The influence of inter-granular coupling on the magnetic susceptibility and critical current density of YBa2(Cu1−xAgx)3O7−δ superconductors prepared by ethylene glycol assisted solvothermal approach

Series of YBa₂(Cu_1−xAg_x)₃O_7−δ (0≤x≤0.09) powders were prepared by ethylene glycol assisted solvothermal approach. X-ray diffraction verified the formation of single phase crystal structure for all the investigated samples, implying the complete solubility of the silver ions into YBa₂Cu₃O₇. The partial substitution of the Ag atoms into the Cu sites caused a decrease of the lattice constant (c) and an increase of the lattice constants, a, and, b, to preserve the orthorhombic crystal structure of YBa₂Cu₃O₇. The scanning electron microscopy depicted that the incorporation of silver ions into copper sites adjusts the random orientations of the YBCO grains and suppresses the formation of grain boundary. The AC magnetic susceptibility measurement revealed that the superconducting performance of the YBa₂Cu₃O₇ is preserved at all Ag concentrations. The critical current density, J_c, measurement revealed that the addition of the Ag into the YBCO caused a strong pinning force is established due to the strong coupling among the grains instead of the weak Josephson junctions and in turn a remarkable increase of the zero field J_c from 2.7 MA/cm² to 9.1 MA/cm² was achieved.     

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.     

Characterization of the superconductor-multiferroic type materials based on YBa2Cu3O7-δ–YMnO3 composites

The effect of YBa₂Cu₃O_7-δ (YBCO) inoculated with a small amount of magnetoelectric YMnO₃ (YMO) is presented. The particulate composites YBCO‒x%YMO (x = 0.10, 0.25, 0.50, 0.75, 1.00 and 5.00 wt%) were investigated for microstructural and physicochemical properties. The YBCO precursor exhibits two characteristic peaks of crystallite sizes around 50 μm and 300 μm after the second calcining process. The vibrational spectra shows a small deterioration of the superconducting state of YBCO−YMO ceramics across the YMO content, which is due to the vanishing of the orthorhombic phase seen as a O(4) band moves towards the higher wave numbers on the Raman scale. From the magnetic measurements one can find that a small addition of YMO (around 1.00 wt%) does not significantly change the superconducting properties of YBCO crystallites, and most of the composites exhibit critical temperature T_c close to 92 K. The direct magneto-resistance measurements at 77 K show critical current densities (J_c) of 205 A cm⁻² for YBCO−0.25%YMO and 35 A cm⁻² for YBCO−5.00%YMO, respectively.     

Magnetic doping effects on the superconductivity of Y1-xMxBa2Cu3O7-δ (M = Fe,Co, Ni)

The discovery of superconductivity in copper oxide compounds has attracted considerable attention over the past three decades. The high transition temperature (T_c) in these compounds, exhibiting proximity to an antiferromagnetic order in their phase diagrams, remains one of the main areas of research. It is believed that magnetic fluctuations provide substance for the exotic superconductivity observed in these compounds. The present study attempts to introduce Fe, Co and Ni magnetic impurities into the superconducting cuprate YBa₂Cu₃O_7-δ with the aim of exploring the T_c behavior. The solid-state synthesis method is exploited to prepare fully oxygenated Y_1-xM_xBa₂Cu₃O_7-δ (Y_1-xM_x-123) (M = Co, Fe, Ni) samples with low levels of doping (0.00000 ≤ x ≤ 0.03000). Systematic measurements are then employed to assess the synthesized samples using AC magnetic susceptibility, electrical resistivity and X-ray diffraction (XRD). The measurements revealed an increase in T_c as a result of magnetic substitution for Y. However, the study of non-magnetic dopings on the fully oxygenated Y_1-xM'_xBa₂Cu₃O_7-δ (Y_1-xM'_x-123) (M' = Ca, Sr) samples showed a decrease in T_c. Quantitative XRD analysis further suggested that the internal pressure could have minor effects on the increase in T_c. The normal state resistivity vs temperature showed a linear profile, confirming that the samples are at an optimal doping of the carrier concentration.     

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.     

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.     

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 YBa₂Cu₃O_7−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 BaFeO_3−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 (J_c), pinning fields (H_P) exhibit γ = 1, the first critical field (H_c1) shows γ = 1/2, and critical temperature (T_c) demonstrates γ = 7/4.     

Synthesis and characterization of Ca3-xLaxCo4-yCuyO9+δ cathodes for intermediate temperature solid oxide fuel cells

The calcium cobaltite Ca_3-xLa_xCo_4-yCu_yO_9+δ with x and y = 0 and 0.1 were synthesized and the electrical, thermal, and catalytic behaviors for the oxygen reduction reaction (ORR) for use as air electrodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs) were evaluated. X?ray diffraction confirms the Ca_3-xLa_xCo_4-yCu_yO_9+δ samples were crystallized in a monoclinic structure and scanning electron microscopic image shows lamella-like grain formation. Introduction of dopants decreases slightly the loss of lattice oxygen and thermal expansion co-efficient. The Ca_3-xLa_xCo_4-yCu_yO_9+δ samples exhibit good phase stability for long-term operation, thermal expansion, and chemical compatibility with the Ce_0.8Gd_0.2O_2-δ electrolyte. Among the studied samples, Ca_2.9La_0.1Co₄O_9+δ shows a maximum conductivity of 176 Scm^?1 at 800 °C. Although the doped samples exhibit a higher total electrical conductivity, an improved symmetrical cell performance is displayed by the undoped sample. Comparing the sintering temperatures, the composite cathode Ca₃Co₄O_9+δ + Ce_0.8Gd_0.2O_2-δ sintered at 800 °C exhibit the lowest area specific resistance of 0.154 Ω cm² at 800 °C in air. In the Ca_3-xLa_xCo_4-yCu_yO_9+δ + GDC composite cathodes, the charge-transfer process at high frequencies presents a major rate limiting step for the oxygen reduction reaction.     

Wetting and spreading of Ca-Y-Ba-Cu-O solution on Y2O3 and CaSZ crucible in growing Y1-xCaxBa2Cu3O7-δ single crystal

Sizable and uniform Y_1-xCa_xBa₂Cu₃O_7-δ single crystals are of significant importance to study high-temperature superconductivity. However, the severe liquid loss resulting from intrinsic wetting property during top-seeded solution-growth (TSSG), makes it difficult to obtain such crystals. Here the reactive wetting performance of the Ca-Y-Ba-Cu-O solution on two types of crucibles was studied. It was identified that the spreading process on the Y₂O₃ crucible is characterized by forming double-layer of Y₂BaCuO₅ and YBa₂Cu₃O_7-δ, while that on the CaSZ crucible (Ca-stabilized ZrO₂) produces the BaZrO₃ layer with CuO phase. In the former case, the liquid has a low energy interface with the top layer of YBa₂Cu₃O_7-δ, leading to strong spreading and creeping behaviors. Conversely, due to a high interfacial energy between solution and BaZrO₃, the CaSZ crucible has a low wettability, particularly beneficial to solve the liquid loss problem. Consequently, with negligible liquid creeping out of CaSZ crucibles, we succeeded in growing a series of homogeneous Y_1-xCa_xBa₂Cu₃O_7-δ single crystals with an acceptable size up to a × b × c = 11.2 × 11 × 4.8 mm³. Moreover the wetting modes of solution on various kinds of crucibles for TSSG in growing doped YBa₂Cu₃O_7-δ single crystals were also elucidated. Most importantly, the understanding gained from this work is broadly applicable for producing other desirable doped-crystals.     

Effects of RE3+ Ionic Radius on Monoclinic Phase Content of 8 mol% REO1.5 Partially Stabilized ZrO2 (RE = Yb,Y, Gd,and Nd) Powder Compacts after Annealing at High Temperature

Powders of zirconia doped with 8 mol% REO_1.5 (RE = Yb, Y, Gd, and Nd) were synthesized by using the sol–spray pyrolysis method. The effects of RE³⁺ ionic radius on monoclinic (m) phase content of powders were investigated. The XRD results showed that the metastable tetragonal (t′) phase underwent a complete phase change to form m and cubic (c) phases after a heat treatment of 50–100 h at 1450°C. A cation size‐dependent reduction in the m phase content of the REO_1.5 partially stabilized ZrO₂ powders was observed. The SEM–EDS analysis of the powders revealed that the RE³⁺ concentrations in the c phases decreased with decreasing the RE³⁺ ionic radius. These results indicate that the stabilizer concentration of the c phase can be attributed to RE³⁺ ionic radii, resulting in different m phase contents. Compared to the REO_1.5 single doped ZrO₂, the m phase contents of 8 mol% (RE_0.5Yb_0.5)–ZrO₂ (RE = Y, Gd, and Nd) powders were significantly reduced. The results prove that the stabilizer with a lower RE³⁺ size is effective in reducing the m phase content of partially stabilized ZrO₂ after annealing at high temperatures.     

Influence of Ba2+ consumption and intermediate dwelling during processing of YBa2Cu3O7 nanocomposite films

Achieving high-critical current densities (J_c) with small artificial pinning centers is a crucial challenge for YBa₂Cu₃O_7−δ (YBCO) nanocomposite thin films fabricated using chemical solution deposition methods. In this work, the YBCO texture, structure purity, and its J_c properties were improved by understanding the influence of preformed ZrO₂ nanocrystals (Ba²⁺ consumption) during the nucleation and growth mechanism. This comprehensive study leads to an additional intermediate dwelling step during thermal process to increase the YBCO nuclei density before the YBCO growth, resulting to a self-field J_c of 5-6 MA/cm² at 77 K for undoped and ZrO₂-doped YBCO films. Counter-intuitively, the space and size distribution of the ZrO₂ nanocrystals in the YBCO matrix are independent of this intermediate dwelling step.     

Low-cost and high-performance 3D printed YBCO superconductors

High-performance YBCO 123 (YBa₂Cu₃O_7-x) bulk superconductor samples were produced using the 3D printing paste-extrusion technique. The YBCO powder obtained after sintering a pre-mixture of Y₂O₃, BaCO₃ and CuO powders at 950 °C was used in the formulation of pastes for extrusion in a 3D freeform printer. The 3D samples printed from pastes containing the pre-mixture powders were sintered, while those produced using the YBCO powder were not. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Raman analysis all confirmed the YBCO phase after sintering, both in the powder and in the samples made with the pre-mixture. Scanning electron microscopy (SEM) images revealed powder grains of heterogeneous size and geometry, as well as grain aggregation, in the sintered samples. Superconducting quantum interference device (SQUID) measurements taken within a fixed magnetic range revealed that the printed pieces have a typical magnetization temperature of 92 K, reaching ?1.43 emu/g and ?1.59 emu/g respectively a zero-field-cooled magnetization (ZFC) for sintered and non-sintered printed samples.     

Effect of F/Ba ratio of precursor solution on the properties of solution-processed YBCO superconducting films

YBa₂Cu₃O_7−x (YBCO) thin films (with thickness of 220–230 nm) and thick films (with thickness of 1.1–1.2 µm) were prepared using low fluorine solutions with different F/Ba ratios (F/Ba=1–4.5). The effect of F/Ba ratio on the properties of the films was systematically investigated. The results showed that films derived from solutions with F/Ba<2, regardless of whether they were thin or thick, showed poor superconductivity due to the formation of BaCO₃ intermediate phase. When solutions with F/Ba≥2 were used, the superconductivity of as-prepared YBCO films was related to not only the film thickness, but also the F/Ba ratio in the solution. It was found that, for thick films derived from F/Ba>2 solutions, the formation of BaF₂/BaOF phase was retarded by the decomposition of Ba_1−xY_xF_2+x (BYF) intermediate phase. We also found that extra fluorine in the solution resulted in a large number of impurities and a-axis grains in the thick films, degrading the film superconductivity. F/Ba=2 was the optimal ratio in the solution to fabricate high-J_c YBCO thick films.     

Synthesis and characterization of multi-colored pigments of LiRE(MoO4+δ)2 (RE = Ce,Pr, Nd,Er) with high near-infrared reflectance

Multi-colored pigments based on rare earth (RE) with the formula of LiRE(MoO_4+δ)₂ (RE = Ce, Pr, Nd, Er) were developed via the solid-state reaction method. Related characterization techniques were used for investigating the crystal structure, morphology characteristic, reflecting property, and color performance of the synthesized pigment. The prepared pigment of LiRE(MoO_4+δ)₂ (RE = Ce, Pr, Nd, Er) shows four colors, namely orange-yellow (Ce), bright green (Pr), lavender (Nd) and pink (Er). Moreover, all of the pigments possess high NIR reflectance in the range of 95–98% at 1100 nm. Remarkably, the average NIR reflectance of LiCe(MoO_4+δ)₂ pigment reaches up to 95.28%, and the NIR solar reflectance is also up to 95.02%. Besides, the pigment of LiCe(MoO_4+δ)₂ exhibits good yellow hue (b* = 75.08). The application practical of LiCe(MoO_4+δ)₂ coated on galvanized sheet exhibits excellent coloring performance. The designed pigments show chemical stabilities in the acid/alkali testing. All of above, the superior performances of color and reflectance from LiRE(MoO_4+δ)₂ provide visual enjoyment for people and exhibit potential for energy savings.     

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.     

Investigation on Energy Transfer and Luminescent Properties of K3Gd(PO4)2:RE3+ (RE = Eu,Tb) Under UV and VUV Excitation

K₃Gd(PO₄)₂:RE³⁺ (RE = Eu, Tb) are prepared by solid‐state reaction and their photoluminescence (PL) properties are investigated under UV and VUV excitation, respectively. The obtained experimental data show that no energy transfer happens among the activator ions Tb³⁺ or Eu³⁺ under UV excitation. Under 147‐nm excitation, the strongest emission intensity of K₃Gd(PO₄)₂:RE³⁺ (RE = Eu, Tb) is obtained when the activator ions Tb³⁺ or Eu³⁺ concentration is 0.8 mol, the integrate emission intensity of K₃Gd_0.2(PO₄)₂:0.8Tb³⁺ is about 204% of commercial phosphor Zn_1.96SiO₄:0.04Mn²⁺ with chromaticity coordinates of (0.340, 0.561) and the decay time of about 5.09 ms under 147‐nm excitation. We analyze the experimental data and propose a possible energy‐transfer mechanism under 147‐nm excitation.     

New versatile synthesis for low dimension superparamagnetic YBa2Cu3O7−x nanoparticles

This paper describes the synthesis and characterization of YBa₂Cu₃O_7−x (YBCO) nanoparticles obtained through an environmentally friendly chemistry approach. Y-, Cu- acetates and Ba trifluoroacetate were used for the synthesis of the precursor gel. Moreover, sucrose and pectin reagents were added as chelating agents inducing the formation of small size oxide nanoparticles. The thermal decomposition process of the precursor powder was investigated by thermal analysis correlated with mass spectrometry. The chemical nature, structure and morphology of the particles were investigated by X-Ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Fourier Transform Infrared Spectroscopy. According to XRD analysis the nanoparticles have an orthorhombic structure and the average diameter between 18–30 nm, additionally confirmed by TEM measurements. The superparamagnetic behavior at room temperature of the YBCO nanoparticles has been clearly evidenced by magnetization measurements. Furthermore, the effect of the annealing atmosphere on the magnetic properties has been studied.     

Correlation between local structure variations and critical temperature of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x superconductor

TiO₂ doping content affects the critical temperature (T_c) and the variations of local structure on Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ. The (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ)_1-x(TiO₂)_x samples were fabricated with the solid-state reaction process, where x = 0, 0.002, 0.004, 0.006, 0.008, and 0.01. The T_c values of the samples were obtained by measuring resistivity versus temperature, indicating that T_c gradually decreased with increasing doping content (x). To explain the obtained degradation of T_c, carrier properties, role of interlayer coupling, and local structure were systematically investigated using Azlamozov–Larkin theory and its Lawrence–Doniach modification for strong anisotropic superconductors. The calculation of excess conductivity at the mean field region showed that the c-axis coherence length (ξ_c) and the effective inter-layering spacing (d) increased with increasing doping content. X-ray diffraction patterns also showed that the bond distances increased with increasing TiO₂ content. The copper valence (V) and carrier concentration (p) of the samples were determined by analyzing the Cu L_2,3-edge X-ray absorption near edge structure spectra. The values of V and p showed the same trend of decreasing with increasing x. A close correlation between the changes in local structure parameters and degradation of T_c of (Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ)_1-x(TiO₂)_x was then probably concluded.     

Intergranular properties of polycrystalline YBa2Cu3O7−δ superconductor added with nanoparticles of WO3 and BaTiO3 as artificial pinning centers

Pure (x = 0.0 wt%) superconducting YBa₂Cu₃O_7−δ (YBCO) sample and added YBCO sample with 0.1 wt% artificial barium titanate (BTO) and 0.1 wt% tungsten trioxide (WO₃) nanoparticles were prepared using the solid-state reaction route. Phase purity was analyzed via the X-rays diffraction technique. Scanning electron microscopy showed a high density of isolated W-rich secondary phases embedded within the YBCO added sample. Furthermore, both WO₃ and BTO nanoparticles tend to reside at the grain boundaries and play the role of bridges connecting the YBCO superconducting granules. Quantitative analysis performed on the areas where nanosized entities induced by BTO and WO₃ phases was evidenced by EDX analysis equipped with SEM instrument. The values of H_c2 increased from 1.6 T for pristine to 3.4 T for BTO/WO₃ added samples. The superconducting parameters determined by AC susceptibility measurements also showed an improvement with WO₃ and BTO nanoparticles co-addition. The value of J_cinter(0) increases from 1.18 kA/cm² for the pristine sample to 5.10 kA/cm² for BTO/WO₃ co-added sample. Hence, the incorporation of artificial BTO and WO₃ nanoparticles into the YBCO superconducting phase could be a useful way to make such compounds available in practical applications.     

Tuning of dielectric properties of (ZnO)x-(CuTl-1223) nanoparticles-superconductor composites

Zinc oxide (ZnO) nanoparticles and Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10−δ (CuTl-1223) superconducting phase were prepared separately by sol–gel and solid-state reaction, respectively. ZnO nanoparticles were mixed with CuTl-1223 to get (ZnO)_x-(CuTl-1223); x=0, 0.5, 1.0 and 1.5 wt% nanoparticles-superconductor composites, which were characterized by different experimental techniques. There was no change observed in crystal structure of host CuTl-1223 phase after addition of ZnO nanoparticles, which provide a clue about the occupancy of these nanoparticles at the grains-boundaries. The inclusion of ZnO nanoparticles was found to reduce the voids and to improve the inter-grains connectivity in the host CuTl-1223 phase. The zero resistance critical temperature {T_c(R=0)(K)} was increased by increasing wt% addition of ZnO nanoparticles in CuTl-1223 matrix. The dielectric properties of these samples i.e. dielectric constants (ε′_r ε′′_r), and dielectric loss (tan δ), were determined by experimentally measuring the capacitance (C) and conductance (G) as a function of frequency at different operating temperatures. The values of dielectric parameters were decreased with the increase of frequency and become constant at certain higher frequency values, while the values of these parameters were increased with the increase of operating temperature values. So, we can tune the dielectric properties of CuTl-1223 superconducting phase by varying the content of ZnO nanoparticles, frequency and operating temperature.