Properties Of YBa2Cu3O7 Research Articles

Effect of Metal Oxides Addition on the Superconducting Properties of YBaCuO

The superconducting properties of YBCO superconductor with ZrO2 addition prepared by different contents were prepared by a unique method so called thermal pyrolysis process to study the effect of the zirconium oxide on the electromagnetic properties and superconducting mechanism of the superconductor. The critical temperature of YBCO superconductor was not predominately dependent upon the zirconium oxide. The maximum magnetism was observed by adding 2% zirconium oxide. The addition of zirconium oxide forming a pinning center of magnetic flux due to ZrO2 phase which was related to the change of electromagnetic properties of the YBCO superconductor. The result indicates that magnetization is proportional to the number of magnetic flux lines passing through the sample. The added ZrO2 appear to contribute the increasing Vickers hardness.

Origin of Surface Morphology Variation During Pulsed Laser Deposition of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7}$ Superconducting Films

The dependence of properties in YBa2Cu3O7 (YBCO) films grown by pulsed laser deposition at different distances from the target to a substrate has been systematically studied. The target to substrate distance DTS is shown to enable simple means for tunability of the critical current density and microstructure of the YBCO films. The variation of structural and electromagnetic properties in the films as a function of DTS has been explained in terms of laser plume propagation model and thin film formation mechanism.

Disordering of the electronic structure of YBaCuO amorphous films upon incorporation of crystalline clusters formed in laser-induced plasma into their composition

The effect of crystalline clusters formed in a laser-induced plasma on the optical properties of YBa2Cu3O6 + x amorphous films prepared by pulsed laser deposition has been investigated. It has been demonstrated that an increase in the number of clusters leads to a gradual disappearance of interference fringes inherent in optically homogeneous media. Simultaneously, the incorporation of metallic and insulating clusters into the amorphous medium results in a decrease in the optical band gap E 0 of the YBaCuO amorphous matrix from 1.28 to 1.06 eV and a considerable decrease in the probability of interband optical transitions with charge transfer O 2p → Cu 3d due to the loosening of the structure and generation of local stresses. It has been revealed that there is an additional band gap E 1, which decreases from 0.25–0.30 eV to zero values with a decrease in the optical band gap E 0. The additional gap has been interpreted as an energy gap between localized states that belong to the valence and conduction bands. A decrease in the density of electronic states in the narrow 3d band leads to the overlap of tails of the density of states, so that the band gap E 1 becomes negative.

Effect of Yb 2O 3 additives on structure and transport properties of YBa 2Cu 3O 7-δ

The effects of Yb 2O 3 particles on the microstructure and transport properties of YBa 2Cu 3O 7-δ (YBCO) were investigated through resistance-temperature (R-T), scanning electron microscope (SEM), X-ray diffraction (XRD) and the critical current density ( J c) versus applied magnetic field ( J c-B) measurements. YBCO powder with Yb 2O 3 additives was synthesized using standard solid state reaction technique. Rietveld refinements of X-ray diffraction showed that both Yb 2O 3 and YBCO phases coexisted in the products. The critical current density ( J c) exhibited a maximum at x=0.05 in YBCO+ xYb 2O 3 systems. Moreover, small additions of Yb 2O 3 in YBCO could enhance J c by applying the magnetic field, although the superconducting temperature ( T c) decreased monotonically with increasing additive content. The characteristic behavior of J c might come from the counterbalance of two effects simultaneously, which was caused by the inhomogeneity of grains distribution in nano-scale and degradation on superconducting properties.

Measurement of thermophysical properties of YBa 2Cu 3O 7−x thin film using picosecond thermoreflectance technique

Simultaneous determination of thermophysical properties of YBa 2Cu 3O 7− x thin film has been carried out using the optical pump–probe method. The thermal diffusivity and thermal effusivity were analyzed from the same picosecond thermoreflectance data. The thermal conductivity and specific heat were then derived from the measured values of the thermal diffusivity and effusivity. The thermal diffusivity, thermal effusivity and thermal conductivity obtained compared favorably with those reported in the literature.

The effect of thickness and substrate tilt on the BZO splay and superconducting properties ofYBa2Cu3O7 − δ films

Highly splayed BaZrO3 nanorods (BZO-NRs) were generated inYBa2Cu3O7 − δ (YBCO) films dopedwith 2 vol% BZO on 5° vicinal SrTiO3 (STO) substrates. It was observed that the splay angle of the BZO-NRs around thec-axis increases with film thickness from about10° at 0.2 µm to35°–40° at1 µm. Although the same trend was observed in BZO-NRs in flat YBCO films, the splayangle at a given thickness and its increase with film thickness are significantlysmaller. The enhanced dispersion of BZO-NRs in vicinal YBCO/BZO-NR filmsresults in a much reduced strain on the YBCO lattice as compared to its flatcounterpart. This led to less disturbed normal-state electron conduction along theab-plane, higherTc values andenhanced Jc values due to improved magnetic pinning.

Influence of BaZrO3 Amount on Microstructure and Properties in YBa2Cu3O7−x Films Prepared by TFA-MOD Process

Epitaxial YBa2Cu3O7−x/BaZrO3 films were prepared by complex metal–organic solutions including Y, Ba and Cu anhydrous trifluoroacetate precursors and Zr acetylacetonate precursors. The influence of the amount of BaZrO3 (BZO) on the structure and properties of YBa2Cu3O7−x (YBCO) films was systematically investigated. The YBCO films having 7 mol % BZO have a maximum critical current density (Jc) value (77 K, 0 T) of 6.0 MA/cm2. The enhanced Jc derives from a high density of BZO nanoparticles existing in the YBCO matrix. With increasing BZO amount, Jc of the YBCO films begins to decrease due to larger particles.

Microstructural changes in epitaxial YBa 2Cu 3O 7 −δ thin films due to creation of O vacancies

Structural and transport properties of YBa 2Cu 3O 7− δ thin films subjected to different heat treatments and, consequently, having different O vacancy contents are investigated. It is observed that lattice parameters of the films follow the trend of the bulk material, indicating that either the additional stresses created in c-axis oriented films by O vacancies are negligibly small or they are relaxed at elevated temperatures. In addition, heat treatment under relatively low O 2 partial pressures, used to create O vacancies, leads to considerable reduction in local variations of lattice spacings in YBa 2Cu 3O 7− δ thin films.

Optimization of the properties of codoped single-domain Y–Ba–Cu–O bulk superconductors

The intrinsic effects of nanoscopic MnO 2 powders addition combined with Fe cation substitutions for copper sites on the microstructure and superconductive properties of YBa 2Cu 3O 7− δ (Y123) melt-solidified bulks have been investigated. On the one hand, an increase in Y 2BaCuO 5 (Y211) particle pushing, leading to an inhomogeneous bulk microstructure, is caused by increasing MnO 2 content due to increased net interfacial energy, Δ σ 0; and, on the other hand, an addition of MnO 2 powders is effective in enhancing both the δT c- type and δl-type pinning. It also shows that the Fe addition helps to optimize the high magnetic field performance and Y211 particle distribution in textured pellets. Further, this experiment suggests that a combination of the element substitution and the nanoscopic particle is a beneficial way to optimize the microstructure and superconductive properties of single-domain bulk superconductors.

Influence of BaZrO3 dopant concentration on properties of YBa2Cu3O6+x films in magnetic fields up to 30 T

The effect of BaZrO3 (BZO) dopant concentration on superconducting properties in YBa2Cu3O6+x thin films is investigated in a wide magnetic field range up to 30 T. Based on the magnetization and resistivity measurements, the optimal BZO concentration for flux pinning is found to be 4% up to 20 T and increasing up to around 8% in higher fields. This result is qualitatively explained by a model where more BZO is needed in order to organize optimal columnar defect structure at high fields because the amount of single BZO particles acting as isotropic point pinning centers is increased, especially in high BZO concentrations. This means that for applications of thin film or coated conductor structures carried out at high magnetic fields, even higher dopant concentration than used in a low-field range should be produced in order to attain the optimal flux pinning conditions.

Enhanced flux pinning in MOCVD-YBCO films through Zr additions: systematic feasibilitystudies

Systematic effects of Zr additions on the structural and flux pinning properties ofYBa2Cu3O7−δ (YBCO) films deposited by metal–organic chemical vapor deposition (MOCVD) have beeninvestigated. Detailed characterization, conducted by coordinated transport, x-raydiffraction, scanning and transmission electron microscopy analyses, and imaging Ramanmicroscopy have revealed trends in the resulting property/performance correlations of thesefilms with respect to varying mole percentages (mol%) of added Zr. For compositions≤7.5 mol%,Zr additions lead to improved in-field critical current density, as well as extra correlated pinning alongthe c-axis direction of the YBCO films via the formation of columnar, self-assembled stacks ofBaZrO3 nanodots.

Synthesis, characterization and melt processing of Y 1−x(Yb 0.9Nd 0.1) xBa 2Cu 3O z superconductors

Effects of a combined substitute of Yb and Nd on Y site on the superconducting properties of YBa 2Cu 3O y have been studied. We synthesized Y 1− x (Yb 0.9Nd 0.1) x Ba 2Cu 3O z compound with x = 0.2, 0.4, 0.6, 0.8 and 1.0. Here, the ratio of Yb–Nd was fixed to be 9:1 for obtaining 123 phase without secondary phases. The melt processing thermal profiles for Y 1− x (Yb 0.9Nd 0.1) x Ba 2Cu 3O z with x = 0.2 and 0.4 and the addition of 40 mol% {Y 1− x (Yb 0.9Nd 0.1) x } 2BaCuO 5 and 0.5 wt% Pt in air were determined on the basis of the thermal analysis results. All samples showed a low grain growth rate, particularly for high x values, which may be partially ascribed to un-optimized thermal schedules. Although almost all the samples exhibited low J c values, the sample with x = 0.2 exhibited T c of 88.8 K and a relatively high J c value of 16,000 A/cm 2 at 77 K for H//c-axis.

YBa2Cu3O7−δ coated conductor cabling for low ac-loss and high-field magnet applications**Contribution of NIST, a US government agency, not subject to copyright. Certaincommercial materials are referred to in this paper to foster understanding. Suchidentification does not imply recommendation or endorsement by NIST, nor does it implythat the materials identified are necessary the best available for the purpose.

The electromechanical properties ofYBa2Cu3O7−δ coated conductors under high axial compressive strain are measured;they show no irreversible degradation in critical current up to−2% strain. The high degree of elasticity of the ceramic layers in these conductors isbeneficial when used in high-field applications, but has not been fully exploited. Theresults presented here lead to the introduction of a new method of producingYBa2Cu3O7−δ coated conductor cabling for use in low ac-loss and high-field magnet applications, wherecoated conductors are wound around a former with a relatively small diameter. Thisconcept allows for full transposition of the conductors, a high cable critical current, lowinductance, and a relatively high engineering current density. The feasibility of theconcept is demonstrated by constructing several prototype cables and by comparingthe cable critical current to that of a straight sample under axial compression.

Melt Processing of YBCO Thick Films Fabricated by Sol Gel Route Powder on YSZ

It is evident that the microstructure and superconducting properties of YBa2Cu3O7−σ (YBCO) thick films are highly dependent upon the route of the precursor. The precursor which was used in the preparation of YBCO thick films was produced using sol gel route technique. The screen printing technique was used in the fabrication of YBCO superconducting thick films on yttria stabilized zirconia (YSZ) substrates. The effect of slow cooling rate and slow cooling window on texturing, microstructure and superconducting properties of the melt processed films was carried out. Optimizing the melt processing program was effective in increasing the molten viscosity, keeping the liquid and hence relatively large grain size that has been obtained. Moreover, grain morphologies like which was found in YBCO bulk materials was observed.

Increase of critical current density with doping carbon nano-tubes in YBa 2Cu 3O 7−δ

The effects of carbon nano-tubes (CNTs) on the crystal structure and superconducting properties of YBa 2Cu 3O 7− δ (Y-123) compound were studied. Samples were synthesized using standard solid-state reaction technique by adding CNT up to 1 wt% and X-ray diffraction data confirm the single phase orthorhombic structure for all the samples. Current–voltage measurements in magnetic fields up to 9 T were used to study the pinning energy U J and critical current density J c as a function of magnetic field at fixed temperature. We find that while T c does not change much with the CNT doping (91–92 K), both U J and J c increase systematically up to 0.7 wt% CNT doping in a broad magnetic field ranges between 0.1 and 9 T and J c in the 0.7 wt% CNT doped sample is at least 10 times larger than that of the pure Y-123. The scanning electron microscope image shows that CNTs are forming an electrical-network between grains. These observations suggest that the CNT addition to the Y-123-compounds improve the electrical connection between superconducting grains to result in the J c increase.

Systematic study of the BaSnO3 insertion effect on the properties ofYBa2Cu3O7−x films prepared by pulsed laser ablation

YBa2Cu3O7−x+BaSnO3 (YBCO + BSO) mixed films with increasing BSO content were prepared onSrTiO3 substrates by pulsed laser deposition fromYBCO+x wt% BSOmixed targets (x = 2, 3, 4, 5, 6, 8 and 9 wt%). Transmission electron microscopy (TEM) images reveal that BSOis incorporated into the YBCO matrix in form of nanorods, whose density andsize increase with increasing BSO content. The pinning properties for the mixedYBCO + BSO film were systematically studied. The 4 wt% sample presents the maximum global pinning forcesFP at all consideredtemperatures: 28.3 GN m−3 near 2 T at 77 K, 103 GN m−3 near 5 T at 65 K, and>241 GN m−3 near 9 T at 40 K.

Controllable generation of harmonics by means of YBa2Cu3O7 − x superconductors

The nonlinear magnetic properties of YBa2Cu3O7 − x high-temperature superconducting polycrystals are investigated. Using the results of investigations as a basis, a method for controlling the amplitudes of generated magnetization harmonics is worked out and a controllable harmonic generator is devised. The amplitudes of the harmonics are controlled by means of a permanent magnetic field or current. The use of YBa2Cu3O7 − x polycrystals makes it possible to produce a spectrum with offering a large number of higher harmonics. An YBa2Cu3O7 − x-based device has a wide dynamic range; its design is simple and reliable in a wide interval of the amplitudes of an input signal.

Effect of Firing Temperature on the Structure and Properties of YBa2Cu3O7−x Films by TFA-MOD Method

YBa2Cu3O7−x (YBCO) films were fabricated on LaAlO3 (LAO) substrate under various firing temperatures (760–870 °C) in the crystallization process by metalorganic deposition (MOD) method using trifluoroacetates. The effect of firing temperature on the structure and properties of YBCO films was systematically investigated. According to the XRD and SEM images, the films fired at low temperature (760–800 °C) showed poor electrical performance due to rough surfaces and impurity phases. However, the films fired at 850 °C showed the highest critical temperature of 90 K and the highest J c of 3.1 MA/cm2 which attribute to the formation of a purer YBCO phase, fewer pores, and stronger biaxial texture.

Anisotropy of the resistivity and critical current density of porous vicinalYBa2Cu3O7−δ films

The anisotropy of electrical transport properties ofYBa2Cu3O7−δ (YBCO) films containing high density nanopores grown on5°,10° and 20° vicinal substrates was investigated. For porous films in the normal state, the resistivity in thelongitudinal direction is comparable to that of reference YBCO films without nanopores. In addition,the ρc/ρab ratios derived from the resistivities in longitudinal and transverse directions of theporous samples fall in the same range as that of twinned single crystal YBCO. Forthe superconducting state, the pore surfaces provide strong magnetic pins tomagnetic vortices, which leads to significantly increased critical current densityJc along the longitudinal direction as compared to that of the referenceYBCO films. This strong isotropic pore surface pinning also increased theJc along the transverse direction as compared to that of nonporous vicinal YBCO films. Thisresult suggests that the effect of nanopores on the electronic structure of YBCO is minimaland the strong pore surface pinning may provide an effective way to enhanceJc after optimization.

Detailed magnetization study of superconducting properties ofYBa2Cu3O7−x ceramic spheres

We present a magnetization study of low densityYBa2Cu3O7−x ceramics carried outin magnetic fields H such that 0.5 Oe<H<50 kOe. It was demonstrated that superconducting links betweengrains may be completely suppressed either by a magnetic fieldH∼100 Oe (at low temperatures) or by an increase of temperature to above 70 K.This property of the present samples allowed us to evaluate the ratiobetween the average grain size and the magnetic field penetration depthλ. Furthermore,at temperatures T>85 K, using low field magnetization measurements, we were able to evaluate the temperature dependenceof λ, which turned out to be very close to predictions from conventional Ginzburg–Landautheory. Although the present samples consisted of randomly orientedgrains, specifics of magnetization measurements allowed for evaluation ofλab(T). Good agreement between our estimation of the grain size and the real sample structureprovides evidence for the validity of this analysis of magnetization data. Measurements ofthe equilibrium magnetization in high magnetic fields were used for evaluation ofHc2(T). At temperaturesclose to Tc, the Hc2(T) dependence turned out to be linear, in agreement with Ginzburg–Landau theory. The value of the temperatureat which Hc2 vanishes coincides with the superconducting critical temperature evaluated from low fieldmeasurements, which is important evidence of the validity of both approaches to theanalysis of magnetization data.