Fluorine-free Metal Organic Deposition Research Articles

Study on rapid growth and improved performance of superconducting YBa2Cu3O7-δ coated conductors assisted by transient liquid phase

This study employs a fluorine-free metal organic deposition method (FF-MOD), with transient liquid phase assistance, to expedite the growth (TLAG) of superconducting YBa2Cu3O7-δ (YBCO) thin films on LaMnO3 metal substrates. The research evaluates the phase formation and performance of YBCO films with varying proportions of preformed BaZrO3 (BZO) nanocrystals. The experimental results indicate that the optimal proportion for incorporating BZO nanocrystals is 5 %, leading to the YBCO film displaying critical current density at 77 K under zero-field conditions. This achievement marks a significant advancement in the rapid growth of YBCO films on metal substrates with enhanced current-carrying capacity. Additionally, the research assesses the changes in overall uniformity and microstrain of YBCO films after the addition of BZO nanocrystals, shedding light on the key factors contributing to performance enhancement and offering insights for future improvements. This investigation offers valuable insights for attaining high-speed, high-performance growth of superconducting YBCO coating conductors.

Introduction of BaMO3 artificial pins into high mixing entropy FF-MOD REBCO thin films

Abstract We have synthesized middle-entropy type REBCO (ME-REBCO) and high-entropy type REBCO (HE-REBCO) superconducting thin films with BaCeO3 artificial pins by fluorine-free metal organic deposition (FF-MOD) method and evaluated their crystallinity and superconducting properties. The c-axis orientation of crystals was confirmed by XRD analysis for all thin films. The superconducting transition temperatures in all films were over 90 K. STEM observation revealed that the crystal lattice of HE-REBCO was slightly distorted compared to a normal GdBCO film. This distortion is expected to be a “backlash” in the crystal and contribute to an increase in the allowable amounts of artificial pins. The critical current densities and flux pinning force densities at 77.3 K were enhanced by Ce doping, indicating that BaCeO3 artificial pins were introduced into the FF-MOD ME-REBCO and HE-REBCO films.

Superconducting Properties of High-Entropy Type RE123 Thin Films by Fluorine-Free MOD Method

We have fabricated a high-entropy type RE123 (HE-RE123) superconducting thin film that RE site is replaced multiple Gd, Sm, Nd, Eu, Y elements, by fluorine-free metal organic deposition (FF-MOD) method for the first time and evaluated their superconducting properties. The crystal structure evaluated by XRD indicated the c-axis oriented RE123 crystal, and elemental analysis confirmed a homogeneous distribution of the five elements at the RE site. The critical temperature of HE-RE123 was 90.4 K, exceeding 90 K. The critical current density of 2.4 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was obtained at 77.3 K, 0 T, which is higher than that of Gd123 films prepared by the same method. The maximum pinning force of HE-RE123 at 77.3 K was 1.2 times higher than that of Gd123.

Rapid phase formation and interfacial reaction of YBa2Cu3O7−δ coated conducts by using high-rate crystallization of fluorine-free chemical solution

In the present work, the high-rate epitaxial growth for superconducting YBa2Cu3O7-δ (YBCO) films on the substrates of LaMnO3(LMO)/IBAD-MgO/Y2O3/Al2O3/Hastelloy is achieved by fluorine-free metal organic deposition (FF-MOD) by rapidly switching the partial oxygen pressure (pO2) at a fixed temperature. Further investigation into the effects of temperature and switching pO2 on the phase transition of YBCO elucidates that the growth mode and microstructural characteristics of the studied films. BaMnO3 heterogeneous particles are observed in localized regions in the films by cross-sectional transmission electron microscopy, which may be generated by the interfacial reactions between the substrate and transient liquid phases. The present work implies the feasibility of FF-MOD for the rapid growth of YBCO films on LMO buffered metallic substrates, regardless of interfacial reactions during the preparation.

Low-Vacuum Pyrolysis of YBCO Films by Using Fluorine-Free Metal Organic Chemical Deposition

The preparation of YBCO superconducting films by using metal organic chemical deposition (MOD) involves low-temperature pyrolysis and high-temperature treatment. The former process generally requires the introduction of water vapor and other gases. The study on pyrolysis in a low vacuum environment and non-carrier gas atmosphere has never been reported. In this work, we explored a low vacuum pyrolysis scheme with simple Argon gas decompression and a carrier-free atmosphere. The effects of heating rate on the microstructure of pyrolysis films were investigated, and the high-temperature treatment temperature (Th) was also optimized. Compared with conventional pyrolysis, the present low-vacuum pyrolysis does not employ the flowing dry or wet gases, facilitating the internal gas release during film decomposition. More importantly, the efficiency was greatly improved with reduced pyrolysis time. The obtained film surface is free of CuO particle, which leads to a lower roughness. We also investigated the effect of Th on the final YBCO film texture and superconductivity. As Th increased from 810 °C to 815 °C, the BaCuO2 phase decreased with enhanced c-axis orientation being evident by XRD and Raman spectra. As a result, the critical current density (Jc) increased from 0.38 MA/cm2 to 1.2 MA/cm2 (77 K, self-field).

Enhancement of self-field critical current density by several-tens-MeV ion irradiation in YBa2Cu3O7 films prepared by fluorine-free metal-organic deposition

An up to 63% enhancement in critical current density (J c) was achieved for 1 μm thick YBa2Cu3O7 (YBCO) films at self-field at 77 K by irradiation with 24–84 MeV Au ions. This enhancement is highly unusual, since in YBCO films, J c at self-field (J c sf) is generally insensitive to ion irradiation, unlike J c in magnetic fields. Our observed film-thickness dependence of the irradiation effect and our microstructure imaging indicate that this rare observation is attributed to an extremely “clean” (i.e. less-disordered) microstructure in the top 700 nm of the layer of our 1 μm thick films prepared via fluorine-free metal-organic deposition. Our results directly indicate that discontinuous 1D vortex-pinning centers (pins) that have the following features effectively enhance MA cm−2-order J c sf at 77 K of YBCO films; namely, 5–10 nm in diameter, ∼20 nm in size along a pin track, have a ∼20 nm gap between the pins in a pin track, and are directed in the c-axis.

Improvement of J c Properties for Hf and La Co-Doped Gd123 Films Fabricated by Fluorine-Free MOD Method

In this study we have successfully fabricated La and Hf co-doped Gd123 thin films on LaAlO3 single crystal substrates by the fluorine-free metal organic deposition method with tetrakishafnium as a new organic metal salt. Hf doping is the effective means to introduce the perovskite nano-structure BaHfO3 as artificial pinning centers (APCs) into REBa2Cu3O y coated conductors. On the other hand, La doping is valid method in promoting high quality epitaxial crystallization of the superconducting phase. By possessing both advantages La 1 mol% and Hf 2 mol% co-doped film achieved high critical current densities of 3.1 MA cm−2 at 0 T, and 0.25 MA cm−2 at 1 T, 77.3 K. The detailed study of the flux pinning revealed that APCs introduced by Hf doping brought about the increase of J c in high fields, and La doping brought about the quality crystallization resulting in the increase of J c in low fields.

Influence of chemical doping on flux pinning of GdBa2Cu3O7−z films

ABSTRACTEpitaxial GdBCO films with Cobalt (Co) and BaZrO3 (BZO) doping were prepared on (00l) LaAlO3 substrate by a self-developed fluorine-free polymer-assisted metal-organic deposition (FF-PA-MOD) approach. The effect of different doping ways on structure and properties of GdBCO films was investigated. Our results show that in-field critical current density (Jc) values of doped films have been distinctly improved compared to the pure film. It is noted that Co-doped film has much larger in-field Jc values than BZO-doped film, especially at higher temperatures. Furthermore, Co-doped GdBCO film shows significantly enhanced surface smoothness and grain connectivity. It is suggested that obviously enhanced Jc–B properties of the film may be attributed to improved surface morphologies and effective flux pinning centres by dilute Co doping. This study may offer another simple and efficient way to obtain the GdBCO-based coated conductors with high current densities.

Intermediate Phase Evolution of YBCO Superconducting Films Fabricated by Fluorine Free MOD Method

The second generation high temperature superconducting tapes, which use ReBCO film as superconducting layer, are considered to have enormous potential in practical applications because of its high operation temperature (up to 77 K), high superconducting performance under strong field and good mechanical properties relative to other practical superconducting wires / tapes. Among its preparation processes, fluorine free-metal organic deposition (FF-MOD) technique has been a research hotspot in recent years because of its unnecessity of vacuum environment, fast pyrolysis and crystallization growth rate, and environmental friendliness. In this paper, YBCO films were prepared on the CeO2 / IBAD-MgO / Y2O3 / Al2O3 / Hastelloy C276 technical substrate by FF-MOD technique. To systematically study the process of its phase evolution, the samples were quenched in different temperatures and followed by the characterization of XRD, ATR-IR and SEM. It is shown that the reaction between BaCO3 and the oxides of Y and Cu elements does not produce YBCO directly, but experienced a more complicated intermediate process. Besides, the formed YBCO crystals are randomly oriented at first, and then converted into a biaxially textured structure.

Structural and superconducting characteristics of YBa2Cu3O7 films grown by fluorine-free metal-organic deposition route

Microstructure and superconducting performance of YBa2Cu3O7 (YBCO) films deposited on LaAlO3 single crystal (LAO) substrates by a fluorine-free metal-organic deposition (FF-MOD) technique, have been studied by means of X-ray reciprocal space mapping (RSM), cross-sectional transmission electron microscopy (TEM) and magneto-optical (MO) imaging. Combining the X-ray diffraction and the TEM cross-sectional analysis, it is revealed that stacking faults, i.e. YBa2Cu4Ox intergrowths, and ab-plane twins are main defects in the FF-MOD YBCO films. Due to the highly epitaxial growth mechanism related to transient liquid phase, the LAO twinned substrate structure is also inherited in the FF-YBCO films. The low-density planar defects containing dislocations parallel to c-axis result in stripy patterns observed in the MO images. For comparison, the low-fluorine (LF) MOD film show a texture mosaic spread in the ab plane and is little influenced by the LAO twinning underneath, implying the severe structural disorder most likely associated with the large amount of small-angle grain boundaries. Moreover, the higher density of stacking faults was also detected by XRD θ−2θ scan in the LF-MOD film. It is suggested that associated partial dislocations formed at the boundary between the stacking faults and YBCO matrix act as strong linear (or dot) pinning centers. These structural characteristics are well in line with the better superconducting performance of the low fluorine-MOD film, in particular under external magnetic field at 77 K. This work offers an in-depth insight into the correlation between the microstructure and superconductivity in the MOD YBCO films.

Effect of lanthanum addition on the fabrication of REBa2Cu3Oy (RE=Gd, Sm and Dy) thin films by metal organic deposition using fluorine-free solutions

The effects of lanthanum (La) additions of 0.5–10 mol% on the superconducting properties and crystal growth of REBa2Cu3Oy (REBCO, RE = Gd, Sm, and Dy) films fabricated by the fluorine-free metal-organic deposition method using 2-ethylhexanate solutions were investigated. La-doped REBCO films showed the decrease in the number density of holes on the film surface and the increase in the XRD peak intensity of the REBCO superconducting phases. La-added GdBCO with La contents of 0.5–3 mol%, and SmBCO and DyBCO films with La contents of 0.5–10 mol% showed improved critical current density (Jc) at the self-magnetic field compared to the pure films. For the GdBCO film, the Jc value at the self-magnetic field increased from 1.32 to 2.38 MA/cm2 upon La addition.

Improvement of Flux Pinning Properties for Hafnium-Doped Gd123 Thin Films Fabricated by a Fluorine-Free MOD Method

In order to enhance the flux pinning force density $F_{p}$ in magnetic fields for REBa2Cu3O $_{y}$ (RE123)-coated conductors, Hf and Zr doping are the very valid way of introducing the perovskite nanostructure as artificial pinning centers (APCs) into the superconductors. However, the studies for Hf-doped RE123 thin films fabricated by the fluorine-free metal organic deposition (FF-MOD), which is the easiest production process, have not been done yet. In this study, we have successfully fabricated Hf-doped FF-MOD GdBa2 Cu3O $_{y}$ (Gd123) thin films on LaAlO3 substrates and investigated their flux pinning properties. Critical temperature for Gd123 thin films indicated around 92 K, and $T_{c}$ varied little by Hf doping. Hf 10 mol% doped film achieved high critical current densities of 2.72 mA⋅cm −2 at 77.3 K under 0 T, and 0.27 mA⋅cm−2 at 77.3 K under 1 T. With increasing Hf-doping amount, $F_{p}$ gradually increased, and the peak of $F_{p}$ shifted to the high magnetic field side. The elementary pinning force and the effective pinning center density also increased. We believe that effective APCs, probably BaHfO3 are introduced into FF-MOD Gd123 thin films by Hf doping.

Influence of Substrate-Film Reactions on YBCO Grown by Fluorine-Free MOD Route

Recently, fluorine-free metal organic deposition routes (FF-MOD) for growth of YBCO superconducting films have attracted increased attentions. In this paper, a comparison study was performed on the YBCO-Ag superconducting thin films deposited on two types substrates, LaAlO 3 and CSD-Ce 0.9 La 0.1 O 2 -y (CLO)/YSZ, respectively. Although conventional TFA-MOD derived YBCO films exhibit high performance on both substrates, the results vary when using the FF-MOD precursor. SEM and XRD results reveal that c-axis and a/b-axis orientations coexist in the YBCO-Ag films grown on the CSD-CLO/YSZ substrate deposited by the FF-MOD route, while the BaCeO 3 by-product is a dominating phase in the fully reacted film. Based on the structural analysis of the partially converted films, we found that interfacial reactions between the film and the CLO cap layer play an essential role on the epitaxial growth of YBCO-Ag films from the FF-MOD solution. Because of the different chemical reaction path compared to conventional TFA-MOD routes, it seems that the polycrystalline BaCeO 3 formation takes place prior to the YBCO-Ag epitaxial growth associated with the melting process, which results in structural deterioration at high growth temperatures and, therefore, no superconductivity. This study indicates the necessity of further reducing the nucleation temperature of YBCO films processed by FF-MOD routes.

Stress mechanism of Y1-xGdxBCO thin film with Gd substitution prepared by F-free metal organic deposition method

The plasma discharge channel in three-dimensional helical shape induced by pulsed direct current (DC) discharge without external stable magnetic field is discovered experimentally. It can be observed by intensified charge-coupled device camera that a luminous plasma structure fast propagates along a helical path in the form of guided streamer (ionization wave). And the propagation of the streamer is stable and repeatable. We take this streamer which propagates along the helical discharge path as the study object, and explain its mechanism by constructing an electromagnetic model. The result shows that the helical shape plasma plumes can exhibit two different chiral characteristics (right-handed and left-handed helical pattern). While the discharge parameters such as pulse frequency, boundary condition, etc. can all affect the propagating characteristics of helical streamers. The electromagnetic radiation driven by pulsed DC power inside the dielectric tube which forms the wave mode is an important source of the poloidal electrical field. The helical steamers form when the poloidal electrical field is close to the axial electrical field. The velocities of the propagation in poloidal and axial direction are estimated respectively, and the hybrid propagation modes involving the interchangeable helical pattern and the straight-line pattern propagating plasmas are explained from the viewpoint of multi-wave interaction. Recently, the second-generation YBa2Cu3O7- (YBCO) high temperature superconducting materials have attracted much attention and become a hot research point. The YBCO coated conductors are widely used in transmission cables, motors, generators and magnetic energy storage systems due to their high critical current densities and high irreversible fields. To obtain high critical current, it is necessary to increase the thickness of YBCO film. However, as the thickness increases, the cracking of the film appears and the a-axis grains form, which causes the critical current density to decrease drastically, hence the critical current declines, i.e., the so called thickness effect appears. In order to overcome the thickness effect, a great many of efforts have been devoted to it. It is realized gradually that the growth orientation of the c-axis can be controlled by the stress of film, which can be achieved through the substitution of Y by Gd and Sm each with a larger ionic radius. However, the systematical study of the evolution of the stress mechanism with the substitution ratio is still lacking due to the extreme complexity of the stress manipulation. Therefore, a series of Y1-xGdxBCO thin films with different substitution ratios is deposited on lanthanum aluminate substrates by the fluorine-free metal organic deposition method in order to reveal the evolution of the stress mechanism with Gd substitution. The growth orientations, microstructures and lattice vibration characteristics of the films are analyzed by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The results show that the lattice constant of the film increases and the orientation of the c-axis changes with the Gd substitution ratio for x increasing to a value less than 0.5, and the blue shift of the O(2)/O(3) mode of the Raman spectrum decreases with increasing x. For x=0.5, the blue shift of the O(2)/O(3) mode vanishes, indicating the free standing film with optimal c-axis orientation. However, with the further increase of Gd content, the film structure is deteriorated, and the performance is degraded as well. The red shift of the O(2)/O(3) mode occurs and the frequency decreases with increasing x. Our results indicate that the stress mechanism can be manipulated by controlling the content of various ionic radii in Y1-xGdxBCO films. The free standing film with optimal c-axis orientation can be obtained through adopting an appropriate substitution ratio, i.e., the ratio of m Y:Gd equaling 1:1. These results suggest that manipulation of the stress mechanism is a promising method to overcome the thickness effect effectively.

The Effects of Elements Doping on the Properties of YBCO Epitaxial Films Prepared by Chemical Solution Deposition

YBa2Cu3O7−δ (YBCO)-coated conductors have wide-ranging potential in large-scale applications such as superconducting magnets and superconducting electric cables, but low current carrying capability restrains the practical application of YBCO-coated conductors at high temperatures and high magnetic fields. It is crucial to develop YBCO-coated conductors with high flux pinning capabilities. In this paper, YBa2Cu3−x Fe x O7−δ (x = 0, 0.0005, 0.001, 0.002, 0.005) and YDy x Ba2Cu3O7−δ (x = 0∼0.5) films were prepared on a LaAlO3 (LAO) single crystal substrate via a fluorine-free polymer-assisted metal organic deposition (PA-MOD) method. The effects of elements doping on the properties of YBCO in different positions of the lattice were investigated. The superconducting critical temperature (T c) decreases, and the superconducting transition width broadens with the Fe and Dy doping. However, the critical current densities (J c) improve at 77 K with Fe doping quantities of xless than 0.005 and Dy doping quantities of xless than 0.5. It means that the current carrying capability of a YBCO film can be improved by doping with appropriate amounts of Fe and Dy.

High-Jc YBa2Cu3O7−x-Ag superconducting thin films synthesized through a fluorine-free MOD method

Obtaining a high critical current density (Jc) remains the main challenge in developing fluorine-free metal organic deposition (MOD) methods to fabricate YBCO superconducting thin films. Silver addition was used to raise the Jc values in this research work. By reacting with propionic acid and ammonia, AgNO3 was initially mixed with YBCO carboxylate precursors dissolved in methanol. High-temperature in situ XRD measurements on the YBCO-Ag powders revealed that silver addition lowers the incongruent melting temperature of YBCO to 760°C and resulted in a smooth surface morphology of the YBCO films at a temperature as low as 760°C. Grain growth and intergranular conductivity were also found to be improved by silver doping. After annealing under optimized conditions, a high Jc of 4.6MA/cm2 was obtained in a YBCO-Ag thin film with 10wt% Ag.

Effect of BaZrO3/Ag hybrid doping to the microstructure and performance of fluorine-free MOD method derived YBa2Cu3O7−x superconducting thin films

It is known that BaZrO3 and Ag can improve the magnetic and transport performance of YBCO thin film through totally disparate ways. BaZrO3 plays the role of flux pinning centers and Ag improves the transparency of the YBCO grain boundaries. However, similar research is rare on the fluorine-free derived YBCO films. In this research, BaZrO3-doped, Ag-doped and BaZrO3/Ag hybrid-doped YBCO films were synthesized through a fluorine-free metal–organic deposition method. BaZrO3 was found to deteriorate the microstructure and performance of YBCO, while Ag-doping was found to enhance the crystallization of YBCO and resulted in a high Jc of 3.87 MA/cm2 in self-field at 77 K. However, the microstructure and performance of the BaZrO3/Ag hybrid-doped YBCO film showed that the positive impact of Ag-doping was totally overwhelmed by that of BaZrO3.

Influence of middle-energy ion-irradiation on the flux pinning properties of YBCO films: Comparison between different synthesis methods

We studied effects of 3-MeV gold-ion irradiation on critical current density (Jc) in YBa2Cu3O7 films prepared by three different deposition methods: fluorine-free metal-organic deposition, thermal co-evaporation, and metal-organic chemical-vapor deposition. The three films showed strikingly distinct responses to the extrinsic pinning-center introduction in their Jc values in magnetic fields, namely, about 300%, 70%, and no enhancement in the above order. Transmission electron microscopy results suggest that this characteristic process dependence is closely related to the microstructure of the as-deposited films.

Influences of calcination temperature on growth and superconducting properties of GdBa2Cu3O7−δ films fabricated by fluorine-free metal organic deposition method

GdBa2Cu3O7−δ is one of the best candidates for the superconducting coated conductors because it has high critical temperature and high critical current density under high magnetic fields. In this study, superconducting GdBa2Cu3O7−δ films were fabricated by fluorine-free metal organic deposition method via two different calcination temperatures, 723K and 873K, to examine the influence of calcination temperature on film growth and superconducting characteristics. Critical temperatures and critical current densities of the sample calcined at 873K were superior to the sample calcined at 723K. In the case of the sample calcined at 723K, the mixture of amorphous and crystalline phases was observed, and that of a- and c-axis oriented grains after the crystallization. In the case of the sample calcined at 873K, the randomly oriented crystalline phases were observed, and the mixture of c-axis oriented grains and (Gd, Al)2BaO4 phase after the crystallization. These microstructural changes caused the differences in superconducting characteristics.

Optimization of a fluorine-free metal-organic deposition to fabricate BaZrO3-doped YBa2Cu3O7−δ film on RABiTS substrates

In this study, we used a systematic route to optimize the fluorine-free MOD process to achieve a high critical current density (Jc) in BaZrO3 (BZO)-doped YBCO films on RABiTS substrates. The BZO content is given by 1 YBCO+x BZO films, where x is moles of BZO per 1 mole of YBCO. We found x = 0.10 to be the optimal BZO content and ∼795–805 °C to be the optimal growth temperature window with 60–90 min processing time. TEM studies show the BZO nanoparticles are ∼20 nm in size and spaced ∼50–100 nm apart. The in-field Jc and the peak pinning force (Fp) of the film grown at the optimal conditions were greatly increased at 77 K relative to pure YBCO films, achieving ∼6.7 GN m−3 at 77 K, H ‖ c in a ∼800 nm thick x = 0.10 film. The angular dependence of in-field Jc measurements also shows greatly reduced angular anisotropy at 1 and 4 T at 77 K due to isotropic pinning by BZO nanoparticles.