Yuri Aparecido Opata

Fluctuation-induced conductivity in melt-textured Pr-doped YBa2Cu3O7-δ composite superconductor

ABSTRACT In 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.

Superconducting Dy1-x(Gd,Yb)xBa2Cu3O7-δ thin films made by Chemical Solution Deposition

Dy1−x(Gd or Yb)xBa2Cu3O7−δ samples were prepared using chemical solution deposition (CSD), based on trifluoroacetate metal-organic decomposition (MOD) methods. Xray diffraction results demonstrated the formation of the RE123 superconducting phase with a strong in-plane and out-of-plane texture. c-lattice constants were observed to decrease for all samples doped with Gd or Yb. Measurements of the onset critical transition temperature (T c ) were found to decrease with increasing Yb content, while only minor changes were observed for samples with Gd. Critical current density (Jc) analysis demonstrated that doping with Yb significantly increased the self-field Jc value from 3.8 MA/cm to 6.0 MA/cm for the pure and 10 % Yb doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field Jc values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.Dy_1-x(Gd or Yb)_xBa₂Cu₃O_7-δ samples were prepared using chemical solution deposition, based on trifluoroacetate metal-organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature (T_c^onset ) were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density (J_c) analysis demonstrated that doping with Yb significantly increased the self-field J_c value from 3.8 MA/cm² to 6.0 MA/cm² for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field J_c values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.

Fluctuation-induced conductivity and phase separation in composite samples (YBa2Cu3O7-δ)1−y–(PrBa2Cu3O7-δ)y

Fluctuation-induced conductivity in composite samples (YBa2Cu3O7-δ)1−y–(PrBa2Cu3O7-δ)y was investigated. The samples with were produced through the solid-state reaction method. Powder X-ray Rietveld analysis for the composites demonstrated that the patterns are identical to that of YBa2Cu3O7-δ. From the critical exponent analysis, it could be observed that the transport properties of composites are governed by the presence of two phases: YBa2Cu3O7-δ and PrBa2Cu3O7-δ. Splitting of the pairing transition was observed and two critical temperatures were identified, but only one is strongly affected by Pr. The composite structure can be thought as a three-dimensional grain percolation system with the structure of Pr-grain and Y-grain unit cell.

Superconducting

Dy1−x(Gd or Yb)xBa2Cu3O7−δ samples were prepared using chemical solution deposition (CSD), based on trifluoroacetate metal-organic decomposition (MOD) methods. Xray diffraction results demonstrated the formation of the RE123 superconducting phase with a strong in-plane and out-of-plane texture. c-lattice constants were observed to decrease for all samples doped with Gd or Yb. Measurements of the onset critical transition temperature (T c ) were found to decrease with increasing Yb content, while only minor changes were observed for samples with Gd. Critical current density (Jc) analysis demonstrated that doping with Yb significantly increased the self-field Jc value from 3.8 MA/cm to 6.0 MA/cm for the pure and 10 % Yb doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field Jc values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.Dy_1-x(Gd or Yb)_xBa₂Cu₃O_7-δ samples were prepared using chemical solution deposition, based on trifluoroacetate metal-organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature (T_c^onset ) were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density (J_c) analysis demonstrated that doping with Yb significantly increased the self-field J_c value from 3.8 MA/cm² to 6.0 MA/cm² for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field J_c values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.

\text{Dy}_{1-x}(\text{Gd},\text{Yb})_{x}\text{Ba}_{2}\text{Cu}_{3}\text{O}_{7-\delta}

Dy1−x(Gd or Yb)xBa2Cu3O7−δ samples were prepared using chemical solution deposition (CSD), based on trifluoroacetate metal-organic decomposition (MOD) methods. Xray diffraction results demonstrated the formation of the RE123 superconducting phase with a strong in-plane and out-of-plane texture. c-lattice constants were observed to decrease for all samples doped with Gd or Yb. Measurements of the onset critical transition temperature (T c ) were found to decrease with increasing Yb content, while only minor changes were observed for samples with Gd. Critical current density (Jc) analysis demonstrated that doping with Yb significantly increased the self-field Jc value from 3.8 MA/cm to 6.0 MA/cm for the pure and 10 % Yb doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field Jc values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.Dy_1-x(Gd or Yb)_xBa₂Cu₃O_7-δ samples were prepared using chemical solution deposition, based on trifluoroacetate metal-organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature (T_c^onset ) were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density (J_c) analysis demonstrated that doping with Yb significantly increased the self-field J_c value from 3.8 MA/cm² to 6.0 MA/cm² for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field J_c values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.

Thin Films Made by Chemical Solution Deposition

We have studied fluctuations on the electrical conductivity in granular Tm1-xPrxBa2Cu3O7-δ (0 ≤ x ≤ 0.10) superconductors. Samples were prepared by the standard solid-state reaction technique. The results are described in terms of the temperature derivative of the resistivity, dρ/dT, and of the logarithmic temperature derivative of the conductivity, dln (Δσ)/dT. The results show clearly that the resistive transition proceeds in two stages: intragranular and intergranular. Also, it was not observed in dρ/dT, near the transition, a structure consisting of two closely separated maxima, as seen in studies with other rare earth elements. Yet, the analysis of the conductivity in the normal phase has shown contributions from critical fluctuations and they were not affected by Pr doping. Below TC, on approaching the zero resistance state, our results show a power-law behavior with critical exponent s ≅ 4.1 for x = 0.00 and s ≅ 2.8 for x = 0.05 sample, indicating a phase transition from a paracoherent to a coherent state of the granular array. This behavior was not observed for x = 0.10 sample, showing that Pr affected the coherence transition.