high-Tc Superconductor YBa2Cu3O7-x Research Articles

Novel Phase YBa2Cu3O5 derived from the High Tc Superconductor YBa2Cu3O7-x

The orthorhombic unit cell of high Tc oxide superconductor YBa2Cu3O7–x is indicated by two-dimensional CuO2 planes spanned in a-b directions. Partial removal of oxygen, down to x > 1, creates an insulating state and randomly distributed oxygen vacancies. An attempt has been made to increase the concentration of vacancies up to some critical value when their ordering could take place, while balance with copper cations will still maintain the original tetragonal structure. Removal of two oxygen atoms per unit cell results in the YBa2Cu3O5 compound and formation of linear Cu1+– O chains. The novel phase is an insulator, and doping in a low (50 –200 mbar) oxygen atmosphere at T < 800 K converts it to a conducting state.

Investigation of structural, dielectric, impedance and leakage current behaviour of green phase of yttrium barium copper oxide:Y2BaCuO5

Comprehensive study of structural, dielectric, electrical, and ferroelectric characteristics of Yttrium Barium Copper Oxide (Y2BaCuO5) ceramic, (accompanying phase of high-Tc superconductor YBa2Cu3O7-X can unravel plethora of fascinating applications. Y2BaCuO5 green phase cuprate has been prepared by employing ceramic fabrication technology. Room-temperature X-ray diffraction data of the polycrystalline sample suggests that it crystallizes in orthorhombic system in non-centrosymmetric Pbn21 spacegroup. The microstructure and elemental composition clearly illustrated by SEM micrograph and EDAX data. Frequency dependence of dielectric parameter has been discussed using Maxwell-Wagner model. Grain and grain boundary effects discussed using Nyquist plots; fitted to RQC and RC-RQC circuits. Temperature and Frequency dependent conductivity behaviour are explained using Arhenius equation and Jonscher power law. NSPT and CBH model of charge transport mechanisms observed. (I–V) charecteristics demonstrates semiconductor behaviour of Y2BaCuO5 and its suitability for rectifier applications. Existence of hysteresis loop at room and high temperature up to 200 °C suggests ferroelectricity in Y2BaCuO5.

Polarization-dependent resonant inelastic X-ray scattering study at the Cu L and O K-edges of YBa2Cu3O7-x

We present a study on the high-Tc superconductor (HTSC) YBa2Cu3O7-x (YBCO) using polarization-dependent X-ray absorption and resonant inelastic X-ray scattering. High-resolution measurements using synchrotron-radiation are compared with calculations using a quasi-atomic multiplet approach performed at the Cu 2p3/2-edge of YBCO. We use a multiplet approach within the single impurity Anderson model to reproduce and understand the character of the localized low-energy excitations in YBCO. We observe a distinct peak at about 0.5eV in O K RIXS. This peak shows dependence on doping, incident energy, and momentum transfer that suggests that it has a different origin than the previously discussed cuprate bimagnons. Therefore, we assign it to bimagnon excitations within the Zhang Rice bands and/or the Upper Hubbard bands, respectively.

Fabrication of YBCO-LSMO-YBCO Lateral Structure with AFM Lithography

We have tried to make the superconductor/half metal/superconductor (SC/HF/SC) Josephson junction to make clear a long range proximity effect. The structure was consisted of high-Tc superconductor YBa2Cu3O7-x and half metallic ferromagnet La0.7Sr0.3MnO3 thin films deposited by pulse laser deposition on SrTiO3(100) single crystal substrates. The SC/HF/SC lateral structure was made by scratching with the atomic force microscope (AFM) probe. We could cut the ditch which has 30nm width and 50nm depth. We have investigated the I-V and R-T measurements of the structure. The structure after the fabrication did not show the superconducting state and we could not find the Josephson current.

ChemInform Abstract: Electronic Structures and Properties of the Charged Model Clusters Relating to High-Tc Superconductor YBa2Cu3O7-x.

ChemInform Abstract: Electronic Structures and Properties of the Charged Model Clusters Relating to High-Tc Superconductor YBa2Cu3O7-x.

Properties of PTO/YBCO Heterostructure on Bare SiC Substrates

ABSTRACTThe lead titanium oxide PbTiO3 (PTO) and High Tc Superconductor YBa2Cu3O7-x (YBCO) capacitor hetero structures have been fabricated by pulsed laser ablation directly on 3C-SiC substrates. X-ray diffraction analysis indicates that both PTO layer and YBCO layer are polycrystalline with a perovskite phase. The zero-field cooling (ZFC) curve of YBCO shows a transition temperature Tc around 60 K with a ΔTc ≈ 10 K in a dc SQUID measurement. The ferroelectric properties of the capacitors were characterized by a RT66A apparatus.

Elastic Anomalies of High-Tc Superconductor YBa2Cu3O7-x between 77 K and 300 K

The shear and compressional wave velocities and attenations in the high-Tc superconductor YBa2Cu3O7-x are accurately determined by the pulse transmission method using a “dual-type cell” at temperatures between 77 K and 300 K. The temperature dependence of shear wave velocities shows the change of three steps. Three attenuation peaks (shear wave) appear at about 80, 170 and 210 K. The peaks correspond to the steps of shear wave velocity. From measured ultrasonic data, the elastic and inelastic properties of aggregates on YBa2Cu3O7-x are reported, and are discussed on the basis of previous reports.

Internal friction associated with magnetic flux pinning in high Tc superconductor YBa2Cu3O7-x

Internal friction Q-1 and resonant frequency fr of the high Tc superconductor YBa2Cu3O7-x (Tc=90 K) were measured as a function of the applied longitudinal magnetic field Ha at temperatures below and above Tc. At 110 K, Q-1 and fr are independent of the applied magnetic field. At 77 K, fr increases continuously when Ha>0, while Q-1 increases abruptly when Ha reaches a certain value. The internal friction Q-1 can be represented by Q-1=Q0-1+dQ-1, where Q0-1 is the background value and dQ-1 is due to the motion of the flux lines around the pinning centres while vibrating stress is being applied. When a cyclic magnetic field was applied, internal friction hysteresis curves were observed. And the area and the shape of the hysteresis loop are related to the condition of pinning of flux lines.

The linear temperature behavior of resistivity and oxygen stoichiometry in YBa2Cu3O7-x

By employing a gettered annealing technique, we studied the relationship between the resistivity ρ(x, T) (20° C ⩽ T ⩽ 300° C) and oxygen content in the high-Tc superconductor YBa2Cu3O7-x · ρ(x, T) is approximately linear for 0.0 ⩽ x ⩽ 0.6, and both the slope dρ/dT and the residual resistivity increase continuously with decreasing oxygen content. A qualitative analysis is given.

The effects of absorption and inelastic scattering of high-resolution electron microscopic images of YBa2Cu3O7-x

The computational procedures necessary to include the effects of physical absorption and the elastic scattering of initially inelastically scattered electrons in a computer-simulated high-resolution electron microscopic image are outlined. Results of a study of this type carried out on the high-Tc superconductor YBa2Cu3O7-x are described, using the plasmon-loss data derived from experimental electron energy-loss spectra, initially by taking the two effects separatedly but also by considering them together, and an assessment of the approximations used is made. The results indicate that, for a specimen thickness of 8 nm, both processes have only a slight effect on the image contrast, but the influence of absorption is the more significant.

The ac Magnetic Response of Superconducting YBa2Cu3O7-x

The nonlinear magnetic response of a high-Tc superconductor YBa2Cu3O7-x has been investigated by the ac induction method. At temperatures below 80 K, the fundamental and the third-higher harmonic susceptibility components of both the pellet and coarse powder samples strongly depends on the field amplitude. Also, M-H curves exhibit a hysteresis which bears a similarity to that of hysteretic superconductors. These characteristics are absent in well-isolated particles. Around the transition temperature, susceptibility components have a behavior distinct from that at low temperature and the magnetic response is nearly reversible. The observed magnetic behavior is interpreted as a superposition of the bulk property and the effect of weak linkage of superconducting particles.

Orthorhombic-Tetragonal Transition of High <i>T</i><sub>c</sub> Superconductor YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-<i>x</i></sub> and Its Behavior in the Release and Absorption of Oxygen during Heat

The high Tc superconductor (YBa2Cu3O7-x) was heated to 920°C in various atmospheres by the same heating schedule, and the change of oxygen concentration in the exhaust gas was continuously monitored with a mass spectrometer. When the superconductors were heated in an oxygen partial pressure above 0.02atm, the tetragonal to orthorhombic transformation occurred completely. However, the superconductivity was lost when the oxygen partial pressure was lower than 0.01atm. These results suggested that the rate of oxygen absorption by the superconductor during cooling was too low at low PO2 to recover sufficient lattice oxygen. The curve of O2 evolution from the superconductor during heating consisted of two peaks. The desorption of O2 at a lower temperature resulted in the transformation from orthorhombic to tetragonal phases.

D.c. sputtering elaboration of thin films of the high-Tc superconductor YBa2Cu3O7-x: evidence for strong film-substrate interactions

Superconducting thin films of YBa 2 Cu 3 O 7−x have been prepared by d.c. sputtering deposition followed by a suitable thermal treatment. The deposition parameters were optimized in order to obtain ideal 1:2:3 composition of the films. A wide variety of substrates were tested, most of them giving evidence for a strong chemical interaction with the film when annealed. To better determine the contamination effects of potential substrates on the properties of YBa 2 Cu 3 O 7−x , a number of foreign elements were diluted in sintered samples for the superconducting matrix. Their influence was evaluated from a.c. susceptibility or magnetization (SQUID) measurements. Superconducting films were thus obtained, mainly on zirconia. BaZrO 3 or YSZ (yttrium stabilized zirconia) sintered plates, with the onset of superconducting transition occuring near 90 K. The width of the transition strongly depends on the crystalline state of the film, which is connected to the applied thermal treatment Les parametres de depot ont ete optimises afin d'atteindre la stoechiometrie ideale 1:2:3. Des supports de nature variee ont ete testes: la plupart d'entre eux presentent une forte interaction chimique avec la couche lors du recuit. Afin de mieux definit les effets de contamination des divers supports sur les proprietes supraconductrices de YBa 2 Cu 3 O 7−x , des elements etrangers ont ete volontairement introduits en petites quantites dans des pastilles frittees de ce materiau. Leur influence a ete etudiee par des mesures magnetiques

High Resolution Electron Microscopy of Grain Boundaries in Sintered High-Tc Superconductor YBa2Cu3O7-x

Grain boundaries in as-sintered high-T c YBa 2 Cu 3 O 7-x were often found to contain thin amorphous layers up to 2nm in thickness. planar grain boundaries parallel to the c plane of one of the crystals tended to have thick layers, while the other boundaries were with layers of negligible width. The boundary width apparently increased in the specimens sealed in a quartz tube, re-heated at 773K and slowly cooled, even though the chemistry of the boundary layer was preserved except oxygen. Even a thin layer of other compounds was found in the c-plane type boundary when the specimen was re-sintered at above 1200K. These phenomena may be explained by the cracking of the interface and a liquidus valley between YBa 2 Cu 3 O 7-x . The deterioration of the resistivity characteristics of the specimen is attributed to these changes of the grain boundaries.