Fluctuation-induced Conductivity Research Articles

Excess conductivity and magnetoresistance analysis for (BSF)x/(Bi, Pb)-2223 composite

This study examined the impact of adding hard ferrite Ba0.5Sr0.5Fe12O19 (BSF) nanoparticles to the Bi1.8Pb0.4Sr2Ca2Cu3.2O10+δ (Bi, Pb)-2223) superconductor phase. The investigation specifically focused on evaluating the critical current density, fluctuation-induced conductivity, and magnetoresistance of nano-(BSF)x/(Bi, Pb)-2223 composite, where 0.00 ≤ x ≤ 0.20 wt.%. The results revealed that the critical current density, Jc, increased with the addition of nano-(BSF) up to x = 0.04 wt.%, reaching a value of 441.20 A/cm2. The Aslamazov and Larkin (A–L) approach has been evaluated the fluctuation-induced conductivity. Several superconducting parameters, including coherence length ζc(0), effective layer thickness d, penetration depth λpd(0), and Fermi energy EF\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${E}_{F}$$\\end{document} showed improvement as the concentration of nano-(BSF) increased up to x = 0.04 wt.%. In addition to Ginzburg–Landau critical parameters, such as the thermodynamic critical field Bc(0), lower critical magnetic field Bc1(0), upper critical magnetic field Bc2(0), and critical current density Jc(0) demonstrated an increase up to x = 0.04 wt.%, followed by a decrease for higher concentrations. The magnetoresistance measurements were performed at various applied DC magnetic fields, with values ranging from 0.29 to 4.44 kG, and were analyzed using the thermally activated flux creep (TAFC) and Ambegaokar–Halperin (AH) models. The calculated flux pinning energy (U) increased with the addition of nano-(BSF) up to x = 0.04 wt.% and then decreased for x > 0.04 wt.%. Furthermore, the transition width (ΔT), was observed to increase as the applied magnetic field values increased. Moreover, the addition of nano-(BSF) increased the field-independent critical current density, Jc,0(0), up to x = 0.04 wt.%, after which it decreased for higher concentrations.

Excess Conductivity Analysis of an YBCO Foam Strut and Its Microstructure.

Struts of a superconducting YBa2Cu3Oy (YBCO) foam prepared by the infiltration growth method on the base of commercial polyurethane foams were extracted from the bulk, and thoroughly characterized concerning the microstructure and the magnetoresistance, measured by the four-point technique. Optical microscopy, electron microscopy, electron backscatter diffraction and atomic force microscopy observations indicate a unique microstructure of the foam struts which shows a large amount of tiny Y2BaCuO5 (Y-211) particles (with diameters between 50 and 100 nm) being enclosed in channel-like grain boundaries between the YBCO grains and a one-of-a-kind surface of the struts covered with Ba3Cu5Oy-particles. The resistance data obtained at temperatures in the range 4.2 K ≤T≤ 150 K (applied magnetic fields ranging from 0 to 7 T) were analyzed in the framework of the fluctuation-induced conductivity (FIC) approach using the models of Aslamazov-Larkin (AL) and Lawrence-Doniach (LD). The resulting FIC curves reveal the presence of five distinct fluctuation regimes, namely, the short-wave (SWF), one-dimensional (1D), two-dimensional (2D), three-dimensional (3D), and critical (CR) fluctuation domains. The analysis of the FIC data enable the coherence length in the direction of the c-axis at zero-temperature (ξc(0)), the irreversibility field (Birr), the upper critical magnetic field (Bc2), the critical current density at T= 0 K (Jc(0)) and several other parameters describing the the material's superconducting properties to be determined. The present data reveal that the minuscule Y-211 particles found along the YBCO grain boundaries alter the excess conductivity and the fluctuation behavior as compared to conventional YBCO samples, leading to a quite high value for Jc(0) for a sample with a non-optimized pinning landscape.

Formation and Fluctuation-Induced Conductivity of (Tl1-xBix)Sr2CaCu2O7-δ(x = 0.1-0.7) Superconductor

Formation and Fluctuation-Induced Conductivity of (Tl1-xBix)Sr2CaCu2O7-δ(x = 0.1-0.7) Superconductor

Fluctuation magnetoconductivity in superconducting Ca10(Pt4As8)(Fe2As2)5 single crystal

Fluctuation-induced conductivity up to μ0H = 14 T for superconducting Ca10(Pt4As8)(Fe2As2)5 single crystal was evaluated from the measured in-plane electrical resistivity, and it was analyzed by Aslamazov-Larkin (AL) theory for zero magnetic field and Ullah and Dorsey (UD) scaling method for magnetic field. A dimensional crossover of superconducting fluctuations from low-temperature three-dimension to high-temperature two-dimension was observed. When the dimensional crossover occurs, a temperature region in which two-dimensional and three-dimensional fluctuations occur simultaneously was found in the intermediate temperature region.

Infrared Spectroscopy and Excess Conductivity Analysis for (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ Composites

In this study, the influence of adding Yttrium iron garnet (Y3Fe5O12) nanoparticles (NPs) on the microstructure and fluctuation-induced conductivity (FIC) of Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconductor was studied. Y3Fe5O12 NPs were produced by the co-precipitation technique. By solid state route, (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ composites, with x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10 wt. % were prepared. The tetragonal unit cell parameters of (Y3Fe5O12)x/Cu0.5Tl0.5Ba2Ca2Cu3O10-δ composites were found to be invariable with Y3Fe5O12 content. The volume fraction of the host phase was increased with Y3Fe5O12 addition till x = 0.04 wt. %. The different vibrational modes of the samples were identified through Fourier transform infrared spectroscopy (FTIR). The transition from normal to the superconducting state, for the prepared composites, was done through d.c resistivity measurements from room temperature down to zero critical temperature (T0). The Aslamazov–Larkin (AL) model was used to examine fluctuation regions in resistivity-temperature curves. At high temperatures, short wave fluctuation was observed. A cross-over between short wave fluctuation and the mean-field region was spotted at lower temperatures. The mean field region for the examined composites was composed of two-dimensional fluctuations along with one-dimensional fluctuation. The coherence length along the c-axis ζc(0), interlayer coupling (J), and anisotropy parameter (γ) were estimated from the Lawrence–Doniach (LD) model as a function of Y3Fe5O12 content.

Annealing Effects on FluctuationInduced Conductivity of (Cu0.5Tl0.25Hg0.25)Ba2Ca3Cu4O12-δ, Superconductor

In the light of the Aslamazov–Larkin theory of fluctuation-induced conductivity (FIC), the excess conductivities of as-prepared, nitrogen-post-annealed, oxygen-post-annealed, and air-post-annealed samples of (Cu0.5Tl0.25Hg0.25)Ba2Ca3Cu4O12–δ have been determined. It is observed from FIC measurements that the crossover of a three-dimensional (3D) to a two-dimensional (2D) behavior of fluctuations is shifted to higher temperatures by the post-annealing of samples in nitrogen, oxygen, and air. We have accredited this behavior to an increase in the grain size and the improved carrier concentration in the conducting CuO2 planes. In addition, it is also noted that, after the post-annealing of samples in nitrogen, oxygen, and air, the width of the three-dimensional region of fluctuations is also enlarged. Furthermore, two distinct parameters (coherence length and interplanar coupling) are also estimated by the Lawrence–Doniach equations and found to be increased by the post annealing in nitrogen, oxygen, and air.

Enhanced thermoelectric properties of polycrystalline CuCrS2−x Se x (x = 0, 0.5, 1.0, 1.5, 2) samples by replacing chalcogens and sintering

The optimization of thermoelectric properties of the CuCrSSe x (x = 0, 0.5, 1.0, 1.5, 2) samples was achieved by substitution in anionic sublattice and sintering at high temperature. The maximum power factor PF ∼ 0.3 mW (m·K)−2 among a series of samples with chalcogen substitution was obtained for CuCrS0.5Se1.5 sample at T = 300 K. The sintering made it possible to obtain the maximum value PF ∼ 2.1 mW (m·K)−2 for CuCrSe2 sample. This is due to a more than threefold increase in the thermopower S(T) in CuCrSe2 sample with a spin-orbital interaction in comparison with CuCrS0.5Se1.5 sample with the same optimal electrical conductivity σ ( 100 S cm−1), but without spin-orbital interaction. In CuCrSe2 sample, sintering effectively reduced the σ to an optimal value, suppressed of the magnetic phase transition in the range of 50–100 K, and the weak localization were replaced by weak antilocalization indicating the appearance of strong spin-orbit interaction below 20 K. As a result, an additional contribution to the S(T) appeared due to the filtration of current carriers caused by the strong spin-orbit interaction. The effect of grain boundaries on the properties σ and S(T) of the samples was investigated. It was established that polycrystalline samples with a high sulfur content were low-conductivity materials consisting of high-conductivity crystallites with the charge carriers concentration cm−3 separated by low-conductivity grain boundaries with fluctuation-induced tunneling conductivity. Both the replacement of sulfur with selenium and sintering led to a decrease in the energy barriers connecting grain boundaries. Selenium-dominated samples (CuCrS0.5Se1.5 and CuCrSe2) had high electrical conductivity with negligible energy barriers between grain boundaries. Logarithmic quantum corrections to the electrical conductivity was observed below 20 K, which indicated a quasi-two-dimensional electron transport in these samples.

Electrical and thermal properties of epoxy composites filled with carbon nanotubes and inorganic particles

The electrical and thermal conductivity of the ternary epoxy composites (CMs) with two-component fillers, multiwall carbon nanotubes (MWCNT)/TiO2, and MWCNT/carbonyl iron (Fe) have been investigated. The increase of the percolation threshold was found for the ternary CMs compared to MWCNT/epoxy CMs. At MWCNT content higher than 3 wt.%, the conductivity of the ternary CMs is much higher than in MWCNT/epoxy. The temperature dependencies of the electrical resistivity were analyzed within the fluctuation-induced tunneling conductivity model. It was found that adding of two-component fillers MWCNT/TiO2 or MWCNT/Fe into epoxy promotes smaller changes in thermal conductivity compared to the two-phase MWCNT/epoxy composites.

Comparative study of structural and fluctuation-induced conductivity in YBa2Cu3Oy added with ZnO and Zn0.95Mn0.05O nanoparticles and nanobelts

In this report, we present the effect of nano-ZnO and nano-Zn0.95Mn0.05O nanoparticles (NPs) and nanobelts (NBs) in polycrystalline superconducting samples of YBa2Cu3Oy (for brevity Y-123). The samples were synthesized using the solid-state reaction. Structural results analyzed via X-ray diffraction showed a similar behavior in all samples while the c parameter increased in the case of samples doped with nanobelts. Measurements of the electrical resistivity’s dependence on temperature revealed that the depression in the superconducting temperature is more pronounced in samples doped with nanoparticles compared to those doped with nanobelts. The excess conductivity in the mean-field region was analyzed using the Aslamazov–Larkin and Lawrence–Doniach models. The effective layer thickness, the zero-temperature coherence length, the wire cross-sectional area, the critical magnetic fields, and the critical current density were also calculated. The Zn0.95Mn0.05O nanobelts are more suitable for enhancing the flux pinning properties of YBa2Cu3Oy.

Investigation of the physical properties of (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ impregnated with mono cobalt(II)-substituted Undecatungstosilicate Nanoparticles

A series of (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ superconducting samples impregnated with different percentage additions of potassium salt {CoSiW11}x nanoparticles (x = 0.00, 0.01, 0.02, 0.04, 0.06, 0.08 and 0.12 wt.%) were prepared using a single-step solid-state reaction technique at ambient pressure. These samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) to study their structures, construction of the synthesized samples and elemental composition, respectively. XRD studies indicate that the tetragonal structure of (Cu0.5Tl0.5)-1223 phase has not changed by the addition of {CoSiW11} nanoparticles the same as for the values of lattice parameters a and c, where they show a non-remarkable change. The relative volume fraction of (CuTl)-1223 phase record a maximum value for x = 0.02 wt.%. The formation of (CuTl)-1223 phase matches the presence of rectangular-shaped plates seen in SEM images. The enhancement of these plates after the addition of {CoSiW11} nanoparticles up to x = 0.02 wt.% agreed with the measurements of relative volume fraction. The mass percentage of all elements was measured using the EDX technique, which shows the distribution composition of both superconductor and nanoparticle compounds. Vibrational mode analyses of oxygen were accomplished via Fourier transform infrared (FTIR) spectroscopy in (CuTl)-1223 phase impregnated with {CoSiW11} nanoparticles. The Oδ oxygen modes observed are almost unaltered while the other oxygen modes of planar CuO2 are slightly softened and hardened. Superconducting transition temperature (Tc) and critical current density (Jc) were determined from the electrical resistivity and I–V measurements, respectively. The results indicate an increase in the Tc values from 125 K for the pure sample to 132 K for x = 0.02 wt.% impregnated samples, while a decrease in the Jc values is observed upon increasing ‘x’ value from x = 0.00 up to 0.12 wt.%. The suppression of these electrical superconducting parameters for x > 0.02 wt.% may be due to an increase of weak links' connectivity among the grain boundaries and growth of impurity phases that affect the formation of (CuTl)-1223 superconductor phase. The fluctuation-induced conductivity (FIC) analysis has been done in the light of the Aslamasov–Larkin (AL) theory to study the fluctuation conductivity Δσ above Tc as a function of reduced temperature for (CoSiW11)x/(CuTl)-1223 superconductor. The results show four non-identical fluctuation regions that are short-wave (Sw), two-dimensional (2D), three-dimensional (3D) and critical (Cr). The zero-temperature coherence length ( $${\xi }_{c}(0)$$ ), the effective layer thickness of the two-dimensional system (d), inter-layer coupling (I), Fermi velocity (vF) and Fermi energy (EF) were evaluated as a function of ‘x’ addition from FIC analysis of the samples and then correlated to the superconductivity order parameters. The superconducting parameters were increased upon the addition of {CoSiW11} nanoparticles.

Excess Conductivity Analysis of Polycrystalline FeSe Samples with the Addition of Ag.

Bulk FeSe superconductors of the iron-based (IBS) “11” family containing various additions of silver were thoroughly investigated concerning the microstructure using optical microscopy and electron microscopy (TEM and SEM). The measurements of electrical resistivity were performed through the four-point technique in the temperature interval 2–150 K. The Aslamazov–Larkin model was employed to analyze the fluctuation-induced conductivity (FIC) in all acquired measurements. In all studied products, we found that the FIC curves consist of five different regimes of fluctuation, viz. critical region (CR), three-dimensional (3D), two-dimensional (2D), one-dimensional (1D), and shortwave fluctuation (SWF) regimes. The critical current density (), the lower and upper critical magnetic fields ( and ), the coherence length along the c-axis at zero-temperature ((0)), and further parameters were assessed with regards to the silver amount within the products. The analyses discloses a diminution in the resistivity and a great reduction in (0) with Ag addition. The optimal silver doping amount is achieved for 7 wt.%, which yields the best superconducting transition and the greatest value.

Microstructure and Fluctuation-Induced Conductivity Analysis of Bi2Sr2CaCu2O8+δ (Bi-2212) Nanowire Fabrics

Resistance measurements were performed on Bi2Sr2CaCu2O8+δ (Bi-2212) fabric-like nanowire networks or nanofiber mats in the temperature interval 3 K ≤T≤ 300 K. The nanowire fabrics were prepared by means of electrospinning, and consist of long (up to 100 μm) individual nanowires with a mean diameter of 250 nm. The microstructure of the nanowire network fiber mats and of the individual nanowires was thoroughly characterized by electron microscopy showing that the nanowires can be as thin as a single Bi-2212 grain. The polycrystalline nanowires are found to have a texture in the direction of the original polymer nanowire. The overall structure of the nanofiber mats is characterized by numerous interconnects among the nanowires, which enable current flow across the whole sample. The fluctuation-induced conductivity (excess conductivity) above the superconducting transition temperature, Tc, was analyzed using the Aslamzov-Larkin model. Four distinct fluctuation regimes (short-wave, two-dimensional, three-dimensional and critical fluctuation regimes) could be identified in the Bi-2212 nanowire fabric samples. These regimes in such nanowire network samples are discussed in detail for the first time. Based on this analysis, we determine several superconducting parameters from the resistance data.

Fluctuational anomalous Hall and Nernst effects in superconductors

In this work we develop microscopic kinetic theory of the anomalous Hall and Nernst effects in superconductors induced by fluctuations in the vicinity of the critical transition temperature. The technical analysis is carried out within the Matsubara diagrammatic technique and linear response Kubo formula with disorder averaging and an analytical continuation. It is shown that asymmetric skew-scattering due to spin–orbit interaction gives rise to a new anomalous Hall conductance promoted by Maki–Thompson interference and density of states fluctuational effects. The side-jump mechanism of the anomalous Hall effect is present only in the density of states contributions. The anomalous Nernst effect is found due to a special nonlinear Aslamazov–Larkin term from the quantum-crossing of interacting fluctuations in a Hikami box with the skew-scattering process. In addition to calculations in the weak-coupling BCS model we also sketch an approach for the account of fluctuational transport effects in the strong-coupling limit. In particular we explore an example of how Keldysh version of the Eliashberg theory can in principle be constructed and estimate fluctuation-induced conductivity within conventional electron–phonon coupling scenario. These ideas may pave the way for further developments of strong coupling theories in applications to fluctuations in unconventional superconductors and anomalous transport responses in particular.

Enhanced coherence length and interplane coupling by Ti doping in (Cu, Tl)-1223 superconductors: Para conductivity analyses

The fluctuation induced conductivity (FIC) analyses of Ti doped (Cu0.5Tl0.5)Ba2(Ca2-xTix)Cu3O10-δ superconducting samples have been carried. Aslamazov-Larkin (AL) and Lawrance-Doniach (LD) models were used to study the FIC in the critical, 3D, 2D and 0D regions. Maki-Thompson (MT) model has been employed to study the effect of the Cooper-pairs on the normal electrons. From these analyses the coherence length along the c-axis, ξc (0), the inter-plane coupling constant, J, the phase relaxation time, τφ , Fermi velocity, VF, and the energy essential for breaking apart the Cooper's pairs, E, are determined. From the cross-over temperature, TG, of critical to 3D regime the Ginsberg number, NG, has been calculated. Using NG and the Ginsburg–Landau (GL) equations, various important parameters like thermodynamic critical magnetic field, Bc(0), the lower critical field, Bc1(0), the upper critical field, Bc2(0), the critical current density, Jc (0), as well as the penetration depth, λp.d, have been calculated. Values of Tc, TG, Tcmf, ξc(0) and J are increased with the increasing Ti contents. All the fluctuation regimes have been shifted to higher temperature and the anisotropy is reduced with the doping of Ti. Also VF and E are found to enhance with Ti doping while the phase relaxation time is reduced. The most probable reason for all these improved parameters is the smaller ionic radius of Ti atom, which brings the CuO2 planes closer together thereby enhancing the density of Cooper pairs in the unit cell. The values of Bc(0), Bc1(0), and Jc(0) are suppressed while the values of λp.d and κ are increased with increased Ti contents. The suppression in the critical fields and current density may be attributed to the decrease in the free energy difference of the normal and superconducting states.

Fluctuation-Induced Excess Conductivity and Infrared Spectra in Y Doped BSCCO Superconductors

We report here the fluctuation induced excess conductivity and IR spectra in Bi2Sr2Ca1-xYxCu2Oy (0.00 < x < 0.50) superconductors. This work is done by using the reported data of Sedky, Physica B 410, 227 (2013), and with the help of Anderson and Zou relation. The logarithmic plots of excess conductivity ∆σ and reduced temperature Є reveal two different exponents corresponding to unique crossover temperature in the slope of each plot. The first exponent is obtained in the normal field region at a temperature of ( << T < 2 ), while the second exponent is obtained in the mean field region at a temperature of (T ~ ). The dimensional exponents are shifted from three dimensional (3D) to two dimensional (2D) for x < 0.30, but it is shifted from 2D to 3D for x = 0.50. Both zero kelvin critical magnetic fields and current density are considerably enhanced by increasing x up to 0.30 followed by a decrease with further increase of x up to 0.50. The vice is versa for the behavior of interlayer coupling, coherence lengths and anisotropy against x. On the other hand, IR spectra show absorption modes in the wave number range of 716-726 cm-1 according to the value of x. These results are discussed in terms of the correlation between carrier concentration, oxygen deficient and effective Cu valance which are induced by Y through CuO2 planes of BSCCO superconductors.

Effect of Cr Substitution on the Formation and Fuctuation-Induced Conductivity Analysis of (Tl<sub>1-x</sub>Cr<sub>x</sub>)Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>7</sub> Superconductor

The (Tl1-xCrx)Sr2CaCu2O7 (Tl-1212) sample with nominal starting composition for x = 0.0, 0.2 and 0.3 were prepared by the solid-state reaction method. The samples were studied by powder x-ray diffraction method and electrical resistance versus temperature measurement. Excess conductivity analysis was carried out using the Aslamazov–Larkin (AL) theory, and the dimension of fluctuation-induced conductivity (λ) was determined. The Lawrence–Donaich (LD) theory was used to calculate the coherence length (ξc(0)), Josephson coupling (J), and γ = (ξab(0)/ξc(0)) of the superconductive samples. Excess conductivity analysis showed that Cr substitution induced 2D-to-3D conductivity transition at the highest transition temperature (T2D-3D) observed at x = 0.3. The calculations based on the Lawrence–Doniach model revealed that the shortest coherence length and weakest inter-plane coupling (J) occurred when x = 0.2. The sample with x = 0.2 and 0.3 showed the Tl-1212 as the major phase. The highest onset temperature of 110 K was observed in the x = 0.2 sample. Our result showed that the formal value of 2.3+ is more important than the Josephson interlayer coupling J in optimizing the transition temperature.

The Influence of Zn on Superconducting Properties of Bi2Sr2Ca1Cu2OX

It was investigated that the influence of Ca substitution by Zn on the specific resistivity, thermal power, and excess conductivity of Bi2Sr2CaCu2OX, Bi2Sr2Ca0.8Zn0.2Cu2OX, and Bi2Sr2Ca0.4Zn0.6Cu2OX polycrystalline samples in the 70–300 K temperature interval. The fluctuation-induced conductivity is analyzed using the Aslamasov and Larkin and Lawrence and Doniach models. The microscopic parameters such as dimensional crossover temperature (Tcr), interlayer coupling strength (J), and zero temperature coherence length along c axis (ξ0) are estimated.

Comparative Study of the Effect of Magnetic Nanoparticle CoFe2O4 on Fluctuation-Induced Conductivity of Y-123 and Y-358 Superconductors

In this study, a comparative investigation of the electrical conductivity fluctuations in nano-CoFe2O4 added to Y3Ba5Cu8O18±x (Y-358) and YBa2Cu3O7−d (Y-123) products is performed. All products were made using the solid-state reaction process. X-ray powder diffraction (XRD) analyses confirmed the formation of different phases. Scanning electron microscope (SEM) analysis shows the reduction of grain size with increasing the quantity of nano-CoFe2O4 particles for both the Y-123 and Y-358 samples. The decrease of grain size is more accentuated in the case of the Y-358 samples compared with the Y-123 ones. The data of conductivity fluctuations are examined in terms of the derivative of the electrical resistivity with respect to temperature and the logarithmic derivative of the conductivity with regard to temperature. The results illustrate the existence of a transition with two stages; intragrain and intergrain. It is demonstrated that the addition of CoFe2O4 nanoparticles affects the electrical conductivity fluctuations, the values of the critical exponents, and the fluctuation dimensionality in YBCO systems.

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.

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.