Magneto-conductivity Analysis for GdBa2Cu3O7−δ Added with Nanosized Ferrite CoFe2O4

Superconducting samples of type (CoFe₂O₄) _x GdBa₂Cu₃O_7?δ , 0.0≤x≤0.1 wt.%, have been prepared by the conventional solid-state reaction technique and characterized using X-ray powder diffraction (XRD) and the scanning electron microscope (SEM). XRD analysis indicates that the orthorhombic structure of Gd-123 is not affected by the nanosized ferrite CoFe₂O₄ addition, whereas the volume fraction of Gd-123 increases with x up to 0.01 wt.%. Nanosized ferrite CoFe₂O₄ has been prepared by Co-precipitation method with grain size about 8 nm. The temperature dependence of electrical resistivity has been measured in zero and 0.44 T magnetic fields. Magneto-conductivity data has been analyzed in terms of Aslamazov–Larkin (AL) and Maki–Thompson (MT) models for layered superconductors, considering the orbital contribution. The superconducting parameters such as the coherence lengths along ab plane ξ _ab (0) and along c-direction ξ _c (0) at 0 K, anisotropic parameter Γ and phase breaking time τ _φ at 100 K have been determined as a function of nanosized ferrite CoFe₂O₄ contents. It is found that the low nanosized CoFe₂O₄ addition contents up to x=0.01 wt.% improves the physical properties of Gd-123, while for x>0.01 wt.% these properties are deteriorated.     

Determination of Superconducting Parameters of GdBa2Cu3O7?δ Added with Nanosized Ferrite CoFe2O4 from Excess Conductivity Analysis

Superconductor samples of the type (CoFe₂O₄) _x GdBa₂Cu₃O_7??? , 0.0??x??0.1?wt.%, were synthesized by the conventional solid-state reaction technique and were characterized using X-ray powder diffraction (XRD) and scanning electron microscope (SEM). XRD analysis indicated that the orthorhombic structure of Gd-123 is not affected by nanosized ferrite CoFe₂O₄ addition, whereas the volume fraction of Gd-123 increased up to x=0.01?wt.%. Excess conductivity analysis of the investigated samples was analyzed as a function of temperature using the Aslamazov and Larkin (AL) model. It exhibited four different fluctuation regions, namely critical (cr), three-dimensional (3D), two-dimensional (2D), and short-wave (sw). The zero-temperature coherence length along c-axis, effective layer thickness of the two-dimensional system, and inter-layer coupling strength were estimated as functions of nanosized ferrite CoFe₂O₄ concentration. In addition, the thermodynamics, lower and upper critical magnetic fields, and critical current density were calculated from the Ginzburg number. It was found that the low concentration of nanosized ferrite CoFe₂O₄ addition up to x=0.01?wt.% improved the physical properties of Gd-123, while for x>0.01?wt.%, these properties were deteriorated.     

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.     

The Low Temperature Microwave Properties of GdBa2Cu3O7?δ and Sr2RuO4

Measurements of the microwave surface resistance R_s and reactance X_s of GdBa₂Cu₃O_7– and Sr₂RuO₄ single crystals are reported in the temperature range 0.4 to 25 K at frequencies from 10 to 20 GHz, using a hollow dielectric resonator technique. The GdBa₂Cu₃O_7– measurements are interpreted in terms of antiferromagnetic alignment of the Gd spins, resulting in a Nèel transition at 2.25 K, with a strongly temperature spin relaxation time both above and below the transition. Above T_c = 1.45 K, the normal state surface impedance of the suspected p-wave superconductor Sr₂RuO₄ agrees rather well with that expected from dc measurements; however, below T_c, we observe an unusual increase in the surface reactance, which we attribute to a long electron relaxation time. Using a two-fluid model, we obtain a normal fluid component that decreases almost linearly with temperature and extrapolates to a finite low-temperature value.     

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.     

Significant Change in Mechanical Properties of YBa2Cu3O7−x Bulk Superconductors Diffused with Sn Nanoparticles

Mechanical behavior of YBa₂Cu₃O_7?x (Y123) superconductors exposed to Sn nanoparticles diffusion is determined by the way of Vickers microhardness (H _v ) conducted at different applied loads (0.245N≤F≤2.940 N). Load dependent microhardness, load independent microhardness, elastic modulus, and yield strength values are estimated from the microhardness curves. Unpredictably, the findings of the H _v values reveal that the undiffused sample and Sn diffused sample prepared at 500 ^°C exhibit reverse indentation size effect (RISE) behavior while the other samples obey indentation size effect (ISE) nature. Further, we extract the load independent (true) microhardness using the Meyer’s law, proportional specimen resistance (PSR), elastic/plastic deformation (EPD), Hays–Kendall (HK) approach and indentation-induced cracking (IIC) model, and compare the true hardness with the apparent hardness.     

Local Structure and Superconducting Properties of Bi 2 Te 3 -Doped YBa 2 Cu 3 O 7 − δ

The samples of (Bi₂Te₃) _x (YBa₂Cu₃ O _7?δ) _1?x (x = 0, 2.5 %) have been synthesized at normal pressure, and the effect of the doping of topological insulator Bi₂Te₃ on the superconductor YBa₂Cu₃ O _7?δ is studied. The diamagnetism properties are investigated by zero-field cooling DC magnetization measurement. In the Bi₂Te₃-doped sample, an enhancement of superconducting fractions is observed, and the superconducting transition temperature (T _c ) increases. For the sample with x= 2.5 %, the phase transition of the tetragonal phase to the orthorhombic phase is observed by X-ray diffraction, and the increase of the degree of local structure disorder is confirmed by extended X-ray absorption fine structure, so it can be concluded that the superconducting fraction enhancement is attributed to the phase transition induced by the addition of topological insulator Bi₂Te₃. Scanning electron microscopy images show that the added Bi₂Te₃ is found to adhere to the surface of YBa₂Cu₃ O _7?δ grains, and it is considered that the strain induced by grains’ interaction leads to the phase transition which enhances the degree of local structure disorder at the same time. An absorption edge shift to the high-energy side is observed by the X-ray absorption near-edge structure. The edge shift can be attributed to the electron transfers from YBa₂Cu₃ O _7?δ to the additives. It is widely accepted that the hole intensity is closely related with T _c , so in YBa₂Cu₃ O _7?δ the added holes by the transition may lead to the enhancement of T _c . Thus, it can be concluded that the topological insulators can produce structural and electronic effect on the YBCO superconductors in the composite materials.     

Improvement of Superconducting Parameters of Bi1.8Pb0.4Sr2Ca2Cu3O10+δ Added with Nano-Ag

Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_10+δ superconductor samples were synthesized by the conventional solid-state reaction technique. Nano-Ag was introduced by small weight percentages (0.2, 0.4, 0.6, 1, and 1.5 weight %) in the final step of the synthesis process. Phase formation and microstructure were investigated using x-ray powder diffraction, differential scanning calorimetry, and scanning electron microscopy. The real elemental-content and oxygen-content were examined using particle induced X-ray emission (PIXE) and Rutherford backscattering (RBS) techniques, respectively. Electrical resistivity as function of the temperature was carried to evaluate the relative performance of samples. Moreover, Electric field-Current density (E–J) characteristic curves were measured at 77 K. The electrical and granular properties were greatly enhanced, indicating more efficient pinning mechanisms. An improvement of the critical current density of 229 % was obtained with x=0.6 wt.%, while the superconducting transition temperature is improved by 2.5 %.     

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.     

Comparison of 2-D Quantum and Thermal Critical Fluctuations of Underdoped Bi2Sr2CaCu2O8+δ with Ultrathin YBa2Cu3O7−δ

This paper addresses two issues. Underdoped Bi-2212 has been shown to exhibit two-dimensional quantum fluctuations, with T _c vs. N _s (0) scaling qualitatively similar to ultrathin YBCO films that are 2-D by construction. The present paper shows that the quantitative difference in scaling is resolved by growing Bi-2212 films that are much smoother than previously used. Also, the absence of 2-D thermal critical behavior from the superfluid density of Bi-2212 films that exhibit 2-D quantum scaling is not likely due to an inhomogeneous T _c smearing out the 2-D thermal transition. Finally, we emphasize that there is as yet no consensus on the physics that drives the T-dependence of N _s at low to intermediate temperatures.     

Stoichiometry Analysis and Normal-State Properties of SmBa2Cu3−x Ru x O7−δ Superconducting Phase

The electrical resistivity of normal and superconducting states for SmBa₂Cu_3?x Ru _x O_7?δ (Sm-123) phase with 0.00 ≤ x ≤ 0.50, prepared by the conventional solid-state reaction technique, was studied. X-ray powder diffraction (XRD), scanning electron microscope (SEM), particle-induced X-ray emission (PIXE), Rutherford backscattering spectroscopy (RBS) and electrical resistivity measurements were performed in order to investigate the effect of Ru⁴⁺ ions substitution in Sm-123 phase. Both the phase formation and superconducting transition temperature T _c enhance up to x = 0.05. For x > 0.05, suppression of both the phase formation and T _c is observed and the superconductivity is completely destroyed around x = 0.50. The normal-state electrical resistivity was analyzed by the two- and three-dimensional variable range hopping (2D-VRH and 3D-VRH) and Coulomb gap CG. The dominant mechanism for Sm-123 phase is CG with x ≤ 0.20 while is 3D-VRH for x ≥ 0.30.     

Physical properties of YBa2Cu3O7−x superconductor sintered at different temperatures

YBa₂Cu₃O_7–x ceramics prepared by sintering at 920 and 1030° C were studied in some detail. Although samples prepared at 920° C had lower density, they had larger transport critical current at 77 K. A correlation between the transport critical current and the magnetic field dependence of the second maximum in the imaginary part of the initial susceptibility was found and discussed. According to our results samples prepared at higher temperature had larger but (in spite of almost ideal density) poorly connected grains.     

Synthesis and magnetic properties of polycrystalline films of Co x Fe y Cr3 − x − y O4 and Cr2O3/CoFe2O4 multiferroics

Magnetic properties of first obtained polycrystalline films of FeCr₂O₄, CoCr₂O₄, and CoFe_0.5Cr_1.5O₄ multiferroics and films of a Cr₂O₃/CoFe₂O₄ composite multiferroic have been studied. In particular, magnetization curves and temperature dependences of the magnetic moment of the samples were measured in the temperature range 4.2–300 K in fields of up to 10 kOe. It was shown that the Curie point of a multiferroic depends on its cation composition. It was found that an exchange bias of the hysteresis loop exists in films of the Cr₂O₃/CoFe₂O₄ composite multiferroic at temperatures below the Néel point of Cr₂O₃ (330 K).     

Percolation Analyses on Transport Properties of YBa2Cu3O7−δ-Ag System

The transport properties of YBa ₂ Cu ₃ O _7– -Ag composite ceramic system have been studied from the viewpoint of the percolation theory. The percolation threshold volume fraction f _c of Ag determined from the electrical resistivity and from the thermal conductivity is f _c =0.125±0.005. This markedly smaller value than the theoretical value ( f _c =0.16) suggests the segregative distribution of Ag. The critical exponent t depends on the component conductivity ratio h = _YBCO / _Ag , which can be explained on the basis of the scaling hypothesis.     

Analysis of deformed YBa2Cu3O7−δ

In this study, polycrystalline YBa₂Cu₃O_7– (123) was deformed under controlled conditions with a confining pressure of 1.0GPa, temperatures of 25, 500 and 800° C, and a strain rate of 10^–4 sec^–1 in order to ascertain the micromechanisms of deformation that give rise to the macroscopic plastic behaviour. The deformed material was analysed using optical microscopy, transmission electron microscopy (TEM), and a SQUID magnetometer to study the effects of deformation on the microstructure of YBa₂Cu₃O_7– and how changes in the microstructure affected the superconducting properties. The results of these preliminary experiments suggest that the 123 material will be very difficult to deform plastically as slip occurs only on the (001) plane. The lack of multiple slip systems implies that this material will show some brittle behaviour up to a very high homologous temperature. Even when plastic behaviour can be sustained for high strains it may require high annealing temperatures to remove lattice imperfections which impede the superconducting currents. Densification by high pressure deformation may make reoxygenation difficult due to the reduced diffusion rates between the grains. These factors combined suggest that traditional fabrication techniques are not applicable to the 123 material. More work needs to be carried out to determine how annealing affects the microstructures of deformed materials and how these changes in microstructure affect the superconducting properties of these materials.     

Sintering of YBa2Cu3O7−x compacts

Heating of YBa₂Cu₃O_7−x compacts above about 930°C is shown to induce liquid formation. Presence of the liquid phase results in excellent densification, but limited superconducting properties. Sintering below 930°C occurs primarily by solid-state diffusion. Although the density of these samples is low, the superconducting properties are similar to those of the dense materials produced via liquid-phase sintering. The highest current densities (≈ 500 A/cm²) have been obtained in these solid-state sintered samples.     

X-Ray and High-Resolution Neutron Diffraction Studies on Nd x Y1−x Ba2Cu3O7−δ Superconductors

A synthesis of neodymium-substituted YBCO superconductor Nd _x Y_1?x Ba₂Cu₃O_7?δ (x=0,0.25,0.5,0.75,1) has been done using a dissolved method in order to obtain homogeneous crystals and higher critical current density. The effects of the substitutions on the structural and magnetic properties of the superconductors after sintering at 970 ^°C have been examined. Crystallinity of the synthesized powders was confirmed using X-ray and high-resolution neutron diffraction (XRD and HRPD) techniques. Rietveld analyses for both diffraction data sets gave increasing lattice parameters with addition of Nd content and decreasing orthorhombicity. Such addition also caused a decrease in occupancy of the oxygen in the O(4) site. Further investigation using SQUID showed critical temperature of the superconductors between 90.9 and 92.0 K. The critical current density (J _c ) was calculated from the magnetic hysteretic loop at 5 K as 40 kA?cm^?2 for Nd_0.25Y_0.75Ba₂Cu₃O_7?δ sample and 100 kA?cm^?2 for Nd_0.5Y_0.5Ba₂Cu₃O_7?δ sample. We also found that increasing Nd content on the Nd _x Y_1?x Ba₂Cu₃O_7?δ superconductor samples can improve their resilience of superconductivity and critical current density.