Interplay of YBCO and Embedded 211 Particles in Melt-Textured YBCO Superconductors

Local orientations of superconducting YBa₂Cu₃O _x (123) and embedded Y₂BaCuO₅ (211) particles within bulk, melt-textured 123 samples are studied on a local scale by means of electron backscatter diffraction (EBSD). The embedded Y₂BaCuO₅ (211) particles do not show any preferred texture, but their presence within the 123-matrix alters the growth of the 123-phase, independent of the orientation. EBSD enables to analyse the interactions between the 123- and 211-phases in detail.     

Magnetization Anisotropy in YBCO Superconductors Prepared MPMG Method

We have studied magnetization anisotropy in a YBa₂Cu₃O₇ sample synthesized by a modified melt powder melt growth (MPMG) method. Magnetization of the sample upon ZFC process was measured as a function of magnetic field oriented both parallel and perpendicular to the c-axis. Magnetization anisotropy parameter γ is determined from remanent magnetization as a function of temperature. Magnetic relaxation measurement has been carried out in selected magnetic fields in both field increasing and decreasing case. At 20 kOe and 25 K for the field increasing case, the activation energy was found to be 53.5 meV and 51.7 meV when H∥c and H⊥c, respectively. Calculations based on the critical-state model can reproduce quite well the experimental data for H∥c and H⊥c where we have chosen n=0.15 and n=0.3, respectively.     

Interplay of Magnetic and Superconducting Subsystems in Ho-Doped YBCO

Journal of Superconductivity and Novel Magnetism - Superconducting and paramagnetic contributions to the magnetization of polycrystalline Y1?xHoxBa2Cu3O7?δ samples were...     

Influence of Irradiation-Induced Correlated and Random Disorder on Flux Pinning in Bulk YBCO Melt-Textured Samples

YBCO melt textured samples were studied after Au ion irradiation of two opposite surface layers of the samples and after proton irradiation. The scaling behavior of the pinning force was studied in order to get information about mechanisms responsible for pinning in the studied samples. Correlated disorder introduced bysurface ion irradiation is effective at high reduced temperatures and leads to the occurrence of a kink in the irreversibility line and to the shift of this line toward higher fields and temperatures. Enhancement of critical current density,increasing with temperature and field, was observed. Random disorder due to proton irradiation does not change the irreversibility line and only provides critical current enhancementdecreasing with temperature and field.     

Frequency Response of AC Susceptibility in Melt Textured YBCO Superconductors

We have reviewed the scaling relations for frequency dependent AC susceptibility proposed by Lee. et al. and other contributions. Based on vortex glass analysis, we derived a scaling equation for the peak temperature of the imaginary part and ac magnetic field frequency f. The peak temperature T_p is found to obey: T_p = Cf^1/(v(z–1))+T_g, where C is a constant, and T_g is the vortex glass temperature. The scaling relationship was applied to our melt textured YBCO superconductors, which was found in good agreement with the experimental data.     

Frequency Response of AC Susceptibility in Melt Textured YBCO Superconductors

We have reviewed the scaling relations for frequency dependent AC susceptibility proposed by Lee. et al. and other contributions. Based on vortex glass analysis, we derived a scaling equation for the peak temperature of the imaginary part and ac magnetic field frequency f. The peak temperature T_p is found to obey: T_p = Cf^1/(v(z–1))+T_g, where C is a constant, and T_g is the vortex glass temperature. The scaling relationship was applied to our melt textured YBCO superconductors, which was found in good agreement with the experimental data.     

MOCVD法制备YBCO高温超导体所需前驱盐的制备研究

通过金属有机源化学气相沉积技术(MOCVD)已可制得Ic达280 A/cm,Ic×L为300330 A.m的高性能YBCO带材,表现出巨大的优势和诱人的应用前景。进一步提高前驱盐的挥发性和批次稳定性不但能降低YBCO带材的生产成本、也能提高其性能稳定性。本研究报道了MOCVD法制备YBCO所需β二酮中间体TMHD及其钇、钡、铜金属有机前驱盐的制备,通过红外光谱和核磁共振谱对其化学结构予以确认;同时以金属钡与TMHD在正戊烷或正己烷中制备了无水β-二酮钡盐(Ba[tmhd]2),随后用五乙烯六胺为辅助配体(L)制备了挥发性更好的无水复合配体钡盐(Ba[tmhd]2.L),并通过热重分析技术比较了各前驱盐的挥发性,结果表明:辅助配体五乙烯六胺对提高钡盐挥发性作用显著。     

Interplay Between Surface Effects and the Magnetic Properties in Polycrystalline Superconductors

The effects of the grain boundaries on the magnetic properties are studied in the polycrystalline superconductors. The interaction of the Abrikosov vortex with both the surface and Josephson junction as well as with other vortices and applied magnetic field are taken into account in this study by the London theory approach. It is shown that the magnetic behavior is strongly dependent of the anisotropy ratio as well as the normalized grain size and the coupling parameter between the grains. The first flux entry field H _p , the lower critical field H _{c 1} and the Gibbs free energy are computed. The vortex–vortex interaction and magnetization M(H) are also investigated.     

The Effect of Dy Doping on the Magnetic Behavior of YBCO Superconductors

The effect of dysprosium (Dy) doping on yttrium barium copper oxide (YBCO) prepared by conventional solid-state reaction method has been investigated by means of XRD, AC susceptibility, and DC magnetization measurements. AC susceptibility measurements for sintered YBCO pellets have been performed as a function of temperatures at constant frequency and AC field amplitude in the absence of a DC bias field. DC magnetization measurements were done at 5, 20, and 77 K upon zero field cooling (ZFC) process. The magnetization measurements showed a paramagnetic behavior existing at high magnetic fields. The magnetic field dependence of critical current density of the samples has been estimated from DC magnetization data. The partial Dy substitution for Y on YBCO superconductors improves the bulk critical current density at high magnetic fields and at high-temperature regions (higher than 20 K).     

Interplay Between Vorticity and Chirality Inside the Vortex Core in Chiral p-Wave Superconductors

The vortex core in chiral p-wave superconductors exhibits various properties owing to the interplay between the vorticity and chirality inside the vortex core. In the chiral p-wave superconductors, the site-selective nuclear spin-lattice relaxation rate T ^–1 ₁ is theoretically studied inside the vortex core within the framework of the quasiclassical theory of superconductivity. T ^–1 ₁ at the vortex center depends on the sense of the chirality relative to the sense of the magnetic field. The effect of a tilt of the magnetic field upon T ^–1 ₁ is investigated. The effect of the anisotropy in the superconducting gap and the Fermi surface is then investigated. The result is expected to be experimentally observed as a sign of the chiral pairing state in a superconducting material Sr₂RuO₄.     

Microwave Spectroscopy in YBCO Superconductors: Influence of Neutron Irradiation on the 123 Phase

The high-T _c superconducting system YBa₂Cu₃O:Li (123) was investigated by microwave absorption. The effect of neutron irradiation on the 123 phase as well as the dependence of the resulting modification both on the neutron fluence and on the doping behavior with Li are discussed. The results show a significant improvement of the superconducting characteristics: critical temperature, phase homogeneity, and critical current densities for a certain neutron fluence. We have found that the optinum neutron fluence for irradiation is 4.98×10²¹ m^–2.     

The Relationship of Magnetic Stiffness Between Single and Multiple YBCO Superconductors over Permanent Magnet Guideway

For YBCO bulk levitating over a permanent magnet guideway (PMG), the magnetic stiffness is connected directly with the pinning properties of the measured sample. An experimental setup has been built to investigate the vertical and lateral magnetic stiffness of five high-temperature superconducting (HTS) bulk arrays over a PMG by two methods: the additive method, i.e., calculating the summation of the measured magnetic stiffness values of each HTS bulk in the array; the direct method, i.e., measuring directly the magnetic stiffness of the HTS bulk array. From the experimental results, it is found that the resultant magnetic stiffness of the HTS bulk array composing of multiple YBCO bulk is related with the magnetic stiffness of each individual single bulk, but the additive method does not predict the magnetic stiffness of the array very well because of the interaction between adjacent HTS bulk. The resultant magnetic stiffness of the HTS bulk array is less than the summation magnetic stiffness of each single HTS bulk. One numerical method is used to calculate the magnetic stiffness for comparing with experimental results. The results may be helpful to the design and optimization of the superconducting magnetic levitation system.     

YBCO-Buffered NdBCO Film with Higher Thermal Stability in Seeding REBCO Growth and Recycling Failed Bulk YBCO Superconductors

In this work, we report a strengthened superheating effect caused by a buffering YBa₂Cu₃O _y (YBCO or Y123) layer in the Nd_1+x Ba_2?x Cu₃O_7?y (NdBCO or Nd123) thin film with MgO substrate (i.e., NdBCO/YBCO/MgO thin film). In the cold-seeding melt-textured (MT) growth, the NdBCO/YBCO/MgO film presented an even higher superheating level, about 20 °C higher than that of nonbuffered NdBCO film (i.e., NdBCO/MgO film). Pole figure (X-ray Φ-scan) measurement reveals that the NdBCO/YBCO/MgO film has better in-plane alignment than the NdBCO/MgO film, which may be the main origin of the enhanced thermal stability. Using this NdBCO/YBCO/MgO film as the seed and under a maximum processing temperature (T _max) up to 1120 °C, we succeeded in growing various RE_1+x Ba_2?x Cu₃O_7?y (REBCO, RE=Gd, Sm, Nd, RE refers to rare elements) bulk superconductors and recycling the failed REBCO (RE=Y) bulks in a simple and feasible process.     

Effects of Lu Doping on the Magnetic Behavior of YBCO Superconductors Prepared by MPMG Method

We report on magnetic behavior of Y _1?xLu _xBa ₂ Ca ₃ O _7?δ (x= 0, 0.5) samples synthesized by a modified melt powder melt growth (MPMG) method at three different sintering temperatures (920, 930, 940 ^°C). Isothermal magnetization measurements were done as a function of magnetic field at 20 and 77 K upon zero-field cooling (ZFC) process. The critical current densities as a function of magnetic field have been estimated from M–H hysteresis loop. Partial Lu substitution for Y on YBCO superconductors improved significantly the bulk critical current density, which is confirmed by field-cooled magnetization and AC susceptibility measurements. Magnetic relaxation measurement has been carried out in remanent magnetization regime. AC susceptibility measurements have been performed as a function of temperature to determine the transition temperature.     

Processing and Properties of Bar-Shaped Single-Seeded and Multi-Seeded YBCO Bulk Superconductors by a Top-Seeded Melt Growth Technique

The fabrication of (RE)-Ba-Cu-O bulk superconductors, where RE is a rare-earth element such as Y, Gd and Sm, is both time consuming and expensive due to the complexity of the melt process and the slow growth rate of large, single grains. In this study, different approaches to the fabrication of bar-shaped, bulk YBCO superconductors are investigated and compared using single- and multiple-seeding techniques via top-seeded melt growth (TSMG). Both the microstructural and superconducting properties of the bulk samples are investigated, including trapped field, critical current density, critical temperature and levitation force. The results of this study indicate that, in general, the superconducting properties of YBCO fabricated by a single-seeded process are significantly better than those of samples fabricated by a four-seeded process for non-bridge seeds. The differences between the samples are less pronounced in the levitation force measurements, however. In this paper, we attempt to explain the reasons for the similarities and differences observed between bulk samples fabricated by the different single- and multi-seeded processes.     

Effect of Na-dopant on the Levitation Force of Single Domain YBCO Bulk Superconductors Fabricated by TSMTG Process

Na-doped single domain YBa_2−x Na _x Cu₃O_7−δ (YBCO, x=0.05, 0.1, 0.15, 0.2, 0.25, 0.3) bulk superconductors were prepared by a modified melt textured process and the effect of Na substitution on the levitation force of YBCO bulks have been investigated. The maximum levitation forces (MLF) are much different for samples with a different Na element content. It is found that the optimum Na element content in YBCO for the strong MLF is around x=0.2. It is also found that the addition of Na could reduce and increase the ATH of the YBCO platelet while x less than 0.1 and larger than 0.1, some of adjacent platelet grains are well intergrown each other in the sample with x=0.2 comparing to the other samples and the influence of the Na addition on the Y211 particle size is not obvious.     

纳米银晶粒镶嵌氧化硅薄膜的光致发光

用SOL GEL法在浮法玻璃表面制备了掺杂纳米银晶粒的二氧化硅薄膜。在室温下测定了其可见光透过率和光致发光谱。研究了样品的光致发光强度与纳米银的掺杂量、镀膜时的提拉速度和热处理温度之间的关系     

嵌有纳米碳颗粒凝胶玻璃的制备及其发光特性

以磷酸三乙酯、硝酸铝和正硅酸乙酯为原料,通过它们的水解制备了ｘＡｌ_２Ｏ_３·ｘＰ_２Ｏ₅·１００ＳｉＯ_２（ｘ＝０．２５～３）凝胶．在６００℃对凝胶进行热处理,使其中的有机基团炭化,从而制备出了镶嵌有碳纳米颗粒的ｘＡｌ_２Ｏ_３·ｘＰ_２Ｏ_５·１００ＳｉＯ_２（ｘ＝０．２５,０．５）凝胶玻璃．在室温下以５３２ｎｍ激光（Ｎｄ：ＹＡＧ）激发,在 ６３０ｎｍ处有一强的发光峰,该发光现象是由镶嵌在凝胶玻璃中的纳米碳颗粒产生的．     

Theoretical Study of Interplay of Superconductivity and Ferromagnetism in Hybrid Rutheno–Cuprate Superconductors RuSr2RCu2O8

We consider the extended two-band s–f model with additional terms, describing intersite Cooper pairs’ interaction between 4f (5f) and conduction electrons. Following Green’s function technique and equation of motion method, self-consistent equations for superconducting order parameter (Δ) and magnetic order parameter (m _f ) are derived. The expressions for specific heat, density of states, and free energy are also derived. The theory has been applied to explain the coexistence of superconductivity and ferromagnetism in hybrid rutheno-cuprate superconductors RuSr₂RECu₂O₈ (RE = Gd, Eu). The theory shows that it is possible to become superconducting if the system is already ferromagnetic. A study of specific heat, density of states and free energy is also presented. The agreement between theory and experimental observations is quite satisfactory.      

Determination of the Intragrain Critical Current Density and Thermogravimetric Analysis on YBCO/Ag Superconductors Irradiated with 60Co Gamma Rays

We investigated the flux pinning behavior induced by gamma irradiation in Y₁Ba₂Cu₃O_(7–x) silver-added samples. The superconductors were prepared through solid-state route and added with silver in amounts of 0-, 6.5-, and 20-wt%, following which the samples were irradiated by high-energy gamma irradiation () at doses of 0, 500, and 1500 kGy at the dosage rate of 8.2 kGy/h. We performed magnetization loops to study the flux pinning of vortex in YBCO/Ag superconductors. We found that silver addition and irradiation on superconductors may increase the width in magnetization loops, which is related to the enhancement in the critical current density, J _c . We established that an interaction between silver addition and irradiation that results in higher values in J _c for YBCO/Ag irradiated samples already exists. The J _c in samples containing 20-wt% of silver decreased with irradiation because a higher content of silver produces small crystals and secondary phases growing. On comparing the TGA analysis for both YBCO and YBCO/Ag samples, we found higher-weight oxygen losses in YBCO silver samples, which suggests that silver increases the oxygen saturation content. The higher oxygen content found on irradiated specimens it is indicative of oxygen losses from CuO chains or CuO₂ planes reached by -irradiation.On leave from