YBa2Cu3O7-x Research Articles

In-plane and out-of-plane anisotropy in the optical and dielectric properties of YBa2Cu3O7-x superconducting film

YBa2Cu3O7-x (YBCO) is a crucial aspect of research in the field of superconducting applications, where its high anisotropy is generally undesirable in strong power transmission. However, from a dialectical perspective, a thorough investigation of material anisotropy can offer an additional degree of freedom to tune potential properties and design innovative devices. This work employed pulsed laser deposition to fabricate a high-quality YBCO thin film (Tc = 89 K) and used the Mueller matrix spectroscopic ellipsometer (MMSE) to determine the complete dielectric tensor of the YBCO film across the ultraviolet to near-infrared spectrum (245–1000 nm), enabling a comprehensive, quantitative study of the optical anisotropy of YBCO. It provided optical constants and dielectric function spectra for different axes. We found that YBCO exhibits birefringence and dichroism both in-plane and out-of-plane. By combining standard critical point (SCP) analysis and first-principles calculations, we identified specific interband transitions related to SCP in the YBCO dielectric spectra, revealing the physical essence of anisotropic optical transitions from a quantum mechanical standpoint. Temperature-dependent studies of the transitions and optical constants were conducted. The work fills a partial void in the optical parameters of the anisotropy of YBCO and holds relevance for understanding the origins of copper-based high-temperature superconductivity.

Changing of the excess conductivity near the irreversibility temperature of the top seeded YBa2Cu3O7−x

A top seeded YBa2Cu3O7-x (YBCO) superconductor was grown using a bulk Nd123 seed crystal. Orientation peaks directed in the c-axis were observed from the X-ray diffraction measurement for the Y123 sample, indicating single crystal behavior. Magneto-resistivity measurements were carried out as a function of temperature under applied magnetic fields up to 4 T. The superconducting transition temperature (Tc) of the sample was obtained to be approximately 93 K and the excess conductivity curve was obtained experimentally from the resistivity measurement at zero magnetic field. The critical exponents were found to be λsfw = 2.26 ± 0.25, λ3D = 0.47 ± 0.03 and λ2D = 0.82 ± 0.07 for the short wave fluctuation (SWF) region and the mean field region characterized by 3D and 2D fluctuations, respectively. The crossover temperature determined from the crossover from 2D to 3D regime was found to be 96.37 K. The irreversible temperatures determined from the magneto-resistivity measurements and the irreversibility field line of the sample was obtained using the giant flux creep (gfc) model. The sample exhibits a behavior consistent with the gfc and the vortex glass model according to the n parameter calculated from the resistivity temperature measurements. The width enlarges with the applied magnetic field and was found to be approximately 4 K at 4 T for the Y123 sample. The sample was in the 3D regime below 96.37 K, while the sample was in the 2D regime between 96.37 K and 101.35 K. On the other hand, the reversible region was confined between 93.95 K and 93.33 K at 0 T. It was observed that 3D fluctuations are dominant in the reversible region, whereas 2D fluctuations are dominant in the irreversible region.

Test of a YBCO thin film based over current limiter employed in battery unit of SMES-battery HESS during charging process

This paper proposes a novel over current protection strategy based on YBa2Cu3O7-x (YBCO) thin film current limiter, to improve the over current stability of the battery unit in superconducting magnetic energy storage (SMES)-battery hybrid energy storage system (HESS) during charging process. The conventional over current protection strategy for battery unit is based on cutting off the operation of the battery unit to remove the fault. Especially, during the charging process, once the battery unit circuit is cut off, the stability and reliability of the HESS will be also reduced. Hence, considering the features of the YBCO thin film in both superconducting state and quench state, it can be deployed as the over current limiter, to keep the stability of the battery unit against the over current fault during the charging process. In this paper, we designed and fabricated the YBCO thin film over current limiter, meanwhile, the preliminary verification experiment was carried out in our laboratory. It can be found from the experimental results that the over current in battery unit can be limited effectively by its quench resistance without cutting off the whole circuit. Besides, the charge voltage fluctuation of the battery unit can be also compensated by using the proposed protection strategy. Thus, the stability and reliability of the battery unit against the over current fault in charging process can be further improved.

Levitation force measurement and characteristics analysis of double sided high temperature superconducting thin film device

In this paper, the levitation characteristics of double sided high temperature superconducting (HTS) thin film device is proposed and measured. Based on the unique advantages such as, passive self-stable levitation, higher payload, lower energy consumption, less maintenance cost, etc., HTS-magnetic levitation (maglev) technology has been applied in the traditional fields (rail transit and energy storage fields) and novel fields (astrophysics, space station microgravity, vibration isolation fields). As the key core components, HTS device should meet the requirements of volume, weight and cost, to improve the system operation efficiency. Thus, considering the low profile, miniaturization and lightweight characteristics of the double sided YBa2Cu3O7-x (YBCO) thin film, we measured its levitation and relaxation characteristics. Meanwhile, we also designed the YBCO thin film with meander-lines, to explore the levitation characteristic evolution mechanism. It can be found from the experimental results that, the single piece of YBCO thin film with/without meander-lines can offer the levitation force more than 400 mN and 800 mN, respectively. The signature of this work is that the double sided YBCO thin film has the potential to be employed as the core device in the special application fields (such as astrophysics and space station), to supply the sufficient micro levitation force in limited volume and weight.

Fine structure of the tracks of several-tens-MeV Au ions in YBa2Cu3O7-x studied by cross-sectional transmission electron microscopy

We studied the morphology of the tracks (irradiation damage) of 44, 66, and 84 MeV Au ions in YBa2Cu3O7-x (YBCO) thin films using cross-sectional transmission electron microscopy (TEM). The electronic energy loss (Se = 11.6, 16.7, and 20.1 keV/nm) ranged near the onset of ion-track formation previously determined by plan-view TEM and critical-temperature measurements (about 13 keV/nm). The morphology changed from 1D arrays of large spheres of about 5 to 10 nm diameter in 44-MeV irradiation to their elongated variant (spheroid) that were statistically pierced by thin-lines of about 1 to 2 nm and 3 to 5 nm diameter in 66 and 84 MeV, respectively. In the same series of Au-irradiated YBCO films, we observed a sudden increase in critical current density at self-field and 77 K between 44- and 55-MeV irradiation, in agreement with the appearance of the thin-line damage in TEM (between 44- and 66-MeV).

Preparation of MgO Self-Epitaxial Films for YBCO High-Temperature Coated Conductors.

Ion beam-assisted deposition (IBAD) has been proposed as a promising texturing technology that uses the film epitaxy method to obtain biaxial texture on a non-textured metal or compound substrate. Magnesium oxide (MgO) is the most well explored texturing material. In order to obtain the optimal biaxial texture, the actual thickness of the IBAD-MgO film must be controlled within 12nm. Due to the bombardment of ion beams, IBAD-MgO has large lattice deformation, poor texture, and many defects in the films. In this work, the solution deposition planarization (SDP) method was used to deposit oxide amorphous Y2O3 films on the surface of Hastelloy C276 tapes instead of the electrochemical polishing, sputtering-Al2O3 and sputtering-Y2O3 in the commercialized buffer layer. An additional homogeneous epitaxy MgO (epi-MgO) layer, which was used to improve the biaxial texture in the IBAD-MgO layer, was deposited on the IBAD-MgO layer by electron-beam evaporation. The effects of growth temperature, film thickness, deposition rate, and oxygen pressure on the texture and morphology of the epi-MgO film were systematically studied. The best full width at half maximum (FWHM) values were 2.2° for the out-of-plane texture and 4.8° for the in-plane texture for epi-MgO films, respectively. Subsequently, the LaMnO3 cap layer and YBa2Cu3O7-x (YBCO) functional layer were deposited on the epi-MgO layer to test the quality of the MgO layer. Finally, the critical current density of the YBCO films was 6 MA/cm2 (77 K, 500 nm, self-field), indicating that this research provides a high-quality MgO substrate for the YBCO layer.

Design and test of a multi capacity integrated HTS thin film reconfigurable current limiter

This paper proposes and tests the YBa2Cu3O7-x (YBCO) thin film based multi capacity integrated high temperature superconducting thin film reconfigurable current limiter (HTS-TFRCL). Generally, reconfigurable concepts are widely employed in the microwave communication and antenna fields to design and fabricate the device with multiple operation performance, by choosing different circuit structures. Thus reconfigurable concept can be employed in the design of HTS thin film current limiter integrated different limiting capacity in one thin film device against the different levels of fault current. Considering there is few relevant work focused on the application of reconfigurable concept design in HTS current limiting field, the YBCO thin film based HTS-TFRCL is proposed and tested for the first time in this paper. It can be found from preliminary verification experiment carried out in our laboratory that, the proposed HTS-TFRCL has the multi current limiting capacity (its current limiting capacities are 50 VA, 90 VA, 120 VA, and 170 VA at 65 VAC, respectively), it can operate as expected to limit the fault currents under different voltages. Therefore, the HTS-TFRCL proposed in this paper can offer the multiple current limiting modes and capacities to limit the different levels of fault current, according to the practical operation requirements, the compactness, fabricating cost, stability and reliability of the current protection system can be further improved.

Interface Effects on Magnetic Flux Pinning in La0.7Sr0.3MnO3/YBa 2Cu3O7-x Bilayers.

The magnetic pinning properties of a ferromagnet/superconductor hybrid structure consisting of a La0.7Sr0.3MnO3(LSMO) layer with various thicknesses on top of a fixed thickness YBa2Cu3O7-x (YBCO) layer are investigated in this article. The existence of a weakly magnetic layer was identified at the interface between YBCO and LSMO by a ferromagnetic resonance (FMR) study. Magnetic moment and anisotropy of the interfacial layer were probed using the angular-dependent FMR study. This layer gives rise to an additional flux pinning contribution to the bulk magnetic pinning from the LSMO layer. Our study provides insight into the complex interface physics in the LSMO/YBCO bilayer system, promoting a new pathway for the development of novel flux pinning-related functionality.

A criterion for determination of the upper critical fields H-=SUB=-c2-=/SUB=- in YBCO thin films with different ion irradiation doses

Magnetotransport measurements were carried out for YBa2Cu3O7-x (YBCO) thin films in external perpendicular magnetic fields of H. The studies were performed both for the virgin samples and for the irradiated ones. Xenon ions were used as an external irradiation. Thus we studied features of the broadening of superconducting transition in YBCO films (virgin and irradiated). The broadening of superconducting drop was analyzed depending on an external magnetic field H, as well as on an irradiation dose nD. When processing the experimental data R(H,T), we studied a criterion for determination of temperature dependence of the upper critical field Hc2(T). The criterion was analyzed depending on the defect concentration in the film corresponding to a certain value of nD. It was found out that for a virgin sample, Hc2 should be determined by the resistance level R=0.4RN inside the superconducting transition, where RN=R(T=100 K). With a gradual increase in nD, this resistance level decreases. At sufficiently high radiation doses nD>7·1012 cm-2, the Hc2(T) phase transition line should be determined by the level R~0. Keywords: thin films, HTSC, xenon ion irradiation, magnetotransport studies, broadening of the superconducting transition, upper critical field, phase transition line, Tinkham's formula, Abrikosov vortices.

Effect of annealing temperature on thermoelectric properties of YBa2Cu3O7-x ceramic

We have studied the effect of annealing temperature on oxygen content and thermoelectric properties of YBa2Cu3O7-x (YBCO) ceramics fabricated by hot-pressing method. The as-calcined powder was subjected to the applied pressure of 70 MPa at 800 °C for 1 h under Ar atmosphere. The YBCO ceramics were then annealed at 700 and 750 °C for 4 h in oxygen atmosphere. The XRD results showed that all samples possessed pure orthorhombic YBCO phase. The annealing process seemed to induce the reduction of the electrical conductivity and metallic-to-semiconducting transition when the annealing temperature was increased. The temperature dependence of ZT showed a close relation to that of electrical conductivity, suggesting the dominant role of the charged carriers present in these samples.

Chemical and Microstructural Nanoscale Homogeneity in Superconducting YBa2Cu3O7-x Films Derived from Metal-Propionate Fluorine-free Solutions.

Research involved in developing alternative energy sources has become a necessity to face global warming. In this context, superconductivity is an appealing solution to enhance clean electrical energy provided that lower production costs can be attained. By implementation of chemical solution deposition techniques and high-throughput growth methods, low-cost nanostructured epitaxial cuprate superconductors are timely candidates. Here, we present a versatile and tunable solution method suitable for the preparation of high-performance epitaxial cuprate superconducting films. Disregarding the renowned trifluoroacetate route, we center our focus on the transient liquid-assisted growth (TLAG) that meets the requirement of being a greener chemical process together with ultrafast growth rates beyond 100 nm/s. We developed a facile, fast, and cost-effective method, starting from the synthesis of metal-propionate powders of Y, Ba, and Cu of high purity and high yields, being the precursors of the fluorine-free solutions, which enable the chemical and microstructural nanoscale homogeneity of YBa2Cu3O7-x (YBCO) precursor films. These solutions present endured stability and enable precise tunability of the composition, concentration, porosity, and film thickness. Homogeneous precursor films up to thicknesses of 2.7 μm through eight layer multidepositions are demonstrated, thus establishing the correct basis for epitaxial growth using the fast kinetics of the TLAG process. YBCO films of 500 nm thickness with a critical current density of 2.6 MA/cm2 at 77 K were obtained, showing the correlation of precursor film homogeneity to the final YBCO physical properties.

Optimizing vortex pinning in YBa2Cu3O7-x superconducting films up to high magnetic fields

The magnetic flux pinning capabilities of YBa2Cu3O7-x (YBCO) coated conductors vary strongly across different regions of the magnetic field–temperature phase diagram and with the orientation of the magnetic field θ. Here, we determine the optimal pinning landscape for a given region of the phase diagram by investigating the critical current density Jc(H,θ,T) in the 5–77 K temperature range, from self-field to high magnetic fields of 35 T. Our systematic analysis reveals promising routes for artificially engineering YBCO coated conductors in any region of interest of the phase diagram. In solution-derived nanocomposites, we identify the relevance of coexisting high amounts of short stacking faults, Cu-O vacancy clusters, and segmentation of twin boundaries, in combination with nanoparticles, for enhanced pinning performance at high magnetic fields and low temperatures. Moreover, we demonstrate that twin boundaries preserve a high pinning energy in thick YBCO films, which is beneficial for the pinning performance at high magnetic fields and high temperatures.

Origin of micro-scale local hotspots during the microwave processing of the YBCO conductive ceramics

In this letter, in situ investigation on the microstructure evolution of YBa2Cu3O7-x (YBCO) ceramics with a high electrical conductivity on a microscopic scale during microwave heating was carried out by the synchrotron radiation computed tomography technique. The experimental results indicate that the local melting exist inside the particle composed of smaller particles, leading to the heterogeneous heating or thermal runaway, which has not been reported elsewhere. Subsequently, considering the conductivity and morphology of YBCO particles, the novel phenomena has been interpreted by the calculated results from a constructed model, and it reveals that the non-uniform distribution of the focused electric field stems from the high conductivity and aggregated-particles of YBCO. Moreover, the high conductivity in combination with more and smaller aggregated-particles will intensify the non-uniformity of the focused electric field and heterogeneous heating for different microstructures.

Ferromagnetism and Superconductivity in CaRuO3/YBa2Cu3O7-δ Heterostructures.

The deposition of a ferromagnetic layer can affect the properties of high-temperature superconductors underneath. We investigated the influence of ferromagnetic CaRuO3 on the properties of YBa2Cu3O7-x (YBCO) superconducting thin films when the layers are either in direct contact or separated by a barrier layer of 5 nm SrTiO3. Detailed measurements of the magnetic moment of the superconductor and ferromagnet as a function of temperature and magnetic field have been performed using SQUID magnetometry. Magnetometry and relaxation measurements show that the modification of the superconducting properties of YBCO strongly depends on the interaction with the ferromagnetic layer on top. The barrier layer has a significant impact on both the supercon-ducting properties of the YBCO film and the ferromagnetic ordering of CaRuO3. The physical properties mentioned above were discussed in correlation with the materials’ structure determined by XRD analysis.

Fine patterned YBCO films grown on flexible nickel–tungsten substrates by photosensitive sol–gel method

In recent years, efforts devoted to the study of processing technologies for flexible devices have been increasing significantly. The fabrication of YBa2Cu3O7-x (YBCO) fine patterns on flexible nickel–tungsten (NiW) substrates is beneficial for the application of flexible superconducting electronic devices. The most challenging task is the simultaneous achievement of fine patterning and biaxial epitaxial growth of YBCO films on NiW substrates. This work reports the application of the photosensitive sol–gel lithography in combination with an all chemical deposition process to prepare fine patterned YBCO films on NiW substrates using gadolinium-doped lanthanum zirconate (LGZO) films as buffer layers. High-quality patterned YBCO films were epitaxially grown on LGZO–buffered NiW substrates, and the well-continuous YBCO patterns on flexible substrates could withstand bending deformations. The superconductivity remains good after the mechanical bending deformation process. These results are useful as guidance for the application of flexible superconducting devices.

Fabrication and Transport Characteristics of YBCO Step‐Edge‐Based Josephson Junction on Revived MgO Substrate

Herein, the combined impact of ion beam milling and postannealing treatment on the transport properties of deposited YBa2Cu3Ox (YBCO) thin film and fabricated step‐edge Josephson junction (JJ) on degraded MgO (100) substrates are investigated, and the obtained results of the YBCO thin film and fabricated step‐edge JJ on treated MgO (100) substrate are compared with the YBCO film and step‐edge junction on a fresh MgO substrate. Structural study reveals the formation of c‐axis‐oriented YBCO thin film on revived MgO substrate which is very much comparable with the YBCO film on fresh substrate. Atomic force microscopy (AFM) technique is used to confirm the step heights of the fabricated step‐edges on fresh, revived, and degraded MgO substrates. After the treatment, the surface roughness of MgO substrate has reduced from 56 to 1.06 nm which is comparable with the fresh MgO (100) substrate. The acquired values of critical temperatures for as‐deposited YBCO thin film on fresh and revived MgO substrates are 89.1 and 88.3 K, respectively, whereas these values are 85.8 and 85.7 K for the fabricated step‐edge junction microbridges on these deposited thin films. For both the fabricated step‐edge junction on the revived and fresh MgO substrate, the superconductor–normal metal–superconductor‐type JJ is confirmed.

Transient increase of Tc and Jc in superconducting/metallic heterostructures

The presence of a metallic layer can influence the properties of high-temperature superconductors underneath. We investigate the influence of metallic structures deposited in form of nanoparticles or continuous layers by electron beam evaporation or ion beam sputtering on the properties of Y1Ba2Cu3O7-x (YBCO) thin films. To generally avoid diffusion of metal atoms an additional barrier layer is introduced. Detailed measurements of the magnetic moment of the superconductor as a function of temperature and magnetic field have been performed using SQUID magnetometry. It is found that the modification of the superconducting properties of coated YBCO strongly depends on the deposition method of the metal on top rather than the type of metal (Ni or Ag), its magnetic properties (ferromagnetic or paramagnetic) or its morphology (nanoparticles or thin film). The main result is a transient increase of the critical temperature Tc and critical current density Jc that was observed for samples prepared by electron beam evaporation.

Evaluation of magnetotransport properties of Au added YBCO ceramics: combination of experimental and advanced theoretical approaches

The purpose of this work is to investigate the change of flux pinning ability, superconducting and physical properties of gold particle addition in the YBa2Cu3O7-x (YBCO) superconducting matrix using temperature dependent resistivity measurements under different applied magnetic fields; namely 0.0, 0.3, 1.0, 2.0, 5.0 and 7.0 T. The room temperature resistivity, transition temperature (Tc), transition width (∆Tc) and mobile hole carrier concentration values for each sample have separately been determined. In addition, we estimated the field-dependent activation energy (U0), irreversibility field (µ0Hirr), upper critical field (µ0Hc2), penetration depth (λ) and coherence length (ξ) with the quantum mechanical approaches related to the fluxoid mechanism for all the samples prepared. It was found that the flux pinning energy values evaluated by Thermally Activated Flux Creep (TAFC) model were determined to be about 11,455 K, 13,413 K, 10,350 K and 9320 K for the undoped, 1 wt%, 5 wt% and 20 wt% Au doped samples, respectively. Moreover, the results obtained showed that the critical temperature, activation energy, irreversibility and upper critical field values were found to depend strongly on the gold content and applied magnetic field strength. The values of µ0Hirr, µ0Hc2, λ and ξ (∆Tc) initially exhibited a slight increment (decrement) followed by a decrease (increase) for the samples with the higher gold-doping concentrations. The possible reasons regarding the observed changes in flux pinning and fundamental superconducting properties due to gold-doping in YBCO superconductors were discussed in detail. We indicated that a certain amount of gold doping has an effective role to form the nucleation centers that serve as the active flux pinning regions in the YBCO system so that the quality of interaction between the superconducting grains and inter-granular coupling strength in the adjacent multilayers can increase remarkably.

Microstructural characterization and superconducting properties of GdBa2Cu3O7-x films prepared by a fluorine-free sol-gel process

This work presents a promising method to fabricate fluorine-free GdBa2Cu3O7-x (GdBCO) films on LaAlO3 (LAO) substrate using a sol-gel technique. The phase transformation during the fabrication process and the influence of sintering parameters including crystallization temperature and oxygen partial pressure on the microstructure and superconductivity were investigated by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The c-axis oriented microstructure of GdBCO films was obtained under the crystallization temperature of 820 °C and oxygen partial pressure of 1.16%. The barium-containing BaCO3 phase can transform into Ba(OH)2, which contributed to the formation of fluorine-free GdBCO. Moreover, scanning transmission electron microscope characterization revealed that stacking defects were formed near the LAO substrate and spread throughout the whole GdBCO matrix with weak superconductivity regions, which acted as effective pinning centers to inhibit flux creep. This resulted in a stronger current-carrying capacity of the GdBCO film than that of YBa2Cu3O7-x (YBCO) film. Finally, a sustainable GdBCO film with the superconducting transition temperature (Tc) of 90 K and the critical current density (Jc) of 1.23 MA/cm2 (77 K, 0 T) was achieved through a simple and effective fluorine-free sol-gel method.

A Grain Boundary Josephson Junction that Supported Many Careers and Led to Applications with Impact

CSIRO is the Australian national science agency and has been working in superconducting electronics since the 1970s. With the discovery of high-temperature superconductivity in 1986, CSIRO supported a team of researchers to work on YBa2Cu3O7-x (YBCO) step-edge Josephson junctions. This junction technology is the basis of many different HTS devices and sensors. The CSIRO team used these devices in a range of systems for many different applications. This paper briefly reports on the development of the HTS YBCO step-edge junction formed on MgO. It also presents several systems developed with a focus on the most successful commercial system so far called LANDTEM™. This system is used for mineral exploration and has been successful in supporting the delineation and discovery of many billions of dollars of ore bodies. Over a 30-year period, the Josephson junction has been the basis of research for the CSIRO superconductivity team and provided all the team members with rich and fulfilling careers.