YBCO Research Articles

Nanoscale Stoichiometric Analysis of a High-Temperature Superconductor by Atom Probe Tomography.

The functional properties of the high-temperature superconductor Y1Ba2Cu3O7-δ (Y-123) are closely correlated to the exact stoichiometry and oxygen content. Exceeding the critical value of 1 oxygen vacancy for every five unit cells (δ>0.2, which translates to a 1.5 at% deviation from the nominal oxygen stoichiometry of Y7.7Ba15.3Cu23O54-δ ) is sufficient to alter the superconducting properties. Stoichiometry at the nanometer scale, particularly of oxygen and other lighter elements, is extremely difficult to quantify in complex functional ceramics by most currently available analytical techniques. The present study is an analysis and optimization of the experimental conditions required to quantify the local nanoscale stoichiometry of single crystal yttrium barium copper oxide (YBCO) samples in three dimensions by atom probe tomography (APT). APT analysis required systematic exploration of a wide range of data acquisition and processing conditions to calibrate the measurements. Laser pulse energy, ion identification, and the choice of range widths were all found to influence composition measurements. The final composition obtained from melt-grown crystals with optimized superconducting properties was Y7.9Ba10.4Cu24.4O57.2.

Introducing multi-source pinning centers into Y–Ba–Cu–O superconductor through addition of BiFeO3 nano-particles

Chemical doping of BiFeO3 (BFO) nano-particles in Y–Ba–Cu–O (YBCO) superconductor was performed using the powder melt and infiltration growth (PM-IG) technique. The results indicate that improved superconducting properties have been observed in 0.2wt% nano-BFO doped sample. The X-ray diffraction (XRD) result performed on the ground powder of 5wt% nano-BFO doped YBCO grain proves the decomposition of BFO phase during the PM-IG process and the formation of Y2Ba4CuBiOy (YBi-2411) phase. Consequently, the addition of BFO could introduce multi-source pinning centers, i.e. YBi-2411 nanoscale particles and Fe element substitutions, which accounts for the improvement in superconducting properties.

Simulation of YBCO Tape and Coils in HTS Maglev System

In the process of running high temperature superconducting maglev train, the AC(Alternating Current) loss of superconducting coil is directly related to its safe operation and operating cost. In this paper, the simulation model was built based on the finite element software COMSOL Multiphysics, and mainly simulated and calculated the AC losses of YBCO(Yttrium Barium Copper Oxide) tape and coils. In this model, as the solving object, the singular and infinite long YBCO tape and coils model was solved with H-formulation and the nonlinear characteristic (E-J constitutive law) and anisotrophy (B-J characteristic) were taken into consideration as the theoretical foundation. Then on the basis of the model under maglev suspension system, AC losses under different amplitude and frequence AC currents were calculated. The results shows that under different frequencies and dynamic components, the local maximum AC loss of YBCO tape and coils occurs when the steady-state DC(Direct Current) current is 30A. Then comparing with old maglev suspension system, the new system can greatly reduce the energy consumption and the material cost.

Running Stability of a Prototype Vehicle in a Side-Suspended HTS Maglev Circular Test Track System

To improve the running speed of the high-T c superconductor (HTS) maglev system, a circular test track system with the maglev vehicle suspending beside the permanent magnetic guideway (PMG) is studied. A test to determine the change in guidance force when a YBa 2 Cu 3 O 7 (YBCO) bulk gets close to and off the center of the PMG is carried out and the curve of relation between levitation gap and vertical eccentric displacement of the YBCO bulk under constant guidance force is obtained. The results show that eccentric motion in the vertical direction may occur during free side-suspended operation of the maglev vehicle in the circular track, which leads to a reduction in levitation gap and an increase in vertical eccentric displacement, decaying and enhancing the guidance force, respectively. Eccentric motion can be effectively restrained by reducing the field cooling height and the weight of the maglev vehicle to improve the running stability of the maglev vehicle. Finally, a circular test track 6.5 m in diameter and 20.4 m in length and a prototype vehicle are designed and constructed on the basis of the side-suspended HTS maglev system.

Preparation of yttrium barium copper oxide superconductive fibers via electrospinning through a lactic-acid gel route

Preparation of yttrium barium copper oxide superconductive fibers via electrospinning through a lactic-acid gel route

In-situ magnetic measurements of substances under extreme conditions

Temperature and pressure are the two most important thermodynamic elements, which determine the existent state of substance. Low temperature and high pressure are significant and key extreme conditions in the modern experimental science, providing new routes for many subjects such as physics, chemistry, materials and biology, and playing an important role in finding new phenomena. The magnetic research under extreme conditions is an important branch of the study of the extreme conditions, which not only presents the magnetic changes of the material under extreme conditions, but also is an important means to explore the high temperature superconductors. In this article, we elaborate the principle and method of measuring the magnetic susceptibility and superconducting transition temperature under high pressure. The in-situ magnetic measurement system under high pressure and low temperature is also briefly introduced, designed and installed by ourselves. Using the in-situ magnetic measurement system, the magnetic transition of iron and the superconducting transition temperature of the yttrium barium copper oxide sample under high pressure are measured.

YBa2Cu3O7−δ long Josephson junctions on bicrystal Zr1−xYxO2 substrates fabricated by preliminary topology masks

YBa2Cu3O (YBCO) films were fabricated by magnetron sputtering with modification of the substrate surface by preliminary topology masks. Formation features of Josephson junctions on bicrystal Zr1−xYxO2 (YSZ) substrates have been considered. The structural and electrical properties of such junctions were investigated. As a result, the presented technology allows us to fabricate YBCO structures on YSZ substrates with a buffer cerium dioxide (CeO2) layer where YBCO film sputtering is the final stage of structure formation. In particular, long Josephson junctions with good characteristics have been fabricated by this technology and measured, allowing us to achieve critical currents of 80 mA for 150 um junctions.

Planar current anisotropy and field dependence of Jc in coated conductors assessed by scanning Hall probe microscopy

The local distribution of the critical current density, Jc, of coated conductors and YBa2Cu3O (YBCO) films on single crystalline substrate was investigated by scanning Hall probe microscopy. The high spatial resolution of the measurements enabled an assessment of dependence of the local Jc on the local magnetic induction, B, and electric field, E. The derived Jc(B)-dependence agreed well with the global Jc obtained from magnetization loops and provided values of Jc at very low fields, which are inaccessible to magnetization and transport measurements. The anisotropic current flow within the film plane was investigated in YBCO films on miscut SrTiO3 substrates and a GdBa2Cu3O film on an MgO buffer layer prepared by inclined substrate deposition on a Hastelloy substrate. The c-axis currents calculated from the Hall maps were significantly larger than previously reported data obtained from direct transport measurements. The planar current anisotropy at 77 K was found to be highly influenced by the microstructure which can either deteriorate the current flowing across the ab-planes or cause enhanced pinning and increase the critical current flowing parallel to the ab-planes.

Study of the Influence of Helical Bending Strain and Perpendicular Self-Field on Critical Current Degradation for Multilayer YBCO Tapes

An experimental investigation of the critical current (I c ) degradation of multilayer twisted yttrium barium copper oxide (YBCO) tapes in self-field was performed. The influence of the number of tape layers (N) and twist pitch (P) on critical current was researched. The results showed that the influence of helical bending strain and perpendicular self-field on critical current degradation was a comprehensive process. No critical current degradation was found when there was just one layer and the twist pitch was over 20 mm. However, the situation would change when the number of tape layers increased. The critical current degradation would increase with increase in helical bending strain or perpendicular self-field. The critical current degradation can reach a maximum of 24.6% when the helical bending strain was 0.23% and the number of tape layers was 5. A mathematic formula was set up to express the comprehensive influence of helical bending strain and perpendicular self-field on critical current degradation. The results can provide an important theoretical foundation for the application of high temperature superconducting tapes and the design of YBCO cables.

NanoSQUID magnetometry of individual cobalt nanoparticles grown by focused electron beam induced deposition

We demonstrate the operation of low-noise nano superconducting quantum interference devices (SQUIDs) based on the high critical field and high critical temperature superconductor YBa2Cu3O7 (YBCO) as ultra-sensitive magnetometers for single magnetic nanoparticles (MNPs). The nanoSQUIDs exploit the Josephson behavior of YBCO grain boundaries and have been patterned by focused ion beam milling. This allows us to precisely define the lateral dimensions of the SQUIDs so as to achieve large magnetic coupling between the nanoloop and individual MNPs. By means of focused electron beam induced deposition, cobalt MNPs with a typical size of several tens of nm have been grown directly on the surface of the sensors with nanometric spatial resolution. Remarkably, the nanoSQUIDs are operative over extremely broad ranges of applied magnetic field (–1 T 1 T) and temperature (0.3 K 80 K). All these features together have allowed us to perform magnetization measurements under different ambient conditions and to detect the magnetization reversal of individual Co MNPs with magnetic moments (1–30) . Depending on the dimensions and shape of the particles we have distinguished between two different magnetic states yielding different reversal mechanisms. The magnetization reversal is thermally activated over an energy barrier, which has been quantified for the (quasi) single-domain particles. Our measurements serve to show not only the high sensitivity achievable with YBCO nanoSQUIDs, but also demonstrate that these sensors are exceptional magnetometers for the investigation of the properties of individual nanomagnets.

Improvements in the processing of large grain, bulk Y–Ba–Cu–O superconductors via the use of additional liquid phase

A major limitation to the widespread application of Y–Ba–Cu–O (YBCO) bulk superconductors is the relative complexity and low yield of the top seeded melt growth (TSMG) process, by which these materials are commonly fabricated. It has been demonstrated in previous work on the recycling of samples in which the primary growth had failed, that the provision of an additional liquid-rich phase to replenish liquid lost during the failed growth process leads to the reliable growth of relatively high quality recycled samples. In this paper we describe the adaptation of the liquid phase enrichment technique to the primary TSMG fabrication process. We further describe the observed differences between the microstructure and superconducting properties of samples grown with additional liquid-rich phase and control samples grown using a conventional TSMG process. We observe that the introduction of the additional liquid-rich phase leads to the formation of a higher concentration of Y species at the growth front, which leads, in turn, to a more uniform composition at the growth front. Importantly, the increased uniformity at the growth front leads directly to an increased homogeneity in the distribution of the Y-211 inclusions in the superconducting Y-123 phase matrix and to a more uniform Y-123 phase itself. Overall, the provision of an additional liquid-rich phase improves significantly both the reliability of grain growth through the sample thickness and the magnitude and homogeneity of the superconducting properties of these samples compared to those fabricated by a conventional TSMG process.

Improved noise performance of ultrathin YBCO Dayem bridge nanoSQUIDs

We have fabricated YBa2Cu3O (YBCO) nano superconducting quantum interference devices (nanoSQUIDs), realized in Dayem bridge configuration, on films with thickness down to 10 nm. The devices, which have not been protected by a Au capping layer during the nanopatterning, show modulations of the critical current as a function of the externally applied magnetic field from 300 mK up to the critical temperature of the nanobridges. The absence of the Au shunting layer and the enhancement of the sheet resistance in ultrathin films lead to very large voltage modulations and transfer functions, which make these nanoSQUIDs highly sensitive devices. Indeed, by using bare YBCO nanostructures, we have revealed an upper limit for the intrinsic white flux noise level .

Exfoliated YBCO filaments for second-generation superconducting cable

The second-generation high temperature superconductor (2G HTS) wire is the most promising conductor for high-field magnets such as accelerator dipoles and compact fusion devices. The key element of the wire is a thin Y1Ba2Cu3O7 (YBCO) layer deposited on a flexible metal substrate. The substrate, which becomes incorporated in the 2G conductor, reduces the electrical and mechanical performance of the wire. This is a process that exfoliates the YBCO layer from the substrate while retaining the critical current density of the superconductor. Ten-centimeter long coupons of exfoliated YBCO layers were manufactured, and detailed structural, electrical, and mechanical characterization were reported. After exfoliation, the YBCO layer was supported by a 75 μm thick stainless steel foil, which makes for a compact, mechanically stronger, and inexpensive conductor. The critical current density of the filaments was measured at both 77 K and 4.2 K. The exfoliated YBCO retained 90% of the original critical current. Similarly, tests in an external magnetic field at 4.2 K confirmed that the pinning strength of the YBCO layer was also retained following exfoliation.

Crossover from magnetostatic to exchange coupling in La0.67Ca0.33MnO3/YBa2Cu3O7/La0.67Ca0.33MnO3 heterostructures

The influence of YBa2Cu3O7 (YBCO) superconductor layer (S-layer) with a varying thickness dYBCO = 20–50 nm on the magnetic coupling between two La0.67Ca0.33MnO3 (LCMO) ferromagnet layers (F-layer, thickness dLCMO = 50 nm) in F/S/F heterostructures (HSs) was investigated by measuring global magnetization (M) in a temperature (T) range = 2–300 K and a magnetic field (H) range = 0–10 kOe. All the HSs were superconducting with the critical temperature (TC) decreasing from = 78 to 36 K with decrease in dYBCO, whereas the ferromagnetic ordering temperature TM = 250 K did not change much. Systematically measured M-H loops of all HSs at both T > TC and T < TC show three main results (a) the two step magnetic reversal above TC converts into a four step reversal below TC in HSs with dYBCO ⩾ 30 nm, (b) the magnitude and magnetic field corresponding to the additional two switching steps show characteristic evolution with T and dYBCO; and (c) the HS with dYBCO = 20 nm shows radically different behaviour, where the two step magnetic reversal above TC continues to persist below TC and converts into a single step reversal at T TC. The first two results indicate magnetostatic coupling between the magnetic domains and the vortices across the two F/S interfaces resulting in reversal dynamics different from that deep within the LCMO layers. Whereas, the result ‘c’ reveals indirect exchange coupling between LCMO layers through the superconducting YBCO layer, which is a clear experimental evidence of coexistence of ferromagnetism and superconductivity in nm scale F/S/F HSs expected theoretically by Sa de Melo (2003 Physica C 387 17–25).

Effects of intense optical phonon pumping on the structure and electronic properties of yttrium barium copper oxide

We investigate the structural modulations induced by optical excitation of a polar phonon mode in YBa$_2$Cu$_3$O$_7$, using first-principles calculations based on density functional theory. We focus on the intense-excitation regime in which we expect that fourth-order phonon-phonon coupling terms dominate, and model the structural modulations induced by pulses of such intensity. Our calculations of the phonon-phonon anharmonicities confirm that the cubic coupling between modes, shown in earlier work to cause a quasi-static change in the apical O - Cu distance and a buckling of the CuO$_2$ planes, is the leading contribution at moderate pump strengths. At higher pump strengths ($\sim$10 MV/cm) the previously neglected quartic couplings become relevant and produce an additional shearing of the CuO$_2$ planes. Finally, we analyze the changes in the electronic and magnetic properties associated with the induced structural changes.

A Novel Superconducting Magnet Excited Linear Generator for Wave Energy Conversion System

In almost every permanent-magnet linear generator (PMLG), demagnetization would greatly degrade the electricity generation capability over time. This paper proposes a novel electromagnetic linear generator (EMLG) for direct-drive power generation from oceanic waves, which consists of superconducting magnets instead of conventional permanent magnets to create sufficiently strong magnetic field to produce electricity. The proposed generator can avoid the demagnetization problem of the conventional PMLG. To verify the feasibility of the new concept, a generator is designed. Yttrium barium copper oxide is used to make the superconducting magnet. The finite-element analysis is performed by using the commercial software package ANSYS/ANSOFT to analyze the performance of the proposed EMLG, and the genetic algorithm has been used to find the optimal pole size, pole pitch, air gap length, and load variation to maximize the output power. Magnetic pole shoes are designed in such a way that they can effectively minimize force ripples and cogging force. The results are analyzed and discussed. The results demonstrate that the proposed generator almost eliminates the demagnetization problem of the conventional PMLG with some other built-in advantages. The maximum efficiency of the proposed generator is found to be approximately 96% without considering frictional and other mechanical losses. The results demonstrate excellent features of the proposed generator.

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

Accessing the High‐Q Dark Plasmonic Fano Resonances in Superconductor Metasurfaces

Superconducting metamaterials at terahertz frequencies has provided a platform for designing switchable plasmonic metamaterial devices. However, since metals at terahertz frequencies are excellent conductors, the superior role of superconductors in designing low‐loss, high quality factor metamaterials remains unclear. In this work, a low asymmetry Fano resonant split‐ring‐resonator is considered in which a regime of extremely low radiative loss is identified where the high temperature yttrium barium copper oxide superconductor meta‐atom supports a sharp high quality factor Fano resonance while an identical metallic resonator does not show the resonance behavior. The radiative and the nonradiative losses are comparable in low asymmetry Fano resonant meta‐atoms. The observation of high quality factor Fano resonance behavior clearly establishes the utility of superconductors over metals in designing lower loss plasmonic metamaterials at terahertz frequencies that may have multifunctional applications in areas that require strong light–matter interactions.

Semifluorinated Alkylphosphonic Acids Form High-Quality Self-Assembled Monolayers on Ag-Coated Yttrium Barium Copper Oxide Tapes and Enable Filamentization of the Tapes by Microcontact Printing.

A custom-designed semifluorinated phosphonic acid, (9,9,10,10,11,11,12,12,13,13,14,14,15,15,16,16,16-heptadecafluorohexadecyl)phosphonic acid (F8H8PA), and a normal hexadecylphosphonic acid (H16PA) were synthesized and used to generate self-assembled monolayers (SAMs) on commercially available yttrium barium copper oxide (YBCO) tapes. In this study, we wished to evaluate the effectiveness of these monolayer films as coatings for selectively etching YBCO. Initial films formed by solution deposition and manual stamping using a non-patterned polydimethylsiloxane stamp allowed for a comparison of the film-formation characteristics. The resulting monolayers were characterized by X-ray photoelectron spectroscopy (XPS), contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To prepare line-patterned (filamentized) YBCO tapes, standard microcontact printing (μ-CP) procedures were used. The stamped patterns on the YBCO tapes were characterized by scanning electron microscopy (SEM) before and after etching to confirm the effectiveness of the patterning process on the YBCO surface and energy-dispersive X-ray spectroscopy (EDX) to obtain the atomic composition of the exposed interface.

Dual ion beam assisted magnetron deposition of biaxially textured YSZ and YBCO/YSZ thin films

Abstract Biaxially textured yttria stabilized zirconia (YSZ) thin films were deposited on polished hastelloy and silicon substrates using ion beam assisted deposition (IBAD). The IBAD apparatus includes a planar magnetron fitted with a crystalline YSZ target to provide the film-forming species, and two Kaufman-type ion beam sources which provide Ar+ ions for bombarding the film during growth. The two ion beam sources were mounted symmetrically at 55° angles to the substrate plane normal, making 110° angle between them. Textured YSZ films were deposited under three different IBAD conditions: (a) films were bombarded by a single ion beam source (SIBAD), (b) films were bombarded by a single ion beam source for a time alternating from the two symmetric directions (AIBAD), and (c) by dual ion beam assisted deposition (DIBAD) where the film was bombarded simultaneously from the two symmetric directions. The X-ray φ-scan results indicate that DIBAD followed by epitaxial growth of YSZ produced the highest degree of biaxial texture in YSZ films. Superconducting yttrium barium copper oxide (YBCO) films deposited on highly textured DIBAD YSZ films had φ-scan full width at half maximum of 7.1° and 5.5° for hastelloy and silicon substrates, respectively.