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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 Jc 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 Jc properties were investigated to realize higher Jc. 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 Jc 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. [ABSTRACT FROM AUTHOR]

Abstract: YBa2Cu3O7− 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 (Ic ) over 200A/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, TFA 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 10m/h in coating/calcination by the MT-RTR calcination furnace showed the values of the critical current density of 1.6MA/cm2 as thick as 1.5μm at 77K under the self fields after firing at the high heating rate in the crystallization. [Copyright &y& Elsevier]

Abstract: 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 YBa2Cu3O7− 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 CeO2 buffered ion-beam assisted deposition (IBAD)-Gd2Zr2O7/Hastelloy substrates from the new starting solution at a wide range of the heating rates in the calcination process (2→25°C/min, 2.3→2.4MA/cm2). Additionally, any degradation of J c performance (higher than 2MA/cm2 at 77K, self-fields) up to about 0.4μm per single coating was not observed in the YBCO films fabricated from the new starting solution at the heating rate of 5°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. [Copyright &y& Elsevier]

Abstract: To improve J C properties in a magnetic field (J C–B) of YBa2Cu3O7− δ (YBCO) films by a TFA-MOD (trifluoroacetates metal organic deposition) method, we fabricated YBCO films with SnO2-doping as artificial pinning centers and investigated the superconducting properties and the crystalline structures. TFA-MOD is expected as a cost-effective method with a non-vacuum system to fabricate YBCO films with high superconducting properties. However, YBCO films have problems that J C decreases in a magnetic field (B). In this study, the TFA solutions with SnO2 for pinning centers were used as starting materials. In the transmission electron microscope image, existence of second phase particles with size of 20–30nm has been observed in the YBCO film. These nano-particles contained Sn-element and distributed randomly in the film. The J C/J C (self field) values of the SnO2-doped YBCO films were enhanced in all magnetic field angles. Therefore it is considered that 3D pinning centers of Sn-compounds were introduced into YBCO film. [Copyright &y& Elsevier]

Abstract: On the research and development of a reel-to-reel TFA-MOD (Metal Organic Deposition using Trifluoro-acetates) process, a present status is reviewed and its future strategy is addressed. As a base of the study, the 90m long tape with uniform Ic distribution of the 300A/cm-width level was obtained on the CeO2 buffered IBAD-Gd2Zr2O7/Hastelloy C276 substrate. The tape has the 56m region with the end-to-end Ic value of 250A, which corresponds to maximum product of Ic × L of 14,000Am. Based on the results, several directions on R&D have been studied such as “higher Ic ”, “higher Ic –B”, “higher production rate both in coating/calcinations and crystallization steps” and lower cost buffer/substrate”. Then, an extremely high Ic value of 735A/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 Ic –B properties, high Ic values of 115 and 35A/cm-width under the magnetic fields of 1 and 3T 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 Jc value of 1.9MA/cm2 was confirmed using the precursor films fabricated at a high traveling rate of 10m/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 Ic value of 250A/cm-width was realized in the 5m tape crystallized with a traveling rate of 3m/h, which is equivalent to 15m/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 (CeO2/LMO/IBAD-MgO/Hastelloy C276) was developed and a high production rate of 24m/h was realized for IBAD-MgO layer using a small ion gun system with the area of 6×22cm2. The grain texturing of the substrate was reached the Δϕ value of 4° in the CeO2 layer. This substrate was applied to the above mentioned multi-turning crystallization furnace for TFA-MOD process. Then, a 5m long tape with 260A/cm-width (@77K. 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. [Copyright &y& Elsevier]

Abstract: YBa2Cu3O y (YBCO) films grown by starting solutions with Ba-poor (Y:Ba:Cu=1:1.5:3, 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. [Copyright &y& Elsevier]

Abstract: YBa2Cu3O7− δ (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=1:1.5:3). 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 Y123 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. [Copyright &y& Elsevier]

Abstract: YBa2Cu3O y (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 multi-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 flow 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,end-to-end value of 250 A was achieved in a 5m long tape fabricated at the production rate of 3m/h using the only two lanes of the entire MT-RTR crystallization furnace with 10 lanes. [Copyright &y& Elsevier]

Abstract: YBa2Cu3O7− δ (YBCO) films were grown on LaAlO3 substrates by a metal organic deposition using trifluoroacetates (TFA-MOD). In this study, effects of calcination condition such as temperature on microstructures and J c properties for the YBCO films were studied. The TFA starting solution was coated on a substrate by a spin-coating method. Then, a two-step heat treatment was applied to the coated films. In the calcination step, the coated film was calcined to form a homogeneous amorphous precursor by increasing the temperature which was varied from 300°C to 500°C at a constant heating rate of 2°C/min. The prepared precursor films were crystallized at a constant condition. As a result, J c value depended on the calcination temperature, YBCO film calcined at 400°C showed the highest J c of 2.5MA/cm2. J c’s for the YBCO films calcined at 300°C and 350°C were 1.9MA/cm2 and 2.0MA/cm2, respectively. On the other hand, YBCO film calcined at 500°C showed the lowest J c of 1.4MA/cm2. Cross-sectional TEM images showed that the YBCO film calcined at 400°C had less pores and small size of pores in the crystallized film randomly throughout the film. Large pores were observed in the YBCO film calcined at 500°C. Also, these large pores were existed near substrate in the YBCO film. It is considered that the differences of these pore formation mechanisms are the main cause of the difference of J c characteristic. [Copyright &y& Elsevier]