Ryo Teranishi

Fabrication and growth mechanism of YBCO coated conductors by TFA-MOD process

Abstract In the development for the coated conductors, the trifluoroacetates-metal organic deposition (TFA-MOD) process using the multi-coating method was applied to form thicker YBa 2 Cu 3 O y (YBCO) films on the CeO 2 buffered IBAD(Zr 2 Gd 2 O 7 )/Hastelloy tape. As a result, in the 5 times coated film with 1.38 μm in thickness, the J c and I c values achieved to be 1.5 MA/cm 2 and 210 A, respectively. Then, we fabricated a 1 m long YBCO tape by the continuous reel-to-reel system. As a result, we confirmed the tape to be homogeneous by XRD analysis. Additionally, we report the theoretical analysis of YBCO growth during post-annealing in the TFA-MOD process considering both the diffusion in the gas boundary layer and the growth kinetics at the precursor/YBCO interface. This model reveals a basic idea of the growth mechanism to define the steady state growth rate, and could explain the experimental results. In addition, it predicts that the growth rate could be estimated from the partial pressure of the water vapor of the inlet gas.

Fabrication processing of Y123 coated conductors by MOD-TFA method

Abstract The metal organic deposition process of YBa 2 Cu 3 O 7− X (Y123) using metal trifluoroacetate precursors is considered to be a strong candidate not only for high J c but also for low cost processing due to its a non-vacuum process. In this work, in order to obtain high I c films, thicker Y123 film processing on LaAlO 3 was investigated using the multi-coating method. In the case of thicker films, it was found that the low partial pressure of H 2 O, P (H 2 O) for the second heat treatment is effective to maintain the entire epitaxial growth for the thick films. Consequently, increasing of I c was realized from single to triple coating films. Further, in order to apply the technique to fabrication of coated conductors on metal, the bi-axially textured buffer layers is necessary to achieve a high in-plane alignment of the superconducting layer. Subsequently, the thicker film processing was applied to the CeO 2 /IBAD-YSZ/Hastelloy substrates using the multi-coating method. The triple coating Y123 film with 1 μm in thickness on the metal substrate shows the J c value of 1.6 MA/cm 2 at 77.3 K in self-fields and the I c performance of 153 A/cm-width.

Growth mechanism of YBCO films in metal organic deposition method using trifluoroacetates

We report the theoretical analysis of YBCO growth during post annealing in the TFA-MOD process considering both the diffusion in the boundary layer and the growth kinetics at the precursor/YBCO interface. As a result, we could obtain the analytical solution of the growth rate of YBCO. Subsequently, the unknown parameters in this solution were evaluated by the experimental measurements of the growth rate. The experimental results of the growth rate showed that it was independent of the film thickness and proportional to the square root of the water vapor pressure. These results suggested that the mass transfer in the gas boundary layer limited the growth rate. This model reveals a basic idea of the mechanism to determine the steady state growth rate, and could explain the experimental results. In addition, it predicts that the growth rate can be estimated from the water vapor pressure of the inlet gas. Consequently, it was confirmed that this growth model is effective for understanding of the growth kinetics in the TFA-MOD process.

Growth mechanism of Y123 film by MOD-TFA process

Abstract In order to clarify the growth mechanism of Y123 film in the metal organic deposition (MOD) process using TFA, transmission electron microscopy (TEM) observation of the quenched samples and measurement of the growth rate under several different conditions were carried out. TEM observation showed that the Y 2 Cu 2 O 5 , BaF 2 and CuO are converted into Y123 by release of HF with supplying H 2 O at the reaction interface. The MOD-TFA process using the multi-coating method was applied to form thicker Y123 films on LaAlO 3 substrates, and the growth mechanism for the Y123 crystallization was investigated. In order to evaluate the growth rate, the electrical resistance of the precursor films during the crystallization was measured by the DC four-probe method. It was observed that the thickness of the Y123 linearly increases with increasing annealing time. This result suggests that the growth rate is limited by the HF diffusion in the boundary layer and/or growing interface kinetics. According to the results from the gas flow rate dependence of the growth rate, it was suggested that the growth of Y123 films in this process might be limited by both the diffusion in boundary layer and the interface kinetics. Then, the growth model, which includes the two limiting systems, was developed. This model reveals a basic idea of the mechanism to determine the steady state growth rate.

Vortex Bose glass in ErBa2Cu3Oy films with size-controlled nanorods

Anomalous changes in irreversibility lines (ILs) and critical current properties depending on growth conditions were demonstrated in ErBa2Cu3Oy films with Ba–(Nb,Er)–O nanorods. Despite the formation of nanorods in the matrix at all growth temperatures (Ts), Bose-glass-like vortex pinning was strengthened with decreasing Ts. In particular, the behavior of ILs can be understood in terms of the morphology of introduced nanorods, and Ts strongly affects the vortex states. Our present study suggests the importance of optimization of growth conditions in the production process of rare-earth-based coated conductors containing nanorods as vortex-pinning centers.

High-Ic YBCO coated conductors by metal organic deposition method using trifluoroacetates

For the development of the YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) coated conductors, processing of the thicker film and long tape have been investigated using the metal organic deposition (MOD) method with the trifluoroacetates solution. About 1 micro-meter thick MOD film was realized by the control of the P/sub H2O/ condition during annealing for the formation of the YBCO layer. The improvement was explained by the competition between the nucleation of the undesirable grains and the epitaxial growth up to the surface. By applying the suitable condition to the metallic substrate system, high critical current density (Jc) and critical current corresponding to 1 cm wide tape (Ic/sup */) were realized as to be 1.6 MA/cm/sup 2/ and 153 A/cm-w in the film with 1 micrometer thickness, respectively. For the fundamental investigation of long tape processing, influence of the gas flow direction during annealing for the YBCO formation was investigated. Although nonuniformities in the X-ray diffraction (XRD) intensities and Jc values were recognized in the film grown under the gas flow parallel to the long direction of the tape, both of them was improved by changing the gas flow direction to the transverse one.

High critical current YBCO thick films by TFA-MOD process

Abstract As a method of the fabrication processes of YBa 2 Cu 3 O 7− x (YBCO), the metalorganic deposition (MOD) process using metal trifluoroacetete (TFA) is considered to be a strong candidate due to its low cost fabrication process for coated conductors with high J c . In our previous work, a triple coated film with 1 μm in thickness was fabricated on a CeO 2 /IBAD–YSZ layer buffered Hastelloy substrate by optimizing the condition of heat treatments such as P H 2 O in the multi-coating method [Physica C 378–381 (2002) 1013]. The J c value of 1.6 MA/cm 2 (77 K in self-field) in this film patterned 100 μm width and the I c * value of 153 A/cm-width at 77 K in self-field were achieved. In order to obtain a thicker film with high overall I c * for 1 cm width, the influence of the heat treatment conditions of P H 2 O , P O 2 , and the temperature in the MOD process was investigated. Subsequently, a 5 times coated film was obtained on a CeO 2 /IBAD–Zr 2 Gd 2 O 7 layer buffered Hastelloy substrate by optimizing the conditions of heating and dip coating. As a result, the overall transport I c value was improved to 210 A and J c value of 1.53 MA/cm 2 was obtained (77 K in self-field).

Direct fabrication of patterned PbS and CdS on organic sheets at ambient temperature by on-site reaction using inkjet printer

Abstract Patterned crystalline films of lead sulfide (PbS) and cadmium sulfide (CdS) have been fabricated on a paper as one of organic sheets by a direct solution reaction at room temperature. A drop-on-demand inkjet printer, which is particularly interesting because it is a noncontact technique, was used to fabricate them. The projected drop of ink travels directly through air to the substrate where a reactant solution is immersed homogeneously. Then, the interfacial reaction between the two solutions can produce solid target materials with a desired pattern on the substrate. This is regarded as a simultaneous process of synthesis and patterning or an on-site fabrication of patterned ceramics. All of the films were fabricated at room temperature without any postfiring/postheating treatments. The optional patterning of these materials with widths of 100 μm has been successful. In addition, it was confirmed that the patterned materials were crystalline and had adequate optical properties. It indicates this method to be effective for direct patterning of various functional materials.

Transmission electron microscopy characterization of nanorods in BaNb2O6-doped ErBa2Cu3O7−δ films

BaNb2O6-doped microstructures as artificial pinning centers in ErBa2Cu3O7−δ films were studied by transmission electron microscopy. The presence of nanorods, which contain niobium, was confirmed from bright-field images and elemental map images. The crystal structure of the nanorod was determined to be cubic perovskite. The lattice constant of nanorods in the ErBa2Cu3O7−δ film was in good agreement with the lattice constant of Ba(Er0.5Nb0.5)O3. Furthermore, parallel Moire fringes were observed in the bright-field images. It has never been confirmed by any other researchers that BaNb2O6 doped into the ErBa2Cu3O7−δ film transforms to Ba(Er0.5Nb0.5)O3 nanorods with a perovskite structure.BaNb2O6-doped microstructures as artificial pinning centers in ErBa2Cu3O7−δ films were studied by transmission electron microscopy. The presence of nanorods, which contain niobium, was confirmed from bright-field images and elemental map images. The crystal structure of the nanorod was determined to be cubic perovskite. The lattice constant of nanorods in the ErBa2Cu3O7−δ film was in good agreement with the lattice constant of Ba(Er0.5Nb0.5)O3. Furthermore, parallel Moire fringes were observed in the bright-field images. It has never been confirmed by any other researchers that BaNb2O6 doped into the ErBa2Cu3O7−δ film transforms to Ba(Er0.5Nb0.5)O3 nanorods with a perovskite structure.

Enhancing the critical current properties of internal Mg diffusion-processed MgB2 wires by Mg addition

The internal Mg diffusion (IMD) process produces a high-density MgB2 layer with high critical current properties, which makes it an attractive and promising method for fabricating MgB2 wires. We have obtained high critical current properties in our previous research. However, IMD-processed MgB2 wires can have unreacted B particles remain in the reacted layer due to the long Mg diffusion distance in the B layer during heat treatment. A reduction in the amount of unreacted B particles is expected to enhance the critical current properties. In this study, we attempted to disperse Mg powder in the B layer as an additive in order to decrease the Mg diffusion distance. We found that a 6 mol% Mg powder addition to a B layer drastically decreased the amount of unreacted B particles and enhanced the critical current density to twice the value for IMD-processed MgB2 wire with no Mg powder added. An analysis is presented that relates the microstructure to the critical current density.