Abstract:We report conductivity fluctuation measurements in the La 1.82 Sr 0.18 CuO 4 high temperature superconducting material. The conductivity fluctuation analysis was performed by utilizing the concept of the logarithmic derivative of the conductivity excess. Close and above the critical temperature T c , we experimentally determine the occurrence of Gaussian and critical fluctuation regimes. Systematic measurements of conductivity as a function of temperature were performed for several values of transport current … Show more
“…According to this table, lower T c values than T LD indicates that the thermodynamically activated Cooper pairs are generated within the grain at comparatively higher temperatures but due to the intragranular disturbances the mean-field critical temperature comes down to lower value. It is possible to infer that the 3D Gaussian regime determines the spatial limit for the obtainment of long-range order of the superconductivity in the material bulk [44]. When the temperature is diminished near T c , first superconductivity is established in the CuO2 planes, as a 2D regime, and crosses up to a well-defined 3D regime [45].…”
In this study, we report the effect of Ag nanoparticles doping on the dimensional fluctuations of superconducting order parameters, crystal structure, and some parameters of Y 1 Ba 2 Cu 3 O 7−δ + × Ag (x = 0.0, 0.06, 0.1, 0.3, and 0.6 wt%) polycrystalline ceramics. By increasing the content of Ag in YBCO matrix, X-ray diffraction (XRD) with the Rietveld refinement technique revealed that the crystal lattice parameters changed and the orthorhombicity decreased slightly. Also, the increase of Ag wt% caused a decrease of superconducting transition temperatures (Tc) which are determined from the standard four-probe method and dropped abruptly. Aslamazov-Larkin (AL) model was used to analyze excess conductivity fluctuation. Lawerence-Doniach (LD) temperature named T LD which is responsible for the dimensional nature of fluctuation inside the grains is influenced by nano-silver combination in the compound. Crossover temperature from 2D to 3D (T LD) decreased in the mean-field region as a resultant dominance of 3D region by increasing of Ag in YBCO matrix. The decrease in zero-resistance critical temperature (T c zero), zero-temperature coherence length along the c-axis ξ c (0), and super layer length d values implies the degradation of inter-grain weak links, more disorder state of samples and unsettling of the mean free path for the charge carriers respectively with addition of silver nanoparticles. The calculations based on AL and LD model showed the highest anisotropy (γ = 1.34681) for the x = 0.6 sample. The size of the Ag ions, being larger compared to Cu ions, and the number of substitution sites affects the coupling between the CuO2 planes and that results in higher anisotropy. Critical magnetic fields B c1 (0), B c2 (0), and critical current density J c (0) were indirectly calculated from the Ginzburg-Landau (GL) number and GL equations. By increasing the doping level of silver nanoparticle, these parameters were found to be higher in Ag-added YBCO samples compared to the pure Y123, meaning better intrinsic flux pinning properties of doped Y123. The silver nanoparticle inclusion reduces the grain size and increases the strength and hardness of the parent compound.
“…According to this table, lower T c values than T LD indicates that the thermodynamically activated Cooper pairs are generated within the grain at comparatively higher temperatures but due to the intragranular disturbances the mean-field critical temperature comes down to lower value. It is possible to infer that the 3D Gaussian regime determines the spatial limit for the obtainment of long-range order of the superconductivity in the material bulk [44]. When the temperature is diminished near T c , first superconductivity is established in the CuO2 planes, as a 2D regime, and crosses up to a well-defined 3D regime [45].…”
In this study, we report the effect of Ag nanoparticles doping on the dimensional fluctuations of superconducting order parameters, crystal structure, and some parameters of Y 1 Ba 2 Cu 3 O 7−δ + × Ag (x = 0.0, 0.06, 0.1, 0.3, and 0.6 wt%) polycrystalline ceramics. By increasing the content of Ag in YBCO matrix, X-ray diffraction (XRD) with the Rietveld refinement technique revealed that the crystal lattice parameters changed and the orthorhombicity decreased slightly. Also, the increase of Ag wt% caused a decrease of superconducting transition temperatures (Tc) which are determined from the standard four-probe method and dropped abruptly. Aslamazov-Larkin (AL) model was used to analyze excess conductivity fluctuation. Lawerence-Doniach (LD) temperature named T LD which is responsible for the dimensional nature of fluctuation inside the grains is influenced by nano-silver combination in the compound. Crossover temperature from 2D to 3D (T LD) decreased in the mean-field region as a resultant dominance of 3D region by increasing of Ag in YBCO matrix. The decrease in zero-resistance critical temperature (T c zero), zero-temperature coherence length along the c-axis ξ c (0), and super layer length d values implies the degradation of inter-grain weak links, more disorder state of samples and unsettling of the mean free path for the charge carriers respectively with addition of silver nanoparticles. The calculations based on AL and LD model showed the highest anisotropy (γ = 1.34681) for the x = 0.6 sample. The size of the Ag ions, being larger compared to Cu ions, and the number of substitution sites affects the coupling between the CuO2 planes and that results in higher anisotropy. Critical magnetic fields B c1 (0), B c2 (0), and critical current density J c (0) were indirectly calculated from the Ginzburg-Landau (GL) number and GL equations. By increasing the doping level of silver nanoparticle, these parameters were found to be higher in Ag-added YBCO samples compared to the pure Y123, meaning better intrinsic flux pinning properties of doped Y123. The silver nanoparticle inclusion reduces the grain size and increases the strength and hardness of the parent compound.
“…Dependiendo de la razón entre los tiempos de colisión y coalescencia, los productos finales pueden ser partículas esféricas relativamente grandes o un aglomerado de pequeñas partículas con estructura semejante a la fractal [9]. Diferentes aspectos de los procesos de colisión y coalescencia de clusters tales como la dinámica, cinética, energéticos y térmicos fueron estudiados ampliamente [10][11][12][13][14]. Sin embargo, acerca de los detalles de los cambios estructurales durante la colisión y coalescencia hay poca información.…”
Mediante la simulación con el método de Dinámica Molecular usando el potencial de interacción de tipo EAM se ha estudiado los aspectos energéticos y estructurales durante la colisión de dos nanopartículas de Cun. Simulamos la colisión de las nanopartículas a diferentes temperaturas debajo del punto de fusión y con diferentes velocidades de impacto. Analizando la variación de la energía potencial durante la colisión identificamos tres etapas claramente definidas. La información sobre los cambios estructurales durante la colisión se obtiene mediante la función de correlación par y la técnica de análisis de pares. Se ha cuantificado la variación en el tiempo de la población de diferentes pares, observándose diversas transformaciones estructurales. Luego se nota una reorganización de átomos hacia una forma más estable mediante la liberación de energía. Durante la colisión de dos nanopartículas icosaedrales iguales (Cu55) se ha observado diferente comportamiento de los pares vecinos 1551 dependiendo de la velocidad de impacto.
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