We measured magnetization hysteresis and zero-field-cooled magnetic relaxation for liquid-quenched Bi-Sr-Ca-Cu-O samples at various temperatures. We found that there is a close correlation between the magnetic behavior and the microstructures of the samples. The magnetization hysteresis greatly increases in the samples with a large amount of crystal defects such as precipitates and stacking faults in the matrix of the material. We also found that the flux creep is reduced as a result of these microstructural changes.

The magnetization and flux creep in YBa2Cu3O7-y +xAg superconducting rings at 77K has been studied experimentally. Decay of the magnetization caused by the induced intergrain current was measured using the ring shaped specimen. The decay in proportion to logarithmic of the time was observed. The pinning potentials (Uo) of about 1.0eV at zero external field and 0. 3eV at 100G were estimated by Anderson and Kim model (1,2). In order to measure the intragrain flux creep, the rings were crushed into powder and pressed to disks without sintering. It was found that the dependence of Uo on external field for the ring was greater than that for the disk.

We have measured the M-H hysteresis loops of n YBa2Cu3Oy: Ag (n = 3,5, and 7), and 3RBa2Cu3Oy:Ag (R = rare earth) as a function of temperature. We have found that the residual magnetization and, hence, pinning, is strong and is independent of n and R, but dependent on the metallurgy. The giant creep rates have been measured and are greater than those of pure 123 samples. Scanning electron microscopy and polarized light microscopy have shown that the presence of silver gives rise to the growth of large grains (~1 mm) in the 123-Ag samples. The field dependence of the critical current density is not strong at high field. We have also measured the resistance in field up to 200 kOe. The resistance remains zero even at 80 K and 200 kOe. The field dependence of the superconducting transition is discussed in terms of phase slippage.

Based on the description of high-Tc cuprate superconductors as intercalation compounds and the van Hove singularity (vHs) concept for these phases, [with its consequences concerning their density of states (dos)] we give a model that explains T2 semi-quantitatively as a function of both hole concentration and stage number and, in a simplified variation, yields a functional dependence of T2 on the CuO2 layer fraction of the unit cell that shows a maximum, as observed.

We have fabricated tunnel junctions between chemically etched single crystals of YBa2Cu3O7-δ and evaporated metal counterelectrodes which exhibit reproducible characteristics. Above the bulk critical temperature of YBa2Cu3O7-δ, Tc, the conductance, G(V), has a linear dependence with voltage and has some asymmetry. Below Tc, additional structure associated with the superconductivity appears in G(V). At T>>Tc there is a reproducible finite zero bias conductance.

We have prepared low leakage tunnel junctions on epitaxial YBa2Cu3O7 (YBCO) films grown on SrTiO3(001) by evaporating Pb counterelectrodes onto chemically etched YBCO surfaces. Structure in the voltage dependence of the tunneling conductance is reproducible and strongly resembles what has been obtained in similarly etched junctions on YBCO single crystals.

Superconducting thin films of YBa2Cu3O7 are prepared in-situ by on-axis, sputter deposition from a single, composite target. Our planar magnetron target composition of Y:Ba:Cu = 1.08:1.76:4.5 sputtered onto MgO at T~750°C in a 600mTorr Ar-O2 atmosphere yields reproducible superconducting films having Tc(R = 0)>80K and stoichiometry 1:2:3, that are shiny and of near epitaxial, crystalline quality. In order to ensure clean interfaces, YBa2Cu3O7/normal metal bilayers (to form SNS' Josephson junctions) and YBa2Cu3O7/normal metal/insulating barrier trilayers (to form SNIS' proximity tunnel junctions) are grown completely in-situ. (The S' = Pb counter electrode is evaporated ex-situ.) A supercurrent and Shapiro steps are observed in microwave irradiated SNS' (N = Ag) small area (5x10-5cm2) junctions. In SNIS' tunnel junctions, high-quality Pb tunneling is observed.

Measurements by photoemission spectroscopy have shown that the chemical environments of alkaline earth cations in HTSC compounds are different from the environments of these ions in the prototype perovskite structures. A recently discovered HTSC compound (Pb2Sr2Ca0.5Y0.5Cu3O8) exhibits the exceptional feature of having a typical HTSC signature for Sr, while Ca shows a perovskite-like signature. The crystal-chemical features of the relevant compounds have been correlated with these observations. These correlations may be indicative of inter-layer electronic interactions.

Thin films of Y1Ba2Cu3Ox,ZrO2, and yttria-stabilized zirconia (YSZ) have been deposited on Si(100) by the UV-laser ablation technique, and characterized by several techniques including x-ray photoemission spectroscopy (XPS) and cross-sectional transmission electron microscopy (XTEM). Si substrates were prepared by several techniques including thermal oxidation, and oxide etching and passivation by hydrogen termination. Certain of these YBCO films (= 250 nm thick) deposited on YSZ buffer layers have excellent superconducting properties. Other YBCO and zirconia films, deposited to 2-5 nm thickness and transferred under dry N2 into UHV, allowed XPS evaluation of the thermal and chemical stability of the interfaces and nearby regions. 2-nm films of YBCO on 15-nm films of SiO2/Si, deposited at 550–670 °C, showed Cu 2p core-level XPS lines similar to those of bulk YBCO (i.e., Cu II) but with two components due to reactions. The Si 2p line showed formation of silica on the YBCO surface at 670 °C and of silicate at 550 °C. XTEM lattice images showed that use of H-terminated Si produced superior interfaces with the zirconia films.

The far infrared reflectance of magnetically-oriented YBa2Cu3O7-δ has been measured from 30–600 cm-1 over the temperature range 300–50 K. A strongly temperature dependent optical anisotropy is observed in this region. The low energy Ē⊥c spectrum displays a high reflectivity associated with the dominant free carrier contribution. Peaks corresponding to phonons are present in the spectrum associated with the direction perpendicular to the high conductivity Cu - O planes. However the reflectivity for Ē∥c is not characteristic of an insulating material but rather shows a metallic-like rise with decreasing photon energy. The plasma frequencies for both polarizations, obtained from fits to the reflectance data, decrease with decreasing temperature. There is some evidence in the parallel conductivity data taken below Tc, for the onset of an energy gap that is substantially smaller than that deduced for the in-plane value; such a result suggests a large gap anisotropy. The parameters describing a number of low frequency phonon modes for Ē∥c have been determined from fits to the R∥ data. Most show a slight softening as Tc is traversed.

We have measured the infrared (IR) reflectance and Raman spectra of electron doped and undoped Nd2CuO4 and Pr2CuO4. Utilizing the results from doped ceramics and undoped ab plane oriented single crystals, we observe and assign all the IR active phonons (3A2u + 4Eu) predicted by group theory. We have also observed the Raman active modes involving atom motion along the c axis. We compare our results to those found in the related hole superconductors based upon La2CuO4.

We have measured the infrared (IR) reflectance and Raman spectra of electron doped and undoped Nd2CuO4 and Pr2CuO4. Utilizing the results from doped ceramics and undoped ab plane oriented single crystals, we observe and assign all the IR active phonons (3A2u + 4Eu) predicted by group theory. We have also observed the Raman active modes involving atom motion along the c axis. We compare our results to those found in the related hole superconductors based upon La2CuO4.

X-ray diffraction, magnetic susceptibility and 119-Sn Mössbauer effect measurements have been performed on Pb2Sr2Eu.5Cu3-xSnx08+z (x = 0.0, 0.1) superconductors. The x-ray diffraction pattern indicated that the samples are single phase materials. The diamagnetic shielding and the Meissner fraction increase with the introduction of Sn in the lattice. The 119-Sn Mössbauer effect measurements have been used to determine the site symmetry and valence state of Sn atom in the superconductor.

We report new results on 119 Sn and 57 Fe Mossbauer spectra of Y1 Ba2 Cu3-z (O, N)7-x, where M is either Sn or Fe, O denotes oxygen and N denotes ni trogen, 0 ≤ X ≤ 0.5, and z = 0.05, 0.1, 0.15, 0.2. The oxygen annealed samples were superconductors, but nitrogen annealed samples were not. The Mossbauer measurements indicate four quadrupole pairs in Y Ba2 (Cu, Fe)3 O7-x, but only three pairs in Y1 Ba2 (Cu, Fe)3 N6.5. In the Sn Mossbauer spectra, the quadrupole splittings of nitrogen annealed samples are larger than that of oxygen annealed samples. In both Fe and Sn spectra, the isomer shifts of oxygen annealed samples are different from that of nitrogen annealed samples. Our study provides some information about the Cu(1) and Cu(2) sites and their surrounding environment in the Y Ba Cu system.

The Y-Ba-Cu-0 systems have been reported to be a high temprature superconductor with above 90K. Optical Study would give us useful informations as a characterization for Y-Ba-Cu-0 systems with an analysis of energy dispersive X-ray system EDS. Optical constants of superconducting Y-Ba-Cu-0 systems are n*=1.6 92-j0.403 for 99.99%(4N) with Y1.00 Bal.90 Cu2.87 and n*=1.604-j 0.441 for 99.99%+ (4N+) with Y1.00 Ba2.18 Cu3.12.

Ion channeling in single crystals of (Y/Er)Ba2Cu3O7–δ reveal an abrupt change (~0.01Å) at the superconducting transition temperature (Tc) in displacements of the Cu and O atoms perpendicular to the [001] direction. This anomalous change in atomic displacements shifts directly with stoichiometry-induced changes in Tc. Blocking patterns indicate no large structural changes across Tc.

The upper critical magnetic field of a series samples of YBa2(Cu1-xNix)3O7 is measured. Other related parameters, such as the lower critical magnetic field Hc1, the Ginsberg-Landau parameter k, the jump in the specific heat ∆C/Tc, the superconducting coherence length ξ, and the penetration depth λ, are calculated from Tc, dHc2/dT and dM/dH. The results show that Hc2(0), and consequently ξ(0), are essentially constant, but Hc and ∆C/Tc decrease with increasing Ni content.

Magnetic phase diagrams of YBa2 (Cu1–xFex)30y and YBa2 (Cu1–xCox)30y were determined by measuring positive muon spin relaxation and magnetic susceptibility (SQUID).

Magnetization and Mössbauer spectroscopy results on aerosol processed YBa2 (Cu1-xFex)307–δ samples are presented. Systematics of Tc(x), x(x) and Fe dopant site occupancies In/I(x) as a function of dopant concentration ‘x’ are deduced and compared to those established on analogous solid-state- reacted samples. The absence of twinning in the aerosol processed grains leads to a random replacement of Cu for Fe in chains and planes of the host structure.

The effects of transition metal dopants on superconductivity in samples of nominal composition Bi2CaSr2(Cu1-xMx)208+δ with M = Co, Fe, Ni and Zn have been investigated for 0 ≤ x ≤ 1. Co and Fe additions progressively suppress the ? of the doped material and result in semiconducting behaviour for x ≤ 0.2. In the ranges 0 ≤ x ≤ .07 and near x = 1.0, x-ray diffraction reveals the samples are essentially single phase but are multiphase otherwise. Ni and Zn dopants have only a very slight effect on Tc; however, EDX analysis reveals these elements are not significantly Incorporated into the superconducting phase.