Magnetic and Electrical Properties of Superconducting Ceramic YBa2Cu3O7−δ Co-doped with Ca and Zn

Superconducting Y_1?x Ca _x Ba₂(Cu_0.98Zn_0.02)₃O_7?δ ceramics with 0≤x≤0.5 have been prepared by the solid state reaction method. Structural, magnetic and electrical properties of the components have been studied. To characterize the samples, X-rays diffraction (XRD), scanning electron microscopy (SEM) and magnetic measurements techniques are used. Obtained results show that increasing the Ca content leads to a significant decrease of the Y123 phase. While, the parasite phase BaCuO₂ increases. For x>0.3, the coexistence of metallic and semiconducting character of samples is observed. DC susceptibility measurements reveal a reduction of the Meissner fraction with Ca doping, suggesting the existence of the flux pining effect.     

Effect of Ti Doping on Structural and Superconducting Property of YBa2Cu3O7−y High T c Superconductor

Dimensional fluctuations of superconducting order parameters in YBa₂(Cu_1?x Ti _x )₃O_7?y (x=0.01, 0.02, 0.04, 0.05) have been analyzed. SEM micrographs reveal the reduced grain size and the formation of TiO₂ nanowires covering over the grains of YBCO matrix. XRD graphs show the unchanged orthorhombic structure. With the increase of TiO₂%, it is found that the superconducting transition temperatures determined from standard four-probe method decrease gradually. Excess conductivity fluctuation analysis using the Aslamazov–Larkin model fitting reveals transition of two dominant regions (2D and 3D) above T _c . 2D to 3D crossover temperature, i.e., the Lawerence–Doniach temperature that demarcates dimensional nature of fluctuation inside the grains is influenced by Ti incorporation in YBCO matrix. The decrease in the Lawerence–Doniach temperature in the mean field region has been observed as a consequent dominance of 3D region with increase in Ti%.     

Dependence of the Structural, Electrical and Magnetic Properties of YBa2Cu3O7?δ Bulk Superconductor on the Ag Doping

The effects of Ag dopants on the superconducting properties of YBCO bulk samples, prepared under solid-state reaction method, have been studied by resistivity?Ctemperature (???CT), X-ray diffraction (XRD), scanning electron microscope (SEM), bulk density, AC susceptibility, DC magnetization measurements, and theoretical analysis. Small Ag substitutions (x??0.10) do not effect T _c of pure YBa₂Cu_3?x Ag _x O_7??? , while we observed small decreases of 1.5?K for larger doping levels (x??0.15). 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 DC bias field. The critical current densities (J _c ) have been estimated as a function of magnetic field from the magnetization data employing Bean??s critical state model. The increase in Ag amount (x) in YBa₂Cu_3?x Ag _x O_7??? (x??0.10) system effectively decreases the intragrain critical current density, which is attributed to the reduced connectivity between the grain boundaries. In the case of small additions (x=0.05), Ag atoms fill partly the pores, leading better crystallization of the grains.     

Zn and Ni Doping Effect on Anomalous Suppression of T c in an Over Doped Region of TlBa2Ca2Cu3O9−δ

Variation of T _c in the over doped region have been investigated for Zn and Ni doped samples of TlBa₂Ca₂Cu₃O_9– to obtain a clue to understand the anomalous suppression of T _c. We expected that if the anomaly in Tl-1223 originates from the stripe order like La-214 system, the suppression of T _c is enhanced by the doping. The results showed that the anomaly disappeared by both of the doping contrary to the expectation so that the possibility of the stripe order was ruled out. Two possible explanations were proposed based on a self-doping mechanism and inhomogeneous charge distribution to crystallography different CuO₂ layers.     

Fabrication of Micro-pipes of YBa2Cu3O7−δ Superconductor

Synthesis of micro-pipes of YBa₂Cu₃O_7−δ superconductor has been carried out for the first time by using chemical method. The shape, size and length of these micro-pipes depends upon dimensions of growth matrix and structure of geometry, i.e., circular, square, rectangular and hexagonal, etc., which could be uniformly coated with superconductor. The onset temperature of diamagnetism of the material is found to be 93 K, which is not shifted to lower values by the application of DC magnetic field; this is most likely due to large surface area provided by micro-pipes to the shielding currents. These micro-pipes behave as pinning centers, hence they can be used for the fabrication of devices that are capable of working in high magnetic fields.      

Microstructure Study at Different Thicknesses of Disc-Shaped YBa2Cu3O7?x Prepared by FQMG Method

The flame-quench-melt-growth (FQMG) method was used for the preparation of bulk YBa₂Cu₃O_7?x (Y123). Both the superconducting and nonsuperconducting regions changing with thickness of superconducting sample were determined by X-ray diffraction (XRD) patterns and also observed at micrographs taken by the polarized optical microscope. It was observed that superconducting forming ratio which was examined for different thicknesses of the sample ranging from 6.54 to 1.58 mm strongly enhanced. This means that a region near the top surface of the sample contains more superconducting phase than the other regions. These observations would be helpful in designing and manufacturing the practical applications of YBCO systems.     

Fluctuation Induced Conductivity in (Cu0.5Tl0.5)Ba2Ca2Cu3O10?δ Superconductor Synthesized at Different Temperatures

The fluctuation induced conductivity (FIC) analysis of (Cu_0.5Tl_0.5)Ba₂Ca₂Cu₃O_10?δ superconductor synthesized at different temperatures has been carried out in the frame work of Aslamazov-Larkin (AL) theory. Almost all the superconducting parameters studied in this research work have been improved with the increase of synthesis temperature up to 850°C, which is most likely due to (Cu_0.5Tl_0.5)Ba₂Ca₂Cu₃O_10?δ superconducting phase stability at this synthesis temperature. The parameters calculated from FIC analysis are cross-over temperature (T ₀), zero temperature c-axis coherence lengths ξ _c (0), interlayer coupling strength (J) and the exponents (λ _3D and λ _2D). The FIC analysis has shown an increase in T ₀ and the shift of three dimensional (3D) Aslamazov-Larkin (AL) regions to the higher temperature with the increase in synthesis temperature up to 850°C.     

Enhanced Magnetic Properties in Cu0.5Tl0.5Ba2Ca2Cu3O10−δ Superconductor Doped with Carbon Nanotubes

Fluctuation-induced conductivity (FIC) analysis in the critical fluctuation region (cr), three-dimensional (3D), two-dimensional (2D), and zero-dimensional (0D) regions is reported for undoped and carbon nanotubes (CNT)-doped Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ (CuTl-1223) superconductors. Samples were synthesized by well-known solid-state reaction method by adding CNT up to 7 wt %. The X-ray diffraction data confirms the single-phase orthorhombic structures following PMMM space group for all the samples. The scanning electron microscope (SEM) images reveal that the carbon nanotubes are present in the spaces between the grains and connect the grains electrically to help the intergranular current flow. From FIC analysis, it was found that the width of critical and 3D regimes are shrunken with the increased CNT doping in the final compound. Also, the coherence length (ξ_c(0)), the Fermi velocity (V _F), and the coupling constant (J) are suppressed with increased CNT doping except for the 0.25 wt % doped sample. The decrease in important superconductivity parameters most likely arises due to low CNT doping which indeed functions as columnar defects that are produced by heavy ion irradiation. In this analysis, we also found that the critical magnetic fields (B _c(0), B _c1(0)) and critical current density (J _c(0)) were found to increase with increased CNT concentration. These observations suggest that addition of CNT (efficient pinning centers) to CuTl-1223 compounds improve the electrical connection between the superconducting grains to result in the improvement of magnetic properties of the final compound.     

Growth of (Cu0.5Tl0.5?x Hg x )Ba2Ca3Cu4O12?δ Superconductor with Optimal Carrier Density in CuO2 Planes and Fluctuation-Induced Conductivity

The growth of (Cu_0.5Tl_0.5?x Hg _x )Ba₂Ca₃Cu₄O_12??? (x=0, 0.25) superconductor with optimal carrier density in CuO₂ planes has been made possible by partial substitution of Hg at Tl sites in (Cu_0.5Tl_0.5)Ba₂O_4??? charge reservoir layer of (Cu_0.5Tl_0.5)Ba₂Ca₃Cu₄O_12??? superconductor. The fluctuation-induced conductivity (FIC) analysis has been carried out on resistivity vs. temperature curves by using Aslamazov?CLarkin (AL) theory and the results have shown three-dimensional (3D) and two-dimensional (2D) fluctuations in order parameters. The microscopic parameters deduced from FIC analysis such as crossover temperature (T _o ), zero temperature c-axis coherence {?? _c (0)} and the interlayer coupling strength?(J) have been improved with Hg substitution. Also, 3D region has been shifted to higher temperature with Hg substitution. In order to verify the optimal carrier density in CuO₂ planes with Hg substitution, the post-annealing experiments have been carried out on these samples in nitrogen and air. These post-annealing experiments have caused under-doping of carriers from the optimal level resulting into a decrease in T _c (R=0) as well as the magnitude of diamagnetism.     

Influence of Boron Doping on Transport Properties of?YBa2Cu3O7?y HTS

The nominally pure and boron-doped YBa₂Cu₃B _x O_7?y samples with B-doping level x varying between 0 and 0.15 were prepared by the solid state reaction. X-ray diffraction analysis shows that all the obtained compounds are single YBa₂Cu₃O_7?y phase. The small additives of boron in YBa₂Cu₃B _x O_7?y (x=0.025 and 0.05) do not essentially affect the critical temperature T _c and it remains near 90 K. The higher-level boron doping causes degradation of T _c and tail remains on the ??(T) curve for x=0.15 at 65 K. Lowest-level boron doping applied leads to a significant improvement in J _c compared to the undoped sample (from 100 A?cm^?2 for a control sample to 147 A?cm^?2 for a B-doped sample with x=0.025). Grain boundary critical current density and superconducting volume fraction decrease with increasing amount of added B₂O₃. The obtained results indicate possibility of boron dopant being entered into the lattice-sites.     

Effect of Artificial Defects on Electric and Magnetic Transport Properties in YBa2Cu3O7−δ Thick Film

The effect of 200 MeV Ag ions on YBa₂Cu₃O_7?δ /5 wt.% Y₂O₃ composite thick films is studied. The structural deformity is analysed with X-ray diffraction showing reduced peak intensity. The decrease of transition temperature as a function of ion fluence has been observed from temperature-dependent resistivity and magnetization measurement. Fluctuation conductivity studied within the framework of Aslamazov–Larkin and Lawrence–Doniach theories fits well for 3D and 2D regimes with the appearance of critical region beyond 3D regime. Pseudogap temperature estimated above 100 K shifts to lower temperature zone as a function of ion doses. We report an enhancement of critical current density and flux pinning due to dual impact of swift heavy ion and Y₂O₃ inclusions at isothermal temperatures 40 K and 60 K.     

Structure and Charge-Transfer Mechanism in Y1?x Ca x Ba2Cu3O7?δ Through Direct Doping

Here we study the effect of Ca doping on the charge-transfer mechanism of polycrystalline YBa₂Cu₃O_7??? compound. The samples of composition Y_1?x Ca _x Ba₂Cu₃O_7??? (x=0.00,0.05,0.10,0.20 and 0.30) are synthesized through standard solid-state reaction route. Carrier doping is controlled by annealing of samples in oxygen and subsequently in reducing atmosphere. Samples are investigated using resistivity, dc magnetization (M?CT) and magnetization with field (M?CH) measurements. With increase of Ca the transition temperature (T _c) decreases in oxygenated samples, whereas the same increases in reduced samples. Further reduction of samples at higher temperatures (>600?°C) though results in non-superconducting nature up to Ca concentration of x=0.20, the x=0.30 sample is superconducting below 30?K. This provides a remarkably simple and effective way to study the relationship between structure, superconductivity, and associated electronic properties. Variation in Cu₁?CO₄, Cu₂?CO₄ and Cu₂?CO₂ bond lengths with oxygen content, is seen through the structural refinement of XRD pattern. The effective coordination of Cu₂ atom with oxygen changes with the change in these bond lengths and hence the holes in the CuO₂ planes. The charge-transfer mechanism from CuO _x chains to CuO₂ planes and thus effective hole doping is discussed in the context of the results observed.     

Physical and Mechanical Properties of GdBa2Cu3O7−δ Added with Nanosized CoFe2O4

Superconductor samples of type (CoFe₂O₄) _x GdBa₂Cu₃O_7?δ , 0.0≤x≤0.1 wt.%, were synthesized by the conventional solid-state reaction technique. The prepared samples were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), electrical resistivity, AC magnetic susceptibility, and Vickers microhardness. Phase examination by XRD indicated that the orthorhombic structure of Gd-123 is not affected by nanosized ferrite CoFe₂O₄ addition, whereas the volume fraction of Gd-123 increased with x up to 0.01 wt.%. Morphological investigations by SEM revealed that the porosity among grains decreased as x increased from 0.0 to 0.1 wt.%. The superconducting transition temperature T _c was estimated from electrical resistivity and the AC magnetic susceptibility measurements. A reduction in T _c was observed as x increased from 0.0 to 0.1 wt.%, consisting with the effect of adding magnetic impurities to HTSCs. Room temperature microhardness measurements were carried out at different applied loads (0.5–10 N) for the study of the mechanical performance of the studied samples. The experimental results were analyzed using Meyer’s law, Hays–Kendall approach, elastic/plastic deformation model, and proportional specimen resistance model. The results showed that all the samples exhibited normal indentation size effect, and Vickers microhardness values were increased as nanosized CoFe₂O₄ addition increased. The analysis showed that the proportional specimen resistance model is the best model for computing the load-independent microhardness values of our samples.     

Effect of Postannealing Process on Bi2Sr2.1Ca0.9Cu2O8+δ Textured Superconductors

Bi-2212 samples prepared by the classical solid-state method have been grown from the melt using the Laser Floating Zone (LFZ) method. They have shown good grain alignment and transport critical current densities (J _c ). After postannealing processes designed to produce the Bi-2212 phase controlled decomposition, J _c values have been increased in an important manner. Maximum values have been achieved when samples were thermally treated at 680 °C for 168 h with improvements around 80 %, compared with the original textured samples. The results clearly indicate that postannealing processes, when adequately controlled, produce the formation of effective pinning centers which are responsible for the increase in the measured J _c values.     

Effect of high valency cations on the (BiPb)2Sr2Ca3Cu4O12+δ compounds

We have produced the (BiPb)₂V _x Sr₂Ca₃Cu_4−y Ti _y O_12+δ compounds by a melt-quenching method. For two different sintering times (185 and 192 hours), the effects of vanadium adding and Ti doping on the structure have been investigated by electrical resistance, scanning electron micrographs (SEM), XRD patterns and magnetic hysteresis loop measurements. It has been found that the high-T _c superconducting phase, (2223), is formed in the samples annealed at 845 ^○C for 185 and 192 h, with concentration x=0.2 and y=0.05. However, with increasing Ti doping the (2223) phase gradually transforms into the (2212) phase. The hysteresis loop areas decrease with increasing Ti concentration and sintering time. Our data have indicated that the critical current, J _c , decreases with increasing magnetic field.     

Effect of Mg and Be Doping on Superconducting Properties of TlBa2(Ca2?y M y )Cu3O9?δ (y=0 and 1.5 for M=Mg, Be) Superconductors

In order to study the effect of an insulating charge reservoir layer, we have synthesized as-prepared and oxygen annealed TlBa₂(Ca_2?y M _y )Cu₃O_9??? (y=0 and 1.5 for M=Mg, Be) superconductors sample at atmospheric pressure using a solid-state reaction method. It has been found that the sample mainly contains tetragonal-1223 phase, but there exist some nominal derivative phases of TlBa₂CaCu₂O_9??? and TlBa₂Ca₃Cu₄O_9??? superconductors. It is expected that doping of Mg and Be in place of Ca results in an increase in superconducting properties. But contrary to our expectation, both the [T _c (R=0)] and magnitude of diamagnetism are decreased with the doping of Mg and Be in the final compound. This may be due to the scattering of the carriers in CuO₂ planes resulting in the suppression of superconducting properties. The carrier concentration in these planes is optimized by carrying out a post-annealing experiment. Furthermore, FTIR absorption measurements are also incorporated.     

Improvement of the Superconducting Transport Properties of YBa2Cu3O7?δ by BaZrO3 Doping

We have doped the YBa₂Cu₃O_7– superconducting ceramics with BaZrO₃ up to 75wt.% and studied the changes of some physical properties. The most important finding is the enhancement of the critical current density, which has a maximum at around 5 wt.% doping level. Compared with the undoped samples, the critical current density is four times higher if the doping compound is introduced prior to the calcination treatment, or two times higher if BaZrO₃ is introduced prior to the sintering treatment. The dependence of the critical current density on the doping level is consistent with the dependence of the Seebeck coefficient. We also observed a very small decrease of the critical temperature. The real density of the samples decreases with increasing doping level as expected from the ratio between the theoretical densities of YBa₂Cu₃O_7– and BaZrO₃, the effect being important for doping levels higher than 25 wt.%.     

Fabrication of the New Y3Ba5Cu8O y Superconductor Using Melt–Powder–Melt–Growth Method and Comparison with YBa2Cu3O7?x

YBaCuO superconducting sample with nominal composition in the stoichiometric ratio of 3:5:8 was fabricated by using the Melt?CPowder?CMelt?CGrowth (MPMG) process. Microstructural property of the sample was examined by X-rays diffraction (XRD) pattern and also observed at micrographs taken by both a polarized optical microscope and a scanning electron microscope (SEM) with energy dispersion analysis of X-rays (EDAX). Identification of chemical composition of the sample was investigated by the SEM-EDAX. Electric and magnetic properties were performed with a standard four-probe dc technique and magnetic levitation force measurements, respectively. In addition, all of these properties were compared with a standard MPMG YBa₂Cu₃O_7?x ?(Y123) superconductor. According to the obtained results, it was determined that empirical resulting formula of the sample was Y₃Ba_4.89Cu_8.17O _y ?(Y358) and also the magnetic levitation force of the Y358 was 169.8 mN under zero-field-cooled (ZFC) regime at 77 K while that of the Y123 was 99.3 mN.     

Broadband Microwave Measurements of Overdoped Y0.9Ca0.1Ba2Cu3O7−δ Films Using Corbino Geometry

The surface impedance of Y_0.9Ca_0.1Ba₂Cu₃O_7?δ thin films was measured using the Corbino spectroscopy method. This special geometry, in which the sample dimensions are well defined by a ring pattern, is ideal for broadband high frequency reflection measurements. Using the complex reflected signal, S ₁₁, measured by a vector network analyzer, one can find the surface impedance of the thin film, from which the complex conductivity can be deduced. In the current work we present the three-standard approach for calibration of the Corbino method and demonstrate the benefits of this approach in measuring superconducting Y_0.9Ca_0.1Ba₂Cu₃O_7?δ thin films up to 20 GHz and down to 6 K. For the data analysis the well-known generalized two-fluid model was implemented, taking into account a film thickness which is much smaller than the normal state skin depth and superconducting penetration depth.