The effect of Ni doping on the electrical and magnetic properties of Y_1-xNi_xBa₂Cu₃O_7−δ delta superconductors

Abstract

The Y 1-x Ni x Ba 2 Cu 3 O 7-δ superconducting samples with low level of Ni concentration were prepared by the standard solid-state reaction. The AC susceptibility, magnetoresistivity, microstructure and the critical current density, J c , of samples as a function of temperature, magnetic field and Ni doping are investigated. The AC susceptibility measurements show that the displacement of the peak temperature T p of the imaginary part of the susceptibility χ″ versus magnetic field was reduced strongly by Ni doping up to an optimum level, which shows the increasing of flux pinning by Ni doping. The J c of samples was derived from AC susceptibility utilizing the Bean model. It shows an increasing in J c by Ni doping, at any temperature or magnetic field, consistent with the results of J c measurements. The magnetoresistance measurements were carried out under magnetic fields up to 1 T and explained by TAFC model. Utilizing this model, the vortex dynamic behaviour and the activation energy U (H) of the compound are investigated. We found that the U (H) increases and the resistive broadening is strongly reduced by Ni doping. The SEM measurements show that the grain sizes are clearly increased and the grain connections are improved by Ni doping. The results of all the observations taken from different measurements are consistent together and indicate the Ni doping has an effective role to improve the intergranular coupling and flux pinning.

Magnetic doping effects on the superconductivity of Y1-xMxBa2Cu3O7-δ (M = Fe, Co, Ni)

“…The grains with different sizes are distributed in the samples. It is observed that the large grain sizes are present in the samples (around 20 μm), which is consistent with the observed maximum activation energy and the maximum measured and estimated Jc [42] for the optimally doped samples.…”

Effects of li doping on superconducting properties of citrate-gel prepared Y1–xLixBa2Cu3O7–δ Compound

“…In other words, T c is almost unchanging even for a Li doping of 10%. This is consistent with the magnetic coupling models and observations reported for cuprate superconductors [23,24], where by magnetic element doping at the Y site (Co, Fe and Ni element doping) T c increased, while the substitution of two non-magnetic elements, i.e., Ca and Sr, results in the T c degradation. The increase in T c through magnetic doping, which was a new observation, confirms the effective role of magnetically mediated pairing in cuprates [24].…”

“…To answer this question, fully oxygenated Y 1-x Li x Ba 2 Cu 3 O 7-δ polycrystalline samples were synthesized with different levels of Li dopant using an optimum citrate-gel and heat treatment process. A renewed investigation was also carried out on a non-magnetic Li-doped system that had shown enhancements in T c and J c values in a previous study of magnetic element doping [23,24]. We show although the Li dopant was non-magnetic and was capable of bearing a high phonon frequency, no remarkable increases were observed in T c , thereby refuting the hypothesis that T c increases with phonon frequency.…”

“…5). The pure sample exhibits a J c of around 100 A.cm -2 [23] for the solid-state sample, whereas a value of 7 times higher was recorded for the citrate-gel samples.…”

Sharp Phase Transition by the Enhanced Lattice Stability of Low‐Temperature Phase of Cr‐Doped VO2

“…This sharpening of the phase transition by Cr doping is very exceptional. In most cases, the phase transitions of materials are smoothed by impurity doping, e.g ., Verwey transition in magnetite, 31 superconducting transitions in high‐temperature superconductors, 32 etc. The transition phenomena become vague by the high‐level Cr doping ( x > 0.05) to VO 2 .…”