YBa2Cu3O7 Films Research Articles

Study of the pinned vortex fraction in the single crystal YBaCuO films

In this work we intend to study the pinned vortex fraction in type II superconductors. The sample used is the YBa2Cu3O7-γ. In continuation one will study the variations of this fraction according to the transport current density for two values of magnetic field (H = 0.6 T and H = 1.2 T) , and different values of temperature. The studied sample is a monocristalline YBaCuO thin film deposited by the ablation laser method on the surface (001) of a SrTiO3 substrate. In zero magnetic field, the resistance vanished a Tc = 90 K. The C-axis of YBaCuO is perpendicular to surface of the film. Electrodes of measurement are in gold and deposited on the surface of the sample in situ by evaporation. The film has a thickness of 400 nm, and a width 7.53 μm. The distance between electrodes of power measurement is 135 μm. Contact resistances were less than 1Ω.

Comparison of the superconducting transition properties of YBa2Cu3O7 nanobridges with and without a twin boundary

We have fabricated nanobridges from YBa2Cu3O7 films deposited on LaAlO3 substrates by using a focused ion beam technique and studied their superconducting transition properties with and without a twin boundary (TB) crossing the bridge. The nanobridge dimensions were 200–500 nm in width and length, and 100 nm in thickness. All the nanobridges studied with or without a TB had a superconducting transition temperature Tc of 90 K with a zero-resistance transition at 86.5 K and high critical current density of ∼1 × 107 A/cm2 at 77 K. However, the current-voltage curves for the nanobridges with a TB showed Josephson tunneling characteristics near the transition, which is in clear contrast to the flux-flow-type transition behavior of those without a TB. According to a crystallographic analysis with d-wave symmetry of YBCO, the small mismatch angle of the TB itself was not sufficient to cause the Josephson effect. Secondary effects, such as stress and strain, are believed to be the origin.

Low-Noise Nano Superconducting Quantum Interference Device Operating in Tesla Magnetic Fields

Superconductivity in the cuprate YBa(2)Cu(3)O(7) (YBCO) persists up to huge magnetic fields (B) up to several tens of Teslas, and sensitive direct current (dc) superconducting quantum interference devices (SQUIDs) can be realized in epitaxially grown YBCO films by using grain boundary Josephson junctions (GBJs). Here we present the realization of high-quality YBCO nanoSQUIDs, patterned by focused ion beam milling. We demonstrate low-noise performance of such a SQUID up to B = 1 T applied parallel to the plane of the SQUID loop at the temperature T = 4.2 K. The GBJs are shunted by a thin Au layer to provide nonhysteretic current voltage characteristics, and the SQUID incorporates a 90 nm wide constriction which is used for on-chip modulation of the magnetic flux through the SQUID loop. The white flux noise of the device increases only slightly from 1.3 μΦ(0)/(Hz)(1/2) at B = 0 to 2.3 μΦ(0)/(Hz))(1/2) at 1 T. Assuming that a point-like magnetic particle with magnetization in the plane of the SQUID loop is placed directly on top of the constriction and taking into account the geometry of the SQUID, we calculate a spin sensitivity S(μ)(1/2) = 62 μ(B)/(Hz))(1/2) at B = 0 and 110 μ(B)/(Hz))(1/2) at 1 T. The demonstration of low noise of such a SQUID in Tesla fields is a decisive step toward utilizing the full potential of ultrasensitive nanoSQUIDs for direct measurements of magnetic hysteresis curves of magnetic nanoparticles and molecular magnets.

Semiconducting YBaCuO films grown on silicon substrates: IR room temperature sensing and fast pyroelectric response

YBa2Cu3O6+x (YBCO) oxides, well known as superconductors for x > 0. 5, are semiconductors (SC) for lower oxygen content. SC films DC sputtered at 150 °C in amorphous form (a-YBCO) exhibited a temperature coefficient of resistance competitive with other bolometric sensing materials. Such deposition conditions are highly beneficial to integrate a radiation detector on a silicon chip bearing already processed readout electronics. IR detector structures have been processed: simple planar or more advanced metal/a-YBCO/metal trilayers. IR response was investigated at 850 nm as a function of the modulation frequency. The planar structure exhibited a regular bolometric response below 100 Hz, then a pyroelectric high-pass response up to 100 kHz. The trilayer device only exhibited the pyroelectric behavior up to 100 kHz . In the pyroelectric regime, detectivity values peaked above 2×108 cm Hz½/W with time constants in the μs range, under both DC biased and unbiased conditions.

4-fold enhancement in the critical current density of YBa2Cu3O7 films by practical ion irradiation

We report an up-to-4-fold enhancement in the in-magnetic-field critical current density at 77 K of epitaxial YBa2Cu3O7 films on CeO2-buffered SrTiO3 substrates by 3-MeV Au2+ irradiation. This indicates that irradiation using an industrially practical ion beam, which generally has kinetic energy less than 5 MeV, can provide a substantial increase in the in-field current performance of high-temperature superconductor films. Transmission electron microscopy results show that point-like defects smaller than 6 nm in diameter were created in the films by the irradiation.

Solution-derived YBa2Cu3O7 nanocomposite films with a Ba2YTaO6 secondary phase for improved superconducting properties

We report on the spontaneous segregation of double perovskite Ba2YTaO6 (BYTO) nanoparticles within YBa2Cu3O7 (YBCO) films forming a nanocomposite with two ternary oxides by the low cost and scalable chemical solution trifluoroacetate approach. Phase orientation, nanostructural and pinning studies are carried out by 2D x-ray diffraction, advanced scanning transmission electron microscopy and transport measurements, respectively. In this complex oxide nanocomposite system (YBCO–BYTO) the majority of the nanoparticles segregated within the (00l)-oriented superconducting matrix are randomly oriented. The presence of randomly oriented nanoparticles plays a key role in the generation of localized highly strained areas within the YBCO matrix which are suggested to strongly affect the superconducting properties. The incorporation of 6–10% of BYTO resulted in a maximum pinning force, at 77 K, three times higher than that obtained for a pristine sample, while Tc was maintained at 89–90 K.

Textured YBCO films grown on wires: application to superconducting cables

Efforts to fabricate superconducting wires made of YBa2Cu3O7 (YBCO) on La2Zr2O7 (LZO) buffered and biaxially textured Ni-5 at.%W (NiW) are described. Wires were manually shaped from LZO buffered NiW tapes. Different diameters were produced: 1.5, 2 and 3 mm. The wires were further covered with YBCO grown by metal organic chemical vapor deposition (MOCVD). We developed an original device in which the round substrate undergoes an alternated rotation of 180° around its axis in addition to a reel-to-reel translation. This new approach allows covering the whole circumference of the wire with a YBCO layer. This was confirmed by energy dispersive x-ray spectroscopy (EDX) analysis coupled to a scanning electron microscope (SEM). For all wire diameters, the YBCO layer thickness varied from 300 to 450 nm, and the cationic composition was respected. Electron backscattering diffraction (EBSD) measurements were performed directly on an as-deposited wire without surface preparation allowing the investigation of the crystalline quality of the film surface. Combining EBSD with XRD results we show that YBCO grows epitaxially on the LZO buffered NiW wires. For the first time, superconductive behaviors have been detected on round substrates in both the rolling and circular direction. Jc reached 0.3 MA cm−2 as measured at 77 K by transport and third-harmonic detection. Those preliminary results confirm the effectiveness of the MOCVD for complex geometries, especially for YBCO deposition on small diameter wires. This approach opens huge perspectives for the elaboration of a new generation of YBCO-based round conductors.

Evaluation of vortex pinning across low angle grain boundary in YBa2Cu3O7 film

Vortex pinning potential across a 5° tilt low angle grain boundary (GB) was evaluated by measuring angular dependences of critical current density in a bicrystal YBa2Cu3O7 film under the variable Lorentz force configuration. Trapping angles of the GB depend on directions in the GB plane (70°–80° and 15°–45° for the c-axis direction and the ab plane one, respectively), due to anisotropic pinning of GB dislocations. Pinning potential across a GB is as large as that of heavy ion irradiated columnar defects, indicating that density and distribution of GBs should be controlled to improve vortex pinning in coated conductors.

Magnetic pinning effects of epitaxial LaxSr1−xMnO3 nanostructured thin films on YBa2Cu3O7−δ layers

The present paper presents the effects of a nanostructured, ferromagnetic La1−xSrxMnO3(LSMO) thin film on the pinning characteristics of an epitaxial YBa2Cu3O7(YBCO) thin film deposited on top. Ordered arrays of LSMO grains were obtained upon growing the film on a terraced (001) SrTiO3 substrate. The analyses of magnetic measurements revealed the presence of a complex vortex pinning mechanism within the YBCO film. With respect to a reference single YBCO layer, an additional pinning potential was observed. Its temperature evolution suggests that a magnetic pinning mechanism is responsible for improved pinning characteristics in the high temperature and field region. Based on the morphology of the underlying LSMO buffer, a strong pinning force is expected to arise due to the anti-dot formations, where a high magnetization gradient exists.

Development of YBa2Cu3O7− δ superconducting thick film on Ba2SmSbO6 substrate material synthesised by combustion technique

Nanoparticles of samarium barium antimonate (Ba2SmSbO6), a complex perovskite has been synthesised using an auto-ignition combustion process. The nanoparticles thus obtained have been characterised using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The particle size of the as-prepared powder was in the range 50–110 nm. Superconducting YBa2Cu3O7− δ material was synthesised through solid-state route and the thick film of YBa2Cu3O7− δ material was fabricated by dip-coating on Ba2SmSbO6 substrate. The prepared samples were subjected to various studies such as XRD, TEM, scanning electron microscopy, and resistivity measurement and the obtained results are presented and discussed.

Structural defects in trifluoroacetate derived YBa2Cu3O7 thin films

We present an accurate description of the structural defects occurring within YBa2Cu3O7 (YBCO) films grown by chemical solution deposition (CSD) based on metal trifluoroacetates (TFA). Transmission electron microscopy (TEM) is the essential tool to identify and evaluate the microstructural defects that might act as natural pinning centers. Our study of TFA–YBCO thin films shows that the YBCO thin films contain a variety of extended defects, such as intergrowths, twin boundaries and dislocations, mainly in the basal plane. These extended defects and their interaction make up a rich variety of key microstructural features that play an important role in the YBCO thin films physical properties and performance.

High critical current density and its magnetic fields dependence in (Sm,Eu,Gd)Ba2Cu3Oy films by using multiple targets

Melt textured bulks of (Sm0.33Eu0.33Gd0.33)Ba2Cu3Oy (SEG123) show high Jc compared with that of YBa2Cu3Oy (Y123), because of nanoscopic network consisting of crossing rare earth (RE) compositional stripes. In this study, we fabricated SEG123 films by using pulsed laser deposition (PLD) method on LaAlO3 (LAO) substrates and evaluated the Jc and Tc in magnetic field. Jc of the SEG123 film was typically 1.4MA/cm2 at 77K in self-field. Jc in self-field of SEG123, Y123 and Sm123 films were almost the same value, however, Jc in magnetic fields showed a notable difference. The Jc of SEG123 film were 62.7kA/cm2 at 5T. We conclude that the Jc in magnetic fields were improved by RE-rich particle made of RE/Ba substitution acting as 3-dimensional pinning centers. Moreover we have confirmed that the superconducting properties changes by varying Sm, Eu and Gd composition ratio.

Temperature dependence of magnetic-field angle dependent critical current density and the flux pinning in YBa2Cu3O7 thin films

The magnetic-field angle dependence of the critical current density Jc(H, θ) was measured over a wide temperature range (20–85K) in high-Jc YBa2Cu3O7 (YBCO) and DyBa2Cu3O7 (DyBCO) epitaxial films belonging to two categories. The films in the first category were prepared by thermal co-evaporation and were characterized by a high density of nanometer-sized precipitates (mostly<7nm), which act as small random (point) pins. The films in the second category were prepared by fluorine-free metalorganic deposition (FF-MOD), whose primary pinning centers were recently revealed to be dislocations (linear pins) associated with stacking faults parallel to the ab-plane. Relatively broad Jc(θ) peaks around H//ab in the shape of a stratovolcano were observed at 77–80K in the co-evaporated YBCO and DyBCO films in the first category, and the Jc(H, θ) data were scaled to be a single curve when plotted against scaled fields using an effective anisotropy parameter. However, the Jc(θ) curves became more gradual at 60–70K and the scaling behavior was broken because the radius of nano-precipitates was not sufficiently smaller than the temperature dependent Ginzburg–Landau coherence length ξ(T) at these temperatures. In contrast, sharp Jc(θ) peaks around H//ab were observed in the FF-MOD YBCO films in the second category at all temperatures in the range 20–85K. Anisotropic scaling analysis showed that the pinning was apparently due to small random pins and pins correlated with the ab-plane, and the linear pins whose radius is sufficiently smaller than ξ(T) can cause the observed Jc(H, θ). The temperature dependence of Jc due mainly to the random pinning was approximately ∼(1−T/Tc)2(1+T/Tc)2 for the FF-MOD thin films (dislocation pins), which is consistent with a simple theoretical model based on core pinning interactions. The T dependence of Jc for the co-evaporated films (nano-precipitate pins) was ∼(1−T/Tc)m (1+T/Tc)2 (m=2.1–2.6), which deviates from m=2.5 expected from the simple theoretical model because nano-precipitates are not sufficiently smaller than ξ(T) at T⩽70K.

Transition properties of a YBa2Cu3O7 nanobridge patterned across a twin boundary of a LaAlO3 substrate

We have fabricated superconducting YBa2Cu3O7 (YBCO) nanobridges across twin boundaries of LaAlO3 (LAO) substrates by using focused-ion-beam etching and studied their critical transport properties. The nanobridges, nominally 150 nm in width, 100 – 120 nm in length, and 100 nm in thickness, showed Tc = 91 K with ΔTc ≅ 1 K and a high critical current density of Jc ≅ 1.5 × 107 A/cm2 at 77 K. Measured current-voltage curves of YBCO nanobridges across the substrate twin boundary showed resistively-shunted-junction characteristics near the transition with an excess current associated with flux flow. High-resolution X-ray diffraction spectra strongly indicated the possibility that the epitaxially-grown YBCO film was also twinned commensurate with twinning of the LAO substrate. Misorientation of the c-axis of YBCO at the twin boundary is believed to create weaknesses that dictate the behavior of the bridge across the twin boundary.

Electroresistance and magnetoresistance effects in superconductor–insulator–ferromagnet hybrid structures

We investigated superconducting YBa2Cu3O7 (YBCO), insulator SrTiO3 (STO), and ferromagnetic La2/3Ca1/3MnO3 (LCMO) multilayered heterostructures grown by pulsed laser deposition (PLD) on 〈100〉 YSZ substrates. These hybrid structures have demonstrated strong superconducting properties, similar to those of YBCO films, with a minimum influence of the ferromagnetic layer. We report unusual transport properties and negative differential resistance above the superconducting transition. The electro- and magnetoresistance effects observed in a hybrid YBCO micro-bridge with a top LCMO layer may be the consequence of phase separation induced by electric current.

Epitaxial Growth of YBa2Cu3O7 Films onto LaAlO3 (100) by Using Oxalates

Abstract Due to the current necessity to obtain epitaxial superconductor films at low cost, we report the growth of YBa2Cu3O7 (Y123) films by chemical deposition. The procedure involved simple steps such as precipitation of stoichiometric amounts of yttrium, barium and copper acetates in oxalic acid (H2C2O4). The precursor solution was dripped onto LaAlO3 (100) substrates with the help of a Fisher pipette. The films were annealed in oxygen atmosphere during 12 h at three different temperatures: 820 °C, 840 °C and 860 °C. After 820 °C and 860 °C annealing, X-ray diffraction (XRD) analysis revealed high intensity of the ( 00l ) reflections denoting that most of the Y123 grains were c-axis oriented. In addition, we also observed a-axis oriented grains (( h00 ) reflexion), minor randomly oriented grains and other phases (such as Y2BaCuO5 and CuO). In contrast, the sample treated at 840 °C, we noticed c – and a-axis oriented grains, very small amounts of randomly oriented grains without formation of other phases. From the magnetization versus temperature measurements, the critical temperatures were estimated at 70K and 90K for the samples annealed at 820 °C and 860 °C respectively.

Partial Substitution of Rare-Earth Ions for Yttrium Through Multi-Layer Precursors in the YBa2Cu3O7 Films Grown by Fluorine-Free Metal Organic Deposition

Abstract We have studied the effects of partial substitution of rare-earth (RE) ions for yttrium in YBa2Cu3O7 films prepared by fluorine-free metal organic deposition. The substitution was conducted through Y/RE multi-layer precursor films. We found that critical current density ( J c) in self field strongly depends on RE elements and increased by up to 44% with respect to an unsubstituted sample. Structural characteristics of the films were investigated using x-ray diffraction and transmission/scanning electron microscope, and we found several characteristic RE-dependences indicative of their close relation to the J c enhancement.

Enhancement of in-field critical current density by irradiation of MeV-energy ions in YBCO films prepared by fluorine-free metal-organic deposition

Abstract We performed irradiation of epitaxial YBa2Cu3O7 films grown on CeO2-buffered SrTiO3 substrates by fluorine-free metal organic deposition with 3-MeV Fe2+ ions to study their effects on critical current density (Jc). We observed an increase of in-field Jc by up to 70%, which did not show a significant field-angle dependence. Since the ion energy used in this study is two orders of magnitude lower than those in majority of the previous works with a similar concept, our results indicate that the enhancement of Jc by ion irradiation in high-temperature superconducting films has wider processing window than previously recognized.

Nanostructured phase formation in YBa2Cu3O7/LaAlO3 and YBa2Cu3O7/CeO2/(Ni-W) prepared by deposition from metalorganic solutions

Continuous, phase-pure, oriented yttrium barium cuprate (YBa2Cu3O7) films have been grown by deposition from metalorganic solutions onto lanthanum aluminate substrates and a nickel-tungsten tape with a barrier ceria layer. A “through” process has been used in which a ceria barrier layer and yttrium barium cuprate film grow from chemical solutions. In all steps of the process, the elemental composition of the deposits (Y: Ba: Cu molar ratio) was close to 1: 2: 3. The nanometer-scale structural evolution and phase formation in the YBa2Cu3O7 films have been studied in detail. Depending on synthesis conditions, yttrium barium cuprate films may consist of three-dimensional, platelike, or flaky micro- and nanocrystallites. The degree of orientation of the atomic lattice of the targeted film may vary from partial ordering to a planar texture with an 〈001〉 axis normal to the substrate and with a pronounced azimuthal orientation of the crystallites. The degree of orientation was higher when trifluoroacetate solutions were used.

Effects of Sm-doping on Structures and Properties of YBCO Coated Conductors Fabricated by TFA-MOD Process

The Sm-doping YBCO films, Y1−xSmxBa2Cu3Oy and Y1SmxBa2−xCu3Oy (x=0.1, 0.3), were fabricated on LAO (00l) single-crystal substrates by TFA-MOD process in order to improve the superconducting properties of YBCO films. The XRD analyses indicated that these samples have a strong c-axis texture, but the secondary phase of BaCuO2 are found from Y1SmxBa2−xCu3Oy films with Sm3+ substitution on Ba2+ sites. High quality surface, better in-plane and out-of-plane texture of the Sm-doping films have been obtained compared with that of the undoped YBCO film. The Y0.9Sm0.1Ba2Cu3Oy films showed the highest value of Tc and Jc in self-field. Superconducting properties of all Sm-doping films are better than those of the pure film. These results strongly suggest that Sm-substitution on Y or Ba sites of YBCO phase is a powerful method to efficiently improve Jc and introduce artificial pinning centers in YBCO films.