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Abstract: We have investigated the influence of the starting solution composition on both the microstructure and superconducting properties of YBa2Cu3O7−x (YBCO) films deposited on CeO2 buffered IBAD-Gd2Zr2O7/Hastelloy substrates and (100)-oriented LaAlO3 single crystals by the advanced TFA-MOD process. The starting solutions with different compositions of molar ratios of Y:Ba:Cu=1.0:1.0–3.0:3.0 were studied. The critical current density (J c) values of the YBCO films fabricated from Ba-rich (molar ratio of Ba/Y>2) starting solutions were low. On the other hand, high J c values were recognized, when the YBCO films were prepared from the Ba-poor (molar ratio of Ba/Y<2) starting solutions. The highest J c value of 3.5MA/cm2 (77K, self-field) was obtained at a Ba/Y molar ratio of 1.4–1.6. Finally, the extremely high critical current (I c) value of 735A/cm-width (77K, self-field) was obtained, when the YBCO film was fabricated on CeO2 buffered IBAD-Gd2Zr2O7/Hastelloy substrates by using the Ba-poor (Ba/Y=1.5) starting solution. [Copyright &y& Elsevier]

We have investigated the influence of the H2O vapour inlet temperature in the calcination on both the microstructure and superconducting properties of YBa2Cu3O7-x (YBCO) films fabricated by the TFA-MOD method, from the viewpoint of the process control in the reel-to-reel system. Low critical current (Ic) values were obtained in the films prepared by introducing the H2O vapour at temperatures less than 200°C. XRD measurements and cross-sectional TEM observations suggest that the YBCO films calcined with the H2O vapour inlet temperature below 200°C revealed a random orientation without the epitaxial growth of the YBCO phase grains. Consequently, it is necessary to introduce H2O vapour from temperatures higher than 250°C in calcination for fabrication of high performance YBCO tapes. In reel-to-reel system, it is important that the humidity management in a low temperature range in the furnace. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated influences of the H2O gas inlet temperature in the calcination process on both microstructures and superconducting properties of YBCO films fabricated by the advanced TFA-MOD process, from the viewpoint of the process control in the reel-to-reel system. Low I c values were recognized in the films which were prepared by introducing the H2O gas from the lower temperature than 200°C. XRD measurements and cross-sectional TEM observations suggest that the YBCO films calcined with the H2O inlet temperature below 200°C revealed a random orientation without epitaxial growth. Consequently, it has been understood that control to keep low partial pressure of the H2O gas in a lower temperature region is important for fabrication of long-length YBCO tapes with high performance by the reel-to-reel system. [Copyright &y& Elsevier]

Abstract: For production of low cost coated conductor tapes, the TFA-MOD (metal organic deposition using trifluoroacetates) process is one of the promising methods and textured NiW alloy substrates are expected to be a candidate for their substrates. However, the superconducting properties obtained on the NiW substrates are not high enough due to lack of understandings on YBCO grain growth on the NiW. In this work, MOD growth conditions such as molar ratio (Ba/Y) of the starting solution, the crystallization temperature and P (O2) (O2 partial pressure) especially on the NiW substrates were studied. Compositional effects of the starting solution on I c values have a trend having the highest value at Ba/Y=1.5, which is similar to those on IBAD substrates, though the I c values of YBCO on NiW are lower. One of the differences between YBCO layers on NiW and IBAD could be explained by the significant difference in a-axis oriented grain growth. The higher temperature and/or the lower PO2 were required to suppress the nucleation for a-axis oriented grain growth on the NiW. 1m-long RTR production exhibited the end-to-end I c value of 221A/cmw, which could be improved further by the optimization of the process conditions. [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: 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: We fabricated Y1−x Sm x Ba2Cu3O y and YSm x Ba2Cu3O y (YSmBCO) films on SrTiO3 (STO) single crystalline substrates and IBAD buffered metallic tapes (PLD-CeO2/IBAD-GZO/Hastelloy) by the advanced TFA-MOD process by mixing TFA salts of Y, Sm, Ba and Cu naphthenate, and tried to improve the superconductivity properties compared with those of the pure YBa2Cu3O7−δ (YBCO). As a result, J c values of Y1−x Sm x Ba2Cu3O y films with x =0.05 or 0.3, which were fabricated on STO substrates, were improved under the high magnetic fields compared with those of the YBCO without substitution. However, Sm segregation was detected near the STO substrate which was obtained by the TEM–EDS (transmission electron microscopy–energy-dispersive X-ray spectroscopy) analysis. On the other hand, Y1−x Sm x Ba2Cu3O y films with x =0.05 and YSm x Ba2Cu3O y films with x =0.3, which were fabricated on IBAD buffered metallic substrates, also improved I c value under the high magnetic fields compared with those of the YBCO without substitution. Moreover, from the TEM-EDS analysis, Y or Sm segregation was not found. The difference in the Sm segregation behavior between the film on STO and CeO2 buffered substrates could be explained by the difference in the ratios of the misfit parameters between YBCO/substrate and SmBCO/substrate. Additionally, it was considered that the above phenomenon might be unique in the MOD system and could not be observed in the PLD system, because of the difference in the crystal growth mechanism. In the film of YSm0.3Ba2Cu3O y , we observed the grains of (Y,Sm)2O3 and (Y,Sm)2Cu2O5 by TEM observation. We will further investigate the origin of pinning centers. [Copyright &y& Elsevier]

Abstract: The crystal growth mechanism of TFA (trifluoroacetates)–MOD (metal organic deposition) derived YBa2Cu3Oy has been investigated to understand the process for higher production rates of the conversion process. YBCO films were prepared by TFA–MOD on CeO2/Gd2Zr2O7/Hastelloy C276 substrates. The growth rates of YBCO derived from Y:Ba:Cu=1:2:3 and 1:1.5:3 starting solutions were investigated by XRD and TEM analyses. YBCO growth proceeds in two steps of the epitaxial one from the substrate and solid state reaction. The overall growth rate estimated from the residual amounts of BaF2 with time measured by XRD is proportional to a square root of P(H2O). The trend was independent of the composition of starting solutions, however, the growth rate obtained from the 1:1.5:3 starting solutions was high as twice as that of 1:2:3, which could not be explained by the composition of BaF2 included in the precursor films. On the other hand, the growth rate measured from the thickness of the YBCO quenched film at the same process time showed no difference between the samples of 1:2:3 and 1:1.5:3. The epitaxial growth rate of 1:1.5:3 was also the same as the overall growth rate of that, which means there was no solid state reaction to form YBCO after the epitaxial growth. The YBCO growth mechanism was found to be as follows; YBCO crystals nucleate at the surface of the substrate and epitaxially grow into the precursor by layer-by-layer by a manner with trapping unreacted particles. The amounts of YBCO and the unreacted particles trapped in the YBCO film are independent of the composition of the starting solution in this step. Unreacted particles react with each other to form YBCO and pores by solid state reaction as long as there is BaF2 left in the film. The Ba-poor starting solution gives little BaF2 left in the film and so the solid state reaction is completed within a short time, resulting in the fast overall growth rate. [Copyright &y& Elsevier]