YBCO Structure Research Articles

Влияние термообработки на изменения структуры сверхпроводящих порошков состава YBCO

Влияние термообработки на изменения структуры сверхпроводящих порошков состава YBCO

Flux pinning characteristics of YBCO: NaNbO3 by introducing artificial pinning centers with different morphology

Introduction of artificial pinning centres in different morphology is a beneficial way to improve the flux pinning properties of a YBCO compound. In the present study, we report the effect of addition of sodium niobate (NaNbO3) nanostructures in two different form i.e. nanorods (NRs) and nanoparticles (NPs) with a varied wt% (0, 0.5, and 1 wt%) on the pinning capabilities of bulk YBCO polycrystalline samples. The orthorhombic crystal structure of YBCO was confirmed by the XRD spectra even in the nanocomposite samples. The existence of NPs or NRs on the surface and between the superconducting grains of YBCO was confirmed by morphological analysis. The critical temperature (Tc) remains almost unchanged as compared to pure YBCO on addition of NaNbO3 nanostructure in YBCO compound upto 1 wt% concentration. Even at higher fields (upto 6 T) and higher temperatures (upto 75 K), the addition of NaNbO3 NPs or NRs in YBCO nanocomposite resulted in a significant increase of ~2.6 times in the critical current density as compared to pure YBCO. In comparison to NRs added YBCO nanocomposite samples, NPs added YBCO nanocomposite samples showed higher improvement. Throughout the entire investigated range of applied field, the maximum pinning force was found for 0.5 wt% NPs added composite sample.

YBCO superconductor added with one-dimensional TiO2 nanostructures: Frequency dependencies of AC susceptibility, FC-ZFC magnetization, and pseudo-gap studies

This article reports the role of adding one-dimensional titanium dioxide nanowires (TiO2-NWs, having 30 nm in diameter and some micrometers in length) on FC-ZFC magnetization, frequency-dependent AC susceptibility, and electrical measurements of the YBCO bulk system. The non-added (A0) and added TiO2-NWs samples (A1) were prepared by solid-state reaction route. TiO2-NWs did not affect the crystalline structure of YBCO. SEM examinations revealed that TiO2-NWs preferred to localize at the grain boundaries filling the pores existing between YBCO grains. FC-ZFC magnetization and frequency-dependent AC susceptibility analysis showed an enhancement of flux pinning properties with TiO2-NWs addition. TiO2-NWs addition affected also the electrical and pseudo-gap analysis of the samples.

Iron diffusivity into superconducting YBa2Cu3O7−δ at oxygen-assisted sintering: structural, magnetic, and transport properties

Optimization of materials exhibiting high-temperature superconductivity for producing controllable nano-devices is crucial for industrial applications. Herein we report a comprehensive study of the diffusion process between YBa2Cu3O7−δ (YBCO) and iron particles. Fe diffusion into the YBCO matrix could be fundamental for multilayer systems with YBCO/Fe-alloy interfaces. We have found that the orthorhombic YBCO structure adopts to 3 wt% Fe, while for higher Fe content, a formation of BaFeO3−δ and iron oxides was observed. Complementary measurements confirmed the strong superconductivity suppression in YBCO-Fe materials containing more than 7 wt% Fe. The YBCO with diffused Fe material retain the unit cell orthorhombicity (max. 3 wt% Fe), and their superconducting properties follow the principle of critical scaling with different exponents (γ). The critical current density (Jc), pinning fields (HP) exhibit γ = 1, the first critical field (Hc1) shows γ = 1/2, and critical temperature (Tc) demonstrates γ = 7/4.

Enhanced critical current density and flux pinning traits with Dy2O3 nanoparticles added to YBa2Cu3O7-d superconductor

Addition of nanosized material in YBa2Cu3O7–d to produce artificial pinning cores is benefit way to enhance the in-field current-carrying capacity and flux pinning properties. In this work, we report the impact of nano-dysprosium oxide particles (Dy2O3) with a size of ̴ 10 nm on the mechanisms and the strength of pinning centers of polycrystalline YBa2Cu3O7–d. Samples of YBa2Cu3O7–d + x Dy2O3 with x = 0.0 and 0.1 wt% were prepared via solid-state reaction way. X-ray diffraction and scanning electron microscope observations were performed to characterize the structure and the morphology of samples. Measurements of D.C magnetization against applied magnetic field from −6 to +6 T were implemented to estimate the critical current density and verify the pinning mechanisms at different temperatures ranging from 77 down to 10 K. The orthorhombic YBCO structure is preserved in both samples, NP–Dy2O3 weakens the grains linkage, drops the zero resistive temperature Tc by 1.6 K and weakens the inter-granular critical current density. Over the measured temperature range and exterior magnetic fields, results showed higher intra-granular current density and a best ability to trap vortex in the 0.1Dy-YBCO composite. Pinning centers were categorized into weak and strong pinning centers. NP–Dy2O3 gives more weight to the strong pinning components.

Trilayer Films of YBa2Cu3O7−x/LaAlO3/YBa2Cu3O7−x with Superconducting Properties Prepared via Sol-Gel Method

The YBa2Cu3O7−x/LaAlO3/YBa2Cu3O7−x (YBCO/LAO/YBCO) heterogeneous trilayer film structures were prepared on the LaAlO3 (001) single-crystal substrate via the sol-gel method. The characteristics of the phase, orientation, and superconducting properties were studied via an X-ray diffractometer and a comprehensive physical property measurement system. The results show that when the LAO layer was thin (<40 nm), the trilayer films were relatively pure and had a high c-axis orientation. When the nominal thickness of the LAO layer increased to 70 nm, non-c-axis oriented grains started to appear in the trilayer film. In this case, the top and bottom YBCO layers exhibited superconducting properties, and the resistance was found to be zero at 80.1 and 72.5 K, respectively. In addition, for the YBCO/LAO (40 nm)/YBCO structure, the intermediate LAO layer was too thin to completely cover the surface of the underlying YBCO. This resulted in point contact and micro-bridge contact in several micro-regions, thus forming a weak connection and exhibiting a current-voltage (I–V) characteristic similar to the direct-current (DC) Josephson effect. On the other hand, for the YBCO/LAO (70 nm)/YBCO structure, the thicker LAO layer could completely cover the underlying YBCO surface, which could isolate the superconducting current between the YBCO layers.

Direct observation of apical oxygen vacancies in the high-temperature superconductor YBa2Cu3O7−x

The properties of the high-temperature superconductor $\mathrm{YB}{\mathrm{a}}_{2}\mathrm{C}{\mathrm{u}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ (YBCO) depend on the concentration of oxygen vacancies (${V}_{\mathrm{O}}$). It is generally agreed upon that ${V}_{\mathrm{O}}$ form in the CuO chains, even at low concentrations where the critical temperature for superconductivity peaks ($x\ensuremath{\approx}0.07$), with only a handful of reports suggesting the presence of ${V}_{\mathrm{O}}$ at the apical sites. In this paper, we show direct evidence of apical ${V}_{\mathrm{O}}$ in optimally doped YBCO samples. Using density-functional-theory calculations, we predict that isolated ${V}_{\mathrm{O}}$ are equally favorable to form in either the CuO chains or the apical sites, which we confirm using atomic-resolution scanning transmission electron microscope imaging and spectroscopy. We further show that apical ${V}_{\mathrm{O}}$ lead to significant lattice distortions and changes in the electronic structure of YBCO, indicating they should be considered on an equal footing with chain ${V}_{\mathrm{O}}$ to understand the superconducting properties of YBCO in the optimal doping region.

Structure and properties of YBCO before and after the short-term exposure of the plasma flow

The results on the structure and electrical resistance of the porous YBa2Cu3O7–δ nanoceramics before and after plasma treatment are shown. It is shown that after exposure to high-enthalpy argon plasma flow, the structural, stoichiometrical and superconducting properties in the volume of this ceramics change slightly. An amorphous layer forms on the surface, the mechanical strength of the inter-granular bonds of which becomes higher than for the material in the bulk.

A Structural Optimization of Ferrite/YBCO Bilayers

Magnetic particles can be used to take advantage of both defect and magnetic pinning in high-temperature superconductors. We combined layers of ferrite+cerium oxide with YBCO to see their effect both on the structure of the YBCO and on flux pinning. The deposition temperature of the ferrite greatly affects its structure and also the saturation magnetization. Combined with YBCO, the magnetic layer distorts the structure of YBCO, although, for example, the critical temperature remains rather unchanged. According to the structural results achieved here, the magnetic pinning layer is best positioned on the top of YBCO. This way, an improvement in J c (B) is seen in all the field range, and also, a clear improvement of the accommodation field was measured. However, it does not play a huge role whether the ferrite is CoFe 2 O 4 , NiFe 2 O 4 , or ZnFe 2 O 4 , all mixed with CeO 2 .

Fabrication of Superconducting YBa2Cu3O7\u2212x Thin Films on Si Wafer via YSZ/CeO2 buffer layers

Fabrication of reproducible superconducting YBa2Cu3O7−x (YBCO) thin films with Tc values above 85 K on Si wafers has been realized by optimizing the thin film deposition process. Prior to the deposition of YBCO thin film on (100) p-type Si wafer, YSZ and CeO2 thin films were deposited as buffer layers by RF magnetron sputtering, and subsequently, YBCO thin film was deposited by dc magnetron sputtering. The deposition parameters such as substrate temperature, process gas pressure, Ar/O2 ratio, and power density were optimized for all layers in order to enhance the whole structure to prevent microcrack formation caused by misfits in crystal lattice parameters and thermal expansion coefficients between Si/YSZ/CeO2 and YBCO. Structural analyses were performed on YSZ and CeO2 layers, and electrical and magnetic measurements were carried out on a YBCO layer by employing XRD, SEM, resistance vs. temperature, and AC magnetic susceptibility vs. temperature measurements, respectively. The YBCO layer was also patterned as microbridges in order to test the durability of the whole Si/YSZ/CeO2/YBCO structure during the standard photolithography and wet etching process commonly used in device applications.

Effect of Al and Ca co-doping, in the presence of Te, in superconducting YBCO whiskers growth.

High-Tc superconducting cuprates (HTSC) such as YBa2Cu3O7 - x (YBCO) are promising candidates for solid-state THz applications based on stacks of intrinsic Josephson junctions (IJJs) with atomic thickness. In view of future exploitation of IJJs, high-quality superconducting YBCO tape-like single crystals (whiskers) have been synthesized from Ca-Al-doped precursors in the presence of Te. The main aim of this paper is to determine the importance of the simultaneous use of Al, Te and Ca in promoting YBCO whiskers growth with good superconducting properties (Tc = 79-84 K). Further, single-crystal X-ray diffraction (SC-XRD) refinements of tetragonal YBCO whiskers (P4/mmm) are reported to fill the literature lack of YBCO structure investigations. All the as-grown whiskers have also been investigated by means of X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Our results demonstrate that the interplay of Ca, Te and Al elements is clearly necessary in order to obtain superconducting YBCO whiskers. The data obtained from SC-XRD analyses confirm the highly crystalline nature of the whiskers grown. Ca and Al enter the structure by replacing the Y and the octahedral coordinated Cu1 site, respectively, as in other similar orthorhombic compounds, while Te does not enter the structure of whiskers but its presence in the precursor is essential to the growth of the crystals.

Magnetic field controlled charge density wave coupling in underdoped YBa2Cu3O6+x

The application of magnetic fields to layered cuprates suppresses their high-temperature superconducting behaviour and reveals competing ground states. In widely studied underdoped YBa2Cu3O6+x (YBCO), the microscopic nature of field-induced electronic and structural changes at low temperatures remains unclear. Here we report an X-ray study of the high-field charge density wave (CDW) in YBCO. For hole dopings ∼0.123, we find that a field (B∼10 T) induces additional CDW correlations along the CuO chain (b-direction) only, leading to a three-dimensional (3D) ordered state along this direction at B∼15 T. The CDW signal along the a-direction is also enhanced by field, but does not develop an additional pattern of correlations. Magnetic field modifies the coupling between the CuO2 bilayers in the YBCO structure, and causes the sudden appearance of the 3D CDW order. The mirror symmetry of individual bilayers is broken by the CDW at low and high fields, allowing Fermi surface reconstruction, as recently suggested.

The influence of magnetic nano metal oxides doping on structure and electrical properties of YBCO superconductor

Superconductor samples of YBa2Cu3O7−δ (YBCO) + x where x = 0.1, 0.2, 0.3, 0.4 and 0.5 wt% of nano metal oxides namely Cr2O3, Co3O4 and Mn3O4 namely are synthesized by the solid-state reaction route. Both x-ray diffraction and electron microscopy have been employed to study the phase identification and the microstructure of these samples. Transition temperature of the samples has been determined by four probe resistivity measurements. The x-ray diffraction patterns indicate that the gross structure of YBCO does not change with the substitution of three types of nano metal oxides with different doping level. The critical transition temperature (Tc) is found to decrease with the increases of doping level. Mn3O4 has highest Tc value which may be due to flux pinning from some defects and the rapid suppression in Tc with increasing concentration of Mn3O4 may be due to the cooper pair breaking and the hole filling in the CuO2 planes.

AC Magnetic Susceptibility and Morphological Development of YBCO HTS Formed from Y:Ba:Cu = 1:2:3 and 3:5:8

Synthesis of superconducting YBCO sample after the earliest sintering stage was made possible by employing Y:Ba:Cu = 3:5:8 precursor ratios. Sintering temperatures used were in the range 840–950∘C. XRD well corresponds to YBCO structure. This study suggests that Y358 is a metastable state that requires the formation of Y123 in the early stages. Various morphological structures were obtained using different sintering profile and stoichiometric ratios. Morphology and AC magnetic susceptibility were correlated and compared to YBCO HTS formed using the standard Y:Ba:Cu = 1:2:3 ratios. The length of intra-to-intergranular in-phase response and the degree of out-of-phase (loss) peak shifting to lower temperature is highly dependent to the morphology and nature of grain boundaries. A good control in morphology by optimizing the temperature profile can address various applications such as in superconducting bulk magnets, films, and devices.

Superconductivity Mechanism in the Modulated Quantum Well of YBCO Structure

The modulated structure by high pressure and the superconductivity of YBCO compounds have been revealed over two decades [1]. However, their nature & mechanism are not yet sufficiently known. Continuing the achieved results [2-3], the present paper aims to evidence how the Quantum Electron-Magnetic Phenomenon, namely the Super-Exchange Interaction of the "active electrons", i.e. the hybridized odd electrons from the Cu ions in the Cu-Y-Cu nanolayer as a Nanowaveguide (NWG), conditions the Superconductivity of YBCO. The 1st key: The nanostructure is of Quantum nature. The active electrons behavior as the Quasi-Free Electrons (QFEs) waving in the Quantum Well (NWG), where they can be favored to a strong Super-Exchange Interaction. Thereby, two types of the spin coupled pairs can be spontaneously formed in the NWG, where just the singlet pairs will play the role of the superconducting Cooper pairs. For studying these nanoeffects, ESR can offer an especially efficacious contribution. The 2nd key: On the basis of the consequences of the Pauli principle, the singlet pair only persists if its QFE cloud overlapping path length L = nλ/2, where λ is the de Broglie wavelength of QFE conditioned by the Nanodimension of the NWG (Fig.1, left). This electron waving status corresponds to an ideal metallic phase occurring in the NWG. The 3rd key: The spin coupling brings about a temperature depending Spin Gap of the QFEs in the NWG. Just this Spin Gaps causes the superconductivity with the phase transition characteristics (Fig.1, right) that exactly and surprisingly correspond with the experimental.

SiO2 nanoparticles addition effect on microstructure and pinning properties in YBa2Cu3Oy

A series of YBa2Cu3Oy (YBCO, Y-123) samples with small amounts (0–1wt%) of nanosized SiO2 particles (30nm) are synthesized in air using a solid-state reaction route. The microstructure has been characterized by transmission and scanning electron microscopy (TEM and SEM) techniques and the magnetic field and temperature dependences of the critical current density (Jc) was calculated from the magnetization measurements and by the standard four-probe method at various temperatures. Flux pinning force density (Fp) is calculated and possibility of the pinning mechanisms prevalent in type II superconductors are investigated. X-ray diffraction analysis shows that the orthorhombic structure of YBCO is maintained. Morphology examination by SEM revealed decreases of grain size with SiO2 addition. High zero resistance temperature Tco value of about 90K was maintained in YBCO with SiO2 concentration ≤0.2wt%. Compared to free added-sample, higher critical current densities were obtained for the YBCO sintered with low concentration SiO2 (≤0.1wt%) in applied magnetic field. TEM observations show the presence of columnar defects (2–3nm in diameter) along the c-axis of YBCO and Si-rich nanophase embedded in the superconducting matrix. These defects are responsible for critical current densities improvement in the magnetic field of YBCO.

Model of Reversible Strain Dependences of Critical Current in YBCO-based Coated Conductors and Epitaxial PLD Films

Reversible strain dependencies of critical current Jc in YBCO coated conductors and epitaxial PLD films are nonlinear, non-monotonous and have two peaks in a certain range of applied field in a contrary to quasi-linear asymmetric reversible dependence in BiSCO films. We have developed a new theoretical model, which takes into account a twin domain structure of YBCO and the anisotropy of uniaxial strain dependence of Tc. Many experimentally observed effects, such as temperature, magnetic field and two-peak strain dependences of Jc, are shown to be described in the framework of suggested model.

Flux pinning improvement of ybco superconducting films with BaZrO3 nanoparticles prepared by chemical solution deposition method

The aim of this study is to introduce artificial pinning centres into the YBCO structure and to investigate the dependence of the critical current on applied magnetic fields. Chemical solution deposition technique is appearing as a very promising method to achieve thin films at low cost. YBCO films with Zr doping have been prepared successfully by the trifluoroacetate metal-organic deposition (TFA-MOD) method through dissolving different amounts of Zr (IV)-2,4-pentanedionate into the precursor solution. The optimum BaZrO3 concentration for Jc improvement in magnetic fields was investigated. The surface morphology of the films was observed by Scanning Electron Microscope (SEM). Phase analysis of the doped and undoped samples was performed by XRD, critical transition temperature (Tc) and critical current densities (Jc) were reported as a function of dopant concentration. The correlation of optimum dopant concentration with microstructure, pinning and superconducting properties was investigated.

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.

A Criterion for Determining Stabilizer Thickness of YBCO Coated Conductors Based on Coil Protection

The purpose of this study is to propose a criterion for determining stabilizer thickness of YBCO coated conductors. The permissible disturbance energy density in high-temperature superconductors (HTSs) is two or three orders of magnitude greater than that in low-temperature superconductors (LTSs). On the other hand, to enhance the reliability and safety of HTS coils, an establishment of a protection scheme assuming a quench caused by a failure in power supply, cooling system or similar problem is also required for HTS coil systems. Quenching produces excessive temperature or voltage in the coil winding; overheating may cause the conductor to meltdown, or high voltage may punch a hole in the winding. To avoid these types of damages in YBCO coils, a suitable stabilizer thickness must be determined for the sophisticated structure of YBCO coated conductors, which are composed of highly textured thin-film on a flat flexible substrate. Therefore, we investigate the appropriate structure for YBCO coated conductors from the perspective of energy dumping (i.e., quench protection). Based on the protection scheme that the stored magnetic energy in the coils is dumped by an external dump resistance prepared as a quench protection, we derive a function that examines the heat balance of a quenching YBCO coil in an adiabatic condition and propose a criterion using the function to determine an appropriate stabilizer thickness for YBCO coated conductors.