The effect of magnetic fields to 15T on the electrical resistance (R) of Bi-Sr-Ca-Cu-O superconductors has been measured at precise temperatures during the transition to the superconducting state. The results show that the temperature at which the externally-applied magnetic field causes a divergence of resistance (R) as a function of inverse temperature is approximately at the same temperature where the positive Hall coefficient begins its steep descent to zero. At slightly higher temperature the Hall coefficient shows a singularity peak akin to a delta function. Internal electric field calculations show that the structure of the superconducting oxides, having more than a single building block polyhedron, gives rise to strong electrostatic fields in the unit cell which in turn causes charge separation or polarization. The charge separation is in accord with the importance of high oxidation states of the multivalence cations and suggests the use of high oxygen overpressure during processing. The magnitude of Tc scales closely with the number of bound holes (associated with the charge transfer excitations) per unit cell. Extensive computer calculations using this model indicate attractive pairing of electrons at inter-electron separations of about 10–15A.

Bismuth superconducting oriented fibers of the compositions 2:2:1:2: and 2:2:2:3 have been grown by the Laser Floating Zone (LFZ) method. Growth conditions have been optimized in order to improve the superconducting properties. The 108 K onset in susceptibility measurements (associated to the 2:2:2:3 phase) only appears well defined when starting from Sr-defective precursors.

Tc variations observed in some Tl-based superconductors were studied. Clear correlations were found between Tc, carrier concentration, and c-axis length. In particular, for Tl2Ba2CuO6, a decrease in oxygen content of about 0.1 per formula unit, which corresponded to a decrease in hole concentration of about 0.2, increased Tc up to about 80K from a metallic non-superconductor, and elongated the c axis by about 0.4%. In addition, as Tc values increased systematic changes in metal-sheet separations were observed. Tc variations caused by a change in oxygen content were also observed in Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10. It was demonstrated that superconductivity appears in a certain appropriate range of carrier concentration similar to those observed in other high-Tc superconductors.

Magnetic studies were performed on the high temperature superconductor Tl2Ca2Ba2Cu3O10 (Tc = 123 K) in the form of a grain aligned composite. Investigations with the magnetic field applied parallel and perpendicular to the sample's cannon c-axes were analyzed to obtain the magnetic penetration depth as a function of temperature and the critical current density Jc(H,T).

Magnetization and resistivity data are presented which show a substantial difference in superconducting transitions for nominal Tl2Ca2Ba2Cu3Ox plates with identical crystal structures grown from two different “melt” compositions. A Tl-O and CuO-rich flux yielded approximately stoichiometric plates which have sharp transitions beginning near 111 K, while a second Tl-O-rich flux produced plates containing more Tl and less Ba with very broad transitions starting near 96 K. These data demonstrate the extreme sensitivity of superconductivity to cation site disorder in the Tl-Ca-Ba-Cu-O system.

The effects of oxygen and helium ion irradiation on the superconducting properties of Tl2Ca2Ba2Cu3010 thin films were investigated. The transition temperature and width were monitored as a function of ion fluence using both magnetization and resistivity measurements. These data suggest that superconductivity is completely suppressed at 0.020 dpa for both He and 0 ion irradiation. Further, the rate of decrease in Tc as a function of deposited energy showed that the dominant mechanism causing damage-induced suppression of Tc in these films was from atomic collisions.

X-ray diffraction and magnetic measurements using a SQUID magnetometer have been performed on the title compounds for 0 ≤ x ≤ 0.9. For 0 ≤ x ≤ 0.5, we have single phase materials. However, a small percentage of an impurity phase is noticed in the x = 0.7 sample, and the x = 0.9 sample is clearly not a single phase material. The transition temperature, the diamagnetic-shielding effect, and the Meissner-effect increase as x becomes larger. We have obtained, approximately, Hc1 ≤ 700 oe and Hc2 ≥ 800 k0e.

Magnetization measurements on cubic Ba0.6K0.4BiO3 crystals, approximately 5µm in radius, have been obtained using a recently-developed electrodynamic force balance technique. The onset of flux entry in an external filed H is marked by a pronounced deviation from a linear magnetization at a critical field H* c1 together with a noticeable reorientation of the crystal near H = 0, a reorientation caused by a field-induced torque on the remanent moment. The dependence of H* c1 on temperature is linear over the temperature range 7K≤T≤30K with a slope approximately a factor of three higher than published values. These higher values of H* c1 imply either intrinsically cleaner material with a reduced Ginzburg-Landau parameter K or higher surface critical fields. These results suggest that the intrinsic properties of high-Tc superconductors may be more accurately reflected in small crystals which are more likely to be of higher quality than larger crystals.

We have employed a novel variable-temperature, variable-field/field-gradient cryogenic levitometer, previously used in levitation experiments, to study the suspension properties of the thallium-based high temperature superconductors. Our results are compared and contrasted with the levitation studies and the singular features of the suspension properties are noted.

Both interstitially Ag-doped Bi1.6Pb0.4Sr2Ca2Cu30y + x(wt%) Ag with x = 0.5, 1.0, 5.0, 10.0, 15.0, and substitutionally doped Bi1.6Pb0.4Sr2Ca2(Cu1-xAgx)0y with x = 0.025, 0.05, 0.10, 0.20, 0.40 systems were studied. Magnetic susceptibility Measurements indicate that both the interstitial and substitutional Ag-doping yield auch higher diaiagnetic signal for ZFC in a field of 60 0e at 5 K. At 80 K, -4πH/H was also enhanced by Ag-doping for H<200 Oe. Substitutionally Ag-doping also enhances the Magnetic critical current for x ≤ 0.2. Possible explanation was discussed.

The expansions of Pb2Sr2Y1-xCaxO8+δ for x=0, 0.2 and 0.4 and Ba2YCu3O6+δ have been determined during heating to 700°C. Thermal and compositional components of the expansion have been identified by using different atmospheres. In N2 only thermal expansion with a CTE~13 ppm/*C is noted, while in O2 compositional effects are domina nt. At 550* the incorporation of 1.2 atoms of oxygen by Pb2Sr2YCu3O8 produces an expansion -0.4%. This behavior contrasts to the -0.2% shrinkage which occurs for Ba2YCu3O6.2 when -0.6 atom of oxygen is added. The different expansion behaviors of the two compounds are explained in terms of their structures and the position of the removable oxygen.

The linear thermal expansion coefficient of YBa2Cu307 as a function of temperature has been studied. An anomaly is observed at 250K. This temperature is found to be dependent on oxygen deficiency.

The thermal conductivities of superconducting, Sr-doped lanthanum copper oxide single crystals have been measured from room temperature to below 100 mK parallel and perpendicular to the copper oxide planes. While the results indicate that the heat conduction is strongly anisotropic, the data have been analyzed in terms of a modified Bardeen-Rickhayzen-Tewordt theory of lattice thermal conductivity. It is shown that while electron scattering plays an important role in limiting the in-plane heat conductivity, this scattering channel is masked by other mechanisms for heat transport across the planes.

Starting from the fact that the YBa2Cu3O7-x oxide superconductor system has a constant magnetic susceptibility at high temperatures for each oxygen deficiency x, and assuming that the charge carriers have a free-electron-like behavior, the observed magnetic susceptibility of the samples at room temperature can be associated to the Pauli paramagnetismus and to the Landau diamagnetism of the charge carriers. This result allows one to calculate the charge carriers density from the magnetic susceptibility in the sample. If besides one assume that by applying an external pressure on the sample, there is a change of the volume of the unit cell, but not in the number of the charge carriers in it, then, it is possible to calculate the Bulk modulus of the YBaCuO system at room temperature starting from these magnetic measurements. The obtained results are of the same order of magnitude to those reported in the literature and obtained from thermodynamic and mechanical measurements.

Partial superconductivity has been observed in bulk polycrystalline samples of YBa2Cu3O7 at temperatures as high as room temperature. The technique used was to measure the current-voltage characteristics of bulk samples in the presence of microwaves and magnetic fields. The measurements have been repeated on three samples that had been prepared separately.

Interest in the titanium boride system stems from a patent disclosure by Vahldiek in 1982. In that disclosure TiBx(x=1.6) crystals were subjected to pressures of 300,000 psi and found to have vanishingly low resistivities at room temperature. In this study we processed TiBx crystals by a variety of techniques and pressurized the samples up to 350,000 psi. No high temperature superconductivity was observed.

Electrochemical behavior of a YBa2Cu3O7 (YBCO for short) superconductor was studied by potentiodynamic scanning in different aqueous solutions with 0.1 M concentration. The electrochemical stability of the YBC0 compound was found to be superior in sulfurous acid, NaC1, or KC1 solutions. The dissolution potential in the above solutions ranges from 36 – 92 mV, polarization wasn't possible. However, E raised up to 360 – 960 mV in acids corr solutions with oxidizing potential including suluric, phosphoric and nitric acids indicating a passive behavior. Polarization was observed in sulfuric, sulfurous, and phosphoric acids depicting their potential to be used as etching solutions in lithography of this oxide superconductor. Its electrochemical behavior in HC1 solution is peculiar and informative. It shows three transitions in the polarization curve, corresponding to 272, 756, and 1013 mV, respectively. This is probably related to the transition in the valence states of copper ions during dissolution which is suppressed in the oxidizing acids. In comparison with metallic copper, the YBCO is more stable in the above solutions. The Galvanic current decreases at the order of A1 > Cu > Ag, when the YBC0 is coupled with each of them in 1 M phosphoric acid solution.

Y-Ba-Cu-O thin films were used for CO2 laser detection. Operation of the Y-Ba-Cu-O detector in both the bolometric and nonbolometric modes were studied. It was found that the detectivity of the superconducting detector was competitive with conventional detectors. The speed was within the instrument resolution of 10 ns. The superconducting film quality is critical to the performance of these detectors.

An important class of electronic devices could be realized with current state-of-the-art high-Tc superconductor (HTSC) thin films if a method were found for the formation of multilevel structures separated by thin dielectric layers. It has been found that such structures can be formed with tantalum oxide as the spacer layer because of its high melting point (1870°C) and good chemical stability at the high temperatures commonly used to anneal thin films of YBaCuO superconductor. Good results have been achieved with thin films prepared by electron beam (EB) sequential deposition from Y, BaF2 and Cu targets onto oriented (100) strontium titanate substrates and oxygen furnace annealing at 850°C to promote the epitaxial alignment and growth of the superconducting crystalline phase. Two-layer structures have been formed by interposing a tantalum oxide barrier deposited by EB evaporation between two successive layers of HTSC films. The transition temperatures of both layers were checked by resistance measurements and found to display superconductivity after annealing. However, the top (second) layer was found to always show a reduced abruptness of the transition characteristic thereby indicating, perhaps, a lesser degree of epitaxial alignment since it makes no direct contact with the substrate surface.

Metalorganic chemical vapor deposition (MOCVD) has the potential of emerging as a major technique for the fabrication of high temperature superconductor devices. In this paper, we present preliminary results of in-situ deposition of Y-Ba-Cu-0 thin films (Tc = 79K) by rapid isothermal processing assisted MOCVD on BaF2/silicon substrates.