Superconducting Properties Of YBa2Cu3O7 Research Articles

Effect of Different Nano-sized MgO Addition on YBa2Cu3O7-δ Superconductor

The effect of nanoparticle with different size on a superconductor is interesting because the size of the coherence length, penetration depth, and the magnetic flux in a superconductor is in the nanometer range. In this paper, we report the effects of different nano-sized MgO (20, 40, and 100 nm) addition on YBa2Cu3O7-δ(MgO)x for x = 0, 0.1, and 0.2 wt.%. X-ray diffraction patterns indicated a single YBa2Cu3O7 (YBCO) phase where the peaks were shifted to larger angles in the 20- and 40-nm MgO-added samples indicating induced stress of first order in the structure. The electrical resistance versus temperature was measured using the four-probe method. The transition temperature, Tc, for the pure YBCO showed Tc = 90 K and was suppressed to 78–80 K for the 20- and 40-nm MgO-added samples. AC susceptibility (χ = χ′ + iχ″) measurements showed a shift in the peak temperature, Tp, of the imaginary susceptibility χ″ towards lower temperatures for 20-nm MgO-added samples but increased with larger MgO (100 nm). This work showed that smaller nano-sized MgO suppressed the superconducting properties of YBCO more compared with the larger MgO.

Effects of graphene oxide doping on the structural and superconducting properties of YBa2Cu3O7−δ

In this research we reported the effects of graphene oxide (GO) doping on the structural and superconducting properties of YBa2Cu3O7−δ (YBCO) high temperature superconductors. We synthesized YBCO powder by sol–gel method. After calcination, the powder mixed with different weight percent (0, 0.1, 0.3, 0.7, 1 wt.%) of GO. Refinement of X-ray diffraction (XRD) was carried out by material analysis using diffraction (MAUD) program to obtain the structural parameters such as lattice parameters, site occupancy of different atoms and orthorhombicity value for the all samples. Results show that GO doping does not change the structure of YBCO compound, Cu (1), Cu (2) and oxygen sites occupancy. It seems that GO remains between the grains and can play the role of weak links. We found that GO addition to YBCO compound increases transition temperature (TC). The oxygen contents of the all GO-doped samples are increased with respect to the pure one. The strain (ɛ) of the samples obtained from Williamson–Hall method, varies with increasing of GO doping. The scanning electron microscopy (SEM) images of the samples show better YBCO grain connections by GO doping.

Filling of electronic density of states in Y-123 superconducting ceramics by nano Nd substitution on Ba site in crystal structure

This comprehensive examination focuses on the effect of the Nd substitution on the phase formation, mechanical, microstructural and superconducting properties of YBa2Cu3O7−x ceramics with the aid of standard experimental measurement tecniques as regards X-ray diffraction (XRD), dc resistivity (ρ-T), Vickers's microhardness (Hv) and scanning electron microscopy (SEM) measurements. For the full characterization of the pure and Nd substituted Y-123 samples, the onset–offset critical transition temperature, variation of transition temperature, crystal structure, grain size, phase purity and lattice parameters are determined and discussed clearly. The results demonstrate that the crucial characteristics given above improve with the increase in the Nd concentration level at the Ba-site in the superconducting core up until a critical value of x = 0.250 after which the characteristics tend to retrograde rapidly due to the transition of optimally doped state to the underdoped state position in the Y-123 superconducting lattice. This is in association with both the hole localization problem of the electronic states in the vicinity of the Fermi level and the presence of more disordered metallic state. The long and short of it is that the excess (0.250 < x) replacement of Ba inclusions for Nd impurities in the system leads to degradation of the major (Y-123) phase or increment of the minor phase (Y-211) in their intrinsic crystal structures with the phase transition from orthorhombic to pseudotetragonal in the crystal structure, being one of the most striking points deduced from this work. At the same time, the mechanical performance shows the similar trend (firstly increase then decrease) with the increase of the Nd inclusions inserted in the Y-123 superconducting matrix. The Vickers microhardness measurement evidences also declare that the plastic deformation is superior to the elastic deformation (no elastic recovery) in the samples presenting RISE behavior.

The effect of thickness and substrate tilt on the BZO splay and superconducting properties ofYBa2Cu3O7 − δ films

Highly splayed BaZrO3 nanorods (BZO-NRs) were generated inYBa2Cu3O7 − δ (YBCO) films dopedwith 2 vol% BZO on 5° vicinal SrTiO3 (STO) substrates. It was observed that the splay angle of the BZO-NRs around thec-axis increases with film thickness from about10° at 0.2 µm to35°–40° at1 µm. Although the same trend was observed in BZO-NRs in flat YBCO films, the splayangle at a given thickness and its increase with film thickness are significantlysmaller. The enhanced dispersion of BZO-NRs in vicinal YBCO/BZO-NR filmsresults in a much reduced strain on the YBCO lattice as compared to its flatcounterpart. This led to less disturbed normal-state electron conduction along theab-plane, higherTc values andenhanced Jc values due to improved magnetic pinning.

Detailed magnetization study of superconducting properties ofYBa2Cu3O7−x ceramic spheres

We present a magnetization study of low densityYBa2Cu3O7−x ceramics carried outin magnetic fields H such that 0.5 Oe<H<50 kOe. It was demonstrated that superconducting links betweengrains may be completely suppressed either by a magnetic fieldH∼100 Oe (at low temperatures) or by an increase of temperature to above 70 K.This property of the present samples allowed us to evaluate the ratiobetween the average grain size and the magnetic field penetration depthλ. Furthermore,at temperatures T>85 K, using low field magnetization measurements, we were able to evaluate the temperature dependenceof λ, which turned out to be very close to predictions from conventional Ginzburg–Landautheory. Although the present samples consisted of randomly orientedgrains, specifics of magnetization measurements allowed for evaluation ofλab(T). Good agreement between our estimation of the grain size and the real sample structureprovides evidence for the validity of this analysis of magnetization data. Measurements ofthe equilibrium magnetization in high magnetic fields were used for evaluation ofHc2(T). At temperaturesclose to Tc, the Hc2(T) dependence turned out to be linear, in agreement with Ginzburg–Landau theory. The value of the temperatureat which Hc2 vanishes coincides with the superconducting critical temperature evaluated from low fieldmeasurements, which is important evidence of the validity of both approaches to theanalysis of magnetization data.

Effect of Ca doping for Y on structural/microstructural and superconducting properties of YBa2Cu3O7−δ

We report systematic studies of structural, microstructural and transport properties of Y1−xCaxBa2Cu3O7−δ bulk samples with 0.20⩾x⩾0.0. The partial substitution of Ca2+ at Y3+ site in YBa2Cu3O7−δ leads towards slightly overdoped regime, which along with disorder in CuO2 planes is responsible for decrease in superconducting transition temperature (Tc) of the doped system. The microstructural variants being studied by transmission electron microscopy (TEM) technique in imaging and selected area diffraction modes revealed an increase in the density of twins with increase in Ca concentration despite the fact that there is slight decrease in the orthorhombicity. This is against the general conviction of decrease in twin density with decreasing orthorhombicity. An increase in twin density results in sharpening of twin boundaries with increasing Ca concentration. These sharpened twin boundaries may work as effective pinning centers. A possible correlation between microstructural features and superconducting properties has been put forward and discussed in the present investigation.

Grain Growth, Microstructure, and Superconducting Properties of Pure and Y2BaCuO5‐Doped YBa2Cu3O7–x Ceramics

Superconducting properties of YBa2Cu3O7–r ceramics have been investigated with the aim of avoiding the weak links that are the principal reasons for low critical current densities in this compound. An efficient grain growth process should be useful in this respect. Superconducting ceramics were prepared from a commercial precursor powder (Hoechst) with or without addition of Y2BaCuO5 and from a gel precursor powder. Grain growth kinetics and densification are first derived under such conditions that control the liquid‐phase contribution. Grain growth in the solid‐state regime is anisotropic, possibly due to anisotropic grain boundary energies. Grains in the fine powder (gel precursor) grow 10 times faster than in the commercial reference but grain size saturates because of steric hindrance. Addition of Y2BaCuO5 particles inhibits grain growth in the solid‐state regime. 211 particles are incorporated into grains when a transient liquid phase is present. Superconducting properties were characterized by 50‐Hz magnetization hysteresis cycles at 77 K under H= 0.2 to 12 mT to probe weak‐link behavior. Additional studies were performed at 5 K using higher fields. Weak‐link contribution is decreased when samples from the gel route are processed in the solid‐state regime (below the peritectic temperature). This may be attributed to the propensity of gel powder to develop, naturally, preferential grain boundaries due to its intrinsic structural anisotropy.

Effects of substrate temperature on growth orientation and superconducting properties of YBa2Cu3O7−x films prepared by metalorganic chemical vapor deposition

The effects of substrate temperature on the structural and superconducting properties of YBa2Cu3O7−x films prepared by metalorganic chemical vapor deposition have been studied in the temperature range of 550 to 690 °C. Highly c-axis oriented films with transition temperatures of 90 K and critical current densities at 77.5 K and 0 T larger than 106 A/cm2 could be produced at substrate temperatures above 650 °C. As the temperature was decreased, the amount of a-axis orientation in the film increased. Films grown at a substrate temperature of 600 °C showed a strong a-axis orientation with a transition temperature of 83.5 K and a critical current density of 4.5×105 A/cm2 at 77.5 K and 0 T.

Grain growth enhancement in silver-doped YBa2Cu3O7−x superconductor

The effects of silver addition on the microstructural and superconducting properties of YBa2Cu3O7−x (YBCO) have been investigated. It was found that the microstructure of silver-doped YBCO samples is characterized by highly oriented platelet-like grains (up to 3 mm × 0.5 mm × 15 μm). The superconducting transition temperatureT itc (R= 0) is decreased with increasing wt% of silver. The critical transport density (J cT) is, however, found to be improved (up to two orders of magnitude) in the doped materials (JitcT (T= 77 K andH = 0 T) = 1250 Acm−2). It is believed that the addition of silver lowers the melting temperature of the system and thereby enhances the decomposition of the compound and promotes grain growth during solidification.

The effect of sintering time on the mechanical and superconducting properties of YBa2Cu3O7- x ceramics

The study was undertaken to illuminate the effect of sintering time on the mechanical and superconducting properties in YBa 2Cu 3O 7- x ceramics. The effect of sintering time on superconducting properties was studied from two viewpoints; (1) residual stress, (2) phase development. The 3-point bending strength of ceramics was higher in tetragonal phase than in orthorhombic phase, and decreased with increasing sintering time. The measured difference in strength between tetragonal phase and orthorhombic phase was attributed to the residual stress resulting from volume change during tetragonal-orthorhombic transformation. With increasing sintering time, T c increased and δ T c decreased. The variation in T c and δ T c for various sintering times was due rather to phase development than due to residual stress.

Effect of silver and silver oxide additions on the mechanical and superconducting properties of YBa2Cu3O7−δ superconductors

The effects of Ag and Ag2 O additions on the mechanical and superconducting properties of YBa2 Cu3 O7−δ superconductors were studied. The addition of 20-vol % Ag resulted in an increase in strength from ≊40 to 75 MPa and a twofold increase in the critical current density (Jc ) of YBa2 Cu3 O7−δ bar specimens. These improvements are believed to be due to the increased density. Furthermore, Ag particles may relax the residual stresses resulting from the expansion anisotropy of individual grains, and may provide increased resistance to crack propagation by pinning the propagating cracks; these effects would also increase the strength. The addition of 30-vol % Ag resulted in an increase in strength to 87 MPa, but it was associated with a decrease in Jc . This decrease in Jc at high Ag content is believed to be due to the presence of oxygen deficient nonsuperconducting tetragonal phase as well as continuous Ag phase. Similar effects were also observed after Ag2 O additions.

The effects of thermal cycling from 5 to 350 degrees C on elasticity and superconductivity of YBa2Cu3O7-δ

The effects of thermal cycling from 5 to 350 degrees C on the elastic and superconducting properties of YBa2Cu3O7- delta have been studied. In internal friction (Q-1) measurements, variation of the peak temperature, peak height and background with thermal cycling was observed. The conductivity transformed from metallic to semiconducting after several thermal cycles. These phenomena are attributed to the decrease of oxygen content. Sample-dependent variations in elastic moduli were observed.

Superconductivity and magnetism in transition-element-substituted YBa2Cu3O7 compounds

Superconducting properties of YBa2Cu3O7 have been investigated by a systematic substitution of 3d transition elements for 10% of the Cu ions. Early transition elements Ti, V, and Cr affect the superconducting temperature of YBa2Cu3O7 only slightly. Local magnetic moment formation is observed in Mn, Fe, Co, and Ni substituted compounds. Tc strongly correlates with the size of the paramagnetic moments, possibly due to scattering from the magnetic sites. Zn displays a phenomenal ability to suppress Tc because of the elimination of the 3d holes. The Zn compositional dependence of Tc indicates that the superconductivity completely disappears at 13–14 at. % of Zn. It is suggested that Zn preferentially substitutes the Cu(2) sites.