = 1T). From the results of microstructural observation, BaZrO3 (BZO) nanoparticles were uniformly dispersed in the films by introduction of Zr-salt into YSmBCO solution. The nanoparticles were maintained uniformly not only along the lateral direction but also along the thickness one. It could be considered that the uniform dispersion of BZO nanoparticles in TFA-MOD REBCO coated conductors may act as flux pinning centers to enhance the J(c) independent from the angle of the applied magnetic fields.