Pure YBCO Films Research Articles

Effect of Chlorine Addition on Texture and Superconducting Performance of YBa2Cu3O7−δ-Coated Conductors

YBa2Cu3O7−δ (YBCO) thin films with the addition of Cl were prepared on Hastelloy tape by the extremely low fluorine metal-organic deposition (MOD) technique. The composition and microstructure of the present samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was revealed that the Cl-added YBCO thin films achieved better texture and density compared with the pure YBCO films. The superconducting properties at magnetic fields were measured using the magnetic property measurement system (MPMS). The results showed that the sample onset transition temperature (Tc, on) did not change significantly after the addition of Cl. The critical current density (Jc) in the presence of YBCO with the addition of Cl increased significantly. Meanwhile, both the Jc and gravitational force (Fp) of the (Cl, Hf) co-added YBCO films were further enhanced at different magnetic fields. The thermodynamic analysis of the BaCO3 removal reaction revealed that the addition of Cl to YBCO formed chlorine compounds, which were effective in avoiding the formation of BaCO3. Further, the calculation results of the Gibbs free energy at different pressure quotients showed that the stability of the relevant chlorine compounds occurred in the order of BaCl2 > CuCl2 > YCl3 and the oxidation of BaCl2 to BaO required a higher temperature compared to BaF2, implying the potential advantages of inhibiting the a-axis growth.

Magnetotransport behavior of YBa2Cu3O7-δ –Sm0.55Sr0.45MnO3 superconducting-ferromagnetic composite thin films

We report a detailed study on the magnetotransport behavior of YBa2Cu3O7-δ -Sm0.55Sr0.45MnO3 (YBCO-SSMO) superconducting-ferromagnetic composite thin films (thickness ∼80 nm) of nominal compositions (YBCO)1-x(SSMO)x (x = 0, 0.08, and 0.14). Films are grown by pulsed laser deposition of the pure and composite targets on (001)-SrTiO3 substrates, and all are single crystalline with the c-axis normal to the plane of the substrate. The Tc(R = 0) of the pure YBCO film is ≈87 K and decreases to ≈75 K and ≈44 K with the incorporation and increase of the ferromagnetic fraction in the superconducting matrix. Successive decrease in the slope of the normal state R-T curves maps the incorporation of the high resistance channels of the SSMO. In an external magnetic field (H), the rate of decrement in the Tc(R = 0) is found to be dTc(R = 0)/dH ∼1.8 K T−1, ∼4.7 K T−1, and ∼2.8 K T−1, respectively for x = 0, 0.08, and 0.14. The upper critical field and the irreversibility field are appreciably depressed in the composite samples and suggest a broadening of the mixed-phase vortex regime. The application of the thermally activated flux flow (TAFF) model shows that the activation energy decreases sharply from U0 = 4314 (910) meV, 498 (130) meV, and 253 (66) meV for YS00, YS08, and YS14, respectively, at H = 0 T (6 T). The analysis of the field-dependent activation energy in terms of and dependence suggests decoupling of the 2D vortices due to the ferromagnetic phase. The hysteresis in the current-voltage characteristics is seen to decrease with an increase in the SSMO content.

Enhanced superconducting performance in solution-derived YBCO–BaZrO3 composite film

YBa2Cu3O7-δ/BaZrO3 (YBCO/BZO) composite film with enhanced flux-pinning performance was prepared on LaAlO3 (LAO) substrate via a fluorine-free sol-gel method in combination with a novel photosensitive sol-gel lithography technique. Owing to the difference of lattice mismatch between the interfaces of YBCO/LAO and YBCO/BZO, high-density stacking faults were successfully introduced into YBCO matrix, which has been confirmed by XRD and HRTEM analysis. Magnetization measurement results indicate that YBCO/BZO composite film has a stronger current-carrying capacity than the pure YBCO film especially under applied magnetic fields. However, the critical current density of YBCO/CeO2 composite film is much lower than that of the pure YBCO film at all the applied magnetic fields due to the chemical reaction between YBCO and CeO2. Therefore, it can be concluded that the flux-pinning performance of YBCO film can be improved by the lattice distortions within YBCO matrix as long as the metal oxide microarrays cannot react with YBCO films.

Heat treatment design of precursor solutions with different fluorine contents for YBa2Cu3O7−x films through the sol-gel approach

The extraordinary high Jc value up to 5.2 MA/cm2 was obtained in the pure YBCO film by optimizing the heat treatment process for the specific precursor solution. The orientation, surface morphology, texture, and performance of YBCO films fabricated by the different low-fluorine precursor solutions and heating rates are systematically investigated for the first time. A reasonable heat treatment strategy is proposed for obtaining satisfactory YBCO films considering the synergistic effect of the heating rate and fluorine content.

Greatly enhanced flux pinning properties of fluorine-free metal–organic decomposition YBCO films by co-addition of halogens (Cl, Br) and metals (Zr, Sn, Hf)

Additive-free YBCO films, as well as those with halogen (X) added, metal (M) added and (X, M) co-added, have been prepared by the fluorine-free metal–organic decomposition method on SrTiO3(100) single crystalline substrates, where X = Cl, Br and M = Zr, Sn, Hf. It was revealed that the addition of both Cl and Br to the starting solution resulted in the generation of oxyhalide, Ba2Cu3O4X2, in the YBCO films, and that the oxyhalide was found to promote the bi-axial orientation of the YBCO crystals. By adding a decent amount of Cl or Br, highly textured YBCO films with high Jc were reproducibly obtained, even when an impurity metal, M, was co-added, while the addition of M without X did not greatly improve Jc owing to the poor bi-axial orientation of the YBCO crystals. Our results suggest that the addition of Br more effectively enhances Jc than the addition of Cl. The pinning force density at 40 K in 4.8 T reached ∼55 GN m−3 with the co-addition of (Br, M). This value is much larger than that of the pure YBCO film, reaching ∼17 GN m−3.

Effect of Yb Substitution on Microstructure and Superconducting Properties of Y1−xYbxBa2Cu3O7−δ Films

The purpose of this study was to improve the critical current density (Jc) of YBa2Cu3O7−δ (YBCO) superconducting films at high magnetic fields. Thin Y1−xYbxBa2Cu3O7−δ (Y1−xYbxBCO) superconducting films on LaAlO3 substrates were prepared by modified low-fluorine metal organic deposition method (LF-MOD) in order to investigate the effect of Yb substitution on the microstructure and superconducting properties of a YBCO-coated conductor. In this study, single-phased, c-axial-aligned Y1−xYbxBCO films were obtained. Yb doping had a little effect on the critical temperature (Tc) and transition width (ΔT) values of Y1−xYbxBCO films. An abnormal phenomenon was observed that the Jc of Y1−xYbxBCO films at low field was smaller than that of the pure YBCO film, but the Jc of Y1−xYbxBCO films at high field was much greater than that of the undoped YBCO film. Compared to pure YBCO film, the Jc values of Y0.75Yb0.25BCO and Y0.25Yb0.75BCO films were enhanced by a factor of 8 at 8 T, 65 K, which meant that chemical substitution of Yb into the Y site could improve flux pinning significantly under the high magnetic field in Y1−xYbxBCO coated conductors.

Angular-Dependent Vortex Pinning Properties of YBa2Cu3O7−δ /Y2O3 Quasi-Multilayers

A series of quasi-multilayers of YBa2Cu3O7−δ (YBCO)/Y2O3 specifically 70 × (m YBCO/n Y2O3) were prepared on SrTiO3 single crystal using pulsed-laser deposition (PLD) with a controlled deposition pulses of m = 40 and n = 2, 5, and 10 for YBCO and Y2O3, respectively. The x-ray diffraction patterns indicate that all the present quasi-multilayers exhibit good c-axis orientation. The angular dependence of critical current density (J c ) on applied magnetic field directions are systemically measured to study the anisotropic vortex pinning performances for those quasi-multilayers. It is revealed that compared with the pure YBCO films, the quasi-multilayers with n = 2, i.e., a proper constituent pulse of Y2O3, exhibits the enhanced vortex pinning abilities in all angles between c-axis orientation and the applied magnetic field direction. As well, such a quasi-multilayer film (n = 2) shows the higher lift factor J c (Θ)/ J c (90°) and much better vortex pinning properties at high fields and high temperatures, showing promising potential for coated conductor application.

Epitaxial growth of BaHfO3 buffer layer and its structure degeneration analysed by Raman spectrum.

BaHfO3 (BHO) has been proposed as a new cap layer material for YBa2Cu3O7−δ (YBCO) coated conductors. Highly c-axis oriented BHO cap layer has been deposited on ion-beam assisted deposition-MgO buffered Hastelloy tapes by direct-current-magnetron sputtering method. The epi-growth of BHO films combined with its properties is investigated in details. The degenerated cubic crystal structure of BHO film is confirmed by Raman spectrum analysis. XRD θ–2θ scan, φ-scan and ω-scan reveal an excellent c-axis alignment with good in-plane and out-of-plane textures for BHO cap layers. SEM and AFM investigations show BHO cap layer a dense and crack-free morphology. Subsequently pure c-axis orientation YBCO film was epitaxial grown on such BHO cap layer successfully, shown BaHfO3 a potential cap layer material for coated conductors.

Enhanced Flux Pinning of YBCO Films by a Simple Self-Decoration Method

Low-concentration $\text{YBa}_{2}\text{Cu}_{3}\text{O}_{7-x}$ (YBCO) precursor solutions (with metallic ion concentrations of 0.05–0.45 mol/L) were prepared. Deposition of the low-concentration precursor solutions led to the formation of YBCO nanodots on the LaAlO3 (LAO) substrates. After that, a high-concentration YBCO precursor solution (with a metallic ion concentration of 1.5 mol/L) was deposited on the nanodot-decorated LAO substrates to form continuous YBCO films. Results indicated that the morphology of the YBCO nanodot had a close relation to its solution concentration. In comparison with a pure YBCO film, the self-decorated YBCO films had a stronger flux-pinning force and a higher critical current density $J_{c}$ under the magnetic field. Through optimization of the precursor solution concentration, a high-performance self-decorated YBCO film was obtained, with a $J_{c}$ value of 7.1 MA/cm2 (at 77 K, 0 T) and a high pinning force of 7.2 GN/m3.

Enhanced superconducting properties of YBa2Cu3O7−δ thin film with magnetic nanolayer additions

Vertically aligned nanocomposite (VAN) (La0.7Sr0.3MnO3)0.5(CeO2)0.5 and pure La0.7Sr0.3MnO3 layers were incorporated into YBa2Cu3O7−δ (YBCO) thin films as bilayer stacks for magnetic flux pinning enhancement. The films show high epitaxial quality, suggested by XRD and TEM study. The critical temperature Tc of the bilayers is about 90K, which is close to that of pure YBCO films, while both the self-field Jcsf and in-field critical current density Jcin-field are largely enhanced. Among all samples, the film with VAN cap layer shows the highest Jc values in all field ranges. This study demonstrates an effective way towards the tunable pinning effect for YBCO coated conductors by both defect and magnetic pinning.

Superconducting properties enhancement of YBa2Cu3O7−δ thin films by BaSnO3 doping

YBa2Cu3O7−δ (YBCO) thin films, doped or undoped with BaSnO3, are deposited on single crystal SrTiO3 substrates using a pulsed laser deposition system. The optimized temperatures for BSO–YBCO and pure YBCO are different, while BSO–YBCO needs higher growth temperature of 850 °C. And the films being grown at different temperatures exhibit very different surface morphologies. The optimized BSO–YBCO film shows higher critical current density values at different measured temperatures compared to the pure YBCO film, either with or without applied magnetic field. The doped sample obtains self-field Jc of 38.5 MA/cm2 at 40 K, 3.2 MA/cm2 at 77 K, which suggests that BSO doping has effective pinning effects for YBCO superconducting properties improvement.

Strongly enhanced flux pinning in the YBa2Cu3O7 −x films with the co-doping of BaTiO3 nanorod and Y2O3 nanoparticles at 65 K**Project supported by the National Natural Science Foundation of China (Grant No. 51272250), the National Basic Research Program of China (Grant No. 2011CBA00105), the National High Technology Research and Development Program of China (Grant No. 2014AA032702), and the Natural Science

YBa2Cu3O7 − x (YBCO) films with co-doping BaTiO3 (BTO) and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates (TFA-MOD). The properties of the BTO/Y2O3 co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM). The optimized content of yttrium excess in the BTO/Y2O3 co-doped YBCO films is 10 mol.%, and the critical current density is as high as ∼17 mA/cm2 (self-field, 65 K) by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density (JC) not only at the self-magnetic field, but also in the applied magnetic field.

Effects of thickness on superconducting properties and structures of Y2O3/BZO-doped MOD-YBCO films**Project supported by the National Natural Science Foundation of China (Grant No. 51272250), the National Basic Research Program of China (Grant No. 2011CBA00105), the National High Technology Research and Development Program of China (Grant No. 2014AA032702), and the Beijing Natural Science Foundation, China (Grant No. 2152035).

We report the thickness dependence of critical current density (Jc) in YBa2Cu3O7−x (YBCO) films with BaZrO3 (BZO) and Y2O3 additions grown on single crystal LaAlO3 substrates by metalorganic deposition using trifluoroacetates (TFA-MOD). Comparing with pure YBCO films, the Jc of BZO/Y2O3-doped YBCO films was significantly enhanced. It was also found that with the increase of the thickness of YBCO film from 0.25 μm to 1.5 μm, the Ic of BZO/Y2O3-doped YBCO film increased from 130 A/cm to 250 A/cm and yet Jc of YBCO film decreased from 6.5 MA/cm2 to 2.5 M A/cm2. The thick BZO/Y2O3-doped MOD-YBCO film showed lower Jc, which is mainly attributed to the formation of a-axis grains and pores.

Enhanced flux pinning in YGdBCO film grown by sol–gel approach

Gd-doping YBCO films were fabricated on LaAlO3 (00l) substrates by sol–gel method using benzoic acid modified trifluoroacetates precursor solution. Effects of Gd doping on texture, microstructure and flux pinning properties of YBCO films were investigated. With optimal Gd-doping, the surface and texture of YGdxBa2Cu3Oy films have been improved. The introduction of ion defects can improve the critical current density (Jc) and flux pinning force (Fp) of the YGdBCO films. The Jc and Fp values of YGd0.1Ba2Cu3Oy film are almost two times higher than that of pure YBCO film in magnetic field. These results indicate that Gd-doping YBCO phase with sol–gel process is a perspective method for enhancement of current carrying capability of YBCO film.

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.

Improvement of Upper Critical Field in YBa2Cu3Oy Films by Substituting 3d Metal for Cu Sites Using Combinatorial Pulsed-laser Deposition

Abstract It is well known that the critical upper field Bc2 is improved by shortening of the coherence length owing to the scattering of electrons in a superconductor. In order to improve of Bc2 in YBa2Cu3Oy (YBCO) films in our study, we substituted 3d metals (M = Zn, Co, Ni, Fe) for the Cu sites of the YBCO films. We used combinatorial pulsed-laser deposition to fabricate different YBa2(Cu1-xMx)3Oy films by continuously changing the amount of substitution metal x, from 0 to 0.01 on a single substrate using. As a result, the superconducting transition temperature Tc and critical current density Jc decreased with increasing amounts of all four variations of substitution metal M. For example, Tc was 82.5 K and Jc at 77 K was 0.15 MA/cm2 in the Co-substituted sample with x = 0.0091. For the substitution of Co and Ni, we confirmed that Bc2 was improved with increasing amount of substitute metal up to x = 0.01. Although Bc2(0 K) of a pure-YBCO film was 101 T, Bc2(0 K) of the Co-substituted sample with x = 0.0091 reached 272 T. On the other hand, the irreversibility field decreased by substituting Zn, Co, Ni, or Fe for Cu.

Strong flux pinning enhancement in YBa2Cu3O7−x films by embedded BaZrO3 and BaTiO3 nanoparticles

YBa2Cu3O7−x (YBCO) films with embedded BaZrO3 and BaTiO3 nanoparticles were fabricated by metalorganic deposition using trifluoroacetates (TFA-MOD). Both X-ray diffraction and transmission electron microscopy revealed that these BaZrO3 and BaTiO3 nanoparticles had random orientations and were distributed stochastically in the YBCO matrix. The unique combined microstructure enhances the critical current density (Jc) of the BaZrO3/BaTiO3 doped-YBCO films, while keeping the critical transition temperature (Tc) close to that in the pure YBCO films. These results indicate that BaZrO3 and BaTiO3 nanoparticles provide strong flux pinning in YBCO films.

Optimization of a fluorine-free metal-organic deposition to fabricate BaZrO3-doped YBa2Cu3O7−δ film on RABiTS substrates

In this study, we used a systematic route to optimize the fluorine-free MOD process to achieve a high critical current density (Jc) in BaZrO3 (BZO)-doped YBCO films on RABiTS substrates. The BZO content is given by 1 YBCO+x BZO films, where x is moles of BZO per 1 mole of YBCO. We found x = 0.10 to be the optimal BZO content and ∼795–805 °C to be the optimal growth temperature window with 60–90 min processing time. TEM studies show the BZO nanoparticles are ∼20 nm in size and spaced ∼50–100 nm apart. The in-field Jc and the peak pinning force (Fp) of the film grown at the optimal conditions were greatly increased at 77 K relative to pure YBCO films, achieving ∼6.7 GN m−3 at 77 K, H ‖ c in a ∼800 nm thick x = 0.10 film. The angular dependence of in-field Jc measurements also shows greatly reduced angular anisotropy at 1 and 4 T at 77 K due to isotropic pinning by BZO nanoparticles.

Localized Pair Breaking Effect in the Quasi-multilayers of YBa2Cu3O7−δ /La0.88Ca0.12MnO3

Quasi-multilayers consisting of superconducting YBa2Cu3O7−δ (YBCO) and ferromagnetic La0.88Ca0.12MnO3 (LCMO), namely p×(YBCO(m)/LCMO(n)) (p: repetition periods, m: YBCO pulse number, and n: LCMO pulse number) are prepared on single crystal LaAlO3 (LAO) by pulsed laser deposition (PLD). X-ray diffraction measurements reveal that both in-plane and out-of-plane textures of the quasi-multilayers are as good as in the pure YBCO films. Nevertheless, the present quasi-multilayer system shows significant modifications in the superconducting properties, as evidenced by the suppressed superconducting transition temperature as well as the critical current density. This indicates that a special pair breaking effect emerges at YBCO/LCMO interfaces, and it is believed to arise from the spin scattering by the local exchange field due to the insulating nature of the ferromagnetic LCMO.

Flux pinning properties of YBCO films with nano-particles by TFA-MOD method

Nano-particles were doped into YBCO films as pinning centers by a metal organic deposition (MOD) method using trifluoroacetates. Two types of initial solution with a cation ratio of Y: Ba: Cu = 1: 1.5: 3 were prepared; one with the dispersion of SnO2 particles with the size of 15-25 nm and the other one with the dispersion of smaller ZrO2 particles with the size of under 8 nm, then the solution was spin-coated on CeO2/Gd2Zr2O7/Hastelloy substrates. The coated films were calcined at 430 °C in oxygen atmosphere and crystallized at 780 °C in low oxygen atmosphere. From the results of X-ray diffraction analysis (XRD), peaks of BaSnO3 were observed clearly in the YBCO film by the starting solution with SnO2. On the other hands, little peaks corresponding to BaZrO3 were observed in the film by the solution with ZrO2. Many CuO segregations were recognized at the surface of SnO2 doped YBCO film in comparison to the YBCO film with ZrO2 doping. From these results, it is indicated that most of SnO2 particles in precursors are react with Ba during heating. Critical current density ( J C) of the YBCO films by both solutions showed higher performance than that of pure YBCO film in magnetic fields.