Trifluoroacetate Metal Organic Deposition Research Articles

Synthesis and characterization of BaIrO3-doped YBCO superconducting thin films via TFA-MOD technique

High-temperature superconducting materials (HTS) are characterized by remarkably high critical current density (Jc) values when exposed to low temperatures and magnetic fields. In the realm of such investigations, various crystalline imperfections, including finely dispersed non-superconducting phases, dislocations, vacancies, grain boundaries, twin boundaries, antiphase boundaries, and insulating regions within grain boundaries, have been recognized as potential sources of pinning centers. However, it is essential to acknowledge that Jc values experience a rapid decline as the temperature rises in the presence of a magnetic field. The primary contributing factors to this decline are attributed to the intrinsic crystalline anisotropy of HTS materials and the thermal fluctuations that prevail at elevated temperatures. Nevertheless, a noteworthy factor in the diminishment of Jc values is the scarcity of efficacious pinning centers. In response to these challenges, a pioneering technology has emerged, revolving around nanostructure engineering for the deliberate creation of artificial pinning centers within HTS materials. In alignment with this approach, the present study endeavors to augment the critical current density and enhance the flux pinning properties of YBa2Cu3O6.56 (YBCO) superconducting films. This augmentation is achieved through the integration of BaIrO3 (BIO) perovskite nanodots, nanorods, or nanoparticles as strategically positioned pinning centers. The films are deposited on a SrTiO3 (STO) substrate employing the Trifluoroacetate Metal–Organic Deposition (TFA-MOD) technique. This research initiative seeks to contribute to the advancement of knowledge regarding the controlled manipulation of artificial pinning centers in HTS materials, particularly focusing on YBCO thin films, with the ultimate goal of enhancing their performance under the influence of elevated magnetic fields.

Monodisperse BaZrO3 nanocrystals and flux pinning effect on upscaling MOD-derived (Y,Dy)Ba2Cu3O7− δ superconducting tapes

In the present work, monodisperse BaZrO3 (BZO) nanocrystals with controllable sizes are successfully introduced into trifluoroacetate metal–organic deposition derived (Y,Dy)Ba2Cu3O7−δ ((Y,Dy)BCO)-coated superconducting tapes to act as effective pinning centers. The BZO nanocrystal addition strategy is extended to upscaling coated conductors as long as hundreds of meters, and as thick as 3.4 μm, of (Y,Dy)BCO layers. The corresponding superconducting performances of BZO-added (Y,Dy)BCO-coated conductors are systematically investigated under various applied magnetic fields and temperatures. It is revealed that the I c (77 K, self-field) of BZO-added tapes decreases linearly with BZO concentration, while the corresponding in-field lift-factors increase for all studied BZO additions. In-field J c values under various fields at low temperatures show that the (Y,Dy)BCO tape with 5%-BZO addition exhibits a better performance than that of other concentrations. Besides, this benefit of BZO addition appears identical for both thin and thick samples, as well as for tapes that are hundreds of meters long. The angular dependence of in-field I c also shows that significant improvement occurs in all the studied angular ranges after nanocrystal BZO additions, demonstrating that the nanocrystal addition strategy is of great value for upscaling commercial (Y,Dy)BCO tape for in-field applications.

Nucleation and epitaxy growth of high-entropy REBa2Cu3O7–δ (RE= Y, Dy, Gd, Sm, Eu) thin films by metal organic deposition

High-entropy REBa2Cu3O7–δ (RE = Y0.7 + Dy0.2 + Gd0.2 + Sm0.2 + Eu0.2) (HE-REBCO) superconducting films doped with multiple rare earth elements were successfully fabricated with thickness up to 800 nm by a trifluoroacetate-metal organic deposition (TFA-MOD). The enhanced entropy change ΔS of the HE-REBCO system promotes the c-axis growth of REBCO thin film in the competition with a/b-axis growth. The microstructure and element distribution were investigated by the transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The results show that HE-REBCO films have a great amount of stacking defects, lattice distortions and various rare earth oxides. Furthermore, the microstrain of HE-REBCO films increases significantly compared to the undoped YBCO and (Y, Dy)BCO films. Finally, the superconducting critical temperature (Tconset) of HE-REBCO films is about 93 K, and the in-field properties are significantly improved, especially at the temperature of about 77 K. The maximum pinning force density (Fp,max) of the HE-REBCO samples at 77 K is 1.7 times higher than that of the undoped YBCO films.

J c and Composition Distribution of YBCO Coated Conductors Fabricated by the TFA-MOD Process

The Trifluoroacetate-Metal Organic Deposition (TFA-MOD) process is one of the most promising fabrication processes for low-cost superconducting coated conductors (CCs) because of its high yield and non-vacuum system. However, in the doping and multi-coating process for the enhancement of critical current (<i>I</i>_c), degradation of <i>I</i>_c often occurs. In this study, to clarify the origin of <i>I</i>_c degradation, we have investigated the local critical current density (<i>J</i>_c) distribution, in-field <i>J</i>_c properties and the variation of composition for TFA-MOD processed YBa₂Cu₃O_y (YBCO) CCs. The local <i>J</i>_c distributions were measured by Scanning Hall-Probe Microscopy for confirming the location of the high&#x002F;low-<i>J</i>_c regions. The CCs were then cut into 3 mm&#x00D7;3 mm or 3 mm&#x00D7;4 mm for dc magnetization measurement. The <i>T</i>_c of the all samples were about 87 K to 90 K. In-field <i>J</i>_c at 77 K was obtained from <i>M</i>-<i>H</i> measurements and all the samples were compared with each other. The in-field <i>J</i>_c of high-<i>J</i>_c sample showed about 100 times higher value than that of the low-<i>J</i>_c sample. Then we have observed the microchemistry and the variation of composition by SEM-EDS. In the high-<i>J</i>_c sample, the grains of the superconducting phase were large in size and were connected to each other. This means that superconducting current could form through the whole sample area and generate a large magnetic moment. On the other hand, in the low-<i>J</i>_c sample, though the superconducting phase could be observed, the grains were small in size and sparse. Therefore, the magnetic moment measured was small. However, it was also suggested that the intra-grain <i>J</i>_c would be almost the same as that of high-<i>J</i>_c sample.

High homogeneity 10 cm long BaTiO3-doped YBa2Cu3O7-δ films by the trifluoroacetate metal-organic deposition process

The trifluoroacetate metal-organic deposition (TFA-MOD) is one of the most appealing routes for the growth of high-quality YBa2Cu3O7-δ (YBCO) coated conductors (CCs) due to its advantages of low cost and high efficiency. However, the puzzle of the inhomogeneities in microstructures and superconducting properties of YBCO CCs prepared based on the TFA-MOD route remain still a challenge. In this paper, 10 cm long YBCO films were prepared under different low-pressure conditions. These YBCO films were deposited on buffered Hastelloy C276 tapes using a dip coater. The effect of different ambient pressures on the microstructure and critical current density of YBCO films was investigated. High critical current density (JC) YBCO coated conductors with good homogeneity were obtained. The JC values (77 K, self-field) at different positions along the length direction of YBCO coated conductor were around 3.5–4 MA/cm2. The results showed that only under a suitable pressure the homogeneities of the microstructure and critical current density along the length direction of coated conductor can be greatly improved. The improvement was mainly ascribed to good texture and the absence of impurity phases BaF2 and Ba4Y2O7 in the films.

Preparation of high performance YGdBCO films by low fluorine TFA-MOD process

YBCO films doped with different contents of gadolinium (Gd) were prepared by the low-fluorine (low-F) trifluoroacetate metal-organic deposition (MOD) method. The effects of flow rate and holding time of the firing (crystallization) stage on the superconducting properties of YxGd1–xBa2Cu3O7–δ (YGdBCO) films were investigated. The phase formation and texture were characterized by the X-ray diffraction (XRD), which indicate that severe degradation of the microstructure will be induced with the inappropriate flow rate. The surface morphology and element distribution were investigated by the scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that increasing the holding time of the firing stage is effective for the further decomposition of residual impurity phase on the surface. The mechanisms of the phase and surface evolution are also discussed. Finally, a high critical current density (Jc) value of 5.4 MA/cm2 was achieved in the Y0.9Gd0.1BCO film fabricated by the cooperative control of the flow rate and holding time of the firing stage, which are contributed to the formation of excellent texture, homogeneous microstructure and dense surface of the YGdBCO films.

Superconducting properties of (Y1−xEux)Ba2Cu3Oy-coated conductors prepared via trifluoroacetate–metalorganic deposition

In order to investigate the effect of the partial substitution of Y by Eu on the superconducting properties of REBa2Cu3Oy (RE: rare earth) films, we fabricated trifluoroacetete-metalorganic deposited Y1-xEuxBa2Cu3Oy, (x = 0.1, 0.23 0.3, 0.4, 0.5) films on metallic substrates with optimal crystallization conditions. The optimized crystallization conditions for fabricating Y1-xEuxBa2Cu3Oy coated conductors with high x composition are relatively high crystallization temperature and low oxygen pressure comparing with YBa2Cu3Oy. The films with high χ exhibit a high critical temperature, irreversible fields, and high critical current density in the high-magnetic region at 77 K. However, the superiority on the critical current density of the films with high χ in self and low fields at 77 K is not necessary conformed. This behavior might be explained by the influence of the melt-growth mode in the film with high x.

Residual stress and strain on microstructure evolutions and superconductivity of REBa2Cu3O7−δ films grown by trifluoroacetate metal organic deposition

This research studies the effects of the residual stress and strain on the microstructure, critical current density, transition temperature, and microwave surface resistance of REBa2Cu3O7−δ (RE, rare earth) thin films grown by trifluoroacetate metal organic deposition. Different concentrations of Dy are introduced into YBa2Cu3O7−δ superconducting thin films. The superconducting transition temperature increases with an increase in the internal strain, while the critical current density exhibits an inverse variation relationship with the residual stress and c-axis length. The current carrying capability of REBa2Cu3O7−δ thin films can be improved by doping with appropriate Dy concentrations, which can be determined based on the residual stress modulation in the REBa2Cu3O7−δ thin films. In addition, no apparent transition of tensile or compressive stresses is observed in the thin films during the residual stress measurements. This paper provides a useful theoretical guidance for effectively improving the superconductivity of REBa2Cu3O7−δ thin films.

Growth of YBCO film by chemical solution deposition with an optimization fluorine process

Trifluoroacetate metal organic deposition (TFA-MOD) with low fluorine contents would bring benefits for the environment and the epitaxial growth of YBa2Cu3Oy (YBCO) film. In this paper, a simple and effective method which could tune the fluorine content and improve the performance of YBCO film was reported. YBCO Low-Fluorine/YBCO Fluorine-Free composites were prepared on LaAlO3 single crystal substrate. During the pyrolysis process, the fluorine would diffuse across the interface of YBCO Low-Fluorine/YBCO Fluorine-Free composites. Both the fluorine in the YBCO Low-Fluorine and the carbon in the YBCO Fluorine-Free could be reduced. It could significantly improve the epitaxial growth and performance of YBCO film.

Enhancement of the in-field critical current density of trifluoroacetate metal organic deposition derived (Y0.77Gd0.23)Ba2Cu3Oy films by annealing of CeO2 buffered R-Al2O3 substrates

We investigate the superconducting properties of (Y0.77Gd0.23)Ba2Cu3Oy [(Y,Gd)BCO] films on as-grown and annealed (600 °C–1000 °C) CeO2 buffered R-plane sapphire (R-Al2O3) substrates using trifluoroacetate metal organic deposition (TFA-MOD). The annealing was found to improve the crystallinities of not only the CeO2 buffer layers but also the (Y,Gd)BCO films. Although the anneal had no apparent effect on the pinning centers of the (Y,Gd)BCO films, the in-field Jc of the (Y,Gd)BCO films grown on the CeO2 buffered substrates improved with increasing annealing temperature. The present results are discussed in terms of the crystallinities and Jc values of the (Y,Gd)BCO films.

Enhancement of In-Field Critical Current Density of BaZrO3-Added (Y, Gd) BCO-Coated Conductors by Using a Multi-Coating TFA-MOD Method

We have investigated the in-field critical current properties in BaZrO3-added (Y, Gd) Ba2Cu 3O7-δ (YGdBCO)-coated conductor fabricated by using a multi-coating trifluoroacetates metal-organic deposition (MOD) method. We compared these properties with EuBCO-coated conductor fabricated by the pulsed laser deposition (PLD) method. The sample using the 30-nm once-coat-layer-thickness d once shows superior in-field J c down to 4.2 K than that of the previous standard coating using 170–nm-thick layer for each coating. From the analysis of E – J characteristics, an analytical expression for J c as a function T and B has been derived. It was confirmed that the high J c region in sample with d once = 30 nm is widely spread in high-temperature and high-magnetic-field region. By comparison with the J c properties of the BaHfO3 -added PLD CCs, the minimum J c, which is estimated from magnetic field angle dependence, shows even higher value up to 5 T of magnetic field at 65 K and up to 3 T at 77 K. From these results, the new MOD-YGdBCO process using the thin once-coat-layer-thickness is very promising for the practically important mid field region such as 3 to 5 T.

Trifluoroacetate metal organic deposition derived (Y0.77Gd0.23)Ba2Cu3Oy films on CeO2 buffered R-plane Al2O3 substrates

(Y0.77Gd0.23)Ba2Cu3Oy [(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, μ0H∥c) critical current densities (Jc). Annealing of the CeO2 buffer layer thus enabled enhancement of not only the self-field Jc for the (Y,Gd)BCO film but also the in-field Jc.

Control of artificial pinning centers in REBCO coated conductors derived from the trifluoroacetate metal-organic deposition process

The metal-organic deposition (MOD) process using metal trifluoroacetate salts (TFA) has the advantages of low-cost and high-scalability for the fabrication of REBa2Cu3Oy (REBCO, RE: rare earth elements) superconducting coated conductors (CCs) with high critical current density, in principle, because of its non-vacuum process. For the magnetic applications of CCs such as motors, magnetic resonance imaging and superconducting magnetic energy storage, further improvement of superconducting performance under magnetic fields is required. However, the in-field superconducting performance of REBCO CCs derived from the TFA-MOD process had been inferior to those derived from the vapor-phase process. In order to improve the in-field performance, the size control of the artificial pinning centers has been known as an effective way. In the early stage, the BaZrO3 (BZO) material, which was one of the effective materials in the CCs by the vapor-phase process, was also introduced in the TFA-MOD-derived CCs. The unique feature of the BZO material in the TFA-MOD process is the shape. The BZO in the TFA-MOD process formed the particle shape, although in the vapor-phase process it has a rod shape with a long axis elongating along the thickness direction. In addition, a special heat treatment for refining the BZO particles was developed, which is called the ‘interim heat treatment’. This heating profile made the in-field characteristics higher, although they were still lower than those of the vapor-phase process. Then, the new MOD process including ‘ultra-thin once coating’ was recently developed for further refinement of the BZO particles. The characteristics of the new TFA-MOD-derived CCs in magnetic fields have become compatible with those of the CCs derived from the vapor-phase process.

Microstructures Property and Improved J c of Eu-Doped YBa2Cu3.6O7−δ Thin Films by Trifluoroacetate Metal Organic Deposition Process

YEuxBa2Cu3.6O7−δ(x = 0, 0.1, 0.3, 0.5) thin films were prepared on buffered substrates by trifluoroacetate metal organic deposition (TFA-MOD). The europium-doped film showed better out- and in-plane texture than the pure YBa2Cu3.6O7−δ thin film and special topography. In the meantime, the superconducting transition temperature Tc was improved with the increase of europium content and spanned a small range when x= 0.5 doping levels. Besides, the Jc value was obviously enhanced with europium addition, and YEu0.3Ba2Cu3.6O7−δ showed the best superconducting properties under self-field. Furthermore, the Jc value was obviously improved under magnetic field, and the enhanced flux-pinning properties was also observed in europium-substituted samples which may be attributed to the good grain connections and the effective flux pinning centers introduced by europium addition. The thickness of prepared film samples were approximately 400 nm. The structure of samples were characterized by x-ray diffraction (XRD), Raman spectrum was used to investigate the crystallization and growth orientation, and the surface morphology of films were got by field-emission scanning electronic microscopy (FE-SEM). Moreover, energydispersive spectroscopy (EDS) was utilized to determine element composition. Spatial distribution of Jc of the film was obtained by mapping analysis of inductive measurement at 77 K. And the superconducting properties under magnetic fields were measured by magnetic property measurement system with a SQUID magnetometer.

Effect of Hf addition on critical current density of (Y,Eu)Ba2Cu3.6O7-δ thin films prepared by trifluoroacetate metal organic deposition

The critical current density (Jc) performance of YBCO coated conductors (CCs) under magnetic field has become a considerable limitation for its commercial application in recent years. It is well known that the proper amount of element doping into the CCs is a convenient method to increase flux pinning and then to enhance the Jc. In the present work, we firstly introduce the co-doping of Eu and Hf and study the effect on the performance of YBa2Cu3.6O7-δ thin films. Three types of high temperature superconducting thin films, i.e., YBa2Cu3.6O7-δ, (Y,Eu)Ba2Cu3.6O7-δ and Hf doped (Y,Eu)Ba2Cu3.6O7-δ were prepared on the oxide buffered metallic substrates by using trifluoroacetate metal organic deposition (TFA-MOD). The component and structure of the as-prepared samples were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and atomic force microscopy (AFM). Superconducting properties were measured with a SQUID magnetometer. It was revealed that the (Y,Eu)Ba2Cu3.6O7-δ thin films exhibit better out-plane and in-plane texture compared with the pure YBa2Cu3.6O7-δ thin film. The Jc of (Y,Eu)Ba2Cu3.6O7-δ thin film was improved compared with pure YBCO thin film. In case of Hf doping, however, the biaxial texture became worse while the in-field Jc performance was enhanced, implying the increase of flux pinning with proper Hf addition.

Transport Performance and Current Distribution of HTS Current Lead Prepared by YBCO Tapes

High-temperature superconducting (HTS) current lead has been prepared by the trifluoro acetates-metal organic deposition (TFA-MOD) processed YBCO tapes. The YBCO tape has higher critical current density J c and better magnetic property than the Bi2223 tape. Furthermore, the thermal conductivity of the YBCO tape with a thin Ag layer is much lower than that of the Ag-sheathed Bi2223 tape. The critical current of the YBCO tapes ranges from 150 to 180 A in liquid nitrogen and self-field. A current lead is composed of eight bundles stacked by two YBCO tapes (16 tapes), Cu end caps, and a pair of stainless-steel boards. Rogowski coils and Hall sensors used for estimation of current distribution are attached on each YBCO bundle. The transport current of 1.6 kA was carried with no voltage on every YBCO tape at 77 K. Although voltage of several tens of microvolts on some YBCO tapes appeared, transport current of 1.8 kA was successfully carried with no quenching. The voltages between the Cu cap and YBCO tapes almost linearly increased with increasing transport current, and they range from 0.75 to 0.93 mV and 1.02 to 1.21 mV at 1.8 kA, respectively. The low voltages correspond to 0.42-0.52 μΩ and 0.57-0.67 μΩ. The low contact resistance results in low joule heating at Cu joints. The current calculated by Rogowski coils in eight bundles varies from 137 to 355 A at 1.8 kA and sweep rate of 800 A/s. Therefore, the imbalance among eight bundles is evaluated to be 218 A. The current of eight bundles calculated by Rogowski coils sums up to 1808 A, which is the slight difference of 8 A in comparison with transport current of 1800 A. Rogowski coils and Hall sensors are effective at evaluating of current distribution for current lead.

Enhanced superconducting properties in MOD-YBCO thick films with CeO2 interlayer

In YBa2Cu3O7-x (YBCO) film there exists thickness effect: the critical current density of YBCO film drops precipitously as the coating thickness increases, especially in the case that the thickness of YBCO film exceeds 1 m. In this paper, we introduce very thin layers of CeO2 into YBCO layers and successfully fabricate the structure of YBCO/YBCO/CeO2/YBCO superconducting thick film. Firstly, YBCO films with two layers are fabricated on a LaAlO3 substrate by a multiple coatings process using a trifluoroacetate metal organic deposition method. Secondly, CeO2 thin films are deposited on YBCO films by RF-sputtering. Finally, we prepare the third YBCO film on CeO2interlayer. No cracks are observed in scanning electron microscopy images of these films; further, the majority of the grains in the films are well-textured and c-axis oriented. The full-width-half-maximum of the out-of-plane texture is measured to be 1.395 for the multilayer YBCO film at a thickness of 2 m Using this multilayer technology, we achieve Jc values of up to 1.36 MA/cm2 (77 K, self-field) in films as thick as 2 m, for an extrapolated critical current of 272 A/cm. We attribute the enhanced performance of the thick YBCO film to the CeO2 interlayer which playsan important role in transmission texture and stress relaxation.

Growth of Highly Epitaxial YBa2Cu3O(7-δ) Films from a Simple Propionate-Based Solution.

Intensive investigations have been conducted to develop epitaxial oxide thin films with superior electromagnetic performance by low-cost chemical solution deposition routes. In this paper, a novel propionate-based precursor solution without involving any other additive was proposed and employed to grow superconducting YBa2Cu3O(7-δ) (YBCO) films on LaAlO3 (LAO) single crystals. The precursor solutions are stable with a long shelf life of up to several months. Since the primary compositions are propionates after evaporating the solvent, the toxic reagents and evolved gases during solution synthesis and heat treatment can be eliminated completely. In this process, rapid pyrolysis and high conversation rate can also be achieved during growth of YBCO films in comparison with the conventional trifluoroacetate metal organic deposition routes. Remarkably, a 210 nm YBCO film exhibits high superconducting performance with a Jc value of 3.7 MA/cm(2) at 77 K, self-field. Nucleation and growth behaviors in the chemical solution process have also been studied. It is revealed that the amount of liquid phase (Ba-Cu-O) is sufficient through the entire thickness within a very short time at high growth temperatures, which results in pronounced densification and fast conversion of the YBCO phase.

Wrinkling of YBa2Cu3O7−x film prepared by trifluoroacetate metal organic deposition

YBa2Cu3O7−x (YBCO) films with wrinkles have been fabricated on LaAlO3(100) substrates by trifluoroacetate metal organic deposition (TFA-MOD). The decomposition behavior of YBCO-TFA gel and the formation mechanism of wrinkles were analyzed by thermal analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. The effects of wrinkles on the texture, microstructure and critical current density of the final crystallized film were also investigated by X-ray diffraction and scanning electron microscopy. The heating rate in the decomposition process was a crucial parameter to control the wavelength and wave amplitude of wrinkles on the surface of YBCO precursor film. Furthermore, the wrinkles of precursor films were transformed into the ridges of crystallized films during the crystallization process. Large ridges resulted in the degradation of texture of YBCO crystallized films. The decrease of critical current density (Jc) of YBCO crystallized films could be ascribed to the formation of ridges, the segregated phases and the degradation of texture. It suggested that the smooth morphology of YBCO precursor films would be beneficial to the enhancement of Jc value.

Influences of BaZrO3 particles on the microstructure and flux pinning of YBCO film prepared by using modified TFA-MOD approach

YBa2Cu3Oy (YBCO) films with BaZrO3 (BZO) particles were fabricated on LaAlO3 (00l) single crystal substrates by benzoate modified trifluoroacetate metal organic deposition (modified TFA-MOD). The influences of BZO particles on the texture, microstructure and the flux pinning properties of YBCO films were discussed. At high level of BZO doping, the BZO particles were considered to play an important role in the formation of a-axis oriented YBCO grains and the degradation of texture. When the optimal BZO content was 5%, the BZO particles as the flux pinning centers could significantly improve the critical current density (Jc) and flux pinning force (Fp) of BZO-doped YBCO film. Jc value of YBCO + 5%BZO film was about 4.9 MA/cm2 at 77 K and 0 T, and the highest Fp value (Fpmax) was about 4.3 GN/m3 at 77 K.