YBCO Target Research Articles

High-density YBCO targets for sputtering with defect-free microstructure prepared by novel infiltration method

In this contribution, we demonstrate a new approach to the preparation of targets based on YBCO high-temperature superconductors, which are being used on large scale for thin-film superconductors deposition. The targets were manufactured by a new infiltration technique in a period of time less than 48 h. The phase composition of the final sample was analyzed by XRD, Rietveld refinement was used for the quantitative analysis. The microstructure of the final sample and the reference sample prepared by conventional target sintering was studied by SEM. The prepared target was also used for thin-film YBCO tape preparation by IJD in order to confirm the suitability of the novel technique. The prepared thin-layer was analyzed via XRD, SEM, EDS and optical microscopy. In addition, isothermal (T = 1250 K and T = 1325 K) isoactivity (pO2/p° = 0.21) sections of the Y-Ba-Cu-O phase diagram were calculated by FactSage program.

Control of the nanosized defect network in superconducting thin films by target grain size

A nanograined YBCO target, where a great number of grain boundaries, pores etc. exist, is shown to hold an alternative approach to future pulsed laser deposition based high-temperature superconductor thin film and coated conductor technologies. Although the nanograined material is introduced earlier, in this work, we comprehensively demonstrate the modified ablation process, together with unconventional nucleation and growth mechanisms that produces dramatically enhanced flux pinning properties. The results can be generalized to other complex magnetic oxides, where an increased number of defects are needed for modifying their magnetic and electrical properties, thus improving their usability in the future technological challenges.

Effect of Target Density on the Surface Morphology of Y-Ba-Cu-O Thin Films Prepared by Ionized Jet Deposition

Ionized jet deposition (IJD) is a pulse electron deposition method. It can be used for the preparation of thin films from a wide spectrum of materials on different substrates. The main benefits of IJD are high flexibility and a possibility to change many of the deposition parameters. Some of them even during the deposition such as acceleration voltage, working gas, substrate temperature, etc. The wide variability of the deposition parameters allows finding the ideal conditions for the preparation of thin films of almost any material. This deposition method has a great potential for a cost-effective scale-up of HTS (High-temperature Superconductors) tapes fabrication. This research is focused on the study of the influence of target density on the microstructure of the deposited YBCO thin layers. The target density has an important role in the morphology of thin films. In this work, the deposition parameters were fixed (except for target density). The distance between substrate and target was 110 mm and substrate temperatures were set to 650 °C. The targets and samples were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and LED Confocal profilometer. Nine different YBCO targets with densities from 3.8 g·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> to 5.6 g·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> were prepared in total. All targets were prepared from a single batch of precursor powder at ambient atmosphere and different sintering temperatures and times.

Diagnostics of target inhomogeneity and influence of YBCO target oxygen content on properties of HTSC 2G samples fabricated by PLD technique

The pulsed laser deposition (PLD) targets used for HTSC 2G fabrication should be uniform and chemically suitable to make long tapes with reproducible critical properties. We investigated inner density distribution of flat YBCO targets using non-destructive neutron introscopy and tomography techniques. The methods are based on absorption of monochromatic neutron beam which is going through the specimen. In first set of targets we measured variance of material density (up to 10-25%) with maxima density located in central layer of the target body. After updating of target fabrication technology no significant density inhomogeneity were detected. The dependence of critical current of superconducting films with thickness of 300 nm deposited on sapphire substrate with appropriate buffer layers using PLD YBCO targets with various oxygen content was also investigated. Oxygen index of YBCO targets vary from 6.12 to 6.85. No significant influence of target oxygen index on critical current density of fabricated films was detected.

人工ピン止め点(APCs)を導入したYBCO 薄膜の表面抵抗の磁場依存性

We investigated the effect of introducing artificial pinning centers (APCs) into YBCO thin films to reduce the Rs in a high magnetic field. YBCO thin films with and without APCs were deposited on MgO(100) substrates by using the pulsed laser deposition (PLD) technique. We used BaMO3 (BMO, M = Zr, Hf) doped YBCO targets. The Rs of thin films was measured at 21.8 GHz with the dielectric resonator method and a DC magnetic field of up to 5.0 T. The Rs values of 1.5 wt. % of the BHO doped films were approximately 1/2 compared with that of the Rs of the pure YBCO films. As a result, YBCO thin films with APCs could provide advantages for NMR application.

Characteristics of YBa2Cu3Oy coated conductors prepared by in-plume method

In order to increase a deposition rate, we prepared YBCO films on metal substrate and SrTiO3 single crystal substrate by in-plume PLD method and compared superconducting properties, deposition rate and composition ratio with those of films prepared by the conventional PLD method. Typical T c of the films prepared by the conventional PLD on the IBAD-MgO substrates were 89.7 K and typical J c were about 3.0 MA/cm2 at 77 K in self-field. On the contrary those of films by the in-plume PLD were 87.9 K and J c were about 0.9 MA/cm2. The deposition rate of the in-plume PLD was 2 μm/hour in thickness which was about twice higher than that of the conventional PLD. A reason of the low superconducting properties would be off-stoichiometry within the film, especially Ba deficient composition. To improve the composition ratio of the films, we used off-stoichiometric YBCO target and investigated the superconducting properties. We were able to improve the composition of the films. However J c values were not improved. The primal reason why the J c values were low would be an outgrowth within the films.

Synergetic Pinning Centers in YBa$_{2}{\hbox{Cu}}_{3}{\hbox{O}}_{\rm x}$ Films Through a Combination of Ag Nano-Dot Substrate Decoration, Ag/YBCO Quasi-Multilayers, and the Use of BaZrO$_{3}$-Doped Target

We report on an original technique for nanoengineered pinning centers that combine three previously reported approaches: substrate decoration, quasi-multilayers and targets with secondary phase nanoinclusions. We have used a 4% BZO-doped YBCO target, and Ag nanodots, all grown by PLD. Such an approach gave interesting results in terms of pinning landscape, as proved by TEM studies. Angle-dependent measurements of critical current Ic showed that, for smaller fields, the absolute maximum in Ic occur for fields perpendicular to the a-b planes, while at larger fields the absolute maximum in Ic occurs for fields parallel to the a-b planes, in both cases with a clear second, local maxima. Measurements also showed a smooth change in the character of pinning with magnetic field, from the out-of-plane to in-plane-dominant pinning. For the out-of-plane magnetic field, the highest Ic-w (critical current per cm width) obtained so far, at 77.3 K, occurred in a 5.8 μm Ag nanodots / BZO-doped YBCO trilayer: 782 A/cm-w in self-field, 167 A/cm-w in 1 T and 18 A/cm-w in 3 T.

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.

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>

Batch production of large-area double-sidedYBa2Cu3O7−δ thin films by DC magnetron sputtering

Using a novel DC magnetron sputtering system, high qualityYBa2Cu3O7−δ (YBCO) thin films were deposited on both sides of twelve pieces of 3-inchLaAlO3(00l) single crystal substrates in one batch. This sputtering system has a rotatable disc sample holder withthe LaAlO3 substrates being positioned in the middle of upper and lower YBCO targets. These twosputter guns are arranged to simultaneously deposit YBCO thin films on both sides of thesubstrate. The rotatable sample holder is an important approach to large scale depositionof high quality YBCO thin films. In this manner, the sputtered species can diffuse wellaround the substrates during one rotation cycle. Furthermore, the anode is installed in theinner of rotatable disc sample holder to avoid negative ion bombardment. Thus, a gooduniformity over the whole area for all the films has been realized. The full-width athalf-maximum (FWHM) values of the (005) rocking curves typically range from0.49° to0.56°. The superconducting critical temperatures fall in the range of89–90 K and the critical current densities are between 3.75 and4.0 MA cm−2 at 77 K. The microwavesurface resistance, RS (77 K, 10 GHz), of the YBCO thin films range typically from 0.56 to0.71 mΩ, which make these films suitable for microwave applications.

Critical current density and pinning potential inYBa2Cu3O7−δ thick filmsablated from a BaZrO3-doped nanocrystalline target

We report on the pulsed laser deposition and characterization of thick(1.27 µm) films ablated from ananocrystalline YBa2Cu3O7−δ (YBCO)target doped with 4 wt% BaZrO3 (BZO), nYBCO/BZO. DC magnetization measurements have shown a four- to five-fold increase in the critical current densityJc and a three- to four-fold increase in the maximum pinning force in comparison with1 µm thick films grown from a commercial microcrystalline YBCO target, at both 77.3and 65 K. We have found that the frequency-dependent critical current densitiesJc(f0/f) estimated from susceptibility measurements are linear in a double-logarithmic plot (wheref is the frequency ofthe AC field and f0 is a macroscopic attempt frequency of about106 Hz), consistent with a logarithmic dependence of the pinningpotential on the current density, and are again several times higher innYBCO/BZO thick films. Fromthe slopes of the Jc(f0/f) dependences we have also estimated the values of pinning potentials in fields between 3 and5 T.

Superconducting Properties of Films Deposited From Micro-, Nanocrystalline and Optimally BZO-Doped YBCO Targets

Thin YBa2Cu3O6+x (YBCO) films are prepared by pulsed laser deposition (PLD) from pure micro- (mu) and nanocrystalline (n) targets and a n-target optimally doped with 3.9 wt% BaZrO3 (BZO). Effects of target grain size and doping on superconducting (SC) properties of the films are investigated using a SQUID magnetometer up to 5 T and transport measurements in pulsed magnetic fiefds up to 30 T. In comparison with mu-films, clearly increased values of jc are observed in n-films. Optimal doping with BZO still increases this difference in high magnetic field range and lengthens the low-field plateau of jc(B) and increases the accommodation field B* which are typically around 110 mT, 160 mT and 500 mT at 5 K in mu-, n- and BZO-doped films, respectiveiy. Transport measurements at T > 65 K show significant improvement of irreversibiiity line (IRL) and jc(B) in films prepared from n-target and BZO-doped target. These improvements of the superconducting properties in high magnetic fiefds make pure and BZO-doped n-films attractive for high field applications.

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.

Insertion of nanoparticulate artificial pinning centres inYBa2Cu3O7−x films by laserablation of a Y2O3-surface modified target

YBa2Cu3O7−x+Y2O3 (YBCO+Y2O3) mixed filmswere prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thinY2O3 sector on the top. The pinning properties for the mixedYBCO+Y2O3 thin filmwere strongly enhanced, especially at the temperatures lower than 77 K: the maximum global pinning forcesFP for theY2O3 doped sampleare 7.8 GN m−3 near 2 T at77 K, 54.5 GN m−3 near 4 T at65 K, and 189 GN m−3 near9 T at 40 K. In the Y2O3-added samples, except for the plane configuration, the angular dependence ofJc showed a plateau, due to the flux pinning by isotropic pinning centres.Y2O3 nanoparticles randomly dispersed inside the YBCO matrix were consistently observed inthe cross-sectional TEM images.

Enhanced high-field performance in PLD films fabricated by ablation of YSZ-addedYBa2Cu3O7−x target

YBa2Cu3O7−x+Y2O3-stabilized ZrO2 (YBCO+YSZ) mixed filmswere prepared on SrTiO3/MgO substrates by pulsed-laser deposition from a YBCO target with a thin YSZ sector on top. TheJc at 77 K for themixed YBCO+YSZ thin filmwas enhanced. The Jc at 77 K for the pure film and the mixedYBCO+YSZ thin film were 1.46and 1.95 MA cm−2 (self field)(and 0.09 and 0.28 MA cm−2 (, B = 5 T)), respectively, even when both films were prepared using the same deposition conditions.The maximum pinning force of a doped film (77 K, ) was 15.9 GN m−3,which is comparable to the value reached by NbTi at 4.2 K. In the YSZ-added sample, the angular dependenceof Jc showed a broad peak at due to the flux pinning by the c-axis correlated defects. Elongated nanorods grown parallel to thec axis were consistently observed in the cross-sectional TEM images.

Investigation of magnetic properties of YBCO film with artificial pinning centers on PLD/IBAD metal substrate

In order to improve the critical current density (Jc) in magnetic fields, we have fabricated YBa2Cu3O7−x (YBCO) coated conductors with artificial pinning centers by pulsed laser deposition (PLD) method on a Hastelloy™ tape buffered by a self epitaxial PLD-CeO2 layer and an ion-beam assisted deposition (IBAD)-Gd2Zr2O7 (GZO) layer. Artificial pinning centers were introduced by the PLD deposition using YBCO target including YSZ particles. The Jc value was improved and abnormal microstructure was found to be effective for pinning. We call this new nano-epitaxial BaZrO3/YBCO structure “the bamboo structure” from its anisotropic growth and morphology. Furthermore, for the 1.16μm in thickness, Ic showed high value of 40.7A at 77K and 3T parallel to the c-axis. Namely, “the bamboo structure” also contribute to strong pinning in magnetic fields parallel to the c-axis in the film as thick as 1.16μm.

Magnetic field dependence of the critical current and the flux pinning mechanism inYBa2Cu3O6+xfilms doped withBaZrO3

Dependence of the critical current on applied magnetic field ${j}_{c}({B}_{a})$ is investigated in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ (YBCO) films prepared by pulsed laser deposition from pure YBCO target and from those doped with 2.9 or $9.0\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ ${\mathrm{BaZrO}}_{3}$. All targets were sintered from nanophase powders made by a citrate-gel process. Transmission electron microscopy images show distributions of ${\mathrm{BaZrO}}_{3}$ particles with typical diameters of $5--10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in the doped films. In comparison with the pure YBCO film the value of ${j}_{c}(0)$ is slightly smaller in the film deposited from the target doped with $2.9\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ ${\mathrm{BaZrO}}_{3}$ and only half in case of $9.0\phantom{\rule{0.3em}{0ex}}\mathrm{wt}.\phantom{\rule{0.2em}{0ex}}%$ doping. Two interesting phenomena in the behavior of ${j}_{c}({B}_{a})$ are observed for the doped films. First, the low-field plateau of ${j}_{c}$ is significantly lengthened and second, in fields above the accommodation field ${B}^{*}$ marking the end of this plateau the rate of decrease of ${j}_{c}$ is strongly reduced. These results are well fitted with a critical state model of superconductors taking into account the self field effects at low applied magnetic fields.

The flux pinning enhancement of YBCO film prepared by PLD using composite targets doped with BaZrO3 nanopowder

BaZrO3 nanopowder was added to YBCO powder to make (BaZrO3)x(YBCO)(100−x)mol.% (BZOx-YBCO) (0⩽x⩽10) composite targets for pulsed laser deposition of superconducting film in order to investigate the effect of the addition of BZO nanopowder in the YBCO target on the flux pinning properties of YBCO coated conductor. All the BZOx-YBCO films were grown on SrTiO3 single crystal substrate under the same conditions in the PLD chamber. The effect of adding BZO to YBCO targets on the flux pinning properties of BZOx-YBCO films has been investigated. No impurity phase was identified, and all the peaks could be indexed as YBCO, BZO, and STO. There were traces of strong pinning centers at low temperature and high magnetic field region (above ∼3T) in BZO6-YBCO film with the addition of ∼6mol.% BZO nanopowder. However, the Tc of the BZOx-YBCO films gradually decreased as the amount of BZO nanopowder added increased.

Control of Porosity and Composition in Large-Area YBCO Films to Achieve Micrometer Thickness and High&amp;lt;tex&amp;gt;$J_rm c$&amp;lt;/tex&amp;gt;on Sapphire Substrates

Relatively thick YBCO thin films (thickness d>0.5 /spl mu/m) ideal for fault current limiter as well as microwave applications have been successfully prepared by large-area pulsed laser deposition (PLD) on CeO/sub 2/-buffered sapphire substrates. The attainment of an unusually high film thickness (up to 2.0 /spl mu/m) without microcracking is attributed in part to the presence of pores correlated with yttrium-rich composition in the films. The effect of using YBCO targets with varied Y:Ba:Cu ratios on film porosity and surface morphology was investigated in detail. Using the optimum target composition, uniform critical current densities (J/sub c/) ranging from /spl sim/4.5 MA/cm/sup 2/ at d/spl sim/0.23 /spl mu/m to /spl sim/1.75 MA/cm/sup 2/ at d/spl sim/0.6 /spl mu/m have been achieved. Characterization of a film with d/spl sim/0.5 /spl mu/m showed low microwave surface resistance values [R/sub s/(77.3 K)/spl ap/2.09 m/spl Omega/ and R/sub s/(20 K)/spl ap/227 /spl mu//spl Omega/ at 22 GHz] comparable to the best YBCO films reported by other studies.

YBCO Films Prepared by PLD Using Nanocrystalline Targets Doped With&amp;lt;tex&amp;gt;$hboxBaZrO_3$&amp;lt;/tex&amp;gt;or Y211

YBCO thin films were prepared by pulsed laser deposition from a pure nanocrystalline YBCO target and similar targets doped with BaZrO/sub 3/ or Y/sub 2/BaCuO/sub 5/ (Y211 phase) in order to investigate the effect of these impurities on magnetic flux pinning. The doped targets were pressed from nanopowders prepared by a sol-gel method from starting solutions whose nominal molar ratios corresponded to compositions YBCO+2.2 and 6.5 wt% BaZrO/sub 3/ and YBCO+3.0 wt% Y211 phase. The biggest changes in the superconducting properties relative to the films prepared from the pure target were observed in the films ablated from the BaZrO/sub 3/-doped targets. Although the doping reduces the critical temperature, the critical current density calculated from the hysteresis loops is significantly increased in external magnetic fields above 0.15 T. Addition of Y211 to the target is found not to be as effective for improving the flux pinning of the films in high magnetic fields as addition of the BaZrO/sub 3/. J/sub c/'s in zero field and 77 K were 1.2 MA/cm/sup 2/ in the pure YBCO film, 1.1 MA/cm/sup 2/ in the 2.2 wt% BaZrO/sub 3/ doped film and 3.2 MA/cm/sup 2/ in the 3.0 wt% Y211 doped film.