Thick (20–300 μm) freestanding polycrystalline films of ceramic YBa2Cu3O6.9 have been obtained by resintering YBa2Cu3O6.9 powder in air after screen printing onto fused silica substrates. An interfacial reaction occurs between the powder and the silica substrate which efficiently detaches the resintered film upon cooling. The magnetization and transport properties of these films are comparable to those for high quality bulk ceramic samples.

A layer of amorphous Mo–Al alloy is formed by ion-assisted solid-state interdiffusion reaction of a Mo/Al bilayer. Xe ion irradiation at 200 °C enhances the long-range diffusion of the dominant moving species while the formation of equilibrium compounds remains inhibited. The idea of using the temperature-dependent ion mixing at intermediate temperatures to promote a solid-state amorphization reaction opens the possibility of growing an amorphous phase in a system where both compound formation and interdiffusion are difficult

Copper/nickel multilayered thin-films prepared by electrodeposition have been examined in cross section by electron energy loss spectroscopy and high-resolution transmission electron microscopy. The results of the examinations provide the first direct experimental evidence of the large composition modulation across successive layers in the thin-film structure and the coherent nature of Cu/Ni interfaces.

Films of Y–Ba–Cu–O have been reproducibly prepared with metal stoichiometry near 1-2-3 by sputter deposition from a single sintered target. Twenty-seven depositions resulted in films with a standard deviation in composition of 1%. For 30 samples deposited on (100) SrTiO3 and annealed, the mean and standard deviation of the critical temperature, Tc (10% above ρ = ο), was 86.2 ± 1.4 K with a transition width (10–90%) of 1.8 ± 1.1 K. The composition and Tc were independent of film thicknesses from 0.09 to 2.5 μm. Critical currents were calculated for samples as a function of thickness from transport and from magnetization measurements. Within the considerable scatter observed of ± half an order of magnitude, the two methods agreed with each other over the thickness range studied. They were both fit with an initial Jc independent of thickness, t, for films up to about 0.3 μm thick followed by a 1/t decrease in Jc for thicker films. Metallographic examination of these films indicated microstructural features consistent with this behavior. Planar TEM images of 0.10 μm thick films showed that high Jc correlated with a film which predominantly has its c-axis normal to the film plane. An alternative structure was also seen, in which regions of the firm had their c-axis along each of the three 〈100〉 SrTiO3 directions, two in the film plane, and one normal to it. This type of film has a much lower Jc.

We propose in this work a new approach, named laser-induced forward transfer, for the rapid deposition and patterning in a clean environment of high Tc superconducting thin films. A stoichiometric high Tc compound is initially deposited in a thin layer on an optically transparent support by laser evaporation or another more conventional technique. By irradiating under vacuum or in air the precoated layer with a strongly absorbed single laser pulse through the transparent support, we are able to remove the film from its support to be transferred onto a selected target substrate, held in contact to the original film. Using this technique, we have successfully transferred with one single pulse, provided by an excimer or a Nd:YAG laser, YBaCuO and BiSrCaCuO precoated thin films on various substrates. The Rutherford backscattering spectrometry experiments do not show any strong modification in the composition of the transferred layer against the source material, and the superconducting phases for the two types of compounds were obtained after subsequent thermal annealing carried out in a furnace around 850–900 °C in O2. For the BiSrCaCuO films transferred onto MgO substrates, we have measured an onset critical temperature of about 90 K with a zero resistance at 80 K.

Gamma-ray-induced surface defects in YBa2Cu3Ox (x ≈ 7) have been investigated by thermally stimulated luminescence (TSL) following storage of the samples in dry (vacuum), oxygen, and 98% relative humidity environments. Irradiation of samples stored in either vacuum or oxygen environments shows that no insulating chemical species are formed on the surface of the superconductor. In contrast, exposure to the humid environment produces various chemical components on the surface, and, consequently, enhances the TSL yield. Comparison of the YBa2Cu3Ox, TSL glow curve and emission spectra with those of BaCO3 suggests that one of the components contributing to the purported YBa2Cu3Ox luminescence is BaCO3. Evidence for formation of other chemical species and the suitability of the TSL technique for their determination are discussed.

An amorphous Ni–B alloy was formed at the interfaces between layers of polycrystalline nickel and amorphous boron during electron-beam deposition of Ni/B/Ni trilayer structures. Formation of the amorphous alloy appears to be thermally-assisted and, in addition, the amorphous alloy regions can be extended by post-deposition ion-beam mixing. The existence of an upper limit to the thickness of the amorphous Ni–B alloy layer which forms (40 nm) indicates that the amorphous layer serves as a reaction or diffusion barrier. It has been shown for the first time that an amorphous metal-boron alloy is produced by thermal solid state amorphization reaction (SSAR).

The possibility of site-selective substitution of 18O into YBa2Cu3O7 was explored. Samples containing various quantities of 18O were prepared by processing in 18O2 both at 950 °C and at 400 °C. The samples were characterized by secondary ion mass spectroscopy (SIMS), temperature programmed desorption (TPD) and reduction (TPR), Raman spectroscopy, and magnetization measurements. Measurements of the shifts in the Raman active modes with 18O substitution and of the ratios of 18O to 16O by TPD, TPR, and SIMS show that even for temperatures as low as 400 °C and times as short as 2 h. 18O is not substituted exclusively into the chain site (O1) in YBa2Cu3O7. In addition, there is no consistent variation in the shifts in Tc with the degree of substitution; therefore, the isotope effect for a sample with 100% 18O cannot be predicted by a linear extrapolation of data obtained for samples with partial 18O substitution. The mechanism of oxygen substitution, the difficulties of measuring the true magnitude of the oxygen isotope shift, and the meaning of the small isotope shift are discussed.

A second order phase transformation in a dielectric ceramic superconductor is shown to relate jumps in physical properties to the ratio of state variables, i.e., to the phase boundary, near the critical point. The major jumps in specific heat, compressibility, permittivity, permeability, and spinodal composition curvature, between the normal and superconducting phases, are found from the continuity of the entropy, volume, electromagnetic fields (with zero fields), and chemical equilibrium. The thermal expansion, pyroelectric effects, and the piezoelectromagnetic effects are important differences between ceramic and metallic superconductors. The most important conclusions from experimental measurements are that the lattice plays a minor role in the superconductor transformation while the magnetoelectric jump may be related to the jump in permeability, i.e., the Meissner effect, and the jump in permittivity. The oxygen miscibility gap which controls order/disorder transformations thermodynamically mandate that only metastable compositions are obtained in the metal oxide, so absolute stability of the system may never be achieved. An explicit criterion to suggest other superconductor systems is given from magnetoelectric materials, i.e., some of the pervoskites.

The kinetics of the reactions that lead to the formation of YBa2Cu3O7−x was investigated starting from various powder mixtures containing different reactants as sources of Ba, Cu, and Y (BaCO3, BaO, CuO, Y2O3. Y2Cu3O5. and BaCuO2). These powders were calcined at 940 °C for various time intervals. Quantitative x-ray analysis was used to determine the relative amounts of the compounds present in the calcined powders. When BaCO3 was used as the source of barium, long calcination times were required to obtain the single phased YBa2Cu3O7−x because of the slow decomposition of BaCO3. This leads to large particles and broad particle size distributions and hence to a lower density of the sintered superconducting pellets. Procedures to attain high density superconducting material are identified on the basis of the kinetic studies. Each of them isolates the slow reaction in a first step and prepares the superconducting material via a rapid reaction in a second step. The kinetic studies reveal the reaction mechanisms that were followed in different cases.

We report the effect of inhomogeneities on the electrical resistivity and ac magnetic susceptibility in Aurivillius-like bismuth mixed phase oxides of the BiO–CuO–(Sr0.5,Ca0.5)O system and propose a crystal structure of the major phase having highest Tc. Nominal Aurivillius compositions with molar ratios of BiO/(Sr0.5,Ca0.5)O = 1/2 are superconductors with Tc ranging from 83 to 107 K, and are accompanied by a large expansion during sintering due to the formation of Kirkendall voids. Tc increases with decreasing of the c lattice parameter. An oxide BiSrCaCu2Ox (n = 2) shows a maximum Tc value of 107 K and an onset of superconductivity at a much higher temperature. It seems that the structure of Bi2Sr2CaCu2Ox consists of an Aurivillius-like phase having two perovskite layers and a Popper mixed phase. The ac magnetic susceptibility showed an overall decrease in susceptibility with time up to 220 days. This appears to be related to the relief of intralattice strain.

A method for preparing YBa2Cu3O7−x from the simultaneous thermal decomposition of the nitrates of yttrium, barium, and copper in an anhydrous fused eutectic of sodium and potassium hydroxide is described. This method eliminates the need for any mechanical grinding or the introduction of carbon containing anions. Products formed are fine powders (∼1 μm) having mole ratios 1.00Y:2.00Ba:3.06Cu.X-ray diffraction analyses reveal that the initial products are Y(OH)3, BaO2, and CuO, which when air calcinated/oxygen annealed at 900–950 °C form the superconducting YBa2Cu3O7−x A mechanism is postulated for product formation as a function of reaction conditions.

The reaction product from an oxide mixture of 1Pb:2Sr:0.75Y:25Ca:2Cu at 960 °C was nearly single phase. The crystal structure of a single crystal, selected from the reaction product, was determined from three-dimensional x-ray diffraction data. The stoichiometry was found to be Pb0.71Cu0.29Sr2(Y0.73Ca0.27)Cu2O7. The tetragonal lattice constants are a = 3.8207(4) Å, c = 11.826(1) Å, space group P4/mmm, Mr = 655.6, Z = 1, Dx, = 6.31 g cm−3, λ(MoKα) = 0.71069 Å. R = 0.0269 for 179 unique observed reflections. The crystal structure is isomorphous with the 1212 phases. The Pb ion at the origin has an occupancy of 0.705 (8) and a Cu ion is located at 0.221, 0, 0 with an occupancy of 0.295. The oxygen ion in the plane of the Pb ions is disordered over a fourfold site with an occupancy of one. An ordered arrangement of this oxygen ion results in a distorted environment for periodically repeated Pb ions. The Pb–O bond lengths to the two oxygen ions above and below the Pb plane are 1.968(14) Å. The Cu ion, displaced from the origin, can be considered as tetrahedrally coordinated. The four Cu–O bond distances in the CuO2 plane are 1.917(6) Å and the bond length to a fifth oxygen atom is 2.304(14) Å at the apex of the square pyramid. A valence sum calculation for Cu in square coplanar coordination yields a value of 2.01. A similar calculation for Cu in the tetrahedral site yields 1.5. Sr is in a monocapped square antiprism coordination polyhedron. Y and Ca atoms occupy statistically the same site and are in cubic coordination. The structure can be described as consisting of CuO2–(Y, Ca)–CuO2 layers with PbO6 octahedra flanking the layers and Sr in the oxygen interstice. The compound is metallic at room temperature and shows no superconducting transition to 20 K.

We have employed high spatial resolution (<50 nm) SIMS to study thin film deposited on SrTiO3, produced by pulsed laser evaporation of bulk stoichiometric YBa2Cu3Ox pellets derived from either BaCO3 or Ba3N2. The grain growth, film-substrate interaction, and carbon contamination of the films were examined as a function of post-deposition anneal temperature ranging between 700 °C and 900 °C. On the surface of both types of film, we found overgrowth crystals, which are enriched in copper, that increased in size from a few tenths of a micron to several microns with increasing anneal temperature. Above 800 °C, the film forms a polycrystalline structure with grain size of ∼1 micron. With increasing anneal temperature, more strontium was observed on the surface of the film. Films prepared from YBa2Cu3Ox targets derived from BaCO3 and Ba3N2 were both contaminated with carbon: however, only the former showed segregated carbon along the grain boundaries of the polycrystalline film annealed at 900 °C.

An electron microscopy study has been carried out to characterize the microstructure of a sintered Gd–Ba–Cu–O superconductor alloy. The GdBa2Cu3O7−x phase in the oxygen annealed sample is orthorhombic while in the vacuum annealed sample it is tetragonal. It is shown that the details of the fine structure in the [001] zone axis convergent beam patterns can be used to distinguish between the orthorhombic form and the tetragonal form. In addition to this matrix phase, an amorphous phase is frequently observed at the triple grain junctions. Gd-rich inclusions have been observed inside the matrix phase.

We show that the Al–Cu–Fe stable icosahedral crystal has an almost perfect icosahedral symmetry, and a reciprocal lattice of the body-centered cubic type.

Raman spectroscopy was employed to study Y–Ba–Cu–O films prepared by multilayer, reactive sputtering from separate Y, Cu, and Ba0.5Cu0.5 targets. A set of films having the composition YxBa2CuyOz with 0.7 < x < 1.8 and 2.8 < y < 3.5 and critical temperature with zero resistance, Tc(R = 0), ranging from 25 to 90 K was studied with the Raman technique. The correlation between Raman data and critical temperature, Tc, was investigated. This technique provides important information concerning the film crystallinity, homogencity, and impurity content (including other phases) which is useful in judging the quality of high Tc superconducting films. We also found that the rapid thermal annealing process is a very efficient way to reduce chemical reactions between the film and the substrate.

Phase formation in the system Bi–Sr–Cu–O has been examined as a function of composition, temperature, ambient atmosphere, cooling history, and annealing time. Ceramic processing and melt crystallization techniques were used. For the ceramic materials (using Bi2O3, SrCO3, and CuO) processed at 700 °C in air the Bi2Sr2CuO6 composition (221) crystallizes to a mixture of CuO, SrCO3, and the rhombohedral Bi2O3 · xSrO solid solution. At 800–830 °C in air for short durations (5 min to 2 h) the reacted products consist principally of the ideal 221 phase with minor amounts of CuO. For longer reaction times (2–400 h) the reacted products consist of the ideal 221-type structure with c = 24.64 Å and a = 3.804 Å, a “collapsed” 221 structure with c = 23.6 Å, and CuO. With increasing reaction time the “collapsed” 221 phase grows gradually at the expense of the ideal 221 phase. The “collapsed” 221 phase is not an oxycarbonate and appears to be a distinct ternary compound near the 221 composition, with a layered structure having a 1 Å smaller stacking repeat. The ideal 221 phase is a solid solution with variable Sr content. With decreasing Sr in the starting mixture [2 to 1.25 atoms per formula unit (afu)] we observe the following: (1) the formation of the “collapsed” 221 structure is inhibited; (2) for the ideal 221 phase the c-cell dimension decreases significantly (0.2 Å) and the a-cell dimension increases slightly (0.02 Å); (3) the low temperature resistivity behavior changes from superconducting with Tc onset of 6 K for Sr>1.5 afu to semiconducting for Sr > 1.5 afu; (4) the positions of the superlattice peaks around the (001) reflections become more incommensurate with respect to the parent structure. Rapid quenching (<5 s) from temperatures near the melting point (900 °C) can raise the superconducting Tc onset to 9 K. Independent of the cell variation with Sr content, quenching causes the c-cell dimension to expand by 0.03 Å on average while the a-cell dimension remains invariant. A small number of oxygen vacancies are quenched in from high temperature, and presumably originate in the Bi2O2 layer. As grown from the melt, crystals of the ideal 221 phase exhibit semiconducting behavior at low temperature; but with an additional high-temperature anneal in oxygen, metallic resistivity is restored with a superconducting onset near 5 K. Ca doping does not increase Tc in the ideal 221 phase. La and Y substitution occurs for Sr in the ideal 221 phase and ruins superconductivity.

There is controversy in the literature regarding the existence of the metastable γ′ phase with an ordered Ll2 structure in rapidly solidified Fe–Ni–Al–C alloys. In this study, the quench rate–metastable structure dependence was examined in the Fe–20Ni–8Al–2C (weight percent) alloy. The effect of silicon on the kinetics of phase formation was studied by adding two weight percent silicon to a base alloy of Fe–20Ni–8Al–2C. Samples were rapidly solidified in an arc hammer apparatus and examined by transmission electron microscopy. In the Fe–20Ni–8Al–2C alloy, the nonequilibrium γ′ and γ phases were found in foils 65 to 100 μm thick. At higher quench rates, i.e., thinner samples, the matrix was observed to be disordered fcc γ with K-carbide precipitates. Samples containing silicon were found to have a matrix composed of γ′ and γ structures when the foils were thicker than 40 μm. At higher quench rates, the matrix was disordered fcc γ with K-carbide precipitates. The nonequilibrium γ′ and γ structures are present in samples with or without silicon, but are observed at higher cooling rates with the addition of silicon. This sensitivity to cooling rate and composition in resulting metastable structures may explain the differences reported in the literature for these rapidly solidified materials.

The Raman line at 1430 cm−1 (M-line) in single crystal La2CuO4−y was studied as a function of doping, temperature, magnetic field, and excitation wavelength. Upon Li doping the line becomes broader, and it vanishes rapidly with Sr-doping. The line also broadens with increasing temperature and increasing applied magnetic field. Resonance enhancement was found for decreasing laser excitation energies but was not as pronounced as the enhancement of several alleged two-phonon lines. Many of these features are correlated with the 2D antiferromagnetic ordering measured in this system by neutron scattering. The possible identification of this line as a one-spin excitation is favored by the data though a two-phonon excitation is also considered.