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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]

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.

• 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]

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]