High-temperature superconducting Y-Ba-Cu-O films were obtained for the first time by using the ionized cluster beam (ICB) method. It was confirmed that the films resulted in superconductor showing the zero resistance at the temperature above 7 7K.

Three ICB sources were used to control the composition of the film, where ionized each cluster of Y, Ba and Cu was ejected simultaneously from the sources to the MgO substrate in high vacuum. The grown film annealed at 930 °C in oxygen atmosphere showed superconducting behaviour in electrical resistance-temperature relationship. The transition temperature to a superconducting state depends on the voltage to accelerate ionized cluster beams and film thickness. The highest temperature obtained to date is 89K.

We report the photoemission spectra from a high quality thin film sample of Y1Ba2Cu3C7-δ at room temperature and bulk samples of Y1Ba2Cu3C7-δ at different temperatures. The experimental data are interpreted within the configuration interaction model of Anderson Hamiltonian. The experimental values for Δ, U and T are determined. We also give the reasons why we think PES data reflect the intrinsic property of the superconductors. Furthermore, we emphasize the importance of the presence of a 3d8-like satellite which signals the strong correlation among 3d electrons.

Self-consistent spin-polarized energy bands have been calculated for tetragonal and orthorhombic La2CuO4. No stable antiferromagnetic order is found in either the stoichiometric compound or oxygen deficient La2CuO3.75. Constraining the occupancy of Brillouin zone boundary states leads to a small antiferromagnetic moment in both systems which is rapidly quenched by Ba doping.

The discovery of superconductivity above liquid nitrogen temperature in copper oxide compounds has resulted in much research activity aimed at understanding the nature of these materials, as well as at using them in practical devices from sensors to levitated trains. Despite this intense interest, there have been relatively few studies of fluctuation phenomena in them. One fluctuation-induced property of interest is the electrical noise power spectrum. Although excess noise above the thermal background in metals is usually observable only in thin films, we report here measurements of significant noise power in bulk composite samples of the nominal 90K superconductors Y1Ba2Cu3O7-δ (YBCO) and Er1Ba2Cu3O7-δ (EBCO) from 77K to 290K. The “excess” noise spectrum (the total spectrum minus the frequency-independent amplifier and thermal noise contributions) is 1/f in shape in the normal state; no 1/f noise is observed while superconducting. The excess noise magnitude is found to be too large to originate from the expected number of charge carriers, and to have an unusual temperature dependence. We discuss two possible explanations for these observations.

Magnetic properties have been investigated for several rare-earth based, polycrystalline samples of high Tc superconductive “123” compounds with magnetic onset temperatures between 90 and 95 K. Analysis of the susceptibility × of samples based on Gd, Ho, and Dy indicates that the superconductive and magnetic properties are independent of one another to a substantial degree. Studies of the critical current density Jc are reported.

The transport Jc of the polycrystalline YBa2Cu3O7-δ superconductor seems to be dominated by weak links between high Jc regions as evidenced by low Jc values and their strong field dependence. The possible effects of thermal expansion-contraction and the tetragonal-orthorhombic transformation on the weak links and the Jc values were investigated by repeated thermal cycling of sintered pellets between -196°C and various high temperatures (600–850°C) using a furnace heating and cooling in an oxygen atmosphere. While more than a five-fold decrease in Jc from -400 to -70 A/cm2 (at 77K in zero field) is observed after 5 temperature cycles between -196'C and 850°C, only a slight decrease (to -370 Atm2) is noticed after 5 cycles between -196*C to 600°C, the temperature span of which is not all that much smaller than the former cycles. Transmission electron microscopy analysis clearly indicates that the drastic deterioration in Jc by repeated phase transformation is caused by increased amount of microcracks on (001) basal planes near the grain boundaries. The results will be discussed in terms of the large thermal expansion anisotropy of this layer-structured compound.

The time-dependent magnetization of single crystal samples of the high temperature superconductor YBa2Cu3O7 has been studied as a function of temperature and magnetic field. Long relaxation times have been found to persist up to the transition temperature, implying that the transition temperature is the upper bound on glass-like behavior.

On the basis of our reentrant-softening model, sound-velocity results in La1.85Sr0.15CuO4 and YBa2Cu3O7−x are shown to be neither dissimilar nor inconsistent with thermodynamic requirements. In both materials, as temperature decreases, the lattice softens just above Tc. Below Tc, this softening is offset by increased stiffness associated with the developing superconducting phase. This model agrees with results from other physical-property measurements, and it predicts that elastic stiffness is higher in the normal state than in the superconducting state.

NMR and NQR results are reported for 63,65Cu in YBa2Cu3O7-δ. Analysis of the high-field NMR spectrum indicates substantial disorder in the copper-oxygen planes. Nuclear relaxation rates are significantly different for copper in the chains and planes both above and below Tc and yield sharply different electron pairing energies on these structural units in the superconducting state.

A low field microwave absorbtion peak was observed with an EPR spectrometer in the new superconducting oxides‥ The peak disappeared above the superconducting transition temperature after exponential decrease with temperature in the transition region. The peak was sensitive to the magnetic fields the sample has been exposed before in the superconducting phase. Magnetic field dependent stochastic oscillations of the EPR baseline are ascribed to flux trapping in Josephson junctions.

Measurements were made of the penetration depth of bulk and powder samples of YBa2Cu3O7-δ. The samples were placed in an inductor which was part of the resonant circuit of a 4 MHz tunnel diode oscillator. The oscillator was stable to at least 1 part in 106 at 77 K. Changes in the sample susceptibility were easily detected by changes in the oscillator frequency. Analysis of the smallest powders fabricated gave a value of the measured penetration depth λmea = 0.23 μm. The measurement methodology is quantitative and the value of Xmea is believed to be an upper bound of the true penetration depth.

The superconducting transition temperature of sintered YBa2Cu3O7 decreases at a rate of 2.7 K/1018 n/cm2 (E > 0.1 MeV) for fast neutron irradiation. The critical current density Jc increases a factor of three at zero field and more than three at nonzero fields for fluences up to 2×1018 n/cm2. At both 7 and 75 K, Jc is decreasing with fluence near 3×1018 n/cm2.

We have synthesized orthorhombic phase YBa2Cu3O7−x superconductors by using metal alkoxides. Cu (II) ethoxide was first partially dissolved in toluene, followed by the addition of Ba-methoxyethoxide and Y-methoxyethoxide in methoxyethanol to further enhance the solution solubility. A homogeneous gel-like paste was obtained both by adding water to the stock solution and by exposing it to the atmosphere. The gels were then vacuum dried and fired at 800 and 850°C in flowing O2. The superconducting transition temperature was 90 +K.

We have used Zn and Ga, two unique dopants having definite valence states and filled 3d levels, to probe the YBa2Cu3O7 superconductor. A small doping of Ga induces an orthorhombic to tetragonal structural transition, but the values of Tc are as high as 81 K in the tetragonal phase. YBa2(Cu1−xZnx)3O7 retains the same orthorhombic structure as the parent compound, but with highly depressed Tc. The oxygen vacancy order, or the linear chain structure, is found to be not essential for the high Tc. Our data suggest that Ga and Zn preferentially substitute Cu(1) and Cu(2) sites, which leads to the conclusion that the most important feature of the high Tc oxide superconductors is the Cu—O2 planes.

The electronic structures of fluorine-substituted YBa2Cu3O7. crystals are studied by means of first-principles calculations. The most likely site of substitution is 0(1) and the most unlikely site is 0(4).

We have fabricated a series of samples of YBa2(Cu1−x Agx)3Oy compounds where 0 ≤ × ≤ 1, with the intention to study the changes in critical current density and the effect of moisture treatment on normal state resistance R in these high transition-temperature superconductors. The samples exhibited a decrease of the transition-temperature Tc vs the Ag concentration x. Tc is about 93 K for YBa2Cu3Oy and 20 KCfor YBa2Ag3Oy, but it is almost unaffected by the presence or Ag for × < 0.2. An enhancement of the critical current density Jc by nearly an order of magnitude for the samples with 0 < × ≤ 0.1 has been observed. Both Jc and R are found to be sensitive to the ambient moisture conditions.

The singularity in the density of states near a Lifshitz point makes a significant contribution to electron exchange and correlation energy, which does not show up in conventional band theory calculations. This paper discusses several consequences of this fact for high temperature superconductivity.

A Raman spectroscopie investigation of specimens of superconducting YBa2Cu3O7−x and semiconducting YBa2Cu3O6+x indicates that in the range 100 to 700 cm-1, the characteristic lines of the superconductor at 13 K, are at 150, 338, 441, 507, 590, and 644 cm-1. Comparison of the Ranan spectra of the superconductor and the semiconductor indicates a mode stiffening of the pair at 338 and 441 cm-1, hut a mode softening of the pair at 507 and 590 cm-1. A factor group analysis leads to a tentative assignment of the Raman and infrared allowed modes. At temperatures 12K < T < 180K the Raman spectra of the superconductor indicate that the phonon mode at 338 cm-1 has an anomalous temperature dependence below the superconducting critical temperature (Tc).

We report a pronounced critical current anisotropy in bar shaped samples formed from different particle sizes as a function of the magnetic field orientation. Anisotropy of the critical current in tape form wires confirms the measurements on bar samples. X-ray measurements indicate a c-axis preference parallel to the compression axis.

The magnetic form factor for Cu in the antiferromagnetic state of a single crystal La2CuO4 has been measured using neutron diffraction. Our result is consistent with Freeman and Watson's calculation for Cu2+, at least up to Q=4Å1, although a plateau between 1 and 3 Å-1 suggests a small contribution of magnetic moment at the out-of-plane oxygen sites. For larger values of Q the form factor for La2CuO4 seems to drop faster than for Cu2+. The sample ordered antiferromagnetically at TN ≃ 185K with an average ordered moment μ = 0.30/μB per Cu atom.