Critical Current Density Values Research Articles

High field vortex phase diagram of Fe(Se, Te) thin films

We report on the (H, T) vortex phase diagram up to 35 T of Fe(Se, Te) thin films deposited on CaF2 substrates as determined by resistivity, Nernst effect and critical current measurements. We found the presence of a large region where the vortex is firmly pinned, allowing the adoption of chalcogenides for low temperature but extremely high magnetic field applications. The fact that high critical current density values—larger than 1 MA cm−2 in self-field and liquid helium—are reached together with a very weak dependence on the magnetic field and a complete isotropy, joined with the very high rigidity of the vortex lattice at very high field, makes the Fe(Se, Te) phase very promising for low temperature (≤4.2 K) and high field (≥25 T) applications.

Effect of Different Nanosized NiO Addition on Ag-Sheathed (Bi1.6Pb0.4)Sr2Ca2Cu3O10 Superconductor Tapes

(Bi1.6Pb0.4)Sr2Ca2Cu3O10–(NiO)x superconductor with x=0, 0.01, 0.02, 0.03, 0.04, and 0.05 wt.% was prepared using the coprecipitation technique. The average size of NiO used was 8 nm and 16 nm. The highest value of the transport critical current density, Jc in the bulk form was observed in the x=0.01 wt.% samples for both sizes. Based on this result, Ag sheathed superconductor tapes with starting composition (Bi1.6Pb0.4)Sr2Ca2Cu3O10–(NiO)0.01 (with NiO particle size 8 and 16 nm) were fabricated using the powder-in-tube method. The effect of these nanoparticles addition on the microstructure, phase formation, and transport critical current density were studied. The Jc of the tape at 77 K in zero fields with NiO (8 nm) addition (4500 A/cm2) was slightly higher than that of NiO (16 nm) added tape (4120 A/cm2). The nonadded tape showed a lower Jc (1080 A/cm2 at 77 K). These results indicated that magnetic nanoparticles such as NiO could act as an effective flux pinning centers leading to the enhancement of Jc in the bulk and tape form. Moreover, NiO with size closer to the coherence length, ξ was more effective in enhancing Jc.

Highly effective and isotropic pinning in epitaxial Fe(Se,Te) thin films grown on CaF2 substrates

We report on the isotropic pinning obtained in epitaxial Fe(Se,Te) thin films grown on CaF2(001) substrate. High critical current density values – larger than 1 MA/cm2 in self field and liquid helium – are reached together with a very weak dependence on the magnetic field and a complete isotropy. Analysis through transmission electron microscopy evidences the presence of defects looking like lattice disorder at a very small scale, between 5 and 20 nm, which are thought to be responsible for such isotropic behavior in contrast to what was observed on SrTiO3, where defects parallel to the c-axis enhance pinning in that direction.

Fluctuation Conductivity of RE1−2x Ca x M x Ba2Cu3O7−δ (RE=Nd, Y and M=Pr, Th) Superconductors

Polycrystalline samples of RE1−2xCaxMxBa2Cu3O7−δ with RE=Nd, Y and M=Pr, Th (with 0.0≤x≤0.10), superconductors were prepared by the standard solid-state method. Resistivity was measured as a function of temperature and doping concentration x. Excess conductivity was analyzed using the modified Lawrence-Doniach (LD) expressions. The fluctuation regions, crossover temperatures, coherence lengths, and effective layer thickness were obtained and the values were compared for both samples. For both samples, it was found that with increasing doping, the crossover temperatures were reduced, while the coherence length decreased. The upper critical field and critical current density were increased with increasing doping concentration due to the introduction of disorder and the enhancement of flux pinning by charge neutral doping. Furthermore, the coherence lengths of the Nd-based samples are larger than that for the Y-based samples by a factor 2. It was found that the value of critical current density in Nd(CaPr)-123 is higher than Y(CaTh)-123, from which it is suggested that CaPr doping is more effective than CaTh doping.

Jc enhancement and flux pinning of Se substituted YBCO compound

Y2/3 Se1/3Ba2Cu3Ox compound was fabricated by using solid state fabrication technique. Optimum heat treatments conditions for Y0.77Se0.33Ba2Cu3Ox were investigated. It was determined that the XRD results of these samples were similar to Y-123 phase with some impurities. Magnetization dependence of applied magnetic fields was measured in the range of 0–9 T at 10–50 K. The symmetric and asymmetric M–H loops were obtained for the samples. Magnetization loops obtained from measurements were successfully described by the extended Valkov–Khrustalev model. The temperature and applied magnetic field dependencies of magnetization of sample were estimated and critical current density of samples was calculated by Bean model and pinning force of samples was calculated by using Lorentz force. It is found from critical current density values that Se additions were acted as a pinning center which increased critical current density.

Evaluation of Mg size dependence on superconductivity of MgB2

<TEX>$MgB_2$</TEX> bulk samples are synthesized through solid state reaction route using Mg precursors with different particle size by keeping the boron precursor unchanged. Scanning electron microscopy study of the fractured surface for all the samples depicts quite distinct structure depending on the Mg precursor. Big size of Mg precursor resulted in to largely elongated and deep pores while smaller one gave roughly ellipsoidal and shallow pore structure. Influence of the Mg particle size on the grain to grain connectivity reflected in the critical current density value which was greater for samples with smaller Mg precursor. All the synthesized samples undergo a superconducting transition at around 36.5 K irrespective of different Mg precursor particle size.

3D like vortex behavior and the thermally activated flux flow mechanism in (Hg0.8Re0.2)Ba2Ca2Cu3Ox superconducting films

Approximately 1 μm thick high quality epitaxial c-axis oriented (Hg0.8Re0.2)Ba2Ca2Cu3Ox superconducting films have been prepared on MgO (100) substrates using spraying technique and post-Hg-Vapor annealing. The effect of the heating temperature–time combinations and the filling factor of Hg (ffHg) on the physical, electrical and magnetic properties of the thick films have been investigated. The XRD investigations showed that the a–b plane of HgRe-1223 phase align parallel to the substrate surface. The best Tc and Tzero were found to be 130.6 and 127.2 K, respectively. The superconducting transition of the films has been measured under applied magnetic field up to 6 T. The results obtained suggested that dissipative resistivity can be explained by thermally activated flux motion below critical temperature under applied magnetic field. The temperature and field dependences of the activation energy in the thermally activated flux flow region have also been investigated. The calculated values of m and α values were found to be 1.42–1.49 and 0.498–0.518 respectively and suggesting a 3D like behavior and the thermally activated flux flow mechanism for all films fabricated. Magnetic properties of the films up to 6 T have also been investigated. The calculated value of critical current density, Jc, was found to be 4.7 × 106 A/cm2 at 10 K for the optimally treated films.

The role of Fe deficiency in FeySe0.5Te0.5 samples prepared by a melting process

Fe content plays a primary role in the structural, magnetic and transport properties of Fe(Se,Te) compounds. In this work we investigate some of these properties in ipo-stoichiometric FeySe0.5Te0.5 samples (y⩽1.00) prepared by a novel synthesis technique, involving a melting process. These samples are characterized by a pore-free microstructure with large and well interconnected grains. The composition Fe0.99Se0.5Te0.5 exhibits the best properties with an optimal critical temperature, sharp resistive and magnetic transitions, large hysteresis loops and high value of critical current density at zero field and 5K.

Characteristics of High-$J_{c}$ GdBCO Coated Conductors Fabricated by the RCE-DR Process

We report the characteristics of GdBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (GdBCO) coated conductors (CCs) on LaMnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LMO)-buffered IBAD MgO template, produced by the Reactive Co-Evaporation Deposition & Reaction (RCE-DR) process. The transport and magnetic critical current density ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) values of GdBCO CC samples were 3.7 and 2.92 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 77 K in self-field for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> // <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> , respectively. Analyses by transmission electron microscopy revealed that a large amount of elongated round Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles with 70-150 nm size and a small amount of the Cu-O phase were trapped in the GdBCO matrix, and a thick layer of the Cu-O phase was also found on the top surface of the GdBCO film, suggesting that the GdBCO film must be grown by the peritectic recombination reaction between Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and a liquid phase. While both the GdBCO film and some Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles grown on the LMO-buffer layer were biaxially textured, the Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles fully trapped in the GdBCO matrix were randomly oriented. The GdBCO film by RCE-DR possessed slightly degraded value of exponent α ~ 0.84 in the power-law relationship <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ~ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</i> and rather large anisotropy in field-orientation dependence of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (θ), and thus refinement of Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> particles may be required for stronger flux pinning.

Superconducting Levitation Using Coated Conductors

The second-generation (2G) YBCO wire has been used for several applications, such as electric power transmission and distribution cables, fault current limiters, MagLev vehicles, electric machines, high field magnets, superconducting magnetic energy storage, etc. The main advantages of 2G wires are: high critical current density values, large scale production, lower manufacturing cost than first generation, and superior performance under high magnetic fields. This work presents a preliminary study of superconducting magnetic bearings (SMB) using 2G wires as passive levitators. A superconducting block using stacked 2G wires was built to evaluate the behavior of coated conductors in the SMB application. The levitation and lateral force between the 2G block and a permanent magnet guideway was measured and compared with the results for an YBCO bulk with approximately the same dimensions. The results indicate that 2G wires have potential for applications with superconducting levitation, but its economic feasibility still depends on the coated conductors price decreasing.

MOD Derived Pyrochlore Films as Buffer Layer for All-Chemical YBCO Coated Conductors

We report a detailed study performed on La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> pyrochlore material grown by the metal-organic decomposition method as buffer layers for YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-x</sub> (YBCO) coated conductors. High-quality epitaxial LZO thin films have been obtained on single crystal (SC) and Ni-5 %at.W substrates. In order to evaluate structural and morphological properties, films have been characterized by means of X-ray diffraction analyses, atomic force microscopy, and scanning electron microscopy. Precursor solutions and heat treatments have been studied by thermogravimetric analyses and infrared spectra with the aim of optimizing the annealing process. Thin films of YBCO have been deposited by pulsed laser ablation on this buffer layer. The best results obtained on SC showed YBCO films with critical temperature values above 90 K, high self-field critical current density values (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> >; 1 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) and high irreversibility field values (8.3 T) at 77 K together with a rather high depinning frequency ν <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> (0.5 T, 77 K) >; 44 GHz as determined at microwaves. The best results on Ni-5% at.W has been obtained introducing in the heat treatment a pyrolysis process at low temperature in air in order to remove the residual organic part of the precursor solution.

Nickel substitution effect on superconducting properties of Bi-2212 ceramics

Abstract The effects of Ni substitution on the properties of high temperature superconductor Bi2Sr2−xNixCa1Cu2Oy were investigated. The samples were prepared by substituting Ni (x = 0.0–0.25) in different ratios by a conventional solid-state reaction method. It is observed that MR (remnant magnetization) enhances in sample N4 due to its better granular structure. Jc is experimentally calculated through dc magnetic–hysteresis loop measurements (M–H), employing the well known Bean’s critical model. It was found that the grain size increases for sample N4 and consequently increases the critical current density values.

Thickness Dependence of Structural and Superconducting Properties of Single-Crystal-Like GdBCO Films Prepared by Photo-Assisted MOCVD

High-quality GdBa2Cu3O7-δ (GdBCO) films with thicknesses of 0.14-1.62 μm were deposited on (100)-oriented LaAlO3 substrates by photo-assisted metal-organic chemical vapor deposition technique. Evaluation of film microstructure and strain-relaxation phenomenon in the growing films and their effects on the crystallographic and superconducting properties of the GdBCO films have been investigated. A single-crystal-like cross-sectional morphology with dense and crack-free surface and no grain boundary visible was observed. The c-axis lattice parameters of the GdBCO films grown with different thicknesses were used to determine the out-of-plane strain. The result shows that the strain could be gradually relieved as film thickness increases. Highly biaxially textured GdBCO films have been obtained. For a 0.31-μm GdBCO film sample, the full-widths at half-maximum were 0.08° and 0.47° for out-of-plane and in-plane orientations, respectively. Such low values were similar to that of single-crystal GdBCO. The highest critical current density (Jc) value is ~ 2.5MA/cm2 (77 K and 0 T). As films were getting thicker, their Jc values decrease gradually. This is mainly attributed to a lack of pinning centers in the thicker films.

The Effect of Silver Inclusion on Superconducting Properties of YBa2Cu3O y Prepared Using Planetary Ball Milling

The effect of Ag inclusion on the structure microstructure and the critical current density of the YBa2Cu3O7−δ sample prepared using the planetary ball milling process has been investigated. YBa2Cu3O7−δ ceramics have been synthesized in air by a solid state reaction method from an oxide precursor powder, which was prepared from the starting powders of Y2O3, Ba2CO3, and CuO via a one-step annealing process in air at 950 ∘C. After planetary ball milling for 4 h of the oxide precursor powders, it was mixed with an AgNO3 solution, and then was dried and uniaxially pressed, and subsequently annealed at 950 ∘C in air. Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDXS) were carried out. To understand the effects of the ball milling on the pinning behavior, magnetic field and temperature dependences on a critical current density have been studied. Analyses show that Ag-milled YBCO samples exhibit higher values of critical current density in applied magnetic field compared to Ag-unmilled one. The better pinning properties of the Ag-milled samples are believed to be due to the microstructure of more fine and uniform distribution of silver and Y-deficient nanosized generated by ball milling.

Critical Current Density Enhancement in High Temperature Superconductors by Flux Pinning

Technological applications of High Temperature Superconductors (HTSC) are limited by Creep, an undesired magnetic vortices movement, creating a pseudo-resistance that depresses both critical current density and critical field. For practical applications (like energy storage systems, current limiters, magnetic bearings, etc.), it is desired to have high values of Critical Current Density (JC) even at higher applied field. Flux Pinning is an established mechanism of enhancing JC in HTSC by Swift Heavy Ion irradiation. This paper explains as to how JC can be enhanced in HTSC and thereby make HTSC technologically more useful. Some recent works and our initiatives in this direction are also discussed. Keywords - Superconductivity, High temperature, Transport properties, Critical Currents, Flux Pinning

The Influence of Surface Morphology of Buffer Layer on the Critical Current Density in YBCO Coated Conductors

1 μm-thickYBa2Cu3O7-δ(YBCO) films were grown on the Y2O3/yttria stabilized zirconia (YSZ)/CeO2buffer layers with different surface morphologies using direct-current sputtering. The critical current density (Jc) value of YBCO was 1.1 MA/cm2when the root mean square surface roughness (Rrms) of the buffer layer was 2.5 nm. As theRrmsof the buffer layer increased to 15 nm, theJcdecreased to 0.3 MA/cm2. X-ray diffraction and scanning electron microscopy showed the strong relevance of the evolution of the structure and surface morphologies of YBCO films with the buffer layer of differentRrms. A model was proposed to explain the influence of surface morphology on the superconducting properties of YBCO films.

Improvement of Film Thickness Uniformity in TFA-MOD Coated Conductors

Abstract TFA-MOD process is expected to be promising for future applications since it can produce high performance YBCO coated conductors with low cost. The dip-coating is adopted as the coating process because of its simplicity and controllability of the overall film thickness. Dip-coated films have uniform thickness along longitudinal direction, but not necessary in transverse direction. In the case of thicker films, the more cracks form during processing at the thicker region near the edges generate and propagate mainly due to tensile and bending strain. So we have to suppress the thickness distribution in transverse direction for thicker films for high I C values. In this study, we found that the thickness distribution was firstly given by meniscus shape and then the solution flew down till it's dried. The solution in the center region drops more since it is slowly dried compared with the edge region. Then, we developed a drying process, which accelerates the drying by blowing hot gas to prevent the coated solutions from dropping. As a result, the thickness uniformity was improved; the thickness ratio of the thick region (edge) to the flat one (center) was improved from 1.35 to 1.07. Furthermore, we successfully produced ~1.5 μm thick films with high critical current density values (> 2MA/cm 2 ) by the new coating process including the force drying step.

MgB2 inclusions in Bi-2223 matrix: The evaluation of microstructural, mechanical and superconducting properties of new system, Bi-2223 + MgB2

This study reports the effect of MgB2 inclusions on the microstructural, electrical, mechanical and superconducting properties of Bi1.8Pb0.4Sr2(MgB2)xCa2.2Cu3.0Oy ceramics with x=0, 0.01, 0.03, 0.05, 0.1, 0.3, 0.5 and 1.0 by use of bulk density, dc resistivity, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transport critical current density (Jc) and Vickers microhardness (Hv) measurements. The samples studied in this work are prepared by conventional solid-state reaction method at the annealing temperature of 840°C for 48h. For the potential technological and industrial applications, the important characteristics such as the normal state resistivity, density, porosity, critical (onset and offset) transition temperature, variation of critical temperature, self-field critical current density, crystallinity, phase purity, lattice parameter, texturing, surface morphology, Vickers microhardness and elastic modulus values are obtained for the pure and MgB2-doped samples and compared with each other. It is found that all the properties given above are sensitively dependent upon the MgB2 concentration in Bi-2223 matrix. The critical transition temperature and critical current density values of the samples are observed to improve significantly for the optimum doping level of x=0.05. The maximum Tconset of 121.3K, Tcoffset of 114.1K and Jc of 463A/cm2 for the sample doped with x=0.05 whereas the minimum values are found to be 118.3K, 101.3K and 235A/cm2 for the material doped with x=1.0 as against 118.6K, 109.4K and 306A/cm2, respectively, for the undoped sample. This may be attributed to the fact that the Bi-2223 system changes from the optimally doped to an underdoped position with the excess of the MgB2 nanoparticles. Furthermore, XRD measurements illustrate that both pure and MgB2 doped superconductors (new system) contain only Bi-2223 and Bi-2212 phases (no different phase of MgB2 or any other cation) and exhibit the polycrystalline superconducting phases with the variable intensity of diffraction lines, confirming that the MgB2 inclusions are incorporated into the Bi-2223 crystal structure in the form of nanoparticles. Besides, the smallest (largest) lattice parameter a (c) is noticed to belong to the sample doped with x=0.05 while the largest (smallest) cell parameter a (c) is observed for the maximum doping level of MgB2 (x=1.0). As for SEM images, similar to the XRD investigations, the former sample has the best crystallinity, texturing, grain connectivity, lowest porosity and largest grain size while the worst surface morphology is observed for the latter sample. Additionally, the bulk porosity analyses for the samples demonstrate that the bulk porosity decreases monotonously with the MgB2 content in the Bi-2223 system up to x=0.05 after which the porosity starts to increase regularly towards to maximum value, leading to the degradation of the grain connectivity. At the same time, the Vickers microhardness values indicate that the samples doped with x=0.01, 0.03 and 0.05 (towards optimally doped state) exhibit reverse indentation size effect (RISE) behavior; on the other hand, the others (towards underdoped state) present indentation size effect (ISE) feature. To sum up, the MgB2 addition in the Bi-2223 superconducting system promotes the velocity of the Bi-2223 phase formation up to the concentration level of x=0.05 beyond which the microstructural, electrical, mechanical and superconducting properties of the Bi-2223 materials studied are found to degrade systematically and in fact reach to their local minimum points for the doping level of x=1.0.

Role of Gd content in Cu(1) and Cu(2) sites on electrical, microstructural, physical, mechanical and superconducting properties of YBa2Cu3−xGdxO7−δ ceramics

This study deals with the effects of partial Gd3+ substitution for the Cu sites on the electrical, microstructural, physical, mechanical and superconducting properties of YBa2Cu3−xGdxO7−δ ceramic superconductors with x = 0, 0.025, 0.050, 0.100 and 0.150 with the aid of dc resistivity, transport critical current density (J c ), X-Ray analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-Ray (EDX), Vickers microhardness (H v ) and density measurements. The samples studied in this work are prepared by the standard solid-state reaction method. The resistivity (at room temperature), critical (onset and offset) temperature, variation of transition temperature, critical current density, hole-carrier concentration, grain size, phase purity, lattice parameter, texturing, surface morphology, element distribution, density, porosity, crystallinity, Vickers microhardness and elastic modulus (E) values of the samples are obtained and compared with each other. The obtained results show that the room temperature resistivity systematically increases with the increment of the Gd content as a result of the hole filling when the onset (T c onset ) and offset (T c offset ) critical temperatures determined from the resistivity curves are found to decrease from 95.2 to 93.6 K and 92.0 to 83.3 K, respectively, showing the presence of impurities and weak links between the superconducting grains. As for the critical current density measurements, the J c values decrease from 132 to 34 A/cm2 as the Gd doping increases. The XRD results give that although the Gd3+ ions substituted tend to occupy both the Cu(1) and Cu(2) sites, the ions are more favorable for the Cu(2) site as a consequence no change of the crystal structure. Besides, the peak intensities belonging to major phase (Y123) decrease monotonously with the increment of the Gd content in the system; however, new peaks belonging to the minor phases start to appear after the doping level of x = 0.0250 beyond which these peaks enhance monotonously, resulting in the decrement of the grain size. Further, the Lotgering indices calculated from the XRD patterns indicate that the texturing of the Y123 grains reduces systematically with the Gd content. According to the SEM investigations, the microstructures of the samples prepared degrade slightly with the content up to the doping level of x = 0.025 after which the morphology suddenly deteriorates due to the appearance of the different phases in the system. EDX measurements show that not only do the elements used for the preparation of the Y123 superconductors with and without Gd content distribute homogeneously but also the level of Cu element rapidly decreases with the increment of the Gd content compared to the other elements, illustrating that the Cu2+ ions may partly be substituted by Gd3+ ions. Moreover, the porosity analyses for the samples depict that the porosity increases with the Gd content, leading to the degradation of the grain connectivity. We also discuss on the mechanical properties of the samples to examine both the elastic modulus and the strength of connection between superconducting grains.

Effect of Ce substitution on structural and superconducting properties of Bi-2212 system

In this study, Bi2Sr2Ca1−xCexCu2Oy, where x = 0, 0.01, 0.05, 0.1 and 0.25, superconducting samples were prepared by solid state method and subsequently used as feed in a laser induced directional solidification (LFZ) process. The physical properties of the samples were investigated by powder X-ray diffraction, scanning electron microscopy, dc-electrical resistance, magnetization, and magnetic-hysteresis loops measurements. It has been found that no significant difference has been observed in the critical transition temperatures of samples except for the sample with the highest Ce additions, which shows the lowest T C compared with the other doped samples. Magnetic hysteresis measurements have shown that the hysteresis loop is greater than the doped samples. In addition, critical current density values obtained from the hysteresis loops measurements by using Bean’s critical state model show a decrease with Ce-addition. All the results indicate that Cerium substitution for Ca produces the deterioration on the superconducting properties, compared with the undoped sample.