Nano- Al2O3 particle addition effects on Y Ba2Cu3Oy superconducting properties

The effects of nano-sized CoFe2O4 particles (10 nm) addition on the structural and the normal state resistivity of YBa2Cu3O7 (noted Y-123) and Y3Ba5Cu8O18 (noted Y-358) polycrystalline were systematically studied. Samples were synthesized in oxygen atmosphere using a standard solid state reaction technique by adding CoFe2O4 up to 2 wt%. Phases, microstructure and superconductivity have been systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical measurements ρ ( T ) . XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations reveal that the grain size is reduced with increasing the content of CoFe2O4. The measurements for the resistivity dependence of temperature show that the depression in superconducting temperature is more pronounced for CoFe2O4 addition in Y-358 compound than in Y-123 one. These results may be attributed to the existence of much more disorder due to a greater number of Cu sites to be substituted by Fe and Co in Y-358 compared to Y-123.

Comparative study of nano-sized particles CoFe2O4 effects on superconducting properties of Y-123 and Y-358

The effect of different weight percentages of nano-Fe2O3 on the properties of Bi1.8Pb0⋅4Sr2Ca2Cu3O10+δ
 superconducting phase was studied. Phase formation, elemental real contents and granular microstructure of the investigated samples were carried out using X-Ray powder Diffraction (XRD), Energy Dispersive X-ray emission (EDX), Proton Induced X-ray Emission (PIXE), Rutherford Backscattering Spectrometry (RBS) and Scanning Electron Microscopy (SEM). XRD data indicated that the volume fraction of (Bi,Pb)-2223 decreased as nano-Fe2O3 wt.% increased. PIXE and EDX analyses showed that the PIXE technique is more accurate for detecting the nano-Fe2O3 than the EDX technique. The oxygen content, determined from RBS, decreased as nano-Fe2O3 wt.% increased. The superconducting properties of the prepared samples were investigated using electrical resistivity and I–V curves, at 77 K, measurements. It was found that the granular structure and the critical current density were improved up to 0.2 wt.% of nano-Fe2O3 addition. The superconducting transition temperature T
 c decreased as nano-Fe2O3 wt.% increased, attributing this to the decrease of the volume fraction or trapping of mobile holes. The enhancement rate of J
 c for (Bi,Pb)-2223 phase added with nano-Fe2O3 is 9 %, which is lower than that of (Bi,Pb)-2223 phase added with SnO2, Ag2O, Al2O3 and MgO. This means that the nano-magnetic addition has the lowest enhancement rate in both J
 c and T
 c.

Effect of Fe2O3 Nano-Oxide Addition on the Superconducting Properties of the (Bi,Pb)-2223 Phase

We present comprehensive neutron scattering studies of nonsuperconducting and superconducting electron-doped Pr0.88LaCe0.12CuO4 +/-delta (PLCCO). At zero field, the transition from antiferromagnetic (AF) as-grown PLCCO to superconductivity without static antiferromagnetism can be achieved by annealing the sample in pure Ar at different temperatures, which also induces an epitaxial (Pr, La, Ce)(2)O-3 phase as an impurity. When the superconductivity first appears in PLCCO, a quasi-two-dimensional (2D) spin-density-wave (SDW) order is also induced, and both coexist with the residual three-dimensional (3D) AF state. A magnetic field applied along the [(1) over bar, 1, 0] direction parallel to the CuO2 plane induces a \"spin-flop\" transition, where the noncollinear AF spin structure of PLCCO is transformed into a collinear one. The spin-flop transition is continuous in semiconducting PLCCO, but gradually becomes sharp with increasing doping and the appearance of superconductivity. A c-axis aligned magnetic field that suppresses the superconductivity also enhances the quasi-2D SDW order at (0.5, 0.5, 0) for underdoped PLCCO. However, there is no effect on the 3D AF order in either superconducting or nonsuperconducting samples. Since the same field along the [(1) over bar, 1, 0] direction in the CuO2 plane has no (or little) effect on the superconductivity, (0.5, 0.5, 0) and (Pr, La, Ce)(2)O-3 impurity positions, we conclude that the c-axis field-induced effect is intrinsic to PLCCO and arises from the suppression of superconductivity.

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Electronic competing phases and their magnetic field dependence in electron-doped nonsuperconducting and superconducting Pr$_{0.88}$LaCe$_{0.12}$CuO$_4$

We report electrical conductivity fluctuation analyses on YBa2Cu3O
 y
 (denoted as YBCO) granular samples added with nanosize ZnMnO (ZnMnO for brevity) and ZnO (30 nm) particles. Nanoparticles are added to the precursor powders during the final sintering cycle of a two-step preparation process. Phase analysis by X-ray diffraction and granular structure examination by transmission electron microscopy (TEM) were carried out. When ZnMnO and ZnO are added to the YBCO, the orthorhombic structure is maintained. TEM and energy dispersive X-ray spectroscopy analysis show the presence of inhomogeneities embedded in the superconducting matrix. The temperature dependence of electrical resistivity in zero magnetic field has been measured on free, 1 wt.% ZnMnO and 1 wt.% ZnO added samples and the effect of microscopic inhomogeneities in the paraconductivity region has been reported. Data about the dimensionality of the thermodynamic fluctuation are obtained by analyzing the excess of conductivity Δσ as a function of the reduced temperature $\varepsilon =\ln(\frac{T}{T_{c}^{mf}}-1)$
 on the basis of the Aslamazov–Larkin theory. In the mean-field region a crossover from 3D to 2D was observed for each sample. 1D behavior of fluctuation conductivity was found at high temperatures (above the 2D regime) for nanoparticle added samples. The zero-temperature coherence length, the effective layer thickness of the two-dimensional system, the wire cross-sectional area for one-dimensional system, critical magnetic fields and critical current density are estimated. Superconducting parameters are affected by the nanoparticle additions.

Excess Conductivity Studies in Zn0.95Mn0.05O and ZnO Added YBa2Cu3Oy Superconductors

The structure and charge transfer correlated with oxygen content are studied by measuring the positron lifetime parameters of the Y0.8Ca0.2Ba2Cu3Oy system with a large range of oxygen content (y = 6.84–6.32). The local electron density ne is evaluated from the positron lifetime data. The positron lifetime parameters show a clear change around y = 6.50 where the compounds undergo the orthorhombic–tetragonal phase transition. The effect of ne and oxygen content on the structure, charge transfer and superconductivity are discussed. With the decrease of oxygen content y, O(4) tends to the Cu(1) site, causing carrier localization, and accordingly, the decrease of ne. This would prove that the localized carriers (electrons and holes) in the Cu–O chain region have great influence on the superconductivity by affecting the charge transfer between the reservoir layers and the conducting layers. The positron annihilation mechanism and its relation with superconductivity are also discussed.

http://iopscience.iop.org/article/10.1088/0953-2048/18/5/005/pdf

Structure and charge transfer correlated with oxygen content for a Y0.8Ca0.2Ba2Cu3Oy (y = 6.84–6.32) system: a positron study

Y 0.8 Ca 0.2 Ba 2 Cu 3 O y samples with large range of oxygen content, have been systematically studied by means of positron annihilation technology, transport property measurements and X-ray diffraction. The positron lifetime parameters have a strong dependence on oxygen content y , and show evident changes during orthorhombic–tetragonal phase transition ( y  = 6.50 ± 0.05). The local electron density n e and vacancy concentration C v are evaluated as a function of oxygen content. The correlations between local electronic structure, O–T phase transition and superconductivity are discussed. n e mainly has an effect on high- T c superconductivity, no direct evidence shows that it is related to the O–T phase transition; and C v is mainly caused by oxygen vacancy. The small increase of T c with decreasing y around y  ∼ 6.80 is due to the charge carriers over-doping, which is confirmed by the change of n e in this work.

Local electronic structure, O–T phase transition and oxygen content in Y0.8Ca0.2Ba2Cu3Oy (y = 6.84 − 6.32) high-Tc superconductors

Effects of high valence ions V 4+ and Ni 3+ substitution on superconductivity are studied systematically for the electron-doped superconducting Pr 1.85 Ce 0.15 CuO 4− δ (PCCO) system. The results indicate that very small amount of V 4+ substitution ( x  ⩽ 0.04) for Cu 2+ site improves the superconductivity, but further substitution ( x  ⩾ 0.06) will depress the superconductivity. Contrasting with V 4+ , Ni 3+ substitution shows a strong suppression on superconductivity, even for extremely small amount substitution of 0.01. Both the change of lattice parameters and the similar 3d electron structure of V 4+ ion to the Cu 2+ ion support the improvement of superconductivity while x  ⩽ 0.04 in the V-substituted PCCO system. The results of Hall effect indicate that high valence ion substitution for Cu 2+ increase the carrier concentration, which is also one reason for the improvement of superconductivity of V 4+ substitution PCCO.

Effect on superconductivity of high valence ions V4+ and Ni3+ substitution for Cu site in Pr1.85Ce0.15CuO4−δ system

Hall coefficient and resistivity are studied systematically for Pr 1.85 Ce 0.15 CuO 4− y (PCCO) and Pr 1.85 Ce 0.15 Cu 0.96 V 0.04 O 4− y with varying oxygen content y . As the annealing temperature increases, T c gradually increases, it proves that high annealing temperature not only reduce the oxygen content by removing the apical oxygen, but also change the electronic structure and, accordingly, improve the coupling of the carriers. Small amount of V 4+ substitution for Cu site improve the superconductivity of electron-doped superconductor PCCO system.

Fen Liu

Papers

Structure and charge transfer correlated with oxygen content for a Y0.8Ca0.2Ba2Cu3Oy (y = 6.84–6.32) system: a positron study

Local electronic structure, O–T phase transition and oxygen content in Y0.8Ca0.2Ba2Cu3Oy (y = 6.84 − 6.32) high-Tc superconductors

Effect on superconductivity of high valence ions V4+ and Ni3+ substitution for Cu site in Pr1.85Ce0.15CuO4−δ system

Electrical transport and the improvement of superconductivity by V4+ substitution in Pr1.85Ce0.15Cu0.96V0.04O4−y system