Pure YBCO Films Research Articles

Film growth of BaZrO3-doped YBa2Cu3O7−δ by using fluorine-free metal–organic deposition

In this study, BaZrO3 (BZO)-doped YBCO films were fabricated on SrTiO3(100) single-crystal substrates by a fluorine-free metal–organic deposition (MOD) process. We added extra Ba and Zr organic salts, which formed well-dispersed ∼10–25 nm sized BaZrO3 nanoparticles in the YBCO films. The in-field critical current density (Jc) and the peak pinning force (Fp) were greatly enhanced in the BZO-doped sample at 77 K relative to pure YBCO films. The optimal BZO content that gave the highest peak pinning force of ∼10 GN m−3 in a ∼180 nm thick film was found to be x = 0.10 for YBCO + xBZO films, where x is moles of BZO per 1 mol of YBCO. The angular dependence of in-field Jc measurements shows the BZO nanoparticles increased Jc over the entire angular range and also reduced the angular anisotropy measured at 4 T at 77 K.

Enhanced flux pinning in MOD-YBCO films with co-doping of BaZrO 3 and Y 2O 3 nanoparticles

A combined BaZrO 3 (BZO) and Y 2O 3 nanoparticles has been achieved in YBa 2Cu 3O 7− x (YBCO) films by metalorganic deposition using trifluoroacetates (TFA-MOD). The formation of integrated nanoparticles increases the critical current density ( J c) of Y 2O 3/BZO doped-YBCO films while keeping the critical transition temperature ( T c) close to that in the pure YBCO films. The YBCO film with 7.0 mol.% BZO and 7.0 mol.% Y 2O 3 showed T c value of 90 K and J c value of 6.5 mA/cm 2 at self-field (0 T, 77 K). The strongly enhanced flux pinning over a wide range of magnetic field can be attributed to the combined different crystal structures of BZO and Y 2O 3 created by optimized TFA-MOD conditions.

Preparation of solution-based YBCO films with BaSnO 3 particles

The YBCO films with BaSnO 3 (BSO) particles were prepared on LAO (0 0 1) substrates by metal organic deposition using trifluoroacetates (TFA-MOD) via introducing SnCl 4 powders into the YBCO precursor solution. It was found that with the increase of the SnCl 4 contents, the slower decomposition and higher temperature for nucleation during the reaction were requested compared to that of pure YBCO film. The YBCO films with different contents of Sn with dense surface and well c-alignment were obtained under optimized heat treatment, and the BaSnO 3 phases were detected by XRD analysis. Litter effect of BSO particles on the T c and J c values of YBCO films was found. All YBCO films with BSO particles had T c values over 90 K and J c values over 1 MA/cm 2. A significant enhancement of J c was observed for YBCO films with BSO particles compared to that of pure YBCO film by the field dependence of J c values. The best property was obtained for YBCO film with 6 mol.% Sn at 77 K under magnetic field. The results showed that the J c value of YBCO film with 6 mol.% Sn was enhanced by a factor of 2 in 2 T, and over a factor of 10 beyond 4 T compared to that of pure YBCO film.

Integrated nanotechnology of pinning centers inYBa2Cu3Ox films

A controlled pinning change from theab-plane dominantto the c-axis dominant has been achieved in a novel method of nanostructuredYBa2Cu3Ox (YBCO) growth. The method is a synchronous self-assembly ofBaZrO3 (BZO) and Ag-assisted YBCO nanothreads. The formation of entangled nanothreads increasesthe critical current density while keeping the critical temperature close to that in pureYBCO films. The nanothreads extend through the whole thickness of thick films, makingthe method suitable for increasing total critical current density per centimeter of width (Ic − w). Two growth mechanisms, the formation of BZO nanorods and YBCOnanocolumns, complement each other, form a coherent structure and producesamples with strong correlated pinning. In addition to the increase inIc − w, correlated pinning leads to an increase in vortex melting temperature in awide range of magnetic fields. The films grown by this method have highIc − w both in low magnetic fieldsalong the c axis and highmagnetic fields in the ab plane of YBCO. Such a superconductor would be suitable for both cable and magnetapplications.

Nanotechnology as a way to overcome the rapid Jc fall with HTS film thickness

We have carried out a comprehensive study of a relation between the nanostructure and electromagnetic properties of the films prepared by pulse laser deposition on LaAlO3 substrates using YBCO targets with BaZrO3 additives. HREM studies revealed that depending on the deposition conditions BZO can precipitate as nanorods normal to the substrate or as BaYZrxOy nano-pancakes. BZO nanorods are formed at lower laser power and higher substrate temperature. Their lattice is rotated by 3-4° to provide matching with matrix without dislocations. In a contrary, the nano-pancakes are surrounded with a great number of dislocations. Mechanisms of the nanostructure formation have been analyzed. Embedding of a proper kind of nanoparticles into HTS films leads not only to a certain increase of the critical current density Jc but to a substantial weakening of its field and thickness dependences compared with pure YBCO films. Negative curvature of I-V-curves (in double-log scale) for YBCO (BZO) films is an evidence of strong pinning on extended defects, such as nanorods and threading dislocations, and/or collective vortex pinning.

Enhanced Flux Pinning in YBCO+YSZ Composite Films Grown by TFA-MOD Method

More attention was paid to the fact that columnar defects generated by introducing nano-particles into YBCO films can improve the in-field superconducting properties of YBCO as pinning centers. Epitaxial YBCO films with self-assembled Yttrium-stabilized Zirconia (YSZ) nano-particles have been successfully prepared by TFA-MOD based on different solutions and the effect of nano-particle dopants on the field properties of YBCO films was investigated by analyzing the results obtained by PPMS according to the Bean Model. The critical current densities (Jc) of YBCO films with YSZ nano-particle were found to be improved with respect to pure YBCO films in range of 0-5 T. The Jc value of YBCO film with YSZ dopant was 0.2 MA/cm2 at 50 K and 4 T field, which is 4 times higher than that of pure YBCO film. Furthermore, an optimized property was observed for YBCO films doped by 6 mol.% YSZ nano-particle shown by the dependence relationship between Jc value and field for YBCO films with different amount of YSZ dopants.

Flux pinning of stress-induced magnetic inhomogeneity in the bilayers of YBa2Cu3O7−δ/La0.67Sr0.33MnO3−δ

Elaborately designed bilayers consisting of epitaxial YBa2Cu3O7−δ (YBCO) and La0.67Sr0.33MnO3−δ (LSMO) films were fabricated by pulsed laser deposition with respect to the investigation into magnetic-dependent vortex pinning effect. The improvement in the critical current density and a pronounced upward shift in the superconducting irreversibility line based on magnetotransport measurements are observed when compared to the pure YBCO film, suggesting the enhancement in flux pinning in the studied bilayer. It is believed that the improved flux pinning for YBCO arises from the magnetic inhomogeneity of the underlying LSMO. Magnetization measurements show a nonuniform magnetic state in the LSMO film, most probably being macroscopically phase-separated clusters with ferromagnetic (FM) and anti-FM domains, which can be caused by the epitaxial strain due to the lattice mismatch. Such a magnetic disorder is hardly affected by the external magnetic field, unlike the magnetic disorder induced by the domain structures of FM materials where the magnetic domains naturally disappear as the applied field exceeds the coercive field. Hence, the present magnetic flux pinning may be stiff in the large magnetic fields, showing good prospects for artificial flux pinning enhancements.

Microstructural and Pinning Properties of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$ Thin Films Doped With Magnetic Nanoparticles

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we report a strong enhancement in the in-field transport properties of the <formula formulatype="inline"><tex Notation="TeX">${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-\delta}$</tex></formula> (YBCO) thin films doped with magnetic <formula formulatype="inline"><tex Notation="TeX">${\rm Fe}_{2}{\rm O}_{3}$</tex></formula> nanoparticles. We incorporated magnetic <formula formulatype="inline"><tex Notation="TeX">${\rm Fe}_{2}{\rm O}_{3}$</tex></formula> nanoparticles with two different architectures by laser ablation of the YBCO and dopant targets. YBCO film thickness was controlled at around 1 <formula formulatype="inline"> <tex Notation="TeX">$\mu{\rm m}$</tex></formula> for all the samples. We conducted a detailed microstructural characterization on all the doped samples by X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM) and compared with the pure YBCO films. A systematic study on the superconducting properties has been conducted on all the thin film samples. The critical current densities at both self-field and in-field (<formula formulatype="inline"> <tex Notation="TeX">$J_{c}^{sf}$</tex></formula> and <formula formulatype="inline"> <tex Notation="TeX">$J_{c}^{in-field}\ ({\rm H}//c)$</tex></formula>) and the critical transition temperature <formula formulatype="inline"><tex Notation="TeX">$(T_{c})$</tex> </formula> of the doped and un-doped YBCO sample were measured by a Superconducting Quantum Interference Device (SQUID). The <formula formulatype="inline"><tex Notation="TeX">$T_{c}$</tex></formula> of the doped YBCO films varies from 84 K–90 K and the <formula formulatype="inline"><tex Notation="TeX">$J_{c}$</tex> </formula> is in the range of 1.2–3.9 <formula formulatype="inline"> <tex Notation="TeX">${\rm MA/cm}^{2}$</tex></formula> (at 65 K) depending on the doping approach. The pinning properties of these doped YBCO films were explored at different temperatures (5 K, 40 K, and 65 K) and correlated with their microstructural characteristics. </para>

Study of Columnar Defect Formation in MOD YBCO Film Using Chemical Doping

This paper describes a promising route to introduce columnar defects into YBCO films by chemical doping process. A series of Y2O3 and BaZrO3 doped YBCO films were fabricated by a TFA_MOD process. The Jc of Y2O3 doped YBCO film was found to be larger than that of pure YBCO film at all fields though no columnar defects were observed. On the other hand, high density nanoscale Zr enriched columnar defects were successfully achieved in Zr-doped YBCO. The size of these defects was as small as 10 nm. Effects of heat treatment temperatures (760degC ~ 820degC), dwell times (0.5 h ~ 3 h) and partial pressures of oxygen (0 ~ 1%) on defects formation in BaZrO3 doped YBCO were investigated. It was found that the formation of columnar defects depends on process conditions. Films with such nanoscale columnar defects exhibited a significant enhancement of Jc at all fields. Maximum pinning force density exceeding 8 GN m-3 was obtained in 5% BZO-doped YBCO films.

Enhancing critical current in YBCO thick films: Substrate decoration and quasi-superlattice approach

For power applications of superconducting films, the critical current density ( J c ) and the thickness of the film ( d) should be as high as possible. Since J c decreases with both thickness and magnetic field, artificial pinning centres in addition to natural ones are required to keep J c high. The earliest cost-effective method used for introducing artificial pinning centres was the so-called substrate decoration, i.e., growing nano-scale islands (nano-dots) of certain materials on the substrate prior to the deposition of the superconducting thin film. Later on another version of this approach proved to be successful: building up a layered distribution of a second phase using a multilayer deposition (quasi-superlattices). Several materials have been used for the creation of artificial pinning centres. Here we report on the artificial pinning centres induced in YBCO thick films by substrate decoration and quasi-superlattice approaches using nano-dots of Pd and non-superconducting YBCO. The cross-sectional AFM images show evidence of c-axis correlated columnar defects. These defects significantly contribute to the pinning of magnetic flux and increase critical current in the films. We observed an important shift of the position of the maximum in the thickness dependence of J c ( B) towards higher thicknesses compared with pure YBCO films by both approaches. A high J c ( B) in our quite thick films provides a very high total critical current per cm of the film width. Critical current as high as 800 A/cm width was achieved in a 2.4 μm thick quasi-superlattice film with non-superconducting YBCO nano-dots.

Formation identification of Y2BaCuO5 and BaCeO3 in MOCVD-processed YBCO films with Ce doping

The influence of nanosized secondary particles, such as those produced viarare-earth doping for example, on magnetic-field-induced flux motion inYBa2Cu3O7−δ (YBCO)-coated conductors has been investigated. In this study, we investigated the influence of Cedoping on nanosized secondary phase formation in YBCO films. Ce-doped YBCO films on singleSrTiO3 crystals were prepared via metal–organic chemical vapor deposition (MOCVD). For the first time, aY2BaCuO5 (Y211)secondary phase was observed in the Ce-doped YBCO film, while the pure YBCO film contained onlya Y2O3 secondary phase. As Ce doping concentration increased to 3 wt%, aBaCeO3 secondary phase developed. This was due to the low solubility limit of Ce for Y in the MOCVD YBCOfilm. Additionally, outgrowths on the Ce-doped YBCO film surfaces and defect structures, such asa-axis grains, were examined.

Heteroperovskite phase formation and magnetotransport properties of YBa2Cu3O7−x/SrRuO3 quasimultilayers

A series of quasimultilayers consisting of YBa2Cu3O7−δ (YBCO) and SrRuO3 (SRO), namely, p×(YBCO(m)/SRO(n)) (p: repetition periods; m: YBCO pulse number; n: SRO pulse number), is prepared on single crystal SrTiO3 by pulsed laser deposition. X-ray diffraction measurements reveal that a heterogeneous phase of Ba2YRuO6 is formed due to the chemical reaction, while both the in-plane and out-of-plane textures of the present quasimultilayers are as good as in the pure YBCO films. The content of Ba2YRuO6 increases as the pulse number of SRO increases, leading to the decrease in superconducting transition temperature (Tc). There is no obvious difference in Tc between the samples with the different deposition sequence orders of YBCO and SRO. The magnetic field dependence of critical current density (Jc) shows an enhanced flux pinning at relatively high fields for all the present quasimultilayers, which occurs at different ranges of fields depending on the applied temperatures. The Jc of the quasimultilayers can reach two times higher than that of pure YBCO films in a wide range of magnetic fields, which shows the promising application for coated conductors.

Superconducting properties of chromium Cr-YBCO grown by pulsed laser deposition

Thin superconducting films of type Chromium incorporated YBa2Cu3CrxO6+δ have been grown by Pulsed Laser Deposition (PLD). The prepared films have been characterized using X-ray powder diffraction (XRD) and Energy Dispersive X-Ray (EDS) analysis. The superconducting transition temperature Tc determined from electrical resistivity measurements was found to slightly increase for low Cr-content (x) and decreases when x > 0.05. Furthermore, the surface morphology of the Cr doped and the pure YBCO films were investigated by Scanning Probe Microscope (SPM).

Over–current carrying characteristics of rectangular–shaped YBCO thin films prepared by MOD method

A fault current limiter (FCL) may be manufactured at competitive qualities and prices by using rectangular-shaped YBCO films which are prepared by metal-organic deposition (MOD) method, because the MOD method can produce large size elements with a low-cost and non-vacuum technique. Prior to constructing a superconducting FCL (SFCL), AC over-current carrying experiments were conducted for 120 mm long elements where YBCO thin film of about 200 nm in thickness was coated on sapphire substrate with cerium oxide (CeO2) interlayer. In the experiments, only single cycle of the ac damping current of 50 Hz was applied to the pure YBCO element without protective metal coating or parallel resistor and the magnitude of the current was increased step by step until the breakdown phenomena occurred in the element. In each experiment, current waveforms flowing through the YBCO element and voltage waveform across the element were measured to get the voltage-current characteristics. The allowable over-current and generated voltage were successfully estimated for the pure YBCO films. It can be pointed out that the lower n-value trends to bring about the higher allowable over-current and the higher withstand voltage more than tens of volts. The YBCO film having higher n-value is sensitive to the over-current. Thus, some protective methods such as a metal coating should be employed for applying to the fault current limiter.

Magnetic pinning‐effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 bilayer

AbstractThe vortex lines of superconductor can be driven by electrical currents, which are often coupled with a reliable control of flux quanta movement by defects or magnetic domains. In this work, the magnetic pinning‐effect in Nd0.7Ca0.3MnO3/YBa2Cu3O7 (NCMO/YBCO) bilayers is investigated. It is found that by increasing the field from 0 to 5 Tesla, the critical current Ic of pure YBCO film at 50 K is suppressed by three orders of magnitude. However, in the NCMO/YBCO bilayer Ic is less sensitive to the field and maintains at the level of 100 mA at high field. This result indicates that the magnetic pining effect of NCMO is much more efficient than the conventional routes, which maybe related to the fine domain structure of NCMO film. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Epitaxial Growth of High-J c NdBa2Cu3O7−δ Films on RABiTS by Pulsed Laser Deposition

NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (NdBCO) films were grown on rolling-assisted biaxially textured substrates (RABiTS) via pulsed laser deposition. c-Axis-oriented epitaxial NdBCO films with high performance were obtained under optimal deposition conditions. Transmission electron microscopy analysis shows that the NdBCO film grown on RABiTS has a clear interface with a CeO{sub 2} cap layer and a nearly perfect lattice structure. The NdBCO film exhibits higher {Tc} of 93.7 K and better in-field J c in magnetic fields and at all field orientations, compared to pure YBCO films.

Flux pinning in MOD YBCO films by chemical doping

A novel nanomaterial synthesis technique has been developed to introduce 0D (particles),1D (columnar defects) and 3D (domains) nanoscale pinning centres in MODY1Ba2Cu3O7 (YBCO) coated conductors. We have succeeded in introducing nanoscale Y enriched particles, nanoscale90° rotated Y1/3Sm2/3Ba2Cu3O7 domains and nanoscale Zr enriched columnar defects into YBCOlayers by different chemical doping. The pinning force density inY2O3-doped YBCO film is found to be larger than that of pure YBCO film atall fields. Also it was found that YBCO films with Sm substituting for Yhave yielded improved critical current density characteristics over a widerange of magnetic fields. Maximum pinning force densities exceeding 7 and8 GN m−3 are obtained in 5% BZO-doped and Sm substituted YBCO films, respectively. Additionally,TEM studies revealed nanoscale Zr enriched columnar defects distributing in the matrix of thec-oriented YBCO film throughout the whole cross section. This indicates that chemicaldoping is a promising fabrication technique to create specific pinning landscapes in YBCOcoated conductors.

YBa2Cu3O7−x + YSZ mixed films with enhanced critical current densities in magnetic field

YBa2Cu3O7−x+YSZ (YBCO+YSZ) mixed films were prepared on SrTiO3/MgO substrates by pulsed laser deposition (PLD) from a YBCO target with thin YSZ sector on the top of the target. In comparison with a pure YBCO film, the Jc at 77K for mixed YBCO+YSZ thin film was enhanced from 1.46MA/cm2 to 1.95MA/cm2 (self-field) and from 0.09MA/cm2 to 0.28MA/cm2 (B∥c, B=5T) even when both films were prepared on the same deposition conditions. In the YSZ-added sample, the angular dependence of Jc shows a broad peak at B∥c, due to the flux pinning by c-axis correlated defects. Consistently, elongated nanorods grown in the direction parallel to c-axis were observed in cross-sectional TEM images.

Angular properties of pure and Ca-substituted YBa 2Cu 3O 7− δ superconducting thin films grown on SrTiO 3 and CeO 2 buffered Al 2O 3 substrates

In this work transport properties of superconducting 10 at.% Ca-substituted YBCO thin films grown on (1 0 0)-SrTiO 3 single crystal substrate (STO) and superconducting pure and 10 at.% Ca-substituted YBCO thin films grown on CeO 2 buffered Al 2O 3 substrates (CAO) have been analyzed as a function of the temperature, applied magnetic field and angle between magnetic field direction and the direction normal to the film surfaces. Particularly, the angular analysis provides an easy way to discriminate between isotropic point defects and correlated pinning sites. Despite the intragrain pinning mechanisms remained unaffected by Ca substitution, a detrimental effect on grain boundary properties clearly emerged for 10 at.% Ca concentration. This effect is enhanced in sample grown on CeO 2 buffered sapphire where a more disturbed grain boundary is expected resulting in an enhancement of the correlated pinning, already observed in pure YBCO films grown on CAO, and in a reduction of the intrinsic pinning efficiency.

Enhancement of critical current density of YBa 2Cu 3O 7 − δ thin films by self-assembly of Y 2O 3 nanoparticulates

YBa 2Cu 3O 7 − δ (YBCO) thin films, possessing high critical current density ( J c), have been synthesized by embedding a homogeneous array of Y 2O 3 non-superconducting nanoclusters/nanoparticles using a pulsed laser deposition technique. The size, interparticle spacing, and density of Y 2O 3 nanoparticles in YBCO thin films were tailored by varying the number of laser pulses in order to determine the optimum size for effective immobilization of vortices. Scanning transmission electron microscopy with atomic number contrast and X-ray diffraction techniques were used to determine the size and structure of the nanoparticles. Both techniques indicate that the Y 2O 3 particles are epitaxial with respect to the surrounding YBCO matrix. The information about pinning of vortices by the nanoparticles was obtained by investigating the behavior of critical current density as a function of temperature and applied field, which in turn determines the vortex density in the sample. The superconducting transition temperature ( T c) of YBCO films with the inclusion of nanoparticles was observed to remain almost the same or decrease marginally (1–2 K) with respect to T c of pure YBCO films deposited under identical conditions. However, J cs of YBCO films embedded with self-assembled nanoparticles were found to be significantly higher than that of pure YBCO films. The J c enhancement was up to five times in high magnetic field, which is a key requirement for practical application of high- T c materials.