Y2BaCuO5 Phase Research Articles

Thermodynamic Properties of Stoichiometric Non-Superconducting Phase Y2BaCuO5.

Y2BaCuO5 often occurs as an accompanying phase of the well-known high-temperature superconductor YBa2Cu3O7 (also known as YBCO). Y2BaCuO5, easily identifiable due to its characteristic green coloration, is often referred to as ‘green phase’ or ‘Y-211’. In this contribution, Y2BaCuO5 phase was studied in detail with a focus on its thermal and thermodynamic properties. Energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed in the study of sample’s morphology and chemical composition. XRD data were further analyzed and lattice parameters refined by Rietveld analysis. Simultaneous thermal analysis was employed to study thermal stability. Particle size distribution was analyzed by laser diffraction. Finally, thermodynamic properties, namely heat capacity and relative enthalpy, were measured by drop calorimetry, differential scanning calorimetry (DSC), and physical properties measurement system (PPMS). Enthalpy of formation was assessed from ab-initio DFT calculations.

Synthesis of Y2BaCuO5 nano-whiskers by a solution blow spinning technique and their successful introduction into single-grain, YBCO bulk superconductors

The ability of single grain Y-Ba-Cu-O (YBCO) bulk superconductors to trap large magnetic fields is due generally to the presence of embedded, non-superconducting Y2BaCuO5 (Y-211) phase particles, in optimum amount, in the superconducting YBa2Cu3O7-δ (Y-123) phase matrix, which increases flux pinning and, hence, critical current density of the bulk material. The presence of smaller particles of Y-211 could be expected to improve further the superconducting properties of single grain, bulk YBCO samples, although the smallest Y-211 particles that have been engineered to date within the bulk microstructure are around 800 nm in size. It is extremely challenging to reduce the Y-211 particle size any further due to problems of particle agglomeration that originate, inevitably, from the effects of surface energy and reactivity at relatively high processing temperatures. In this work, we report a novel approach to the fabrication of Y-211 pinning centres in bulk YBCO superconductors in the form of nano-whiskers manufactured by a solution blow spinning technique. The Y-211 nano-whiskers, of which 62% were smaller than 500 nm, were added to the YBCO precursor powders to produce a single grain bulk sample by the buffer-aided top-seeded melt growth (BA-TSMG) processing technique. The resulting YBCO single grain, of diameter 20 mm, was able to trap a magnetic field of 0.63 T at 77 K with an associated critical current density of 3.9 × 104 A/cm2 in self-field. The results of this study demonstrate clearly that the use of Y-211 nano-whiskers is a promising route for enhancing flux pinning in bulk YBCO single-grains, which is potentially significant for the development of high field engineering applications.

Effect of CuO on microstructure and conductivity of Y-doped BaCeO3

Effect of CuO additions on sinterability and conductivity of BaCe0·85Y0.15O2.925 was studied. Two different amounts, 0.75 and 1.5wt% with respect to the pure powder, were considered. Microstructural characterization showed that for smaller additions Cu was completely incorporated on B-site of the perovskite, while formation of the secondary phase Y2BaCuO5 was detected when higher amount of CuO was added. Enhanced cations diffusivity at grain boundary is responsible for a pronounced reduction of sintering temperature and grain growth. Density as high as 96–97% of theoretical value was obtained when sintering at 1000°C for 2h.As long as Cu is incorporated in the perovskite, higher conductivity and lower activation energy of grain core were found. In addition, total conductivity of 0.75wt% doped material was limited by fine grain size that resulted in apparent poor conductivity of the grain boundary.On the contrary when Cu segregates in the Y2BaCuO5 phase, overall conductivity increased mostly because of the contribution from the electronic conductivity of that phase.

Influence of layered precursor pellets on the growth and properties of Y-Ba-Cu-O bulk superconductors by top-seeded melt-textured growth

It is well known that a fine and homogeneous distribution of Y2BaCuO5 (Y211) phase particles in single-grain Y-Ba-Cu-O (YBCO) bulk superconductors is essential for improving field-trapping ability. However, the size and concentration of Y211 phase particles in the fully melt-processed superconducting bulk increase significantly with the distance from the seed, which results in the accumulation of Y211 phase particles and the degradation of superconducting properties. In this paper, we report a new method of fabricating single-grain YBCO using layered precursor pellets. Using the top-seeded melt-textured growth process, single-grain YBCO bulk superconductors of about 22 mm in diameter and 9 mm in thickness were fabricated from layered precursor pellets and standard precursor pellets, respectively. The layered precursor pellets consist of precursor powders with 40 mol% Y211 at the top, 30 mol% Y211 in the middle and 20 mol% Y211 at the bottom of the whole pellets, while standard precursor pellets are prepared from precursor powders with only 40 mol% Y211. The growth morphology, microstructure and magnetic flux properties of the layered samples and standard samples were comparatively studied. The results proved that the layered precursor pellets allow a sufficient growth in the c-growth sector and a more uniform distribution of the Y211 phase in the matrix. The distribution of Y211 phase particles is qualitatively explained by the prevalent trapping/pushing theory. The trapped field at 77 K reaches 0.8 T, nearly 29% higher than the standard sample. The present results are very valuable for further improving the properties of YBCO bulk superconductors.

Processing and Properties of Bulk Y–Ba–Cu–O Superconductors Fabricated by Top Seeded Melt Growth from Precursor Pellets Containing a Graded CeO2 Composition

The existence of a zone containing a low concentration of Y2BaCuO5 (Y-211) phase particles in the vicinity of the seed in single grain, bulk Y–Ba–Cu–O (YBCO) superconductors fabricated by the top seeded melt growth (TSMG) technique has been reported, suggesting the presence of low intrinsic magnetic flux pinning, and hence reduced trapped field, in this region of the sample. The possibility of introducing additional pinning centers in the vicinity of the seed in single grain YBCO, therefore, may be effective in improving the applied magnetic properties of these technologically important materials. Single grain, bulk YBCO superconductors fabricated from precursor pellets containing a graded CeO2 composition have been prepared corresponding to a secondary phase content of 2 wt % CeO2 beneath the seed and 1 wt % CeO2 at the outer, “U” shape cross-section, of the sample. The resulting graded single grain YBCO superconductors exhibit enhanced trapped field compared to standard YBCO superconductors fabricated by TSMG from precursor pellets containing purely 1 wt % CeO2. The influence of CeO2 content on the microstructure, growth process, and superconducting properties of bulk, single grain YBCO superconductors fabricated by TSMG has been investigated and used to explain the increased trapped field ability of the graded composition.

Investigation the Properties of Y-Ba-Cu-Oxide Superconductors Prepared by Hydraulic Pressing and Molding

Levitation applications of superconductors require the fabrication of bulk ceramic superconductors with special shapes. The conventional hydraulic pressing is not suitable for the production of superconductors with complicated forms, so we have applied slip casting to shape bulk superconductors. Superconducting powders with different YBa2Cu3Oy (123) and Y2BaCuO5 (211) phase content and different (Pt, Pb, Ce) additives were prepared by solid-state reactions. The nonsuperconducting (211) particles can be considered as flux pinning centres; thus the magnetic properties can be influenced by their amount and particle sizes. The addition of a few weight percent of dopant in the nominal composition can modify the particle size and distribution of the (211) grains. We have investigated and compared the phase compositions, morphologies and magnetic levitation forces of bulk superconductors formed by hydraulic pressing and moulding. The shielding abilities of a moulded superconductor were simulated with the COMSOL Multiphysics 4.4 software.

The processing and properties of single grain Y–Ba–Cu–O fabricated from graded precursor powders

The preparation of single grain, Y–Ba–Cu–O (YBCO) bulk superconductors by top-seeded melt-growth (TSMG) usually involves precursor powders that contain a uniform distribution of the constituent YBa2Cu3O7−δ (Y-123) and Y2BaCuO5 (Y-211) phase compounds. However, it has been observed that the concentration of Y-211 particles in the fully melt processed superconducting bulk increases significantly with distance from the seed, which results in a degradation of superconducting properties towards the edge and bottom of the sample. Here we investigate the effect of preparing bulk YBCO superconductors by TSMG using spatially graded Y-211/Y-123 precursor powder. The graded precursor bulks were prepared with a maximum composition of 40 wt% Y-211 in the vicinity of the seed, which decreased to 30 wt% and then 20 wt% towards the bottom and edge of the green body. Standard samples were melt processed from precursor powders containing 30 wt% Y-211 to enable comparison. The field trapping ability, Tc and Jc, of three graded and two standard samples were investigated and compared statistically. The distribution of Y-211 particles along different growth directions of the samples was analysed, and any crystallographic misorientation was investigated. The observed distribution of Y-211 particles in YBCO is explained qualitatively by trapping/pushing theory, and its correlation with the superconducting properties of the melt processed bulk samples has been analysed. Finally, the practical feasibility of the graded technique is evaluated.

Coexistence of ferromagnetism and spin glass behavior in antiferromagnetic Y2BaCuO5

We report the synthesis of a series of Y2BaCuO5 samples by varying the annealing temperature with a citrate pyrolysis technique. X-ray diffraction patterns, scanning electron microscopy and transmission electron microscopy observation show the formation of a columnar Y2BaCuO5 phase and these samples are composed of many irregular particles with different particle size. Magnetic measurements show that these samples exhibit room temperature ferromagnetism and the saturation magnetization decreases with increasing sintering temperature. Post-heating treatment under argon atmosphere can enhance the ferromagnetism greatly, suggesting that the magnetism is attributed to the surface oxygen defects. By measuring magnetization versus temperature curves after zero field cooling with various applied magnetic fields, two magnetic phase transitions located at about 11 and 110K are revealed. The position of the peak at about 11K is independent of the magnetic field; the other peak, however, becomes rounder and shifts to lower temperatures with increasing the magnetic field, showing a strong field dependence. In addition, the virgin magnetization curves with the measured temperature below 110K display an S-type. These features are suggestive of an antiferromagnetic phase transition at about 11K and a spin glass transition at about 110K.

New method for introducing nanometer flux pinning centers into single domain YBCO bulk superconductors

Single domain YBCO superconductors with different additions of Bi2O3 have been fabricated by top seeded infiltration and growth process (TSIG). The effect of Bi2O3 additions on the growth morphology, microstructure and levitation force of the YBCO bulk superconductor has been investigated. The results indicate that single domain YBCO superconductors can be fabricated with the additions of Bi2O3 less than 2wt%; Bi2O3 can be reacted with Y2BaCuO5 and liquid phase and finally form Y2Ba4CuBiOx(YBi2411) nanoscale particles; the size of the YBi2411 particles is about 100nm, which can act as effective flux pinning centers. It is also found that the levitation force of single domain YBCO bulks is increasing from 13N to 34N and decreasing to 11N with the increasing of Bi2O3 addition from 0.1wt% to 0.7wt% and 2wt%. This result is helpful for us to improve the physical properties of REBCO bulk superconductors.

Effect of magnetic particle additions on flux pinning in bulk Y-Ba-Cu-O superconductors

Abstract In order to increase the critical current density of high temperature superconductors, it is commonly employed to disperse nonsuperconducting particles as flux pinning centers into the superconductive matrix. For Y-Ba-Cu-O bulk superconductors Y2BaCuO5 (Y211) phase particles are known to be effective pinning centers. It has been proposed that magnetic particles are more efficient pinning centers, since they will have a stronger positive interaction with quantized fluxoids. A combined addition of Y211 and magnetic metal fine powders has been reported to be effective in improving flux pinning performances. Therefore, in this study we aimed at improving the pinning forces of Y-Ba-Cu-O bulk superconductors by introducing the Fe-Al-Si-based alloys that are ferromagnetic. We also studied the effect of the addition of γ-hematite, which is non-magnetic, in order to compare the contribution to the flux pinning enhancement. For comparative study, we measured the trapped field in single-domain bulk superconductors and found that a small addition of Fe-Al-Si based ferromagnetic powders and γ-hematite improved field trapping ability.

Superconducting properties of Y-Ba-Cu-O bulk with BaSnO3 addition

Dispersion of non-superconducting phase particles is commonly employed in melt textured REBa2Cu3O7-δ (RE123; RE: rare earth element) bulk superconductors in order to improve the critical current density. It has been clarified that the interfaces of RE2BaCuO5 (RE211) and RE123 matrix contribute to the flux pinning, and therefore, the critical current density can be enhanced due to the refinement of RE211 particles. In recent years additions of RE2Ba4CuMOy (M=Zr, Nb, Ta, Mo, U, Sn, and Re) particles have been investigated in an attempt to improve the pinning performance. While the common particle size is around 1-5 μm for the RE211, the size of RE2Ba4CuMOy particles is much finer and typically 50∼300 nm, implying that the pinning may be improved with the dispersion of RE2Ba4CuMOy particles. In this study, we have studied the effects of the BaSnO3 addition to Y2BaCuO5 (Y211) powders. It was found that two different compounds of Y2Ba4CuSnOy and Y2BaCuO5 phase particles were co-produced by adding BaSnO3 to Y211. These powders were added to the precursor and subjected to the melt-textured process to grow bulk Y-Ba-Cu-O superconductors of 20 mm diameter with the top-seed melt growth process. The finished bulk samples were observed with optical microscopy and subjected to trapped field measurements with Hall sensors. The trapped field measurements showed that BaSnO3 addition was effective in improving the field trapping ability.

Noise properties of nanoscale YBa2Cu3O7−δJosephson junctions

We present electric noise measurements of nanoscale biepitaxial YBa2Cu3O(7-x) (YBCO) Josephson junctions fabricated by two different lithographic methods. The first (conventional) technique defines the junctions directly by ion milling etching through an amorphous carbon mask. The second (soft patterning) method makes use of the phase competition between the superconducting YBCO (Y123) and the insulating Y2BaCuO5 (Y211) phase at the grain boundary interface on MgO (110) substrates. The voltage noise properties of the two methods are compared in this study. For all junctions (having a thickness of 100 nm and widths of 250-500 nm) we see a significant amount of individual charge traps. We have extracted an approximate value for the effective area of the charge traps from the noise data. From the noise measurements we infer that the soft patterned junctions with a grain boundary (GB) interface manifesting a large c-axis tunneling component have a uniform barrier and a SIS like behavior. The noise properties of soft patterned junctions having a GB interface dominated by transport parallel to the ab-planes are in accordance with a resonant tunneling barrier model. The conventionally patterned junctions, instead, have suppressed superconducting transport channels with an area much less than the nominal junction area. These findings are important for the implementation of nanosized Josephson junctions in quantum circuits.

Transition of Y2BaCuO5 phase in powder melting processed YBa2Cu3O7−x superconductors

The morphology and the formation of Y2BaCuO5 phase in powder melting processed YBa2Cu3O7−x superconductors were investigated. The experimental results show the heat treatment can not change the shape of Y2BaCuO5 particles in powder melting processed samples. The formation of round Y2BaCuO5 phase is due to relative content of each constitution of precursor powders in powder melting process. For powder melting process, the excessive liquid phase is eliminated, which restrains the preferred growth of Y2BaCuO5 particles.

Soft Nanostructuring of YBCO Josephson Junctions by Phase Separation

We have developed a new method to fabricate biepitaxial YBa2 Cu3 O7-δ (YBCO) Josephson junctions at the nanoscale, allowing junctions widths down to 100 nm and simultaneously avoiding the typical damage in grain boundary interfaces due to conventional patterning procedures. By using the competition between the superconducting YBCO and the insulating Y2 BaCuO5 phases during film growth, we formed nanometer sized grain boundary junctions in the insulating Y2 BaCuO5 matrix as confirmed by high-resolution transmission electron microscopy. Electrical transport measurements give clear indications that we are close to probing the intrinsic properties of the grain boundaries.

Fluctuation conductivity along the c-axis and parallel to the ab-planes in melt-textured YBa2Cu3O7− samples doped with Y211 phase

Abstract We report measurements of in-plane and out-of-plane fluctuation conductivity under low applied magnetic fields up to 500 Oe in two melt-textured YBa2Cu3O7−δ (YBCO) samples. 3D-Gaussian and genuine critical 3D-XY-E fluctuation regimes were identified in the conductivity parallel to the ab plane. In addition, a regime beyond 3D-XY was observed in the immediate vicinity of the superconducting transition of the in-plane fluctuation conductivity. The 3D-XY-E scaling was also identified in the fluctuation conductivity along the c-axis in the sample with smaller content of the Y2BaCuO5 (Y211) phase. This result indicates that the superconducting state in YBCO has a three-dimensional character, in contradiction to some studies suggesting that critical phenomenology is fundamentally distinct in orientations parallel or perpendicular to the Cu–O2 planes of the high-temperature superconductors. However, the results suggests the presence of a sub-dominant order-parameter component in YBCO that has an appreciable projection along the c-axis.

Growth and Structural Characterization of Needlelike Crystals in the Y−Ba−Cu−O System

A system formed by a bar of Y2BaCuO5 (Y211) phase supported on two YBa2Cu3Ox (Y123) pellets was processed by thermal treatment at high temperature. The first effect was a change in chemical composition inside the bar, yielding new phases: mostly Y123 and BaCuO2. Their concentrations were higher near the bar ends. A second, very interesting result was the growth of two kinds of acicular crystals underneath the whole bar: green, transparent Y211 needles and needles with a green core of Y211, covered by a Y123 layer. Micro Raman and SEM analyses clearly identified the two different phases. XRD inspection has confirmed that Y211 crystals are high-quality single crystals. The preferential growth direction for Y211 needles is along the crystallographic b axis. A possible explanation, based on the VLS mechanism, for their growth is suggested.

Artificial flux pinning centers in large, single-grain (RE)-Ba-Cu-O superconductors

Second-phase, nanoscale inclusions of composition Y2Ba4CuMOy (M=U, Nb, Ta, W, Mo, and Re), which form artificial pinning centers, have been introduced into large, single-grain [rare-earth (RE)]-Ba-Cu-O superconductors. A significant improvement in critical current density is observed in these samples, due presumably to various combinations of normal conducting, paramagnetic, and geometrical properties of the Y2Ba4CuMOy particles in the superconducting (RE)Ba2Cu3O7−δ (RE-123) phase matrix. These Y2Ba4CuMOy phase particles are chemically stable in the Ba-Cu-O liquid during peritectic solidification, unlike Y2BaCuO5 (Y-211) phase particles in Y-Ba-Cu-O, which opens a processing window for the fabrication of nanostructured large, single-grain (RE)-Ba-Cu-O superconductors with enhanced flux pinning for high-field engineering applications.

Thickness dependence of microstructure and critical current density of Yba2Cu3O7−δ on rolling-assisted biaxially textured substrates

The change in microstructure associated with the decrease in critical current density (Jc) of Yba2Cu3O7−δ (YBCO) films with increasing thickness was examined. Samples of pulse laser deposited YBCO films varying in thickness from 0.19 to 3.0 μm on rolling-assisted biaxially textured substrates with an architecture of CeO2/YSZ/CeO2/Ni were prepared by tripod polishing for cross-sectional electron microscopy. More randomly oriented grains in the upper portion of the YBCO film surface were observed with increasing film thickness, resulting in less cube texture. In addition, increases in mismatch across the boundaries of the c-axis grains with increasing time during deposition, along with the development of BaCeO3 and Y2BaCuO5 phases at the YBCO/CeO2 interface, contributed to the degradation of film properties. Surface outgrowths of the YBCO film were examined as well as the defect structures and second-phase formations within the films.

Phase Transformations in the Y2BaCuO5, «Ba3Cu5O8» and Y2BaCuO5-«BaCuO2» Systems

Peritectic interaction of Y2BaCuO5 and Y2BaCuO9-d phases with the Y-Ba-Cu-O system flux melt has been modeled. The sequence of phase transformations in the Y2BaCuO5-«Ba3Cu5O8» and Y2BaCuO5-«BaCuO2» systems when forming the YBa2Cu3O7-d single crystal compound has been established.

Mono-domain YBa2Cu3Oy superconductor fabrics prepared by aninfiltration process

A novel process for the fabrication of a new form of YBa2Cu3Oy (123) superconducting material, with thedimensions of a thick film and the microstructure of a melt-texturedsingle-domain bulk is described. The process allows the fabrication of 123as a self-supporting fabric or as a thick film on various substratematerials. The process, which is generic and economical, uses commerciallyavailable Y2O3 fabrics as a precursor material. The Y2O3 cloth is infiltrated with barium cuprates and copper oxidesfrom a liquid-phase source, then converted into Y2BaCuO5(211) phase and eventually to 123. The nucleation and growth of the 123phase is controlled by seeding the cloth with an oriented heterogeneous MgOor Nd123 seed. Interesting application areas for the new form of the 123mono-domain fabric are discussed.