YBa2Cu3O7-δ Research Articles

Thick Secondary Phase Pinning-Enhanced YBCO Films on Technical Templates

The critical current I c (B) of YBa 2 Cu 3 O 7-δ (YBCO) coated conductors can be increased by growing thicker superconductor layers as well as improving the critical current density J c (B) by the incorporation of artificial pinning centers. We studied the properties of pulsed laser deposited BaHfO 3 (BHO)doped YBCO films with thicknesses of up to 5 μm on buffered rolling-assisted biaxially textured Ni-5 at% W tape and alternating beam assisted deposition textured Yttrium-stabilized ZrO 2 layers on stainless steel. X-Ray diffraction confirms the epitaxial growth of the superconductor on the buffered metallic template. BHO additions reduce the film porosity and lower the probability to grow misoriented grains, hence preventing the J c decrease observed in undoped YBCO films with thicknesses >2 μm. Thereby, a continuous increase in I c at 77 K is achieved. A mixed structure of secondary phase nanorods and platelets with different orientations increases J c (B) in the full angular range and simultaneously lowers the J c anisotropy compared to pristine YBCO.

Design Study of a 10-kW Fully Superconducting Synchronous Generator

In this paper, a 10-kW/150-r/min fully superconducting synchronous generator was designed and sent for manufacturing, which installs high temperature superconducting coils in both the stator and the rotor. It has a basic structure of eight poles and nine slots. The concentrated winding was adopted, and there are 16 field coils and 18 armature coils wound by using 5-mmwide YBa 2 Cu 3 O 7-δ (YBCO) tapes. The total tape consumption is around 2.0 km. Iron cores assembled by silicon-steel sheets will be installed in both the stator and the rotor. The peak gap field of 0.87 T can be achieved with a 42-A excitation current in field coils. The armature electric loading can reach 400 A/cm at the rated output. The present machine is designed to be cooled by using liquid nitrogen. The cryogenic structure can be divided into two parts: the conduction-cooled rotating part for field coils, and the immersion-cooled static part for armature coils. Both parts share the same vacuum chamber. A novel thermal insulated torque coupling will be installed to link the cold rotor and the warm shaft. The ac loss of armature coils was studied by H-formulation and it is within a reasonable range.

Sudden Short-Circuit Test of 22-kV YBCO Triaxial Superconducting Cable

For the power line between a power generator and a step-up transformer, isolated power bus (IPB) is generally used. The present IPB has a normal cylindrical conductor made of aluminum or copper at the center of the outer jacket and generates very huge Joule loss. To decrease it, superconducting buses have been developing. In this study, a 22-kV 3-kA triaxial superconducting bus was designed and fabricated with YBa2Cu3O7-d (YBCO) tapes and the various kinds of properties were investigated. Previously, the ac and lightning impulse withstand voltage test, critical current Ic test, and ac loss measurement were conducted and it was shown that the developed triaxial superconducting cable met the designed specifications. In this paper, a sudden short-circuit test of a 2-m-long triaxial cable was carried out by using a 200-MVA short-circuit generator. For protection, each phase of the cable was connected to a XLPE cable with a length of 3 m and a cross-sectional area of 250 mm 2 in parallel. Three-phase short-circuit current of 25 kA was applied to every phase of the cable bath-cooled with liquid nitrogen at 77 K for 2 s. As a result, the following tremendous phenomenon was demonstrated. Any phase of the triaxial cable kept a flux-flow state and did not quench. Short-circuit current was shared between the superconducting cable and the connected XLPE cable, and the branch current ratio varied even during one period of 60 Hz. The numerical simulation was also conducted to explain the phenomenon theoretically. That should contribute to the instantaneous recovery to a normal operation after a short-period interrupt of the circuit.

Interplay between current driven ferromagnetism in charge ordered antiferromagnetic Pr0.5Ca0.5MnO3 and superconducting YBa2Cu3O7−δ thin film multilayer

Thin film multilayer heterostructure of alternate YBa2Cu3O7-δ (YBCO) and Pr0.5Ca0.5MnO3 (PCMO) with thickness of each layer ∼60 nm has been deposited on (100) oriented SrTiO3 substrate by Pulsed Laser Deposition technique. A half portion of the base YBCO layer was masked in situ using mechanical shadow mask and in the remaining half portion, five alternate layers of PCMO and YBCO thin films were deposited. Magnetoresistance measurements were carried out under externally applied magnetic field and injection current. A noticeable damped oscillation of the superconducting transition temperature (TC) of this multilayer with respect to magnetic field is seen. Curiously, the field at which the first minimum in TC occurs, decreases as an injection current is driven perpendicular/parallel to the multilayers. Both these phenomena indicate that ferromagnetic correlation can be induced in antiferromagnetic PCMO thin films by (1) external magnetic field, or (2) injection current. While (1) is well researched, our study indicates that ferromagnetism can be induced by small amount of current in PCMO thin films. This unusual behavior points towards the strongly correlated nature of electrons in PCMO.

Macroscopic Magnetic Coupling Effect: The Physical Origination of a High-Temperature Superconducting Flux Pump

We have uncovered at the macroscopic scale a magnetic coupling phenomenon in a superconducting YBa2Cu3O7-δ (YBCO) film, which physically explains the mechanism of the high-Temperature superconducting flux pump. The coupling occurs between the applied magnetic poles and clusters of vortices induced in the YBCO film, with each cluster containing millions of vortices. The coupling energy is verified to originate from the inhomogeneous field of the magnetic poles, which reshapes the vortex distribution, aggregates millions of vortices into a single cluster, and accordingly moves with the poles. A contrast study is designed to verify that, to provide the effective coupling energy, the applied wavelength must be short while the field amplitude must be strong, i.e., local-field inhomogeneity is the crucial factor. This finding broadens our understanding of the collective vortex behavior in an applied magnetic field with strong local inhomogeneity. Moreover, this phenomenon largely increases the controlled vortex flow rate by several orders of magnitude compared with existing methods, providing motivation for and physical support to a new branch of wireless superconducting dc power sources, i.e., the high-Temperature superconducting flux pump.

Analysis of YBCO high temperature superconductor doped with silver nanoparticles and carbon nanotubes using Williamson–Hall and size–strain plot

This paper sets out to investigate and compare the effects of Ag nanoparticles and carbon nanotubes (CNTs) doping on the mechanical properties of Y1Ba2Cu3O7-δ (YBCO) high temperature superconductor. For this purpose, the pure and doped YBCO samples were synthesized by sol–gel method. The microstructural analysis of the samples is performed using X-ray diffraction (XRD). The crystalline size, lattice strain and stress of the pure and doped YBCO samples were estimated by modified forms of Williamson–Hall analysis (W–H), namely, uniform deformation model (UDM), uniform deformation stress model (UDSM) and the size–strain plot method (SSP). These results show that the crystalline size, lattice strain and stress of the YBCO samples declined by Ag nanoparticles and CNTs doping.

Properties of LSMO/YBCO cross-strip type junctions

The properties of a La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7-δ (YBCO) interface in thin film LSMO/YBCO cross-strip type junctions were investigated by means of electrical transport measurements. Resistance vs. temperature and current-voltage dependences, as well as conductance spectra, were used to characterize the electrical parameters of the interface. The results indicated a low resistance (below 10 Ω), while the dielectric properties of the interface pointed to the presence of a 10-nm wide and 40-meV high dielectric potential barrier. The oxygen vacancies in both LSMO and YBCO films at the interface and the charge transfer through the interface were both considered to explain the insulating character of the LSMO/YBCO interface.

Synthesis and properties of YBa2Cu3O7-δ – Y2Ba4CuWO10.8 superconducting composites

YBa2Cu3O7-δ (YBCO) is a well-known high-temperature superconductor. However, its critical current density and thus maximum trapped magnetic field can be improved significantly by introducing the secondary phases (artificial pinning centers). In this contribution, we successfully prepared YBCO single-grain bulks with Y2Ba4CuWO10.8 phase serving as a source of pinning centers. This phase was prepared by solid-state reaction and further refined by milling. In the next step single-grain YBCO bulks with homogeneously distributed Y2Ba4CuWO10.8 were prepared by top-seeded melt growth. Precursors as well as the final product were characterized by XRD, SEM and EDS. The phase composition of YBCO bulks containing Y2Ba4CuWO10.8 was analyzed using Rietveld analysis. Thermal stability of YBCO bulk was studied by STA. Furthermore, PPMS was used to study electrical resistivity and critical current density. Bulk superconducting properties such as levitation force and trapped field ability were also measured.

Structures and properties of buffer layers with nanometer thickness for PBCMO/YBCO epitaxial multilayers

Insulator buffer layer materials, PrBa2(Cu1-xMx)3O7-δ (PBCMO), with M = Al and Ga with different portions were synthesized to improve better buffer-layer materials for fabricating superconducting devices from YBa2Cu3O7-δ (YBCO) superconductor. Neutron and X-ray diffraction data reveal that the structures of PBCMO and YBCO are the same and their lattice parameters are well matched, while the resistivity shows that PBCMO have much higher resistivity than PrBa2Cu3O7 (PBCO). Epitaxial multilayers of PBCMO/YBCO were fabricated by laser ablation to explore the effect of PBCMO layer thickness on YBCO superconducting layers. Superconductivity was not found above 4.2 K for one unit cell thickness of YBCO. As the thickness of PBCMO was varied with constant thickness of YBCO films, the transition temperature of the multilayers remains unchanged even though the PBCMO layer is made as thin as the unit cell of 12.5Å. The difference indicates that PBCMO is better buffer layer and is adequate to insulate YBCO films in the multilayers and to cut off the superconducting coupling between YBCO layers.

A HIGH RETURN LOSS OF MICROWAVE BANDPASS FILTER USING SUPERCONDUCTING ELECTROSPUN YBCO NANOSTRUCTURES

A high return loss (-30 dB), small size (100 mm2) and broad bandwidth (1.5 GHz) microwave bandpass filter has been designed using finite element modelling and developed using the superconducting YBa2Cu3O7-δ (YBCO) thin films deposited on a (10 × 10 mm2) LaAlO3 substrate by spin coating. The thin films have been prepared by electrospinning and solid-state techniques. The microwave properties of filter circuits were experimentally determined using the vector network analyser (VNA) at room temperature (300 K) and in the presence of liquid nitrogen (77 K). The solid-state filter showed high return loss (i.e. -22 dB) at operating frequency of 9.7 GHz and broad bandwidth of 1.5 GHz, which is consistent with the simulation results. The insertion losses for YBCO filters are ~-2, ~-1.5 and ~-3 dB for the normal, nanoparticle and nanorod respectively. However, the electrospun filters exhibited lower performance due to the nano-structural properties of YBCO samples at nanoscale which make these sample have a large band gap compared to solid-state sample. The results indicate that the filter design and simulation result are reliable. Hence, HTS YBCO could be a potential microwave bandpass filter in industry.

Abnormal Transport and Magnetic Properties Induced by Change of the Phase Volume Ratio for YBa2Cu3O7-δ /La0.67Sr0.33MnO3 Hybrids

Two elaborately designed hybrids consisting of superconducting YBa2Cu3O7-δ (YBCO) and ferromagnetic La0.67Sr0.33MnO3 (LSMO), namely 20 × (YBCO(m)/LSMO(100 − m)) are prepared on single crystal SrTiO3 (STO) by pulsed laser deposition (PLD) with 20 being repetition periods and m = 90 and 10, respectively, which represents YBCO pulse number in a period. The films show highly c-oriented and epitaxial quality, suggested by XRD 𝜃–2𝜃 scans and pole figures. The 20 × (YBCO90/LSMO10) sample with a large YBCO volume fraction exhibits the typical character of a metal superconductor at about 90 K, while its transition width reaches 9.1 K, which is nearly eight times of that of the pure YBCO film. Above the superconducting transition temperature, a superparamagnetic signal rather than ferromagnetic behavior is observed, which may be associated with a diluted system consisting of the ferromagnetic nanoparticles embedded in the superconducting films. For the hybrid with a small YBCO volume fraction, i.e., the 20 × (YBCO10/LSMO90) sample, its transport behavior at normal state is insulating, and it is found that the Mott variable range hopping conduction dominates in this insulating phase in the temperature range 70–310 K. Obviously distinguishable insulator to superconductor (IS) transition occurs at 52 K, but the superconducting diamagnetic signals are very weak in the magnetic measurements below the IS temperature. For this sample, the magnetization loop at 100 K is ferromagnetic, yet manifested by a reduced coercive field and residual magnetization as compared with a pure LSMO film. In fact, both hybrids represent two kinds of nanocomposites, i.e., superconducting nanoparticles in a ferromagnetic matrix and ferromagnetic nanoparticles in a superconducting matrix, which benefits to study interfacial interactions due to an increased interface to value ratio and reduced size effect.

Comparison study of the flux pinning enhancement of YBCO superconductor with BZO and BZO + Y2O3 mixed phase additions

Adding nanophase defects to YBa2Cu3O7-δ (YBCO) superconductor thin films is well-known to enhance flux pinning, resulting in an increase in current density (Jct). While many previous studies focused on single phase additions, the addition of several phases simultaneously shows promise in improving current density by combining different pinning mechanisms. This paper compares the effect of the addition of two insulating, nonreactive phases of barium zirconium oxide (BZO) and yttrium oxide Y2O3, both as a single addition of BZO and as a double addition in conjunction with Y2O3. Processing parameters vary the target composition volume percent of BZO from 2-6 vol. %, while maintaining 3 vol. % Y2O3, and the remaining vol. % YBCO. Pulsed laser deposition produced thin films on LaAlO3 (LAO) and SrTiO3 (STO) substrates at various deposition temperatures. Comparison of strong and weak flux pinning mechanisms, current densities, critical temperatures, and microstructures of the resulting films will be presented. Films produced from the 2 vol. % BZO + 3 vol. Y2O3 doped YBCO target at a deposition temperature of 825 °C attained the highest current density. The addition of second phase Y2O3 impacted the film microstructure, resulting in more isotropic behavior when compared to the YBCO films doped with only BZO.

The Improvement of Utilization Ratio of Metal Organic Sources for the Low Cost Preparation of MOCVD-synthesized YBCO Films based on a Self-heating Technology

We have successfully applied metal organic chemical vapor deposition (MOCVD) to synthesize biaxially textured YBa2Cu3O7-δ (YBCO) superconducting films on the templates of LaMnO3/epitaxial MgO/IBAD-MgO/solution deposition planarization (SDP) Y2O3/Hastelloy tape. The YBCO films have obtained dense and smooth surface with good structure and performance. A new self-heating method, which replaced the conventional heating-wire radiation heating method, has been used to heat the Hastelloy metal tapes by us. Compared with the heating-wire radiation heating method, the self-heating method shows higher energy efficiency and lower power consumption, which has good advantage to simplify the structure of the MOCVD system. Meanwhile, the utilization ratio of metal organic sources can be increased from 6% to 20% through adopting the new self-heating method. Then the preparation cost of the YBCO films can be also greatly reduced.

Effect of Y2BaCuO5 Nanoparticle Doping on Critical Current Density of YBa2Cu3 O 7-δ Bulk Superconductor

This study presents the effect of Y2BaCuO5 (Y211) nanoparticle doping on critical current density and critical temperature of YBa2Cu3 O 7-δ (YBCO) superconductor. Y211 nanoparticles with different particle sizes ranging from 34 to 455 nm were synthesized by a sol-gel method, then doped into the YBCO superconductor by 0.5, 1, and 2 wt.%. Samples were characterized using X-ray diffraction and scanning electron microscope measurements. The standard four-probe technique was used to measure the critical current density at 77 K. The results showed that in the all-doped samples, critical current density was higher than that of the pure sample. It was found that in the samples containing 1 and 2 wt.% of Y211 nanoparticles, by increasing the size of nanoparticles, the J c was increased, but in samples containing 0.5 wt.%, the J c decreased. The maximum critical current density of 64 A/cm 2 was obtained for the samples doped with 2 wt.% of 455 nm Y211 nanoparticles. Also, it was observed that the critical temperature slightly decreased with nanoparticle doping.

Effect of template post-annealing on Y(Dy)BaCuO nucleation on CeO2 buffered metallic tapes

Substrate engineering is very significant in the synthesis of the high-temperature superconductor (HTS) coated conductor. Here we design and synthesize several distinct and stable Cerium oxide (CeO2) surface reconstructions which are used to grow epitaxial films of the HTS YBa2Cu3O7-δ (YBCO). To identify the influence of annealing and post-annealing surroundings on the nature of nucleation centers, including Ar/5%H2, humid Ar/5%H2 and O2 in high temperature annealing process, we study the well-controlled structure, surface morphology, crystal constants and surface redox processes of the ceria buffers by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electronic microscopy (FE-SEM), respectively. The ceria film post-annealed under humid Ar/5%H2 gas shows the best buffer layer properties. Furthermore, the film absorbs more oxygen ions, which appears to contribute to oxygenation of superconductor film. The film is well-suited for ceria model studies as well as a perfect substitute for CeO2 bulk material.

Enhanced Flux Pinning Properties of YBCO Thin Films With Various Pinning Landscapes

Pinning enhancement for YBa2Cu3O7-δ (YBCO) thin films is critical for their future applications such as superconducting cables, generators, and motors. In this study, several pinning landscapes are introduced and compared for improving the superconducting properties of YBCO thin films. First, BaZrO3 (BZO) nanoparticles have been doped into YBCO matrix providing uniform defect pinning centers and resulting in the superconducting property enhancement. Second, a magnetic nanocomposite of (La0.7Sr0.3MnO3 (LSMO))x(CeO2)1−x (with compositions of LSMO and CeO2 varied from 50:50 to 70:30) has been incorporated into YBCO as either a cap layer or a buffer layer. Using this approach, both magnetic pinning and defects pinning are introduced in the systems. Third, multilayers of (LSMO)0.5 (CeO2)0.5/YBCO have been deposited to achieve uniform defect and magnetic pinning effects through the film thickness. The superconducting properties (critical temperature $T_{c}$ , and especially the critical current density $J_{c}$ ) are compared for all the YBCO films with different pinning landscapes, and the corresponding pinning mechanisms are also discussed for each case. It is found that the pinning effect of YBCO film with magnetic nanocomposite layer is more significant under lower applied field, compared to the BZO-YBCO film. Through this comparison study, optimum pinning landscapes with combined defects and magnetic pinning approaches are proposed.

Influence of Substrate Tilt Angle on the Incorporation of BaHfO3 in Thick YBa2Cu 3O7‐δ Films

High critical current densities can be realized in high-temperature superconductors, such as YBa 2 Cu 3 O 7-δ (YBCO), by controlling the density, shape, size, and direction of a secondary phase. Whereas the dependence on the growth rate and deposition temperature has been widely studied as key parameters for nano-engineering the pinning landscape, the vicinal tilt of the substrate surface might have an additional influence. Therefore, we deposited 6 mol% BaHfO 3 (BHO)-doped YBCO on SrTiO 3 (STO) substrates with vicinal angles α between 0° and 40° to identify the influence of the tilt on the growth mode of BHO. An undisturbed epitaxial growth of the superconductor as well as an epitaxial integration of the BHO phase in the YBCO matrix is observed for all vicinal angles investigated. The critical temperature is constant up to α = 20°, whereas the self-field critical current density at 77 K starts to decrease above 10°. A detailed structural analysis of the film cross sections showed that the growth mode of BHO changes already for a vicinal tilt of 2° from a pure c-axis oriented growth to a layered structure with BHO aligned parallel to the YBCO ab-plane. We identified a strong influence of such a microstructure on the current flow in BHO-doped YBCO films on STO substrates as well as on MgO-based coated conductors prepared by inclined substrate deposition.

Stability Diagram of YBa2Cu3O7-δ in Low Oxygen Pressures

We report the phase stability of YBa 2 Cu 3 O 7-δ (YBCO) in low oxygen pressure (P O 2 ) region of 1-900 mTorr. For this study, the amorphous Y-Ba-Cu-O precursor films were deposited on LaAlO 3 (LAO) (001) substrate at 200°C by pulsed laser deposition. As-deposited precursor films were annealed at various high temperatures in a given PO 2 , quenched using a reel-to-reel furnace, and then their phases and microstructures were analyzed to accurately determine the stability line of YBCO and its decomposition reaction. The stability line of YBCO in the PO 2 regime of 1-200 mTorr on the PO 2 versus 1/T diagram can be expressed by the equation of Log PO 2 (Torr) = 9.79 - 11 783/T (K -1 ), and the ternary peritectic decomposition of YBCO ↔ Y 2 O 3 + YBa 3 Cu 2 O 6.5 (Y132) + Liquid(L 1 ) occurs at the stability boundary. In 250-900 mTorr, it can be expressed by the equation of Log PO 2 (Torr) = 12.67 - 15 276/T (K -1 ), and the ternary peritectic decomposition of YBCO ↔ Y 2 BaCuO 5 (Y211) + Y132 + Liquid (L 2 ) occurs at the stability boundary.

Novel Design of Band-Pass Waveguide Filter With HTS E-Plane Insert

In this paper, the idea of a band-pass filter (BPF) with HTS E-plane insert in the cross waveguide is implemented in Ka-band. The advantage of this approach is to solve the problem of mounting HTS insert into the body of the metal waveguide in order to ensure good electrical contact. A three-step method for the synthesis and design of such a filter is proposed and implemented. The method includes synthesis of the normalized prototype filter, sequentially iterative synthesis of filter geometry, and the final synthesis with optimization using numerical electrodynamic analysis of the entire geometry. It is shown that for the narrowband BPF, resonance windows in the E-plane insert should be performed with accuracy better than ±0.2 μm. The characteristics of such filters are expected better or not worse than their counterparts on the basis of rectangular waveguides, but at less stringent conditions of fastening HTS insert in the body of the waveguide. For fabricating the BPF, epitaxial HTS YBa2Cu3 O7-δ films sputtered on both sides of MgO single crystal dielectric substrate of 0.5 mm thickness were used. The difference between losses in the produced filter and its simulated sample is explained with insufficient accuracy of making resonance windows in the HTS insert.

Artificial control for nucleation and growth rate of YBa2Cu3O7-δ coated conductors prepared by low fluorine chemical solution deposition

The influence of various gas flow conditions on the nucleation and growth rate of YBa2Cu3O7-δ (YBCO) coated conductors in the high-temperature heat treatment stage of low fluorine chemical solution deposition (LF–MOD) process have been investigated, including the gas flow rate and gas flow direction. The results indicated that film-growth rate is faster while a-axis oriented phase coexisted with c-axis in the films at the higher gas flow rate. And YBCO (00l) grains grew slowly while a-axis oriented phase also nucleated easily on the end of the long films along gas flow direction. It could be caused by large quantities of HF gas accumulating from the chemical reaction for converting YBCO phase. Hence, the crystal mechanism of various LF–MOD methods can be supposed as still “BaF2” process as the TFA-MOD method, and orientation nucleation and growth rate of YBCO films can be artificial control by adjusting the gas flow conditions.