Low-fluorine Solution Research Articles

Optimization of the Crystallization Process of TFA-MOD ErBCO Films on IBAD-Substrate Under Low-Pressure Conditions via DSD Approach

Crystallization in a sub-atmospheric reactor could achieve higher production rate while dramatically reducing the flow rate of high-purity carrier gas. Due to enhanced supersaturation conditions at low total pressure, it is necessary to find the optimum processing window to avoid misoriented growth. This is extensive and incomplete when using one-factor-at-a-time experiments as significant parameters are often correlated. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">We prepared ErBa₂Cu₃O_7-<i>_δ</i> (ErBCO) films by the TFA-MOD route with low-fluorine solutions on technical IBAD template with CeO₂ top buffer layer in an industrial reel-to-reel furnace. We used a novel design-of-experiment (DOE) technique, the Definitive Screening Design (DSD), to identify significant factors for improving critical temperature and microstructure of the films. Within the investigated range, lower crystallization temperature as well as lower total pressure are beneficial. With the new process window, the self‑field critical current density at 77 K was successfully increased from almost zero to 1 MA/cm². This shows that DSD is an attractive approach to optimize the CSD process under low-pressure conditions to enhance the growth rate or possibly achieve a reduction of carrier gas flow rate by a factor <i>p</i>_tot/<i>p</i>_atm of 3.3 for equal output as the atmospheric reactor. Further improvement of <i>J</i>_c is necessary and possible.

Low-Fluorine Ba-Deficient Solutions for High-Performance Superconducting YBCO Films

High-performing superconducting YBa2Cu3O7–x (YBCO) films are fabricated by a chemical solution deposition methodology through novel barium-deficient low-fluorine solutions. The precursor solutions, distinguished for being straightforward, inexpensive and eco-friendly, allow us to reduce the growing temperature of YBCO down to 750 °C. We investigated the influence of the growing temperatures on both the microstructure and superconducting properties of YBCO films by using conventional thermal annealing and flash-heating approaches. A clear correlation between the growing temperature (Tg) and the superconducting performance of the films was obtained with improved performances observed at low Tg.

Investigation of the crystallization process of CSD-ErBCO on IBAD-substrate via DSD approach

REBa2Cu3O7-δ (REBCO, RE: rare earth, such as Y and Gd) compounds have been extensively studied as a superconducting layer in coated conductors. Although ErBCO potentially has better superconducting properties than YBCO and GdBCO, little research has been made on it, especially in chemical solution deposition (CSD). In this work, ErBCO films were deposited on IBAD (ion-beam-assisted-deposition) substrates by CSD with low-fluorine solutions. The crystallization process was optimized to achieve the highest self-field critical current density (Jc) at 77 K. Commonly, for the investigation of a CSD process involving numerous process factors, one factor is changed keeping the others constant, requiring much time and cost. For more efficient investigation, this study adopted a novel design-of-experiment technique, definitive screening design (DSD), for the first time in CSD process. Two different types of solutions containing Er-propionate or Er-acetate were used to make two types of samples, Er-P and Er-A, respectively. Within the investigated range, we found that crystallization temperature, dew point, and oxygen partial pressure play a key role in Er-P, while the former two factors are significant for Er-A. DSD revealed these significant factors among six process factors with only 14 trials. Moreover, the DSD approach allowed us to create models that predict Jc accurately. These models revealed the optimum conditions giving the highest Jc values of 3.6 MA/cm2 for Er-P and 3.0 MA/cm2 for Er-A. These results indicate that DSD is an attractive approach to optimize CSD process.

Effect of fluorine on the intermediate phase evolution for GdBCO film growth

Four simple low fluorine solutions with different fluorine contents were developed to grow GdBa2Cu3Oy (GdBCO) superconducting films, and the total fluorine contents were adjusted from 0 to 19.2% in comparison with the standard trifluoroacetate acid (TFA) solution. The thermal decomposition and crystallization of low fluorine solutions were investigated to understand the role of fluorine on the intermediate phase evolution for the growth of GdBCO film. With increasing fluorine content, the decomposition reaction region became narrow. Fluorine could catalyze the reaction and make pyrolysis abruptly. Furthermore, the evolution of intermediate phase was great affected by the change of fluorine content, which might lead to the change of microstructure and performance of GdBCO film. At the case of 11.5%, the intermediate phases contained BaF2, BGF, Gd2O3 and copper oxide without BaCO3 residue. And GdBCO film with the epitaxial growth, uniform microstructure and Jc of 1.58 MA/cm2 could be acquired. The optimization of intermediate phase derived from precursor solution would be helpful for high performance of GdBCO films.

Stranger APCs: Study of Surface Decoration Material for YBCO Films

In this contribution, we report on the study of the vortex pinning properties of YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) film grown on decorated substrate to obtain an improvement of magnetic field dependence of the critical current. Surface-decorated SrTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (STO) substrates have been obtained by polymer assisted deposition (PAD) with BaZrO3 (BZO) nanoislands uniformly distributed over the substrate surface. Thanks to the high density of the polymer, the viscosity of the solution can be easily adjusted to tune nanoislands' density. Typical values of nanoislands' diameter and height are around 20-50 and 3-5 nm, respectively. YBCO films, derived by metal-organic decomposition (MOD) using low-fluorine precursor solution, were successfully grown on both bare and BZO-decorated STO substrate. Results indicated that surface decoration is effective to enhance pinning at both 77 and 65 K in the whole field range up to 7 T. As a matter of fact, the value of critical current doubled with respect to YBCO film grown on bare STO at 77 K and 1 T.

Heat treatment design of precursor solutions with different fluorine contents for YBa2Cu3O7−x films through the sol-gel approach

The extraordinary high Jc value up to 5.2 MA/cm2 was obtained in the pure YBCO film by optimizing the heat treatment process for the specific precursor solution. The orientation, surface morphology, texture, and performance of YBCO films fabricated by the different low-fluorine precursor solutions and heating rates are systematically investigated for the first time. A reasonable heat treatment strategy is proposed for obtaining satisfactory YBCO films considering the synergistic effect of the heating rate and fluorine content.

Zirconium distribution in solution-derived BaZrO3 - YBa2Cu3O7-δ epitaxial thin films studied by X-ray photoelectron spectroscopy

Superconducting YBa2Cu3O7-δ films with different amounts of BaZrO3 nanoinclusions were deposited on SrTiO3(001) by low-fluorine chemical solution deposition with the aim of introducing artificial vortex pinning centres. The Zr concentration over the film thickness could be determined by X-ray photoelectron spectroscopy combined with Ar+ ion etching. The Zr/Y ratio has a constant behaviour in the film's bulk. Zr segregation occurs near the surface and Zr diffusion into the substrate is observed near the interface. Conversely, Sr and Ti from the substrate diffuse into the films. Y3d lineshape analysis and X-Ray Diffraction data pointed out that Ti diffusion causes the formation of Y-Ti-O based spurious phases.

Development of low-fluorine solution route and UV photolysis process for YBa2Cu3O7−x coated conductors

Abstract

Epitaxial YBa2Cu3O7−x nanocomposite films and coated conductors from BaMO3 (M = Zr, Hf) colloidal solutions

Superconducting nanocomposites are the best material choice to address the performance required in power applications and magnets working under high magnetic fields. However, it is still challenging to sort out how to achieve the highest superconducting performance using attractive and competitive manufacturing processes. Colloidal solutions have been recently developed as a novel and very promising low cost route to manufacture nanocomposite coated conductors. Well dispersed and stabilized preformance nanoparticle solutions are first prepared with high concentrations and then mixed with the YBa2Cu3O7 metalorganic precursor solutions to generate colloidal solutions to grow the nanocomposite films. Here we demonstrate, for the first time, that non-reactive BaZrO3 and BaHfO3 perovskite preformed nanoparticles are suitable for growing high quality thin and thick films, and coated conductors with a homogeneous distribution and controlled particle size using this fabrication method. Additionally, we extend the nanoparticle content of the nanocomposites up to 20%–25% mol without any degradation of the superconducting properties. Thick nanocomposite films, up to 0.8 μm, have been prepared with a single deposition of low-fluorine solutions using an ink jet printing dispenser and we demonstrate that the preformed nanoparticles display only a very limited coarsening during the growth process and so high critical current densities Jc(B) under high magnetic fields. These films show the highest critical currents achieved so far based on the colloidal solution approach, Ic = 220 A/cm-w at 77 K and self-field, and they still have a high potential for further increase in the film thickness. Finally, we also show that nanocomposite YBa2Cu3O7–BaZrO3 coated conductors based on an alternating beam assisted deposited YSZ buffer layer on stainless steel metallic substrates can be developed based on these novel colloidal solutions. Non-reactive preformed oxide perovskite nanoparticles are therefore very promising elements to further advance the colloidal solution approach in the implementation of low cost and high performance coated conductors for high magnetic field applications.

Epitaxial superconducting GdBa2Cu3O7−δ/Gd2O3 nanocomposite thin films from advanced low-fluorine solutions

We have employed the CSD method to synthesize GdBCO and GdBCO–Gd2O3 nanocomposite 250–300 nm thin films. For this we have designed a new low-fluorine solution never used before in the synthesis of GdBCO thin films that allows us to reduce the HF release by 80% and increase the reproducibility of the pyrolysis process. The growth of these thin films required a new thermal process to be designed, which we refer to as ‘flash-heating’, where the heating rate is extremely fast (∼600 °C min−1). The structure and the superconducting properties of the pristine GdBCO films are excellent, showing a (00 l) epitaxial orientation of the GdBCO grains and Tc values that reach 92.8 K, which means an enhancement of more than 1 K with respect to standard YBCO films. The calculated Jc inside the grains () also presents remarkable values: (5 K) ∼ 40 MA cm−2 and (77 K) ∼ 3.3 MA cm−2. Finally, the GdBCO–Gd2O3 nanocomposites films, with a 20% mol of Gd2O3, exhibit superior superconducting properties and pinning performances with respect to GdBCO pristine films.

Effect of F/Ba ratio of precursor solution on the properties of solution-processed YBCO superconducting films

YBa2Cu3O7−x (YBCO) thin films (with thickness of 220–230 nm) and thick films (with thickness of 1.1–1.2 µm) were prepared using low fluorine solutions with different F/Ba ratios (F/Ba=1–4.5). The effect of F/Ba ratio on the properties of the films was systematically investigated. The results showed that films derived from solutions with F/Ba 2 solutions, the formation of BaF2/BaOF phase was retarded by the decomposition of Ba1−xYxF2+x (BYF) intermediate phase. We also found that extra fluorine in the solution resulted in a large number of impurities and a-axis grains in the thick films, degrading the film superconductivity. F/Ba=2 was the optimal ratio in the solution to fabricate high-Jc YBCO thick films.

Chemical Solution Deposition of Epitaxial YBa&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;Cu&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;7-x&amp;lt;/sub&amp;gt; /CeO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;/ La&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;Zr&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;7&amp;lt;/sub&amp;gt; Multilayer Films on Biaxially-Textured Ni-W Tapes

CeO2/La2Zr2O7 composite buffer layers were deposited on Ni-W tapes using chemical solution method. YBa2Cu3O7-x (YBCO) films were then deposited on the CeO2/La2Zr2O7 composite buffer layers using a low-fluorine solution route. Effect of the annealing temperature and annealing atmosphere on the texture of the CeO2 layers was investigated. It was found that CeO2 film annealed at 1000°C under the atmosphere of N2 containing of 5vol. %H2 shows a high degree of c-orientation on La2Zr2O7 (LZO) film. Effect of oxygen partial pressure on the properties of YBCO films deposited on the CeO2/LZO buffer layers was also investigated. The YBCO annealed under N2 containing of 500ppm O2 shows the optimal properties, with critical current density (Jc) of 1MA/cm2 at 77K, 0T.

High Critical Current Density of YBa2Cu3O7-x Superconducting Films Prepared through a DUV-assisted Solution Deposition Process.

Although the solution deposition of YBa2Cu3O7−x (YBCO) superconducting films is cost effective and capable of large-scale production, further improvements in their superconductivity are necessary. In this study, a deep UV (DUV) irradiation technique combined with a low-fluorine solution process was developed to prepare YBCO films. An acrylic acidic group as the chelating agent was used in the precursor solution. The acrylic acidic group was highly sensitive to DUV light at 254 nm and significantly absorbed UV light. The coated gel films exposed to DUV light decomposed at 150 °C and copper aggregation was prevented. The UV irradiation promoted the removal of the carbon residue and other by-products in the films, increased the density and enhanced the crystallinity and superconductivity of the YBCO films. Using a solution with F/Ba = 2, YBCO films with thicknesses of 260 nm and enhanced critical current densities of nearly 8 MA/cm2 were produced on the LaAlO3 (LAO) substrates.

Thick REBaCuO superconducting films through single-coating of low-fluorine metallorganic solution

A high critical current Ic is crucial for the application of high temperature superconductors YBa2Cu3O7-δ in energy efficient power devices and wires.In this paper we report the fabrication of thick (YGd)1.3Ba2Cu3O7−x films on a metal substrate using low-fluorine metal organic deposition method. The effects of the film thickness on the microstructure, texture and superconductivity properties of the films were evaluated. In order to increase the film thicknesses by single coating, the influence of withdrawal speed during the dip coating on resulting thickness are investigated with the other processing parameters fixed. It is revealed that there is a maximum thickness for a certain starting solution. Here we used 3 different solutions, Conventional Low Fluorine solutions with 2M and 2.5M, and super low-fluorine solution with 2.5M. The maximum thicknesses of about 710nm, 1280nm and 1460nm were obtained, respectively.

Chemical Solution-Derived YBa2Cu3.3 O 7-d /CuO Multilayer Structure-Coated Conductors on Oxide-Buffered Metallic Tapes

An approach based on the insertion of a CuO layer in YBa2Cu3 O 7-d (YBCO)-coated conductor was proposed and demonstrates high current-carrying ability. The multilayer architecture was deposited on oxid-buffered Hastelloy tapes using a metal organic deposition (MOD) process (low-fluorine solution route). It was revealed that the introduction of a CuO layer was effective to avoid the presence of a-axis grain and pores of the YBCO films, which were frequently observed in multilayer films. Presently, the thickness of the multilayer films was almost 1.5 µm. Based on the improvements of the surface quality and c-oriented texture which were proved by X-ray (??-2??, f, and ?)-scan, AFM images, and SEM (surface and cross-section) images, the critical current density (Jc) of YBCO films with middle CuO and bottom CuO are 2.0 MA/cm 2 and 2.5 MA/cm 2 (at 77 K, self-field), respectively.

Manipulation of YBCO film properties by the introduction of perovskite BaTiO3 nanodots as substrate decorations

Perovskite BaTiO3 (BTO) nanodots were deposited on LaAlO3 (LAO) substrates using the BTO precursor solutions with various low concentrations. Subsequently, YBa2Cu3O7-x (YBCO) superconducting films were deposited on the BTO-dots decorated LAO substrates through a low-fluorine solution method. High BTO dots (with heights of 30–50nm) and short BTO nanodots (with heights less than 30nm) were produced using a solution with a concentration of 0.025mol/L, which could not be produced using solutions of other concentrations. We found a significantly enhanced flux pining force in the YBCO film deposited on the BTO-dots decorated LAO substrate. Because of the joint pinning effect of the high BTO dots and short BTO dots, the high-performance YBCO film with a critical current density of 8.42MA/cm2 and a flux pinning force of 9.58GN/m3 was produced on the LAO substrate.

Development of Low-Fluorine Solution for YBCO Film Growth

We developed a simple and stable precursor solution containing low fluorine content to fabricate YBa 2Cu 3O y (YBCO) films on CeO 2/YSZ/CeO 2 buffered NiW substrates. The fluorine content in the precursor solution could be controlled at 23.1% by tuning the ratio of barium trifluoroacetate to barium acetate. Fast pyrolysis process and smooth surface of YBCO precursor films could be acquired by using the low-fluorine solution. The phase, texture, microstructure, and superconducting properties of YBCO film were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscope, and four-probe method, respectively. The crystallized YBCO film showed good out-of-plane and in-plane textures. A high critical current density $J_{c}$ of ∼3 MA/cm 2 (77 K, 0 T) could be obtained in the YBCO/CeO 2/YSZ/CeO 2/NiW sample derived from the low-fluorine solution. The results indicate that the controllable fluorine content solution could be useful for epitaxial growth of YBCO films on buffered NiW substrates.

Low AC Loss Inkjet-Printed Multifilamentary YBCO Coated Conductors

Impressive performance has been achieved in $(\text{RE})\text{Ba}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ (REBCO) coated conductors, but for many applications, the high cost and ac losses remain prohibitive. Inkjet printing methods combine scalability and low equipment cost with high-resolution patterning, potentially addressing both issues by enabling the production of multifilamentary coated conductors without subtractive processing. The successful production of multifilamentary superconducting $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ (YBCO) structures by inkjet printing of a low-fluorine YBCO precursor solution on SS/ABAD-YSZ/CZO substrates is reported. Two approaches have been developed. In the first method, YBCO filaments were directly deposited on the buffered substrate by piezoelectric printing; and in the second approach, CeO2 tracks were first printed to pattern a subsequently overprinted YBCO film, creating a multifilamentary structure by an inverse technique. Scanning Hall probe measurements have been used to compare the filamentary structures and critical currents achieved by both methods, and a $J_{c}$ of up to 3 MA cm−2 has been obtained at 77 K. For the inverse printing approach, the ac hysteresis losses have been also measured and compared with theoretical models.

Optimization of fluorine content in TFA-MOD precursor solutions for YBCO film growth

Several low fluorine solutions containing different contents of fluorine were prepared by a chemical process. The fluorine contents in these solutions with respect to the conventional all-trifluoroacetate solution were calculated as 0%, 7.7%, 15.4%, 23.1%, 30.8%, 38.5% and 53.8%. YBa2Cu3O7−x (YBCO) films were deposited on LaAlO3 and CeO2/MgO/Al2O3/Hastelloy substrates using these low fluorine solutions. The phase formation, texture and microstructure of the YBCO films were characterized by x-ray diffraction and scanning electron microscopy. The decomposition mechanism of the low fluorine solution was also discussed. The results indicate that the ratio of F/Ba and the carbon content in decomposed powders could be controlled by adjusting the fluorine content in the precursor solutions. Fluorine had a great influence on the phase transformation, nucleation and growth of YBCO film during the crystallization process. The optimization of fluorine content was in the range of 15.4%–23.1%, which contributed to the good texture, homogeneous microstructure and high Jc value of the YBCO crystallized films.

Ag Doping Effects on Y0.5Gd0.5Ba2Cu3O7−δ multilayers derived by low-fluorine metalorganic solution deposition

Various artificial multilayers consisting of Y0.5Gd0.5Ba2Cu3O7−δ (YGdBCO) superconducting films were built up on an oxide buffered Hastelloy substrate using the low-fluorine metallorganic deposition method (MOD). Microscopic and superconducting performances are studied on composite YGdBCO multilayer films with and without alternate ultrathin layers of Ag, which comparatively demonstrates the Ag doping effects in such architectures. X-ray diffraction and scanning electron microscopy imply that the growth thermodynamic parameters of the YGdBCO are modified, resulting in a better c-axis orientation and a higher in-plane texture, as well as a superior surface, and finally give rise to great improvement of superconducting performance. To understand the above Ag doping effects further, the critical Gibbs free energy ΔG*(r) on nucleation of MOD-YGdBCO films on the biaxially textured buffer layers is analyzed with respect to the additions of Ag, which shows the competition between a-axis and c-axis growths subject to supersaturation. As a consequence, Ag additions may reduce the supersaturation at the growth interfaces, and hence give rise to a wider window of c-axis nucleation.