Inhomogeneity Induced Conductivity Fluctuation in YBa2Cu3O7−y /Cr2O3 Composite

Dimensional fluctuations of superconducting order parameters in YBa₂Cu₃O_7?y +xCr₂O₃ (x=0.0, 2.3, 4.4, and 6.1 wt.%) has been analyzed. SEM micrographs reveal the reduced grain size with the incorporation of magnetic Cr₂O₃ particles in the YBCO matrix. XRD graphs show the unchanged orthorhombic structure and improved oxygen ordering in the composite samples. With the increase of Cr₂O₃ wt.%, it is found that the superconducting transition temperatures determined from standard four-probe method decreases gradually. Excess conductivity fluctuation analysis using Aslamazov–Larkin model fitting reveals transition of two dominant regions (2D and 3D) above T _c . 2D to 3D crossover temperature, i.e., Lawerence–Doniach temperature that demarcates dimensional nature of fluctuation inside the grains is influenced by Cr₂O₃ incorporation in YBCO matrix. The decrease in Lawerence–Doniach temperature in the mean field region has been observed as a consequent dominance of the 3D region with an increase in wt.% of Cr₂O₃ in the composite.     

Study of Structural Modification and Fluctuation Induced Electrical Conductivity in \text {YBa}_{2}\text {Cu}_{3}\text {O}_{7-y}+x \text {BaSnO}_{3} Superconductor Composite

A series of \((1-x) \text {YBa}_{2}\text {Cu}_{3}\text {O}_{7-y} + x \text {BaSnO}_{3 }(x = 0.0, 0.1, 0.3, 0.5, 1.0, 2.5, 5.0\,\text {wt}{\%})\) samples were prepared using the solid-state reaction method. XRD graphs confirm the orthorhombic structure in pristine as well as in composite samples. Raman spectra show the presence of all the vibration modes in pure as well as in the composite samples. In addition, some defect-induced modes have also appeared in the higher weight % BSO-added sample, and no loss of apical oxygen O(4) at 500 cm \(^{-1}\) occurs due to BaSnO \(_{3}\) (BSO) addition. Microstructural analysis reveals the unchanged grain size with the incorporation of dielectric BSO particles in the YBCO matrix. Superconducting transition temperature determined from standard four-probe method decreases with the increase of BSO wt%. Excess conductivity fluctuation analysis using Aslamazov–Larkin model fitting reveals transition of two dominant regions (2D and 3D) above \(T_\mathrm{c}\) . 2D to 3D crossover temperature i.e. Lawrence–Doniach temperature that demarcates dimensional nature of fluctuation inside the grains is influenced by BSO incorporation in YBCO matrix.     

Effect of Ti Doping on Structural and Superconducting Property of YBa2Cu3O7−y High T c Superconductor

Dimensional fluctuations of superconducting order parameters in YBa₂(Cu_1?x Ti _x )₃O_7?y (x=0.01, 0.02, 0.04, 0.05) have been analyzed. SEM micrographs reveal the reduced grain size and the formation of TiO₂ nanowires covering over the grains of YBCO matrix. XRD graphs show the unchanged orthorhombic structure. With the increase of TiO₂%, it is found that the superconducting transition temperatures determined from standard four-probe method decrease gradually. Excess conductivity fluctuation analysis using the Aslamazov–Larkin model fitting reveals transition of two dominant regions (2D and 3D) above T _c . 2D to 3D crossover temperature, i.e., the Lawerence–Doniach temperature that demarcates dimensional nature of fluctuation inside the grains is influenced by Ti incorporation in YBCO matrix. The decrease in the Lawerence–Doniach temperature in the mean field region has been observed as a consequent dominance of 3D region with increase in Ti%.     

Temperature Response of BaZrO3-Inclusion to YBa2Cu3O7−δ Probed by Magneto-Transport Measurements

This paper reflects a simple and practically scalable technique, in which attempts have been made for preparation of fine BaZrO₃ (BZO) as defects in YBa₂Cu₃O_7?δ (YBCO) superconductor, to enhance superconducting properties. The texture growth of YBCO + xBZO (x=1.0,2.5,5.0 and 10.0 wt.%) composites has been made through solid-state reaction route by employing calcined YBCO and sub-micron sized powders of BZO. The phase formation, texture and grain alignment were analyzed using XRD and SEM. The magnetoresistivity data obtained as a function of temperature (T) in the tail region shows two key features: first an anomalous secondary peak at $T_{c_{\mathrm{on}2}}$ well below 92 K as a function of BZO content with varying magnetic fields, and secondly a drop in global resistivity transition temperature (T _c0) following the incorporation of excess BZO to the grain boundaries. Impurities appear to reduce $T_{c_{\mathrm{on}2}}$ greatly to the lower-temperature values as a function of BZO content and to influence the onset of $T_{c_{\mathrm{on}1}}$ in presence of varying magnetic fields. The findings of this investigation suggest the presence of multiple transition temperatures in the composites.     

Synthesis and Characterization of Superparamagnetic Co3O4@ZnO Nanocomposite

We report the sequential polyol synthesis of Co₃O₄@ZnO nanocomposite. Firstly, Co₃O₄ was synthesized and ZnO was produced on the surface of the as synthesized Co₃O₄ NPs in the same pot. The nanoparticles have been investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), and physical properties measurement system (PPMS) of Quantum Design. The weight percentage of phases were found as 26.3 % for ZnO and 73.5 % Co₃O₄ (crystal thickness ratio \(D_{\mathrm{Co}_{3}\mathrm{O}_{4}}/ D_{\mathrm{ZnO}}= 1.38\) ) by using the generalized reference intensity ratios (RIRs) method. Superparamagnetism in Co₃O₄@ZnO nanocomposite at room temperature was first detected with high Ms value of 10 emu/g, and the non-hysteric curve with nearly saturated nature at high fields. This non-hysteric and nearly saturated nature at 15 kOe is the nature of superparamagnetic structures.     

Electrical conductivity of polycrystalline tin dioxide and its solid solution with ZnO

Electrical conductivity (σ) of “pure” and ZnO doped SnO₂ has been measured at different temperatures and oxygen partial pressures ( \(p_{{\text{O}}_{\text{2}} } \) )- From the variation of electrical conductivity of these materials three partial pressure ranges have been identifieD. In the high partial pressure rangeσ increases with decreasing \(p_{{\text{O}}_{\text{2}} } \) followed by a \(p_{{\text{O}}_{\text{2}} } \) independent region at lower \(p_{{\text{O}}_{\text{2}} } \) ´s and finally increases once again with a further decrease of \(p_{{\text{O}}_{\text{2}} } \) . These variations have been explained on the basis of an anti-Frenkel type defect structure and an interstitial solid solution of ZnO in SnO₂. The activation energy for the conduction process has been estimated and the values are found to differ in two different temperature ranges. In the low temperature range the conductivity is attributed mainly to the chemisorption of oxygen on the surface of the specimen.     

Determination of Superconducting Parameters of GdBa2Cu3O7?δ Added with Nanosized Ferrite CoFe2O4 from Excess Conductivity Analysis

Superconductor samples of the type (CoFe₂O₄) _x GdBa₂Cu₃O_7??? , 0.0??x??0.1?wt.%, were synthesized by the conventional solid-state reaction technique and were characterized using X-ray powder diffraction (XRD) and scanning electron microscope (SEM). XRD analysis indicated that the orthorhombic structure of Gd-123 is not affected by nanosized ferrite CoFe₂O₄ addition, whereas the volume fraction of Gd-123 increased up to x=0.01?wt.%. Excess conductivity analysis of the investigated samples was analyzed as a function of temperature using the Aslamazov and Larkin (AL) model. It exhibited four different fluctuation regions, namely critical (cr), three-dimensional (3D), two-dimensional (2D), and short-wave (sw). The zero-temperature coherence length along c-axis, effective layer thickness of the two-dimensional system, and inter-layer coupling strength were estimated as functions of nanosized ferrite CoFe₂O₄ concentration. In addition, the thermodynamics, lower and upper critical magnetic fields, and critical current density were calculated from the Ginzburg number. It was found that the low concentration of nanosized ferrite CoFe₂O₄ addition up to x=0.01?wt.% improved the physical properties of Gd-123, while for x>0.01?wt.%, these properties were deteriorated.     

Thermal conductivity of high-T c crystals: Dependence on magnitude and orientation of magnetic field,and effect of Zn doping

We present precise measurements of in-plane thermal conductivity for superconducting single crystals of YBa₂Cu₃O_7?x (YBCO) withT _c =92 and 60 K, Bi₂Sr₂CaCu₂O₈ (BSCCO), and of Zn-doped YBCO. Magnetization and thermal conductivity data obtained with the same 90-K YBCO crystal demonstrate a close relationship between the magnetic thermal resistivity and the internal magnetic fieldB in a superconductor in the mixed state. For all superconductors studied here, the magnetic thermal resistivity is a sublinear function of magnetic field. The origins of the nonlinearity are discussed. Angular dependences of the magnetic thermal resistivity have been shown to depart from the anisotropic 3D superconductor model and are in quantitative agreement with a quasi-2D model. Implications for spatial modulation of the order parameter are made.     

Correlation of luminescent properties of ZnO and Eu doped ZnO nanorods

ZnO and ZnO:Eu nanorods were originally synthesized by concussion method. The nanorods present a wurtzite nanostructure with dispersive distribution morphology. The average diameter and length of the nanorods are about 80 nm and 2 μm, respectively. The best concussion time, concussion frequency, the function of HMT and the growth mechanism are presented in this paper. This method is simple, economical, and environmentally mild. We believe other kinds of ZnO nanostructures could be obtained by this method when appropriate agents are added. However, because of the different chemical properties between trivalent RE ions and the cations of ZnO, it is rather difficult to incorporate RE ions into the lattice of semiconductors effectively via a wet chemical method. Based on our experiments, the sample of $ {\text{ZnO}}:{\text{Eu}}^{3 + }_{1\% } $ is single-phase and its PL signal is stronger than other single-phase $ {\text{ZnO}}:{\text{Eu}}^{3 + }_{X} $ samples. So 1% content of Eu³⁺ was chosen as the best doping concentration.     

Effect of Y 2 Ba4CuBiO y Nanoparticles Doping on the Levitation Force of Single-Domain YBCO Bulk Superconductor by Top-Seeded Infiltration Process

The top-seeded infiltration and growth process (TSIG) is a very effective method for the preparation of YBa₂Cu₃O_7?x (YBCO) bulk superconductors. In this paper, single-domain YBCO bulk superconductors with different ratio of nanoscale Y₂Ba₄CuBiO _y (YBi2411) inclusions have been fabricated by TSIG process. The growth morphology, microstructure and levitation force of the YBCO bulks have been investigated. The amount of nanoscale YBi2411 added to Y₂BaCuO₅ (Y211) is in the range from 0.5 wt.% to 5 wt.%. It is found that the optimum proportion is obtained in the sample with 3.0 wt.% YBi2411 addition. The results are very helpful for the fabrication of high-quality single-domain YBCO bulk superconductors.     

On the Relationship Between the H-Tensor and the Concentration Tensor and Their Bounds

For composite materials, two quantities that are useful for characterizing the contribution of inhomogeneities in a matrix material to the overall properties are (1) the individual H-tensor, H _i , which describes the contribution of a single inhomogeneity and (2) the overall strain concentration tensor, which describes the relationship between the overall volumetric strain to the average strain of all of the inhomogeneities. In this paper, we develop a relationship expressing the overall H-tensor, ${\mathcal{H}}$ , in terms of the overall strain concentration tensor. An important feature of the derivation is that it allows for rigorous upper and lower bounds on the overall H-tensor. In the special case that the inhomogeneities are all the same, with the same orientation, then ${\mathcal{H} = {\bf H}_i}$ , and the results derived for ${\mathcal{H}}$ also hold for H _i .     

Magnetoresistance of Superconducting Granules and Grain Boundaries in Ceramic YBa2Cu3O7−δ High-Temperature Superconductors in Weak Magnetic Fields

The objective of the work is to establish the contribution of superconductive granules and grain boundaries (weak links) in magnetoresistance ρ value of YBa₂Cu₃O_7?δ granular high-temperature superconductor (HTS) at T<T _c. The current-voltage characteristics (CVCs) $E(j)_{H_{\mathrm{ext}} = \mathrm{const}}$ of YBa₂Cu₃O_6.95 ceramic samples were measured in H _ext (0≤H _ext≤≈500 Oe) magnetic fields. The CVCs $E(j)_{H_{\mathrm{trap}} = \mathrm{const}}$ of the samples magnetized in H _treat magnetic fields were measured at H _ext=0. Based on the CVCs, $\rho(j)_{H_{\mathrm{ext}} = \mathrm{const}}$ , ρ(H _ext) _j=const and $\rho(j)_{H_{\mathrm{treat}} = \mathrm{const}}$ dependences were reestablished. The comparative analysis of $\rho(j)_{H_{\mathrm{ext}} = \mathrm{const}}$ and ρ(H _ext) _j=const dependences indicates the magnetic field redistribution between grain boundaries and superconductive granules influence on transport and galvanomagnetic properties of granular HTS. The superconductive grain magnetoresistance ρ _g was established to be significantly lower than ρ _J value of Josephson medium.     

Enhanced Magnetic Properties in Cu0.5Tl0.5Ba2Ca2Cu3O10−δ Superconductor Doped with Carbon Nanotubes

Fluctuation-induced conductivity (FIC) analysis in the critical fluctuation region (cr), three-dimensional (3D), two-dimensional (2D), and zero-dimensional (0D) regions is reported for undoped and carbon nanotubes (CNT)-doped Cu_0.5Tl_0.5Ba₂Ca₂Cu₃O_10?δ (CuTl-1223) superconductors. Samples were synthesized by well-known solid-state reaction method by adding CNT up to 7 wt %. The X-ray diffraction data confirms the single-phase orthorhombic structures following PMMM space group for all the samples. The scanning electron microscope (SEM) images reveal that the carbon nanotubes are present in the spaces between the grains and connect the grains electrically to help the intergranular current flow. From FIC analysis, it was found that the width of critical and 3D regimes are shrunken with the increased CNT doping in the final compound. Also, the coherence length (ξ_c(0)), the Fermi velocity (V _F), and the coupling constant (J) are suppressed with increased CNT doping except for the 0.25 wt % doped sample. The decrease in important superconductivity parameters most likely arises due to low CNT doping which indeed functions as columnar defects that are produced by heavy ion irradiation. In this analysis, we also found that the critical magnetic fields (B _c(0), B _c1(0)) and critical current density (J _c(0)) were found to increase with increased CNT concentration. These observations suggest that addition of CNT (efficient pinning centers) to CuTl-1223 compounds improve the electrical connection between the superconducting grains to result in the improvement of magnetic properties of the final compound.     

Effects of Mn and Gd Co-substituted into ZnO on Structural and Magnetic Properties

We have worked on the structural and magnetic properties of Zn_0.99?xMn_0.01Gd _x O _δ (for x = 0.02, 0.03, and 0.04) compounds prepared by using a sol–gel method. The x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectroscopy were used to understand the structural properties of the samples. We observed that co-substitution of Mn (1 %) and Gd (2–4 %) into the ZnO does not change the hexagonal structure. Scanning electron microscope (SEM) images show us that the grain size decreases with the increasing amount of the Gd into the ZnO matrix. The magnetic properties of the samples have been investigated by using magnetic hysteresis and DC susceptibility measurements. The ZMG1 sample shows a weak ferromagnetic behavior at room temperature, whereas the ZMG2 and ZMG3 samples exhibit a paramagnetic nature. Furthermore, it is also found that the magnetizations of the samples decrease with increasing Gd content in the ZnMnO system due to the enhancing interaction between Gd ³⁺ ions. We summarize that the co-substitution of Mn and Gd into the ZnO generates a room-temperature ferromagnetism, but it still needs more work to obtain strong and high coercivity magnetic loops for applications.     

Non-ohmic Electrical Transport Properties Above the Critical Temperature in Optimally and Underdoped Superconducting YBa2Cu3O6+x

The resistivity and the Hall effect as a function of current density and temperature in the normal state of very thin films of YBa₂Cu₃O_6+x are measured with a fast pulsed-current technique. The in-plane longitudinal and transverse (Hall) conductivities are reduced in intense current densities up to several $\mathrm{MA\,cm}^{-2}$ . In optimally-doped samples, this non-ohmic effect is limited to temperatures below 100?K. In a moderately underdoped sample, however, the non-linearity extends to the temperature range from T _c =53?K to ??150?K. The non-linear part of the Hall conductivity does not scale with a critical exponent, thus excluding classical amplitude fluctuations of the superconducting order parameter as possible origin.     

Excess Conductivity Analysis of Bi1.8Pb0.4Sr2Ca2Cu3O10+δ Added with Nano-ZnO and Nano-Fe2O3

Superconductor samples of type Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_10+δ added with nano ZnO and Fe₂O₃ were synthesized by the conventional solid-state reaction technique. The samples were characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and electrical resistivity measurements. Excess conductivity analysis of the investigated samples was carried out as a function of temperature using Aslamazov and Larkin (AL) model. The analysis showed four different fluctuation regions namely critical (cr), three-dimensional (3D), two-dimensional (2D) and short-wave (sw). The zero temperature coherence length along c-axis, effective layer thickness of the two-dimensional system and inter-layer coupling strength were estimated as a function of nano-oxides concentration. In addition, the thermodynamics, lower and upper critical magnetic fields as well as critical current density were calculated from the Ginzburg number N _G . It was found that the low concentration of nano-ZnO addition up to x=0.2 wt.% improved the physical properties of (Bi,Pb)-2223 phase. In contrary, these properties were deteriorated for x>0.2. These results indicated that the addition of a low amount of nano-ZnO during the final processing of (Bi,Pb)-2223 samples can be effectively improved the flux pinning ability, while the addition of a high amount of nano-ZnO decreased the volume fraction and increased the resistance of grain boundaries. Moreover, the addition of nano-Fe₂O₃ had a negative effect on the superconducting parameters of the (Bi,Pb)-2223 phase. This behavior was attributed to the decrease in the volume fraction of (Bi,Pb)-2223 phase with the increasing of nano-Fe₂O₃.     

Influence of Ce Substitution at Sr-Site on Superconducting Fluctuation Behavior and Infrared Absorption of Tl0.9Bi0.1Sr2?x Ce x Ca0.9Y0.1Cu1.99Fe0.01O7?δ (x=0–0.20) Ceramics

Ce substituted Tl_0.9Bi_0.1Sr_2?x Ce _x Ca_0.9Y_0.1Cu_1.99Fe_0.01O_7??? (x=0?C0.20) samples were synthesized to determine the effects of the higher valence ion substitution on superconductivity and structure of the Fe-doped Tl1212 derivatives. The normal state behavior for x=0 showed semiconductor-like behavior which gradually turned to metallic behavior with increasing Ce at x=0.05?C0.15. However, further substitution of Ce for x>0.15 turned the normal state to insulating behavior. The zero critical temperature, T _{c zero} increased from 65.4?K (x=0.05) to 71.0?K (x=0.10), but slightly decreased for x>0.10 indicating the optimum value of average copper valence was achieved at x=0.10. Excess conductivity analysis using the Aslamazov Larkin, AL and Lawrence?CDoniach, LD models revealed two-dimensional, 2D to three-dimensional, 3D transition of superconducting fluctuation behavior, SFB with the highest transition temperature, $T_{\mathrm{2D}\mbox{-}\mathrm{3D}}$ at x=0.10. FTIR analysis in conjunction with XRD results showed softening of FeO₂/CuO₂ planar oxygen mode from 610.5?cm^?1(x=0) to 605?cm^?1(x=0.20) which is suggested to be related to possible increase of inter plane coupling, J and this is supported by computed results based on the LD model. The enhanced J increases superconducting coherence length along c-axis, ?? _c (0), and hence lowers anisotropy, ?? resulting in enhanced superconducting properties.     

Microstructure of ZnO films synthesized on MgAl2O4 from low-temperature aqueous solution: growth and post-annealing

The microstructure of ZnO films synthesized from low-temperature (90 °C) aqueous solution on (111) MgAl₂O₄ single crystal substrates was characterized by X-ray diffraction, high-resolution scanning electron microscopy, conventional and high-resolution transmission electron microscopy. To examine the thermally activated microstructural evolution of the ZnO, both as-deposited and annealed films were characterized. The ZnO films were confirmed to have a ZnO $ [10\bar{1}0](0001)\left\| {{\text{MgAl}}_{ 2} {\text{O}}_{4} [011](1\bar{1}1)} \right. $ orientation relationship, with Zn polarity normal to the surface. Despite their highly oriented nature, the ZnO films have a columnar grain structure with low-angle (<2.5°) grain boundaries. In addition to lattice dislocations forming low-angle grain boundaries, threading dislocations were observed, emanating from the interface with the substrate. In annealed films, thermally generated voids were observed and appeared to preferentially form at grain boundaries and dislocations. Based on these characterization results, mechanisms are proposed for film growth and microstructural evolution. Finally, the diffusion coefficient of vacancies via dislocations at grain boundaries in the produced ZnO films was estimated.     

Doping Effect of Y2Ba4CuMoO y Particles on Microstructure and Superconducting Properties in Polycrystalline YBa2Cu3O7−δ

Synthesis of polycrystalline YBa₂Cu₃O_7?δ (YBCO) + x mol.% Y₂Ba₄CuMoO _y (Y-24Mo1) (x=0.0, 0.1, 0.2, 1.0, 2.0 and 20.0) superconductors have been done in air via a standard solid state reaction technique. The effects of Y-24Mo1 particles on the microstructure and the superconducting transition temperature were systematically investigated through XRD and SEM techniques. When Y-24Mo1 was added to the YBCO, the orthorhombic structure maintained even at the highest concentration. Tiny peaks of Y-24Mo1 having (022) orientation and some other impurity were detected in the XRD spectrum when x=20.0. SEM results reveal the presence of some entities, and these entities changed with increase of Y-24Mo1 content. The Y-24Mo1 addition modifies the normal state resistivity of samples from metallic to semiconducting, and is accompanied by a two-step transition. Moreover, low Y-24Mo1 concentration leads to a relatively sharp superconducting transition and a broad transition take place for Y-24Mo1 addition greater than 0.2 mol.%. These results can be induced by the inhomogeneities, by the change of the effective coupling strength, and by the variation of the coupling between grains.