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Fluctuation-induced conductivity up to μ0 H = 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.

In this study, the performances of Y 1-x (Tb) x Ba 2 Cu 3 O 7- δ (Y-123) and Y 3-x (Tb) x Ba 5 Cu 8 O 18- δ (Y-358) advanced ceramics prepared by sol-gel preparation route are investigated by the advanced characterization methods including X-ray diffraction (XRD), temperature dependent resistivity (ρ-T), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and energy distribution spectroscopy (EDS) measurements and theoretical approaches. The EDS results illustrated that the Tb impurities were replaced successfully by the yttrium sites in the YBa 2 Cu 3 O 7-y main matrix. Similarly, it was noted that the presence of excess impurities in the crystal structure led to the oxygenation problems. Electrical properties were determined by temperature dependent resistivity (ρ-T) measurements. ρ-T results indicated that Tb doping reduced the critical transition temperature (T c) values for the transition to superconductivity for all samples in two YBCO phases. Although it appears to have negative effects of Tb ions on the number of mobile charge carrier concentrations in the σ antibonding in-plane Cu-O bonds, bipolaron formations in the polarizable lattices, oxidation states, and amplitude of the pair wave function of both phases, the other valuable properties (morphology, crystallinity quality, interaction between adjacent layers, critical current density, and flux pinning ability) were noted to improve remarkably in the case of the optimum amount in the Y-123 superconducting phase. In this context, the Y-358 superconducting phase was harshly affected by the substitution due to the change of the ortorombicity, localization problem, impurity phases, structure stabilization, crystal structure quality, crystallization system, homogeneities of oxidation states, oxygen ordering degree, and impurity scatterings. Besides, the analysis of the fluctuation induced conductivity indicated that the Y-123 ceramics with longer c -axis coherence length and less anisotropic nature exhibited well superconducting properties. Additionally, the doping ratio of x=0.01 led to the formation and distribution of more nucleation centers for the thermal fluxon motions of 2D pancake vortices. Similarly, the optimum Tb doped Y-123 system exhibited much durable to applied field strengths due to the best interaction quality between grains. Accordingly, this study recommended that the Y 1-x (Tb) x Ba 2 Cu 3 O 7- δ advanced ceramic structure with new functionalities can find much more application areas in innovative, heavy-industrial technologies, and advanced engineering-related sectors. [Display omitted] • Y-123 and Y-358 advanced ceramics were prepared by sol-gel preparation. • The magnetization and J c values of the Y-123 and Y-358 samples were found to generally reduce by Tb addition amount in the main system. • The porosity and crystallographic irregularity of the Y-358 phase were more negatively affected by increasing the doping ratio (after 5% Tb doping) than those of the Y-123 phase. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 T= 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 (Jc), the lower and upper critical magnetic fields (Bc1 and Bc2), the coherence length along the c-axis at zero-temperature (ξc(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 ξc(0) with Ag addition. The optimal silver doping amount is achieved for 7 wt.%, which yields the best superconducting transition and the greatest Jc value.

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.

Fluctuation-induced conductivity (FIC) of glucose as a carbon-doped MgB sample was investigated in the presence of a magnetic field in the range of 0-14T. Different concentrations (0-8%) of glucose-doped MgB samples were prepared using planetary dry ball milling and then employed standard solid-state reaction method on these samples. The prepared samples were characterized by X-ray diffractometer. The resistive transition broadening of all the samples becomes wider as the magnetic field was increased. The results of doped MgB explained in terms of temperature derivative of the resistivity, d $${\rho/{\rm d}T}$$ with temperature. The mean field transition temperature ( $${T_{{c}}^{{\rm mf}}}$$ ) has been taken from the peak of the temperature derivative of resistivity plot for different doped samples. It is clear that $${T_{{c}}^{{\rm mf}}}$$ of d $${\rho/{\rm d}T}$$ shifted to lower temperature region as we increase the magnetic field of the doped samples. Lawrence and Doniach model has been employed for the present study. The variation of FIC against inverse reduced temperature ( $${{\varepsilon}^{-1})}$$ for different concentrations of glucose-doped MgB samples was measured with varying applied field. The enhancement of coherence length observed as we decrease the value of T and $${T_{{c}}^{{\rm mf}}}$$ for 5 and 8% C in glucose-doped MgB samples when subjected to a different field. [ABSTRACT FROM AUTHOR]

In this work, a cylindrical YBaCuO(Y123) sample having 20 mm diameter and 8 mm height was prepared by the cold-seeding method using an Nd123 seed, and the crystal growth process was performed in an alumina crucible with a YO layer. The structural orientation of the specimens was measured by an X-ray diffractometer (XRD). As a result of the X-ray diffraction data, only (00 l) peaks were observed, indicating that all specimens are highly oriented with the c-axis perpendicular to the top surface. Resistivity measurements of a 1.5-mm-thick rectangular sample were performed by a standard four-probe method at temperatures between 60 and 100 K at a rate of 4 K/min using a Physical Properties Measurement System (PPMS) under various constant magnetic fields from 1 to 5 T with the magnetic field parallel to the c-axis, which is the direction of pressing into the zero-field cooling regime (ZFC). Fluctuation-induced conductivity analysis was performed to investigate the availability of the sample for technology. The analysis showed that the critical exponents were in agreement with theoretical values; thus, it was seen that superconducting properties of the sample were good and the 3D fluctuation was dominant. Because of the large c−axis coherence length ( ξ (0)) and small anisotropy, the superconducting properties became better. Furthermore, the fluctuations were reduced, and it was understood that the effective availability of the sample in technology will be possible. [ABSTRACT FROM AUTHOR]

superconducting bulk samples have been synthesized by using two-step solid state reaction method. We investigated the effects of planes on the structural and superconducting transport properties of superconducting family. These samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) absorption spectroscopy and DC-resistivity measurements. These samples are -axis length oriented and have shown orthorhombic crystal structure. All the samples have shown metallic variations of resistivity from room temperature down to onset of superconductivity. The zero resistivity critical temperature increases with the increase in superconducting planes and normal state resistivity systematically decreases, which show the density of inadvertent defects decreases in the final compound. The apical oxygen phonon modes are hardened as observed in the FTIR absorption measurements. The intrinsic microscopic superconducting parameters, such as the cross-over temperatures, coherence length along -axis at 0 K, inter-layer coupling , inter-grain coupling and fermi velocity , were extracted from the fluctuation-induced conductivity (FIC) analysis. FIC analysis also showed the improvement in superconductivity with the increase in planes. [ABSTRACT FROM AUTHOR]

• Observation of excess conductivity by superconducting fluctuations in undoped Ca 10 (Pt 4 As 8)(Fe 2 As 2) 5. • Determination of superconducting parameters through superconducting fluctuation model. • Observation of 3D to 2D crossover in superconducting fluctuations. • Coexistence of 3D and 2D superconducting fluctuations in the temperature region near the crossover. Fluctuation-induced conductivity up to μ 0 H = 14 T for superconducting Ca 10 (Pt 4 As 8)(Fe 2 As 2) 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. [ABSTRACT FROM AUTHOR]

The effect of preparation temperature on the superconducting properties of CuTlBaCaCu O samples has been explored. With the increase of preparation temperature beyond 840 °C, the observed superconducting parameters are suppressed which might be due to impurities caused by the volatility of some constituents such as thallium and oxygen deficiencies as well in the final compound. The shift of three-dimensional (3D) Aslamazov-Larkin (AL) regions to the lower temperature and the decrease in the crossover temperature and with the increase of preparation temperature beyond 840 °C is observed by using the fluctuation-induced conductivity (FIC) analysis. A direct correlation between the zero resistivity critical temperature T( R = 0), the zero-temperature coherence length ξ(0), the crossover temperature T, as well as carrier concentration has also been observed. [ABSTRACT FROM AUTHOR]

Superconductivity has been improved by partial substitution of slightly higher electronegative (M=Bi, Hg) elements at Tl sites in (CuTlM)BaO ( x=0,0.25) charge reservoir layer of (CuTlM)BaCaCuO superconductor. These samples were characterized by X-ray diffractometry, dc-resistivity, ac-susceptibility, FTIR absorption spectroscopy, and fluctuation-induced conductivity (FIC) analysis. The FIC analysis has been carried out in the light of Aslamasov-Larkin (AL) theory on the resistivity versus temperature curves of (CuTlM)BaCaCuO superconductor. The microscopic parameters such as cross-over temperature ( T), zero-temperature coherence length ξ(0), inter-layer coupling ( J), and critical exponents ( λ and λ) have been determined from FIC analysis of these samples and tried to correlate them to the superconductivity order parameters. A direct correlation between the cross-over temperatures ( T) and zero resistivity critical temperature { T( R=0)} and carrier concentration in these samples has been observed. The improvement in T( R=0) and the shift of 3D AL region to higher temperature values with the doping of Bi and Hg have also been observed. [ABSTRACT FROM AUTHOR]

The growth of (CuTlHg)BaCaCuO ( x=0, 0.25) superconductor with optimal carrier density in CuO planes has been made possible by partial substitution of Hg at Tl sites in (CuTl)BaO charge reservoir layer of (CuTl)BaCaCuO superconductor. The fluctuation-induced conductivity (FIC) analysis has been carried out on resistivity vs. temperature curves by using Aslamazov-Larkin (AL) theory and the results have shown three-dimensional (3D) and two-dimensional (2D) fluctuations in order parameters. The microscopic parameters deduced from FIC analysis such as crossover temperature ( T), zero temperature c-axis coherence { ξ(0)} and the interlayer coupling strength ( J) have been improved with Hg substitution. Also, 3D region has been shifted to higher temperature with Hg substitution. In order to verify the optimal carrier density in CuO planes with Hg substitution, the post-annealing experiments have been carried out on these samples in nitrogen and air. These post-annealing experiments have caused under-doping of carriers from the optimal level resulting into a decrease in T ( R=0) as well as the magnitude of diamagnetism. [ABSTRACT FROM AUTHOR]

Abstract: The electrical resistivity ρ(T) versus temperature data of as-prepared and O2-annealed Cu0.5Tl0.5Ba2(Ca2−y Mg y )(Cu0.5Zn2.5)O10−δ (y=0, 0.5, 1.0) samples is analyzed for fluctuations induced conductivity analysis in the temperature regime well above the critical temperature. The analysis has been carried out employing Aslamazov and Larkin (AL) and Lawrence and Doniach (LD) models. The coherence length, inter-planar coupling, exponent and dimensionality of fluctuations are determined from this analysis. It has been observed in as-prepared and oxygen post-annealed samples that the crossover temperature associated with two distinct exponents and the excess conductivity data fits very well with the two-dimensional (2D) and three-dimensional (3D) AL equations. The cross-over temperature T o is shifted to lower temperatures with enhanced Mg doping. The width of 3D AL region is reduced with increased Mg doping, however, some improvement is observed after post-annealing in the oxygen atmosphere. Moreover, a decrease in the coherence length along the c-axis is observed with the doping of Mg in the final compound. We have elucidated from these analyses that higher thallium contents in the final compound promote a decrease in the density of mobile carriers in CuO2 planes, which suppresses the coherence length along the c-axis and superconductivity parameters. [Copyright &y& Elsevier]

The temperature dependence of the resistance in the presence of magnetic field showing evidence of fluctuation effects is reported in a single crystal C15 Laves-phase superconductor CeRu2. Measurements performed in different magnetic field strengths indicate that the observed fluctuation effects in this low TC superconductor can be scaled using three-dimensional-scaling functions. [Copyright &y& Elsevier]

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 T = 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 ( J c ), the lower and upper critical magnetic fields ( B c 1 and B c 2 ), the coherence length along the c-axis at zero-temperature ( ξ c (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 ξ c (0) with Ag addition. The optimal silver doping amount is achieved for 7 wt.%, which yields the best superconducting transition and the greatest J c value. [ABSTRACT FROM AUTHOR]

Resistance measurements were performed on Bi 2 Sr 2 CaCu 2 O 8 + 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, T c , 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. [ABSTRACT FROM AUTHOR]