YBCO Thick Films Research Articles

Possibilities of the Master Mask Method in Analysis of Characteristics of Planar HTSC Structures Depending on Superconducting Film Thickness

In contrast to traditional methods for obtaining planar superconducting structures based on YBCO films, in which the topology is formed by etching or ion implantation, the topology in the master mask (MM) method is set at the initial stage of structure preparation, during the MM formation, and the YBCO deposition is the final stage. The superconducting elements of the structure are formed in MM windows, and insulating regions appear between them. Having fixed the topology of superconducting bridges at the MM formation stage, we measured their characteristics depending on the YBCO film thickness, performing deposition cycles sequentially. After each YBCO deposition cycle, we measured the structure parameters of the film as well as the critical temperature and current in the bridges, including the bridges with the Josephson junctions formed on a bicrystal substrate.

High-transition-temperature nanoscale superconducting quantum interference devices directly written with a focused helium ion beam

In this work, we present nanoscale superconducting quantum interference devices (SQUIDs) with dimensions as small as 10 nm from the high-transition-temperature superconductor YBa2Cu3O7−δ (YBCO). The SQUID features and Josephson junctions are directly written into a 35-nm thick YBCO film with a focused helium ion beam. We integrate these nano-SQUIDs with directly written nano-isolated inductively coupled control lines to demonstrate a low power superconducting output driver capable of transimpedance conversion over a very wide temperature range of 4–50 K.

Superconducting HfO2-YBa2Cu3O7−δ Nanocomposite Films Deposited Using Ink-Jet Printing of Colloidal Solutions

To reduce the fabrication costs while maximizing the superconducting and pinning properties of YBa2Cu3O7−δ (YBCO) nanocomposite films, the drop-on-demand ink-jet printing technique was used to deposit colloidal YBCO inks onto LaAlO3 substrates. These inks containing preformed HfO2 nanocrystals were carefully adjusted, prior to the jettability, as the droplet formation depends on the rheological properties of the inks themselves. After carefully adjusting printing parameters, 450-nm thick pristine YBCO films with a self-field critical current density (Jc) of 2.7 MA cm−² at 77 K and 500-nm thick HfO2-YBCO nanocomposite films with a self-field Jc of 3.1 MA·cm−² at 77 K were achieved. The final HfO2-YBCO nanocomposite films contained dispersed BaHfO3 particles in a YBCO matrix due to the Ba2+ reactivity with the HfO2 nanocrystals. These nanocomposite films presented a more gradual decrease of Jc with the increased magnetic field. These nanocomposite films also showed higher pinning force densities than the pristine films. This pinning enhancement was related to the favorable size and distribution of the BaHfO3 particles in the YBCO matrix.

Synthesis of thick YBCO films up to 3.0 μm on metallic substrates by a fluorine-free metal organic decomposition method

We improved the critical current properties of fluorine-free metal organic decomposition processed YBCO thin films prepared on buffered metallic substrates by increasing the thickness of the films. YBCO films prepared using a conventional one-time growth exhibit a maximum Ic (77 K, ∼0 T) value of ∼100 A per 1 cm width for a film with a thickness of 0.8 μm, and Ic decreases with further increases in the film thickness due to the generation of impurity particles and micro-cracks. In this study, a multiple growth process was adopted for the preparation of thick films to avoid these problems. The Ic of films prepared using this method monotonically increased with the film thickness. YBCO films with a thickness of ∼3.0 μm recorded a quite high Ic (77 K, ∼0 T) value for ∼210 A cm−1 width. Additionally, the in-field Jcs at 20 K and 40 K were found to increase almost proportionally to the film thickness.

Influence of artificial pinning centers on structural and superconducting properties of thick YBCO films on ABAD-YSZ templates

Recent efforts in the development of YBa2Cu3O7−x (YBCO) coated conductors are devoted to the increase of the critical current Ic in magnetic fields. This is typically realized by growing thicker YBCO layers as well as by the incorporation of artificial pinning centers. We studied the growth of doped YBCO layers with a thickness of up to 7 μm using pulsed laser deposition with a growth rate of about 1.2 nm s−1. Industrially fabricated ion-beam textured YSZ templates based on metal tapes were used as substrates for this study. The incorporation of BaHfO3 (BHO) or Ba2Y(Nb0.5Ta0.5)O6 (BYNTO) secondary phase additions leads to a denser microstructure compared to undoped films. A purely c-axis-oriented YBCO growth is preserved up to a thickness of about 4 μm, whereas misoriented texture components were observed in thicker films. The critical temperature is slightly reduced compared to undoped films and independent of film thickness. The critical current density Jc of the BHO- and BYNTO-doped YBCO layers is lower at 77 K and self-field compared to pure YBCO layers; however, Ic increases up to a thickness of 5 μm. A comparison between films with a thickness of 1.3 μm revealed that the anisotropy of the critical current density Jc(θ) strongly depends on the incorporated pinning centers. Whereas BHO nanorods lead to a strong B∣∣c-axis peak, the overall anisotropy is significantly reduced by the incorporation of BYNTO forming a mixture of short c-axis-oriented nanorods and small (a–b)-oriented platelets. As a result, the Jc values of the doped films outperform the undoped samples at higher fields and lower temperatures for most magnetic field directions.

Superconducting properties of nano-sized SiO2 added YBCO thick film on Ag substrate

The microstructure and the flux pinning capability of SiO2-added YBa2Cu3Oy thick films on Ag substrates were investigated. A series of YBa2Cu3Oy thick films with small amounts (0–0.5 wt%) of nano-sized SiO2 particles (12 nm) was prepared. The thicknesses of the prepared thick films was approximately 100 µm. Phase analysis by x-ray diffraction and microstructure examination by scanning electron microscopy were performed and the critical current density dependence on the applied magnetic field Jc(H) and electrical resistivity ρ(T) were investigated. The magnetic field and temperature dependence of the critical current density (Jc) was calculated from magnetization measurements using Bean’s critical state model. The results showed that the addition of a small amount (≤0.02 wt%) of SiO2 was effective in enhancing the critical current densities in the applied magnetic field. The sample with 0.01 wt% of added SiO2 exhibited a superconducting characteristics under an applied magnetic field for a temperature ranging from 10 to 77 K.

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.

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.

Surface Morphology and Profile Analysis for Five-Layer YBa2Cu3O7−δ Thick Films Prepared by Low-Fluorine Metallorganic Deposition

Thick YBa2Cu3O7−δ (YBCO) films grown by metallorganic deposition (MOD) are very significant for high-performance superconducting wires. In the present work, the modified MOD method with reduced fluorine content in precursor solution (namely LF-MOD in the following) is applied to prepare the YBCO films with the purpose of reducing the processing time as well as increasing thickness. Five-layer YBCO films with a thickness of more than 2.5 μm are achieved after the effect of high-temperature annealing time (ta) on the morphology and texture of YBCO films is systematically investigated. It is suggested that an annealing time as long as 6 h appears necessary to achieve a good performance for such a thick YBCO film. To understand the evolution of texture with thickness, plasma etching is employed to characterize the profile morphology at different depths inside the films, revealing the a-axis grains together with the impurity phases arising from the incomplete reaction mostly present at the top surface only.

Local Orientation Variations in YBCO Films on Technical Substrates - A Combined SEM and EBSD Study

Scanning electron microscope imaging and electron backscatter diffraction are applied to 400 nm thick YBCO films grown on Ni-9at.%W and ABAD-YSZ tape. On Ni-9at.%W tape, the orientation of YBCO strongly varies from grain to grain, which is attributed to the different orientations of the underlying substrate grains with regard to the surface normal. On ABAD-YSZ, the structures causing the orientation variations are observed on a micrometer scale only, which is attributed to the granularity of the template. In contrast to Ni-9at.%W where no preferred misorientation axis is notable within single substrate grains, the misorientation of YBCO on the ABAD-YSZ tape is primarily caused by lattice rotations about the sample normal.

Influence of YBa2HfO5.5 – ‘derived secondary phase’ on the critical current density and flux-Pinning force of YBa2Cu3O7−δ thick films

Enhancement in critical current density (Jc) and flux pinning force (Fp) in superconducting thick films of YBa2Cu3O7−δ (YBCO) added with small quantities of nanopowders of HfO2, BaHfO3 and YBa2HfO5.5, coated on YBa2ZrO5.5 substrate by dip-coating technique is reported. Critical current density measurements were done over an applied magnetic field using standard four probe technique and the results are compared with that of pure YBCO. High critical current density (Jc) of ∼4.84MA/cm2 at 77K in self-field was obtained for 2wt% of YBa2HfO5.5 added YBCO. A systematic increase in Jc observed in YBCO films prepared by the addition of nano HfO2, BaHfO3 and YBa2HfO5.5, attributed to the formation of a non-reacting ‘derived secondary phase’ YBa2HfO5.5 (YBHO) in the YBCO matrix. YBCO–YBa2HfO5.5 composite thick films have showed eightfold increases in Jc (3.29MA/cm2) at 77K and 0.4T compared to pure YBa2Cu3O7−δ film (0.37MA/cm2), while maintaining a high transition temperature (Tc). The development of effective pinning centers in nano particle added YBCO thick film have enhanced the flux pinning force from 1.8GN/m3 for pure YBCO to a maximum value of 13.15GN/m3 for YBCO–YBa2HfO5.5. X-ray diffraction and energy dispersive spectroscopic analysis confirmed the presence of secondary phase, derived in the matrix.

Required Crack-Preventing Chemicals and Chemical Background for Single-Coated Technology to YBCO Thick Films by TFA-MOD

Single-coating technology for metal-organic deposition using trifluoroacetate (TFA-MOD) is indispensable, because single-coated film has no intermediate layer that causes fatal deterioration in superconducting properties. This technology requires a crack-preventing chemical (CPC). Our group reported several CPCs at ASC2008. With the CPCs, we obtained single-coated thick films with thickness of over 1 micrometer. Some CPCs cause crack formation and increase carbon and fluorine residues in the resulting superconducting films. The objective of this study is to discover CPCs that cause no crack formation. Our study concludes that CPCs for TFA-MOD must have the following attributes: no branch structure, no ether bonds, no chemical double bonds in the carbon chain, strong acidity (pH -1 to 1), -(CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )- chain, and hydrogen terminations. Among more than 1 000 000 organic chemicals, there are only two series of chemical groups that work effectively as CPCs in TFA-MOD : H-(CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> -COOH and HOCO-(CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> -COOH.

Ultralow-fluorine sol–gel deposition of thick YBCO multilayer films

Three kinds of low-fluorine YB2Cu3O7−x (YBCO) starting sols with F/Ba = 6, 4 and 2 were applied to fabricate multilayer YBCO films on LaAlO3 substrates by multi-coating technique. Influence of the fluorine content in the sols and the thickness of single-coated layer on the properties of multilayer YBCO films was discussed in detail. The critical current density (J c) of multilayer YBCO films derived from F/Ba = 6 and 4 sols dropped sharply with thickness. However, using sol with F/Ba = 2, the J c of multilayer films decreased slowly with thickness. Moreover, the thinner the single-coated film, the less the amount of a-axis-oriented grains inside the multilayer films, resulting in the improvement in J c of the final thick films. Through multi-coating technique, YBCO films as thick as 1.1–1.2 μm were prepared. The J c of the optimized thick YBCO films reached a high value of 4.23MA/cm2 at 77 K, 0T. Compared with the YBCO films derived from other low-fluorine sols, the YBCO films prepared using the ultralow-fluorine sol with mole ratio of F/Ba = 2 show the higher superconducting current transportation ability. Using this solution, the “thickness effect” of multilayer thick YBCO films is degraded obviously. Moreover, lowering the thickness of every layer film through controlling the withdrawal speed can also suppress the formation of a-axis grains, thus enhancing the critical current density of final thick YBCO films.

Effects of thickness on superconducting properties and structures of Y2O3/BZO-doped MOD-YBCO films**Project supported by the National Natural Science Foundation of China (Grant No. 51272250), the National Basic Research Program of China (Grant No. 2011CBA00105), the National High Technology Research and Development Program of China (Grant No. 2014AA032702), and the Beijing Natural Science Foundation, China (Grant No. 2152035).

We report the thickness dependence of critical current density (Jc) in YBa2Cu3O7−x (YBCO) films with BaZrO3 (BZO) and Y2O3 additions grown on single crystal LaAlO3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD). Comparing with pure YBCO films, the Jc of BZO/Y2O3-doped YBCO films was significantly enhanced. It was also found that with the increase of the thickness of YBCO film from 0.25 μm to 1.5 μm, the Ic of BZO/Y2O3-doped YBCO film increased from 130 A/cm to 250 A/cm and yet Jc of YBCO film decreased from 6.5 MA/cm2 to 2.5 M A/cm2. The thick BZO/Y2O3-doped MOD-YBCO film showed lower Jc, which is mainly attributed to the formation of a-axis grains and pores.

YBa2Cu3O6+xSemiconductors Fabricated Using the Aerosol Deposition Method for IR Sensors.

In this study, YBa2Cu306+x (YBCO) thick films were investigated for their application in uncooled microbolometers. YBCO powders were prepared using the conventional mixed oxide method and were deposited on an SiO2/Si substrate using the aerosol deposition method (ADM) at room temperature. As a result of thermogravimetry and differential thermal analysis (TG-DTA) of YBCO powder, an endothermic peak was observed at approximately 820 °C. The powder was calcined at 880 °C. The deposited film were annealed at 600-750 °C (O2:Ar = 1:1, pO2) and their structural and electrical properties were investigated at varying annealing temperatures. From X-ray diffraction (XRD) results, all films displayed the typical XRD patterns of the tetragonal phase and the second phase was observed. The thickness of all the YBCO thick films was approximately 15.7 µm. As a result of the temperature coefficient of resistance (TCR = 1/R * dR/dT), the YBCO thick films annealed at 700 °C showed the maximum value of -3.1%/°C and all YBCO thick films showed typical NTCR (negative temperature coefficient of resistance) properties, displaying decreased electrical resistance with an increase in temperature.

Magnetic shielding performances of YBa2Cu3O7−δ-coated silver tubes obtained by electrophoretic deposition

We report a complete procedure to achieve multilayer YBa2Cu3O7−δ (YBCO) thick films by electrophoretic deposition on silver tubes using a suspension of YBCO powder in butanol. With the aim to optimize the magnetic shielding performances of the coatings, we have carried out an extensive investigation of the influence of the deposition parameters, the multilayer deposition sequence and the intermediate/final heat treatments on the coating microstructure. Using the optimized conditions, a 24-layer YBCO coating has been successfully prepared on an 80 mm long Ag tube: the melt growth processed multilayered YBCO thick film thus obtained can shield an applied magnetic field of 1.9 mT at 77 K, the highest value per thickness unit reported so far in the literature for these materials.

Dependences of microwave surface resistance of HTS thin films on applied dc magnetic fields parallel and normal to the substrate

We investigated the dc magnetic field and temperature dependences of microwave surface resistance (Rs) of high-temperature superconductor (HTS) films. Previously, we reported that the surface resistance RsRs(n) under a dc magnetic field applied normaly to the substrate increased when increasing the applied magnetic field. For NMR application, we have to examine the Rs(p) under the dc magnetic field parallel to the substrate. We measured the Rs(p) of the YBCO and DyBCO thin films with a thickness of 500 nm deposited on a MgO (100) substrate using the dielectric resonator method at 21.8 GHz, and a dc magnetic field of up to 5 T. In a zero magnetic field, the values of Rs(n) and Rs(p) were 0.35 mQ at 20 K. Under the dc magnetic field, the Rs(n) and the Rs(p) also increased with increasing magnetic field, however, the Rs(p) had a lower magnetic field dependence and the value was about 1/10 of that of the Rs(n). The Rs(p) at 16.4 T and at 700 MHz could be estimated by the two-fluid model. The Rs(p) value was about 1/2600 compared with that of copper at 20 K. As a result, we clarified that 500 nm thick YBCO and DyBCO thin films could provide advantages for NMR application.

Microwave complex conductivity of the YBCO thin films as a function of static external magnetic field

A sapphire rod resonator operating at microwave frequencies was used to determine the electric properties of 600 nm thick YBCO films in the superconducting state. The rigorous electromagnetic modelling was applied to transform the measured Q-factor and the resonant frequency to the complex conductivity of high accuracy, which was previously shown to describe the intrinsic properties of superconductor thin films in more precise manner than the complex impedance. Static external magnetic field induces typical transition to normal state due to introduction of magnetic vortices into the sample. Observed magnetic hysteresis has the origin in the strong temperature dependent pinning. Additional energy absorption at about 1.5 T was observed.

Epitaxial growth of MOCVD-derived YBCO films by modulation of Cu(tmhd)2 concentration

Metal–organic chemical vapor deposition was applied to fabricate YBa2Cu3O7−δ (YBCO) films on single-crystal LaAlO3 (001) substrates for its high deposition rate, easy adjustment on film composition, and low requirement on vacuum apparatus. The effects of Cu(tmhd)2 concentration in the precursor on the properties of YBCO films were systematically investigated. X-ray diffraction (XRD) reveals that the mole ratio of Cu/Ba in the precursor from 0.77 to 0.97 is helpful to improve the crystallization and out-of-plane orientation of YBCO films; however, it hardly affects the in-plane texture. Scanning electron microscope (SEM) shows the dense, crack-free but rough surface, on which there are Cu–O and Ba–Cu–O outgrowths identified by energy-dispersive spectrometer (EDS). As the mole ratio of Cu/Ba increasing, the average size of Ba–Cu–O precipitates keeps increasing and the film composition becomes inhomogeneous at the mole ratio of Cu/Ba of 0.97. The 250 nm thick YBCO film prepared at the mole ratio of Cu/Ba of 0.91 shows the critical current density (J c) of 4.0 MA·cm−2 (77 K, 0 T).

Magnetic and structural characterization of inkjet-printed TFAYBa2Cu3O7−x/MODCZO/ABADYSZ/SS coated conductors

The superconductor industry is demanding new methodologies to manufacture km-long, high quality coated conductors at high growth rates, using cost-effective, scalable processes. We report on the fabrication by an all-chemical deposition method of highly textured, thick (0.9 μm) inkjet-printed YBCO films, using a Ce0.9Zr0.1O2 (CZO) capping layer deposited by MOD, on top of robust, buffered ABADYSZ/SS substrates. Thinner, 0.25 μm spin-coated YBCO films were also analyzed for comparison. The structural study performed by x-ray diffraction, optical, AFM, SEM and TEM microscopy demonstrates the success of the capping layer for enhancing the planarity of the as-received tape and obtaining highly homogeneous and well-textured YBCO films. DC magnetometry granularity analysis was used to determine the mean superconducting grain diameter, ∼2.5 μm, and the intra- and intergranular critical current densities of the coated conductors (CCs). For the thin, spin-coated sample, high self-field intragrain critical currents were measured (, 3.3 MA cm−2 at 5, 77 K). For the thick, inkjet-printed tape was reduced by ∼30%, but, notably, the percolative critical current, , was only ∼10% smaller at 5 K, thanks to good preservation of the texture. At 77 K, was achieved, implying a critical current of Ic = 117 A/cm-width. AC susceptibility measurements allowed us to demonstrate the high homogeneity of the fabricated CCs, and investigate the magnetic vortex-pinning phase diagram. Remarkably, the thick, inkjet-printed sample showed comparable irreversibility line (IL) and activation energy for thermal depinning, Ue(H), to the thin sample. The present results open new perspectives for the fabrication of high quality-to-cost ratio, all-chemical CCs with yet higher Ic values by inkjet printing multideposition of thicker YBCO layers.