YBa2Cu3O7‐δ superconductor bulks composited by Y2BaCuO5 nanoparticles derived from homogeneous nucleation catastrophe

The refinement of Y₂BaCuO₅ (Y211) particles is a matter of significant importance in fabricating high‐performance YBa₂Cu₃O_7‐δ (Y123) superconductor bulks by top‐seeded melt growth (TSMG). However, coarsening and epitaxial growth naturally occur to the preexisting Y211 grains in the conventional process, causing an unwanted size enlargement. Here, for the first time, we report a novel TSMG approach in which instead of Y211, modified precursor powders (MPP, Y₂O₃, and Ba₂Cu₃O_x) were employed. As a result, massive numbers of Y211 nanoparticles were derived from the homogeneous nucleation catastrophe through peritectic solidification of Y₂O₃+Ba_x‐Cu_y‐O→Y211. Correspondingly, superior property of trapped field was achieved from the MPP‐processed bulk.     

Low temperature ruthenium catalyst for ammonia synthesis supported on BaCeO3 nanocrystals

The nanocrystalline barium cerate (BaCeO₃) was synthesized and examined as a support promoting ammonia synthesis catalyzed by particulate Ru. It was quite worthy noting that Ru/BaCeO₃ catalyst exhibited superior activity to the conventional ruthenium catalysts supported on γ–Al₂O₃, MgO and CeO₂ at low reaction temperature. The characterization including XRD, HRTEM, XPS and TPR results demonstrated that electronic interaction between Ce (IV) and Ru metals combined with strong metal-support interaction was responsible for such high catalytic activity at low reaction temperature.     

Almost complete peritectic reaction in YBa2(Cu1−xFex)3O7−δ crystallization involving nanosized primary phase

Study on peritectic reaction is a matter of significant importance in materials science, which generally involves in the solidification of most functional oxide materials, for example, the YBa₂Cu₃O_7?δ (Y123) superconductor could be grown via a reaction of Y₂BaCuO₅ (Y211) + Liquid→Y123. Due to its crystallization characteristic, the growth of those materials does not entirely proceed, which severely impedes the development of industrialized process. Thus the realization of a complete peritectic reaction is an interesting issue for both theory and experiment. Here, we report an almost complete peritectic reaction occurring in the growth of YBa₂(Cu_1?xFe_x)₃O_7?δ crystals using modified melt‐growth. Our findings remarkably show that Y211 almost fully reacted with liquid to generate Y123, remaining approximately 1 vol%, evidently lower than that in the normal case. The nature of this unconventional phenomenon is clarified that the Fe‐doping elevates the nucleation barrier in the peritectic melting of Y123 and causes a massive homogeneous nucleation catastrophe, leading to nanosized and dispersive Y211 particles, which readily and almost fully dissolve in the subsequent peritectic solidification of Y123. Most importantly, the new conception derived from this work is promising for reviving other functional materials, which are disregarded due to their incomplete peritectic reactions.     

Novel Loading‐Free Joining Process for YBCO Single‐Grain Bulks

We report a novel joint fabrication method for YBa₂Cu₃O_7?x (Y123) bulk superconductors without pressure loading, based on a well‐controlled high‐temperature process. Due to the direction of the heat fluxes in a box furnace, the surfaces of the joined samples melt first, and the crystal morphology of the original YBa₂Cu₃O_7?x bulks remains. After the joining process, part of the texture zone is used as a seed to grow new texture crystals for nucleation during cooling. Finally, a high‐quality artificial grain boundary forms without acting as a weak link, which is supported by the trapped field distribution. Details of the joint are presented, including its microstructure and micro‐orientation. Moreover, the trapped field values at 65 and 45 K are presented.     

Significant Improvement of Superconducting Properties in Nano‐NiFe2O4‐Doped Y–Ba–Cu–O Single‐Grain Superconductor

Introduction of refined second‐phase particles in superconducting YBa₂Cu₃O_7?x (Y‐123) matrix is known to be an effective route to improve the δl‐type pinning and the performance of Y–Ba–Cu–O (YBCO) single‐grain superconductors, while the δT_c‐type pinning induced by spatial fluctuations in matrix composition is also important and contributes to the in‐field J_c performance and high‐field applications of bulk superconductors. In this communication, chemical doping of nano‐sized NiFe₂O₄ (mean size 50 nm) in single‐grain YBCO superconductor is performed using a novel top‐seeded infiltration growth (TSIG) technique based on a solid source pellet (SSP) of nano‐Y₂O₃ + BaCuO₂. The results indicate that, significant improvement of bulk performances including levitation force (33.93 N) and trapped field (0.3628 T) has been observed in the 0.2 wt% nano‐NiFe₂O₄‐doped sample, which are much higher than the undoped sample (28.81 N and 0.2754 T). T_c measurement indicates that, a decreased onset T_c of about 87.5 K and a broadened transition width of about 5 K are observed in the NiFe₂O₄‐doped sample, indicating appearance of weak superconducting regions in superconducting matrix caused by Ni and Fe substitutions in Y‐123 crystal lattice. This study supplies a practical approach to increase the YBCO bulk performance significantly.     

Comparison of the catalysed decomposition of hydrogen peroxide over superconducting and insulating barium cuprates—kinetics of decomposition over Y2BaCuO5

Catalytic activities of two non-conducting cuprates (Ba₂Cu₃O₅, Y₂BaCuO₅) and a superconducting cuprate YBa₂Cu₃O_7–δ, prepared by two different methods, were compared using H₂O₂ solution. The two non-conducting barium cuprates were found to be about two orders of magnitude more active than the superconducting perovskite-like YBa₂Cu₃O_7–δ. The near coincidence of the kinetic curves for the catalysed decomposition of H₂O₂ over YBa₂Cu₃O_7–δ, prepared either from the perovskite-like Ba₂Cu₃O₅ and Y₂O₃ or from its components, proves that Ba₂Cu₃O₅ is essential in the formation of YBa₂Cu₃O_7–δ. First-order kinetics were observed for the catalysed decomposition of H₂O₂ solution over the non-perovskite Y₂BaCuO₅ at the initial stages of the reaction, similar to that of the superconducting perovskite catalyst. A tentative scheme of the possible catalytic reactions for the decomposition of H₂O₂ solution over the insulator Y₂BaCuO₅ is given.     

Continuous solidification of YBa2Cu3O7−x by isothermal undercooling

Growth kinetics and microstructural development of single crystal YBa₂Cu₃O_7−x (Y123) superconductors, prepared by a melt texturing method under isothermal undercooling conditions, were investigated. At small undercooling, ΔT = 6 K, the initial growth of Y123 crystal was terminated at a size of ∼8 mm × 8 mm in the semisolid phase before the entire sample was fully solidified through the peritectic reaction. With incremental increase of ΔT, the growth of the crystal continued so that the whole sample (22 mm diameter and 8 mm thickness) solidified as a single crystal. Termination of the crystal growth at a given undercooling temperature was attributed to the coarsening process of Y211 particles in the melt associated with their surface energy contributions. Isothermal growth of large size Y123 single crystal requires a continuous supply of Y solute to the solidification interface which can be achieved by continuing dissolution of coarsening Y211 particles through further undercooling of the melt.     

A comparative study of (Ce) and (Gd) doping influence on the superconducting properties of YBCO ceramics

This work is devoted to investigate the structural and electrical properties of the Ce, Gd-doped YBCO superconductors bulk ceramics. YBa_2-xRE_xCu₃O_7−δ (x = 0, 0.01, 0.05, 0.1) (RE = Gd, Ce) samples were prepared by means of conventional solid-state reaction. X-ray diffraction analysis was carried out to identify the present phases in the as-prepared samples followed by the determination of their lattice parameters. Fourier Transform Infrared Spectroscopy (FTIR) was used to identify the functional groups. Furthermore, the morphology and the surface roughness of the studied samples were characterized using Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). Vickers Micro-hardness of the as-prepared samples was examined. Besides, the electrical resistivity measurements were achieved to determine the critical transition temperature T_C and the critical current density J_C.The effect of Ce and Gd additions is clearly noticed in the obtained results, where all the prepared samples are superconductors with the presence of Y123 as a major polycrystalline phase. From the XRD patterns, the intensities of the Y123 corresponding peaks decrease with further increasing the Ce and Gd contents. In addition, the variation of the cell parameters was significant after additions of both Ce and Gd, which affect the grain size and the oxygen content of the YBa_2-xRE_xCu₃O_7−δ system. An improvement of the structure and surface roughness is observed on SEM and AFM images. Likewise, Vickers micro-hardness has increased after the Ce and Gd additions. Although, the critical transition temperature T_C was not further increased upon Ce or Gd additions compared to the undoped YBCO samples. Nevertheless, an exception has been recorded with an increase of T_C for YBa_2-xRE_xCu₃O_7−δ with (RE = Gd, x=0.01) to reach 88 K. In contrary, an improvement of the deduced critical current density J_C was achieved for all Ce-doped YBCO samples unlike those of Gd-doped samples.     

A Novel Top‐Seeded Infiltration Growth Technique for Fabricating Y–Ba–Cu–O Single‐Grain Superconductor Nano‐Composites

Top‐seed infiltration and growth technique (TSIG) is proposed to fabricate Y–Ba–Cu–O (YBCO) single‐grain superconductor nano‐composites, in which a solid source composition of nano‐Y₂O₃ + BaCuO₂ and a liquid source composition of Y₂O₃ + 10BaO + 16CuO are employed. As can be seen, this novel technique uses just one source of precursor powder of BaCuO₂, so it is more simplified and efficient. Microstructural observation indicates that fine Y₂BaCuO₅ (Y‐211) inclusions with a size from dozens of nanometers to about one hundred nanometers are successfully introduced in YBa₂Cu₃O_7?x (Y‐123) superconducting matrix, which can act as more effective pinning centers for improving the bulk performance. Superconducting property measurement shows that, a maximum trapped field of 0.36044 T is present at the center of the sample after magnetization by a permanent magnet (B = 0.5 T). These results prove that our proposed TSIG technique is a practical method for fabricating YBCO bulk superconductor nano‐composites with high performance.     

Performance of spray deposited Gd-doped barium cerate thin films for proton conducting SOFCs

Doped barium cerate is a promising solid electrolyte for intermediate temperature fuel cells as a protonic conductor. In the present paper, the nanocrystalline Gd-doped barium cerate (BaCe_0.7Gd_0.1Y_0.2O_2.9) thin films have been successfully deposited on alumina substrate by spray pyrolysis technique. The films deposited from 0.1 M concentration and annealed at five different temperatures were characterized with different physio-chemical techniques. The BCGY is crystallized in orthorhombic perovskite structure with slight shift to the lower 2θ value compared with barium cerate (BC) and yttrium doped barium cerate (BCY). The grain growth and hence densification is also investigated by using SEM and AFM. The grain growth is almost complete at 1000 °C and the surface of the film appears to be smooth with typical roughness of 152 nm. Raman spectrum of BCGY film shows intense band at 463.8 cm⁻¹ compared to pure BC and BCY indicating the presence of more oxygen vacancies due to Gd doping. The proton conductivity of BCGY thin film in moist atmosphere is 1×10⁻³ Scm⁻¹.     

Catalytic behavior of YBa2Cu3O7-x in the partial oxidation of ethanol to acetaldehyde

The partial oxidation of ethanol to acetaldehyde was performed over YBa₂Cu₃O_7-x in a flow reactor. The catalytic characteristics of YB₂Cu₃O_7-x were compared with those of an individual oxide comprising the YBa₂Cu₃O_7-x . The structural change of YBa₂Cu₃O_7-x and the other catalysts after the reaction was measured by means of XRD and XPS, and it was found that the high oxidation state of copper in YBa₂Cu₃O_7-x was responsible for the higher activity and the higher selectivity for acetaldehyde.     

Catalytic behavior of YBa2Cu3O7-x in the partial oxidation of methanol to formaldehyde

The partial oxidation of methanol to formaldehyde was studied over YBa₂Cu₃O_7-x catalyst in a flow reactor. The structural change of YBa₂Cu₃O_7-x before and after the reaction was measured by means of XRD and iodometric titration method. The catalytic characteristics of YBa₂Cu₃O_7-x for the partial oxidation of methanol to formaldehyde was due to copper ions. It was found that Cu⁺² was responsible for the higher selectivity for formaldehyde.     

Fabrication of YBa2Cu3O7−x (YBCO) superconductor bulk structures by extrusion freeforming

Practical applications of high temperature superconductors may require them to be processed into complex geometries. In this work, slurry-based extrusion freeforming coupled with high temperature treatment was attempted for the fabrication of bulk YBa₂Cu₃O_7−x (YBCO) superconducting structures. YBCO parts with approximately 93% of the theoretical density were successfully fabricated after sintering at 940 °C for 60 h, with the obtained constituent phases strongly dependent on the heat treatment temperature and duration. A high critical transition temperature (T_C=92 K) and good magnetic levitation ability could be obtained after optimization of the heat treatment conditions. Overall, the experimental results demonstrate that extrusion freeforming is a feasible and effective technique for fabricating YBCO superconductors that have desirable configurations and good superconductivity properties.     

Thermal reactivity of YBa2Cu3O7-δ with Al2O3 addition in air atmosphere

The high–temperature thermal reactivity of YBa₂Cu₃O_7-δ (Y123) compound with Al₂O₃ addition (0.5–10?wt%) was investigated and the thermal processes were described. Experimentally obtained results showed that Al₂O₃ firstly reacted with Y123 at temperatures far below the peritectic melting point of Y123. During this solid state reaction Al partially diffused into Y123 and formed a solid solution. Also, the formation of Al-rich complex oxides, mainly with barium, and basic secondary phases as Y₂BaCuO₅ and CuO, was observed with increasing Al₂O₃ content. The formation of additional secondary phases with Al₂O₃ provoked their reactivity with Y123 or between themselves. After increasing the temperature of the powder mixtures above the peritectic melting point of Y123 it was found that Al was incorporated in Y123 at higher concentrations than during the solid state reaction. The reason for that could be a partial or full dissolution of Al-rich complex oxides formed at lower temperatures which in turn increased the source of Al for the incorporation in Y123.The thermal behaviour of powder mixtures was investigated with the help of simultaneous differential thermal analysis and thermogravimetry. Morphology and microstructure were examined using powder X-ray diffraction and scanning electron microscopy in combination with energy dispersive X-ray spectroscopy.     

Plastic Forming of High‐Tc YBa2Cu3O7−x Bulk Superconductors

The large bulk high‐T_c YBa₂Cu₃O_7?x (YBCO) superconductor samples were prepared by plastic‐forming method. We examined the effects of the solvent and the crystallinity of YBCO powder on the composition, crystallinity, and superconducting properties of YBCO sheet samples (sample size: 50 mm × 50 mm× 3 mm). By changing the solvent from water to turpentine oil, the leaching of Ba²⁺ ions from YBa₂Cu₃(OH)_y multimetallic hydroxide particles used as an inorganic binder and the YBCO powder were reduced. This results in the composition of the grain boundaries of fired YBCO sheet samples to be the same as the composition of YBa₂Cu₃(OH)_y multimetallic hydroxide particles. Changing nondoped YBCO powder prepared by sintering to 5 wt% Pt‐doped YBCO powder prepared by melt texturing, J_c value of YBCO sheet samples changed from about 700 to 6,106 A/cm² at 77 K.     

Corrosion behavior of high-temperature superconductor YBa2Cu3-yAgyO7-x in the presence of water

Because of the presence of water vapor, YBa₂Cu₃O_7-x degrades easily in the atmosphere and thus very difficult to put it to practical use. When Cu is partially substituted with Ag, however, there is not much a decrease in the critical temperature (T_c) : T_c is 89 K compared with 91 K without substitution. Moreover, partial substitution of Ag increases density, hardness, and superconducting particle size and above all improves considerably its stability in water. In this study YBa₂Cu₃O_7-x and YBa₂Cu_3-yAg_yO_7-x as a result of a partial substitution of Ag for Cu were synthesized by pyrophoric method. We investigated their stabilities in water by XRD, SEM, and EPMA after immersing samples in distilled water for 3 hours. We can see that YBa₂Cu_2.94Ag_0.06O_7-x was the largest particle size and anticorrosion behavior.     

Research of both γ-irradiation and La2O3 addition on structural and magnetoresistivity of Bi-2223 bulk superconductors

In this study, we investigate the effects of both gamma irradiation and the addition of lanthanum oxide (La₂O₃) on the Bi_1.85Pb_0.35Sr₂Ca₂Cu₃O_y (Bi-2223) bulk superconductors. Pure and lanthanum-added samples prepared by the solid-state reaction method were analyzed before and after gamma irradiation using various methods such as X-ray powder diffraction (XRD), the temperature dependence of resistivity under magnetic field (ρ-T). Bi-2223 + x La₂O₃ samples with x = 0.0, 1.0 and 5.0 wt% were fabricated. The synthesized samples were then subjected to gamma irradiation at different intensities, and the effects of radiation on the structural, electrical, and magnetic properties of the materials were examined. For this purpose, Bi-2223 superconductors in the form of discs were produced and cut into two pieces. One piece was exposed to gamma radiation under high vacuum conditions. The phase analyzes of the materials were carried out by XRD. Then, electrical analysis of the materials was made by measuring resistance under a magnetic field.     

Characterization and creep properties of proton-conducting Yb-doped barium cerate

Polycrystals of Yb-doped barium cerate with composition BaCe_0.95Yb_0.05O_3−δ have been synthesized via a solid-state reaction route. The ceramic has a single orthorhombic perovskite phase, and the crystallographic unit cell is almost unperturbed with respect to undoped BaCeO₃. The compound exhibits a homogeneous distribution of equiaxed and submicron grains. The high-temperature mechanical properties have been studied for the first time. Mechanical tests were carried out in compression between 1100 and 1250 °C in air at constant initial strain rate. A gradual brittle-ductile transition was observed with increasing temperature and/or decreasing strain rate. Grain boundary sliding is the main deformation mechanism in the ductile region. In this regime, the true stress-true strain curves display an unusual behavior, with an initial strength drop followed by an extensive steady-state stage. This behavior is accompanied by the emergence of new, fine grains along the boundaries and triple junctions of the original grains during deformation.     

Tuning the peak effect in the Y1−xNdxBa2Cu3O7−δ compound

Polycrystalline Y_1−xNd_xBa₂Cu₃O_7−δ (x=0.02, 0.11, and 0.25) superconductors are synthesized. Nd atoms are uniformly distributed over grains. The magnetization loops of the samples have a pronounced second peak in a wide temperature range. The magnetization data are analyzed using the extended critical state model. It is found that the order-disorder transition of the vortex lattice is affected by doping with neodymium and temperature; the second-peak field and width decrease monotonically with increasing x value. The undoped polycrystalline YBa₂Cu₃O_7−δ compound is assumed to exhibit the peak effect in higher magnetic fields.     

Radiation shielding and structural features for different perovskites doped YBa2Cu3Oy composites

The increased demand for ionizing radiation in various fields led to the search for new shielding substances. In this study, five samples of perovskite oxides (BaTiO₃, SrTiO₃, BaTiO₃–SrTiO₃, and PbZr_0.2Ti_0.8O₃) doped YBa₂Cu₃O_y ceramics were prepared to explore their structure and ability for exploitation in the radiation shielding field. The structural properties were explored by using the XRD technique. The XRD results showed an orthorhombic structure for all prepared ceramics. The crystallite size reduces gradually from 96.19 to 66.63 nm with adding different perovskite oxides into the composites. The density shows a variation from about 5.89 to 6.23 g/cm³. The mass attenuation coefficient (MAC) was defined experimentally (MAC)_exp and theoretically (MAC)_the to check its validity. The maximum relative difference between (MAC)_exp and (MAC)_the is 7.83%. YBa₂Cu₃O₇/(PbZr_0.2Ti_0.8O₃)_2% and YBa₂Cu₃O₇/(BaTiO₃–SrTiO₃)_2% samples showed superior gamma shielding properties and mass stopping power (MSP) for charged particles, respectively, while the pristine YBa₂Cu₃O₇ sample has a better fast neutron removal cross-section (Σ_R). From the obtained results, it can be seen a slight variation in shielding properties, indicating the ability to use the different ceramic samples as radiation shielding materials.