Strength Of Superconductors Research Articles

Effects of critical current density on mechanical properties of cylindrical superconductors

High-temperature superconductor has high critical temperature, high transport current capacity and low energy consumption, which correspondingly offer the wide applications in the field of electric power. As an important concern, the mechanical properties of superconductor carried with transport current have received extensive attention. Still, its mechanical properties in various electromagnetic environments are under study. Most of previous studies are based on the assumption of uniform distribution of critical current density, and only few researches based on the non-uniform distribution of critical current density are carried out. In this work, the mechanical flux pinning response of cylindrical superconducting structures is studied. Considering the non-uniform features of critical current density along the radial direction, the distribution law of induced magnetic field and current for the cylindrical superconducting structure is obtained based on the Bean model. Combined with the plane strain method, the analytical expression of magnetic flux pinning force, stress and magnetostriction in the superconducting structure are obtained. The results show that the uneven distribution of critical current density causes the flux pinning force to change, which further leads the superconductor`s local radial stress to vary with the critical current density. When the transport current flowing through the superconductor is increased in the ascending field, the radial stress and the hoop stress both appear compressive. The non-uniform distribution of critical current density has no significant effect on the overall trend of the internal stress, but displays an obvious influence on the stress distribution, and the superconducting structure is compressed and deformed. The results are consistent with those in the uniform case. When the transport current decreases during field descending, the critical current starts to reverse from the outermost part, then the compressive stress and tensile stress exist simultaneously. The hoop stress has a discontinuous point at the discontinuous portion of the critical current density, thus the damage probability is higher than that of the uniform distribution. In other words, the shear strength of superconductor is required to be higher for application. Also, the degree of magnetostriction is higher when the distribution of critical current density is set to be uniform, that is, the non-uniform distribution of the critical current density causes the superconducting structure to undergo greater deformation. Therefore, in engineering applications, the structural strength of the superconducting material must be enhanced to cope with the challenge from the uneven distribution of critical current density.

Effect of neutron irradiation on microstructure and strength of Bi-2212 phase superconductor

The sustainability of superconductors when exposed to radiation environment is vital for the materials to be used as components and devices in nuclear reactors. In this investigation, TRIGA MARK II research reactor with neutron flux of 2.00 × 1011 / cm2s was used as the neutron source to study the effect of neutron irradiation on microstructure and physical strength of Bi2Sr2CaCu2 (Bi-2212) superconductor. Results between non-irradiated and irradiated samples have been analyzed with respect to phase formation, microstructure and strength of the superconductor. The bulk samples were synthesized using the conventional solid-state reaction method. Molar ratio of Bi2O3, Sr2CO3, CaCO3, and CuO were mixed according to its ratio into composition of Bi:Sr:Ca:Cu = 2:2:1:2. The powder were palletized and sintered at 840°C for 48 hours. Characterization of the samples was done via X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The XRD patterns for the non-irradiated and irradiated samples show well-defined peaks of which could be indexed on the basis of a Bi-2212 phase structure. XRD patterns also indicate that irradiation did not affect the Bi-2212 superconducting phase. From observation of the XRD pattern and microstructure, there is indication that a small amount of Bi-2212 is decomposed into Cu2O and other impurities while a significant amount of un-reacted Bi-2212 particles embedded at the grain boundaries. For the non-irradiated samples, the microstructure was found to be more textured and thus enhanced the strength of the samples. For the neutron irradiated samples, the results show disorganization of grains orientation and formation of porous structure that led to reduction in overall strength of the Bi-2212 superconductor.

Non-Fermi-liquid to Fermi-liquid transports in iron-pnictide Ba(Fe1−xCox)2As2 and the electronic correlation strength in superconductors newly probed by the normal-state Hall angle

Electrical transports in iron-pnictide Ba(Fe1−xCox)2As2 (BFCA) single crystals are heavily debated in terms of the hidden Fermi-liquid (HFL) and holographic theories. Both HFL and holographic theories provide consistent physic pictures and propose a universal expression of resistivity to describe the crossover of transports from the non-Fermi-liquid (FL) to FL behavior in these so-called ‘strange metal’ systems. The deduced spin exchange energy J and model-dependent energy scale W in BFCA are almost the same, or are of the same order of several hundred Kelvin for over-doped BFCA, which is in agreement with the HFL theory. Moreover, a drawn line of W/3.5 for BFCA in the higher-doping region up to the right demonstrates the crossover from non-FL-like behavior to FL-like behavior at high doping, and shows a new phase diagram of BFCA. The electronic correlation strength in superconductors has been newly probed by the normal-state Hall angle, which found that, for the first time, correlation strength can be characterized by the ratios of Tc to the Fermi temperature TF, J/TF, and the transverse mass to longitudinal mass.

Angular dependence of isothermal remanent magnetization of sputtered YBCO thin films

Because of their intrinsic layered structure, high temperature superconductors are suitable systems for studying the strong anisotropy of their superconducting properties. In fact, the response of a sample to an external magnetic fieldH depends generally not only on the magnitude but also on the orientation ofH. Since remanent magnetization is a measurement of the effective flux-pinning strength in superconductors, it depends upon both the temperature and the applied field, as well as on the history of processing and the angle between the applied magnetic field and the crystallographic axis directions. In this framework we report the studies of the angular dependence of remanent isothermal magnetization Mrem in YBCO sputtered films. The projections of the remanent magnetization on the direction of the magnetometer axis were measured for each of the films. The results show the orientational preference for flux trapping, related to intrinsic features. Moreover, an angular dependence of the remanent magnetization can be calculated in good agreement with the experimental data.

Effects of the n→s transition on the strength of superconductors

Abstract In the transition from the normal (n) to the superconducing (s) state the creep rate of metals increases, while with deformation at constant strain rate a relaxation of the flow stress ensues. In a model developed to account for these and allied observations, phonons, emitted (n→s) or absorbed (s→n) in pairing and depairing respectively in the process of the dissolution of filamentary forms of intermediate phase retained at dislocations to temperatures somewhat below and above T c, induce transient changes in the rates of thermal activation of the creep and relaxation. Pairing (n→s), as well as relaxation of the Cooper pair density (s→n) in the core regions of edge dislocations, is linked in the model to the occurrence of local thermal spikes. Their magnitudes are taken to be linear in the Ginzburg-Landau pair-breaking function α(T) assigned to gradients in the BCS gap-parameter at the centres of the dislocations. On introducing α/k into the equations of logarithmic creep and stress relaxation as measure of the temperature changes associated with the transients, available experimental results are well accounted for.

Effective Interaction Strength in Superconductors

A semiempirical extension of the BCS model to intermediate- and strong-coupling superconductors is used to derive a set of simple rules by which the following thermodynamic quantities can be related to one another: the absolute-zero energy gap $2{\ensuremath{\Delta}}_{0}$; the critical field ${H}_{0}$; the critical temperature ${T}_{c}$; the jump $\ensuremath{\Delta}\mathrm{C}$ in specific heat at ${T}_{c}$; and the slope at ${T}_{c}$ of the critical-field curve, ${(\frac{\mathrm{dh}}{\mathrm{dt}})}_{1}$. The procedure determines an effective interaction strength ${N}_{0}{V}^{*}$ (larger than the value of ${N}_{0}V$ obtained from $\frac{{T}_{c}}{{\ensuremath{\Theta}}_{D}}$) for each superconductor. A temperature-variation of this ${N}_{0}{V}^{*}$ is the major departure from the original BCS model. ${N}_{0}{V}^{*}$ is obtained for 9 superconductors from their specific-heat jumps, and used to predict values of the ratios ${(\frac{\mathrm{dh}}{\mathrm{dt}})}_{1}$, $\frac{{\ensuremath{\Delta}}_{0}}{k{T}_{c}}$, and $\frac{\ensuremath{\gamma}{{T}_{c}}^{2}}{{V}_{m}{{H}_{0}}^{2}}$ which agree well with experiment. The resulting values for the effective cutoff ${\ensuremath{\Theta}}_{c}$ lie close to $\frac{{\ensuremath{\Theta}}_{D}}{9}$.