Superconducting Samples Research Articles

Effect of magnetic field on the flux pinning mechanisms in Al and SiC co-doped MgB2 superconductor

MgB2 superconductor samples co-doped with 0.02 wt. Al2O3 and 0–0.05 wt. SiC were studied by magnetization – magnetic field (M-H) loop measurements at different temperatures. The critical current density has been calculated by the Bean model, and the irreversibility field, Hirr, has been obtained by the Kramer method. The pinning mechanism of the co-doped sample with 2% Al and 5% SiC was investigated in particular due to its having the highest Hirr. The normalized volume pinning force f = F/Fmax as a function of reduced magnetic field h = H/Hirr has been obtained, and the pinning mechanism was studied by the Dew-Houghes model. It was found that the normal point pinning (NPP), the normal surface pinning (NSP), and the normal volume pinning (NVP) mechanisms play the main roles. The magnetic field and temperature dependence of contributions of the NPP, NSP, and NVP pinning mechanisms were obtained. The results show that the contributions of the pinning mechanisms depend on the temperature and magnetic field. From the temperature dependence of the critical current density within the collective pinning theory, it was found that both the δl pinning due to spatial fluctuations of the charge-carrier mean free path and the δTc pinning due to randomly distributed spatial variations in the transition temperature coexist at zero magnetic field in co-doped samples. Yet, the charge-carrier mean-free-path fluctuation pinning (δl) is the only important pinning mechanism at non-zero magnetic fields.

Flux pinning mechanism in codoped-MgB2 with Al2O3 and SiC

MgB2 superconductor samples, co-doped with 0.02 wt of Al2O3 and 0.02 wt SiC, have been examined by M-H loop measurements and calculation of the critical current density based on the Bean model. Normalized volume pinning force, f = F/Fmax, as a function of the reduced magnetic field, h = H/Hmax has been obtained at each temperature. Hughochi flux pinning model, which was included the normal point pinning, the normal surface pinning, and the pinning based on spatial variation in the Ginzburg–Landau parameter, was used to study the flux pinning mechanisms. It was found that the Δκ effect and the normal point pinning mechanisms play the main role in the flux pinning at the magnetic field lower than Hmax and the contribution of the Δκ mechanism increases with the increasing temperature, while the contribution of normal point pinning mechanism decreases. At magnetic field larger than Hmax, the only mechanism that acts as the flux pinning was the normal surface pinning mechanism.

Study of YBa2Cu3O7−δ Superconductor/Graphene Oxide Composite

The aim of this research was to fabricate YBa2Cu3O7−δ (YBCO) superconductor composite with graphene oxide nanosheets and to study the effect of the graphene oxide nanosheets on YBCO superconductor properties. For this purpose, the samples of pure superconductor and superconductor composite with 0.001, 0.01, and 0.1 wt.% graphene oxide were synthesized. First, graphite oxide was made by Hummer’s chemical method; after that, graphene oxide nanosheets were produced by bath-keeper ultrasonic. Then, different amounts of graphene oxide were added to the process of superconductor fabrication, which was made by solid-state reaction method. The samples were characterized and studied by Meissner effect test, XRD analysis, FESEM imaging, EDX measurement, and ac magnetic susceptibility. The critical current density (Jc) of samples was measured by four probes method. The results showed that by increasing the weight ratio of graphene oxide, Jc and Tc decrease.

Локализованные волны в слоистых сверхпроводниках

Локализованные волны в слоистых сверхпроводниках

Simulated increase of critical currents in heterogeneous hybrid superconducting samples

Increase in critical currents of hybrid superconducting samples in the presence of arrays of defects and applied magnetic field are studied numerically via the Time Dependent Ginzburg Landau equations, with the link variable technique. The results show that a gradient of density in the distribution of defects seems to be the most relevant factor for the highest increases in critical currents. Arching structure of the distribution is not a necessary feature for high increases, contrary to what was claimed before with conformal arrays. The results are obtained with the use of complex order parameter instead of a model of individual vortex dynamics, suggesting some potential limitations of this formulation.

Excess Conductivity Investigation of Y3Ba5Cu8O18±δ Superconductors Prepared by Various Parameters of Planetary Ball Milling Technique

Superconducting samples of type Y3Ba5Cu8O18±δ were elaborated by using a planetary high-energy ball milling (HEBM) technique with various parameters. Phases, microstructure, and superconductivity have been examined using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electrical resistivity measurements. SEM investigation shows the occurrence of nanoentities embedded into the superconducting matrix for samples prepared by a ball milling technique. The main objective of this study is to investigate the influence of ball milling parameters on the fluctuation-induced conductivity (FIC). The electrical resistivity versus temperature, ρ(T), above T c was analyzed using Lawrence–Doniach (LD) and Aslamazov–Larkin (AL) models. Different fluctuation regimes indicated by short-wave fluctuation (SWF) and three-dimensional (3D), two-dimensional (2D), one-dimensional (1D), and critical region (CR) fluctuations were identified. The coherence length at zero temperature, the effective layer thickness, the critical magnetic fields, and the critical current densities are determined. The superconducting parameters strongly depend on the planetary ball milling technique, and the results are explained in relevancy to the microstructure. It was found that the achievement of a microstructure with well-dispersed nanoentities is an effective way for introducing pinning centers for enhancing critical current density and flux pinning capability of bulk Y-358.

Influence of strain on transport characteristics of HTSC

By using the Monte-Carlo method, the dependencies of transport characteristics of a type-II superconductor on the degree of bending strain applied to the sample have been numerically studied. Multiple series of voltage-current characteristics have been acquired for a sample of a high-temperature superconductor for different numbers of strain-induced cracks, as well as various point defects concentrations and different values of external magnetic field. Some peculiarities of the voltage-current characteristics have been detected. Average vortex configurations have been acquired showing that in the points of peculiarities the vortex lattice “freezes” in spaces between cracks. The results for the increasing number of cracks have shown a significant degradation of critical current density.

Fluctuation-induced conductivity in melt-textured Pr-doped YBa2Cu3O7-δ composite superconductor

ABSTRACTIn this study, the effects of thermal fluctuations on the electrical conductivity in melt-textured YBa2Cu3O7-δ, Y0.95Pr0.05Ba2Cu3O7-δ and (YBa2Cu3O7-δ)0.95–(PrBa2Cu3O7-δ)0.05 composite superconductor were considered. The composite superconductor samples were prepared through the top seeding method using melt-textured NdBa2Cu3O7-d seeds. The resistivity measurements were performed with a low-frequency, low-current AC technique in order to extract the temperature derivative and analyze the influence of the praseodymium ion on the normal superconductor transition and consequently on the fluctuation regimes. The results show that the resistive transition is a two-step process. In the normal phase, above the critical temperature, Gaussian and critical fluctuation regimes were identified, while below the critical temperature, in the regime near the approach to the zero-resistance state, the fluctuation conductivity diverges as expected in a paracoherent-coherent transition.

Superconductivity in ThPd2Ge2

Our on-going search for unconventional superconductors among the ThTE2Ge2 phases (TE is a d-electron transition metal) revealed that ThPd2Ge2, which crystallizes with a body-centered tetragonal ThCr2Si2-type structure, exhibits superconductivity at low temperatures. In this paper, we report on the electrical transport and thermodynamic properties of a polycrystalline sample of this new superconductor, extended down to 50mK. The experimental data indicates weakly-coupled type-II superconductivity with Tc = 0.63(2) K and µ0Hc2(0) = 32(2) mT.

Mechanical properties of the (BaSnO3)x/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ superconductor phase

In this study, we carried out the Vickers microhardness for Cu0.5Tl0.5Ba2Ca2Cu3O10−δ, (Cu0.5Tl0.5)-1223 superconducting phase added with BaSnO3 nanoparticles. BaSnO3 nanoparticles were prepared by the co-precipitation technique, while the superconductor samples of type (BaSnO3)xCu0.5Tl0.5Ba2Ca2Cu3O10−δ, with 0.00 ≤ x ≤ 1.00 wt.%, were prepared by the conventional solid-state reaction method. Vickers microhardness (Hv) was measured at room temperature and was computed by taking the average of three hits at different locations on the specimen surface. The measurements were performed as a function of the applied load (F = 0.98–9.80 N) and the dwell time (t = 10–59 s). The Hv values were found to be strongly dependent on both the BaSnO3 content and the dwell time. Furthermore, the load independent Vickers microhardness was analyzed using Meyer’s law and different models such as the Hays–Kendall approach (HK), the elastic/plastic deformation model (EPD), the proportional specimen resistance model (PSR) and the modified proportional specimen resistance model (MPSR). The PSR model is found to be the most adequate model in explaining the load independent microhardness for the (BaSnO3)x/(Cu0.5Tl0.5)-1223 superconductor phase. Some important mechanical parameters such as Young’s modulus (E), yield strength (Y), fracture toughness (K) and brittleness index (B) were calculated as a function of x. It was found that the addition of proper concentrations of BaSnO3 nanoparticles enhanced the mechanical properties of the prepared samples. The time-dependent microhardness was investigated according to indentation creep experiments showing that the operative creep mechanisms in the studied samples were diffusion creeps at low loads followed by grain boundary sliding as well as dislocation creeps for higher loads.

The Influence of Pinning Centers in the Magnetization of the Mesoscopic Superconductors

In this work, we study the mesoscopic superconducting samples with pinning centers using the time-dependent Ginzburg-Landau theory (TDGL). The pinning centers are introduced via the phenomenological function f(r) Sorensen et al. (Physica C 533, 40–43 2017). We calculated the magnetization curves M(H) for some distances d from the boundary of the sample to the position of the pinning center. From this investigation arises the relation between the first magnetic field H p and the distance d. It shows that the pinning centers located close to the boundary of the sample decrease H p , and also the existence of two regimes of the penetration of the vortices. The magnetization curves revel the existence of ruddle of jumps for low magnetic fields for small distances d, indicating a complex vortex penetration.

Suppression of the superconducting gap near d-wave nodes caused by the structural disorder in fine-crystalline YBa2Cu3Oy high-Tc superconductors

The low-temperature (2 K ≤ T ≤ 10 K) specific heat of the series of fine-crystalline samples of YBa2Cu3O y high-Tc superconductor optimally doped with oxygen and having different degrees of nanoscale structural inhomogeneity has been studied at the applied magnetic field H = 8 T. The result are compared to those obtained for the equilibrium polycrystalline samples with different oxygen contents y. Information on the quasiparticle excitations in the magnetic field near d-wave nodes of the gap function is obtained. The changes introduced by the structural inhomogeneity to the nodal gap slope (νΔ) in the k-space, which is a key parameter of high-Tc superconductors, have also been studied. It is found that νΔ increases with the degree of structural disorder, but the superconducting transition temperature remains nearly the same (Tc = (91.5 ± 0.5) K). It is shown that this is possible if superconductivity is suppressed not only at the nodal point but also near it (owing to the structural disorder). In this case, the density of states in such parts of the Fermi surface is nonzero even at zero temperature, promoting the existence of the linear in temperature contribution to the specific heat (~γ(0)T), which is characteristic of metals.

Enhancement of Critical Current Density of MgB2 by Glutaric Acid Doping: a Simultaneous Improvement on the Intrinsic and Extrinsic Properties

In this study, we report an enhancement of critical current density of bulk MgB2 superconductors by glutaric acid (C5H8O4) doping. The effects of glutaric acid doping on MgB2 lattice resulted in a record self-field J c of the order of 106 A/cm2. A simultaneous improvement in the connectivity, pinning force, and H c2 is the major factor that determined excellent J c performance. X-ray diffraction analysis showed that samples were single-phase MgB2 with a minor trace of impurities. A dramatic change in grain morphology and homogeneity in grain distribution was found in the SEM images of doped samples. We observed that homogeneity in grain distribution played a crucial role in the connectivity and the upper critical field (H c2) of the doped samples. We were able to introduce a new dopant through a two-step mixing approach which is suitable to overcome the degradation of low field and self-field J c reported for carbon-doped MgB2 superconductor samples.

Experimental study of quench in a short sample of Bi-2223/AgMg tape in a conduction-convection cooling regime

Superconducting magnets based upon high temperature superconductors (HTSs) are more stable than low temperature superconductors (LTSs). This means that the minimum quench energy (MQE) of a HTS is higher than that of a LTS. However, disturbances such as flux jump, wire movement and epoxy cracks can cause a thermal runaway. In this case, HTSs are vulnerable because of the low normal zone propagation velocity (NZPV) thus HTS magnets are not self-protecting. To design a safe operating point for such magnets, quench characterization and the cooling mode are important. In this article, the normal zone propagation evolution of a short sample of Bi-2223/AgMg high temperature superconducting tape has been investigated by applying localized heat pulses. Experiments were carried out based on cryogenic stabilization in N2 vapor. To enhance the thermal stability, the superconductor sample is mounted on a copper plate which is immersed in liquid nitrogen up to the given height. By increasing the current, we measured the rate of decrease of the MQE, the superconducting stability factor, the rate of increase NZPV, and the protection parameter against quench.

Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T’-Superconductors

In this review article, we show our recent results relating to the undoped (Ce-free) superconductivity in the electron-doped high- T c cuprates with the so-called T’ structure. For an introduction, we briefly mention the characteristics of the electron-doped T’-cuprates, including the reduction annealing, conventional phase diagram and undoped superconductivity. Then, our transport and magnetic results and results relating to the superconducting pairing symmetry of the undoped and underdoped T’-cuprates are shown. Collaborating spectroscopic and nuclear magnetic resonance results are also shown briefly. It has been found that, through the reduction annealing, a strongly localized state of carriers accompanied by an antiferromagnetic pseudogap in the as-grown samples changes to a metallic and superconducting state with a short-range magnetic order in the reduced superconducting samples. The formation of the short-range magnetic order due to a very small amount of excess oxygen in the reduced superconducting samples suggests that the T’-cuprates exhibiting the undoped superconductivity in the parent compounds are regarded as strongly correlated electron systems, as well as the hole-doped high- T c cuprates. We show our proposed electronic structure model to understand the undoped superconductivity. Finally, unsolved future issues of the T’-cuprates are discussed.

Thermopower of NiO/(Bi, Pb)-2223 composite

Solid-state reaction method was used to prepare superconductor samples with nominal composition of (NiO)x(Bi1.6Pb0.4)Sr2Ca2Cu3O10−δ,where 0.0 ≤ x ≤ 0.2 wt%. The prepared samples were characterized by X-ray diffraction (XRD) as well as scanning electron microscopy (SEM). XRD patterns indicated that the addition of nano-NiO particles to (Bi, Pb)-2223 did not affect the tetragonal structure and their lattice parameters. The thermopower coefficient was measured as a function of temperature from 250 K down to 77 K, using a standard differential technique. The results were analyzed according to the two-band (Fermi-liquid) and the two-band with an extra linear term models. Pseudo gap temperature (T*), Fermi energy (EF) and Fermi temperature (TF) values were calculated and discussed in terms of nano-NiO additions.

Role of ruthenium content on studying excess conductivity and magneto-conductivity of SmBa2Cu3−xRuxO7−δ phase

Superconducting samples of type SmBa2Cu3−xRuxO7−δ were prepared by a solid-state reaction technique. The electrical resistivity ρ(T) versus temperature for all prepared samples was measured in the absence and presence of magnetic field (0.44 T). The electrical resistivity data at zero magnetic field was analyzed using Aslamazov–Larkin (AL), Lawrence–Doniach (LD) and Maki–Thompson (MT) models in terms of fluctuation induced excess conductivity. Coherence length along c-axis $${\xi _c}\left( 0 \right)$$ , effective layer thickness of superconducting layers $$d$$ , the thermodynamic critical magnetic field $${B_c}(0)$$ , penetration depth $$\lambda (0)$$ , lower critical magnetic field $${B_{c1}}$$ , upper critical magnetic field $${B_{c2}}$$ , critical current density $${J_c}(0)$$ , Fermi velocity $${v_F}$$ , phase relaxation time of Cooper pair $${\tau _\varphi }$$ , coupling constant $$P$$ and energy required to break apart Cooper pair $${E_{{pb}}}$$ were calculated as a function of Ru-content. The magneto-conductivity data was analyzed using AL and MT models for layered superconductors. Coherence length along ab plane $${\xi _{ab}}(0)$$ and $${\xi _c}\left( 0 \right)$$ at 0 K, $${\tau _\varphi }$$ at 100 K and $${E_{{pb}}}$$ were also calculated as a function of Ru-content. The partial substitution of Cu2+ ions by Ru4+ ions up to 0.05 improved the superconducting properties of Sm-123 phase.

Measurement of mass attenuation coefficients for undoped and boron nitride–doped magnesium diboride superconductors in the x-ray region 8.04–59.5 keV

ABSTRACTIn this study, mass attenuation coefficients of the undoped and 2% boron nitride–doped magnesium diboride superconductor samples were investigated. Mass attenuation coefficients were measured at 8.04–59.5 keV x-ray energies by using a high-purity germanium detector with a resolution of 182 eV at 5.9 keV. It is observed that mass attenuation coefficients in undoped and doped magnesium diboride samples decrease with increasing photon energy, and doping with the boron nitride leads to increase the absorption of the electromagnetic radiation.

Síntesis del superconductor YBa2Cu3O7- δ mediante sinterización por descarga luminiscente anormal

En este trabajo se reporta la síntesis del superconductor YBa2Cu3O7-δ mediante el método no convencional de sinterización por plasma en el rango de descarga luminiscente anormal (DLA). Las muestras se sometieron a diferentes temperaturas y tiempos de sinterización. Como referencia se usó una muestra superconductora obtenida por el método convencional (horno resistivo). La caracterización estructural de estas muestras se hizo por difracción de rayos X y refinamiento con el método de Rietveld. El comportamiento superconductor se determinó mediante el análisis de las curvas de magnetización en función de la temperatura según los procedimientos experimentales de enfriado en campo magnético cero (zero field cooling, ZFC) y enfriado con campo magnético aplicado (field cooling, FC). Las muestras sinterizadas por DLA presentaron características estructurales (ortorrómbica Pmmm) y superconductoras con una temperatura crítica de Tc~ 92 K, similares a las obtenidas por el método convencional, pero con una significativa reducción en las temperaturas y tiempos, bajo un ambiente adecuado de presión en el proceso de sinterización. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat.

Development of resistance and temperature measurement system for cryogenic equipment

Cryogenic equipment is used especially for the research on superconductors as the tools to create a condition of low temperature and high magnetic field. However, it needs the measurement system to be used to analyze the material properties. This work developed a control program of resistance measurement system using instruments of current source, nanovoltmeter and temperature controller. We designed and developed a measurement system by building a connection of the instruments and creating a new control program. The created control program can be revised or modified easily when we have to replace or add the instruments. LabVIEW program was used as a control program, and designed for measuring the resistance and controlling the temperature. Four-point probe method was used to measure the resistance value, a sensor to determine the temperature and a heater to control the temperature. The developed measurement system was tested using standard superconductor sample. It clearly showed the graph of the temperature dependence of resistance. And it showed sharp drop of resistance around 98K, indicating its critical temperature.