Superconductivity near 30 K in the La-Ba-Cu-O system, first observed by Bednorz and Müller [1], was soon found to be attributable to the K2NiF4-type (at room temperature) compound La(2-x)BxxCuO4 [2]. Substitution of Sr and Ca for Ba yielded superconducting systems, also with high superconducting transition temperature Tc. Replacement of La by Y led to the discovery of the 90 K superconductors.

The temperature dependent magnetization, M(T), of superconducting BaErCuO and BaYCuTiO was measured via the BTi SQUID susceptometer. In the zero field cooling case, M(T) of BaErCuO was found to be similar to that of Pb. But, M(T) of BaYCuTiO was found to decrease rapidly with T and be almost linear in T. However, in the field cooling case the fluxoids were found to be trapped at all T below Tc, and its amount was found to depend on Ts at which the sample starts to be cooled, as observed in Pb. The ergodic limiting points were not observed within the chosen parameters. The irreversibility of magnetization observed in both BaErCuO and BaYCuTiO is attributed to the fluxoids, trapped during the field cooling process.

We report measurements of the reflectivity of bulk samples, films and single crystals of high Tc materials. The data are fitted with the Mattis-Bardeen theory to obtain gap values. For sintered samples we find 2Δ/kTc = 2.6, while for YBa2Cu3O7-y films and single crystals 2Δ/kTc = 6.4 and 7.7 respectively.

Polarized Raman scattering spectra at 300K and 20K are reported for a single crystal of La2CuO4-y before and after annealing in oxygen at 1000°C for 24 hours. Oxygenation strongly quenches the temperature sensitive line at ∼1430 cm-1 (for T ∼ 300K) in the “as grown” crystal, previously identified with magnon-pair excitation associated with two-dimensional antiferromagnetic ordering. In addition, the phonon spectrum is greatly modified by the addition of oxygen, indicating a more uniform local crystalline environment after oxygenation. Raman scattering is thus a sensitive probe of the effect of oxygenation on the near surface magnetic and phonon properties of La2CuO4-y.

We report low and high field vibrating sample magnetometry results and resistance measurements on a highly oriented, single-phase sample of Y1Ba2Cu3O7−x. We find no anisotropy for the low-field (1mT) Meissner effect or trapped flux. Ratios for high field (to 1.9 T) and ρab/ρc are ∼ 2 and 3.6 respectively. Both are different from single-crystal results, a difference we attribute to grain boundary effects.

We have fit our first principles LAPW band structure results for the high Tc superconductor La2CuO4 to a tight-binding Hamiltonian that contains s, p, and d interactions from the three components of these materials. Our fit reproduces very accurately the 17 lower bands of this material and especially the Fermi surface.

The shape of the normalized temperature derivative of the dc susceptibility provides useful information about superconducting materials. We propose that the position of the derivative peak be defined as the transition temperature Tc and the width of this peak define its sharpness.

Low-field non-resonant microwave absorption in an EPR spectrometer has been observed in the superconducting state of different samples of the new high-T oxides, YBa2Cu3O7-δ and La1.8Sr0.2CuO4. It has been attributed to flux slippage occurring at the Josephson junctions existing in the granular composite material. The dependence on particle size, temperature, microwave power, DC modulation amplitude and magnetic field has been studied.

We have measured the specific heat, C, in the temperature range 0.3 to 20K and in magnetic fields up to 12 Tesla of several compounds related to the high-Tc superconductors. The linear term in C for YBa2Cu3O7−x is only weakly dependent on oxygen concentration in the range 0 ≤ × ≤ 0.7. The linear term in C changes by less than 10% at 10 Tesla for La1.98Sr.02CuO4, whereas for YBa2Cu3O7−x it is obscured by additional field-dependent structure. Magnetic ordering anomalies are observed in YBa2Cu2O5 at 10.6 K and in BaCuO2+6 at 9.3 K.

We have performed semiempirical tight-binding calculations of the electronic structure of YBa2Cu3O7, with dand s orbitals included for all the metal atoms and p and sorbitals for oxygen. Here we report studies of oxygen vacancies on the O(1) chain sites in YBa2Cu3O7-y. The modification of the density of states ρ(E) and the shift of the Fermi energy Ep were calculated for 0 < y ≤ 1.0. The Fermi energy is found to increase monotonically with y, confirming the expectation that oxygen vacancies act as donors. Also, ρ(EF)is found to decrease with y.

Via electrical property measurements (conductivity, thermopower) at 700°C on sinter-forged YBa Cu O, it was YBa2Cu3O7−x, it was determined that conduction occurs via small polaron conduction in the tetragonal phase. From the thermopower and oxygen content the distribution of copper valence states was determined.

Electron energy loss measurements on superconducting oxides are correlated with an acoustic plasm on branch whose energy and width is highly sensitive to the alloy composition. Changing oxygen content reveals structure in the electron cross section which tracks the changes in the superconducting transition temperature.

The heat capacities of single phase samples of Ba2DyCu3O7 and Ba2ErCu3O7 which were prepared by the method of powder-calcination have been measured over the temperature range 13–300 K by using a laboratory-made adiabatic calorimeter. A typical second-order type of anomaly was observed due to the superconducting phase transition at 92.5 K in Ba2DyCu3O7 and at 91.2 K in Ba2ErCu3O7. From the heat capacity jump at the transition temperature, the electronic heat capacity coefficient was estimated as 30 mJ·K-2.mol1 for Ba2ErCu3O7 and 32 mJ·K-2. mol-1 for Ba2ErCu3O7. Large differences were found in the low temperature heat capacities between the two samples, which were analyzed on the basis of Schottky-type of anomalies owing to the magnetic ions of Dy and Er.

There is considerable interest in the interplay, of superconductivity and magnetism in La2CuO4. Several groups [1–3] have noted signs of superconductivity in nominal La2CuO4, and antiferromagnetism has been reported[4] in La2CuO4-y with y>0. The superconductivity previously reported was of a filamentary nature because although resistance drops to near zero were observed, only small Meissner effects (∼10-3 to 10-4 of perfect diamagnetism) were observed. In this paper we describe our studies of. ceramic samples of La2CuO4-y, loaded with oxygen by high pressure. This technique results in substantial incorporation of O2 in the material (of the order of 0.3 to 0.4% by weight) and in gross changes in the bulk resistivity and magnetization as well as discernable changes in the lattice parameters of the material.

A systematic study of the influence of oxygen depletion on the carrier concentration and the occurence of superconductivity in a single-phase 1–2–3 Y-Ba-Cu-Oxide material is presented. This is accomplished by successive measurements of the Hall and electrical resistivities, ac-susceptibility, and x-ray diffraction on the same sample, in which the oxygen deficiency is controlled and determined from thermogravimetry. With increasing oxygen depletion, we monitor how the 93K orthorhombic superconductor, with an estimated carrier concentration of 0.6·1022 carriers/cm3 at 100K, is transformed into a tetragonal semiconductor with a very low carrier concentration.

Spectra of the oxygen K-edge extended x-ray absorption fine structure (EXAFS) of the superconducting compound Y-Ba-Cu-O were obtained by measuring the total electron yield as a function of incident x-ray energy at temperatures between 77K and 300K. This technique affords a convenient way for probing the local environment around the oxygen atoms and soft modes in the lattice.

Bulk samples of YBa2Cu3O7−x have been homogenously irradiated with 3 MeV electrons at temperatures below 20 K. Whereas the superconducting transition temperature, Tc, drops dramatically with increasing dose the width of the transition remains unchanged (Δ Tc ≤ 1.5 K). The normal state resistance at 100 K increases substantially during the electron irradiation. Several irreproducible experiments can be interpreted with a radiation induced, unstable increase of Tc.

We report the first combined high pressure (up to 30 kbar) and low temperature (10 K - 300 K) single crystal X-ray diffraction study of the tetra-gonal-orthorhombic transition in La2−xCuO4-δ(x=0.12). Superstructure reflections of the orthorhombic phase were used to characterize the transition. The transition temperature, TT–O, is found to decrease under pressure and the orthorhombic phase is suppressed above about 15 kbar. These results confirm that both phases are superconducting and suggest to attribute a previously reported kink in dTc/dP to different rates of increase of Tc for the tetragonal and orthorhombic phases.

The interactions of YBa2Cu3O7-δ type high Tc superconductors with other metals and oxides are of significant technical importance because of the need for i) proper stabilizing normal metal for composite superconductor wire, ii) nonreactive crucible materials for melt processing or crystal growth, and iii) suitable nonpoisonous substrate materials for thin film/thick film superconducting devices. For these reasons, and also for the purpose of exploring possible improvements in Tc, Jc and mechanical properties, the effects of various metal and oxide additions (1–40% by weight) have been investigated. It is shown that many of the elements in the periodic table deteriorate the superconducting properties to a various degree ranging from a broadened transition or reduced Tc to a complete elimination of the superconducting behavior. However, silver, gold and cadmium were relatively benign or slightly improved the properties. These benign materials have potential for practical application in superconducting composites.

We have performed Rutherford backscattering spectroscopy (RBS) and axial channeling on single crystals of the high-temperature superconductor YBa2Cu3Ox. The results demonstrate good crystal quality and cation stoichiometry in the as-grown samples. We observe some surface disorder, and estimate from the surface-peak intensities that there is roughly one formula unit of misregistered atoms per unit cell, or one molecular monolayer of surface disorder.

We have studied the surface disorder induced in these crystals by various surface processing treatments, and have tried to achieve solid-phase epitaxial regrowth of disordered surface layers. Preliminary results have been obtained on the annealing of 100 nm amorphous layers formed on the surface of single crystals by 30 keV oxygen ion implantation. The Ba in the amorphous layer was found to segregate strongly to the surface for annealing temperatures as low as 500°C, although the crystalline phase does not decompose even at much higher temperatures.