High quality bulk YBa2Cu3O7−x was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated (900 °C, 18–24 h in air, followed by 500 °C, 5 h in O2). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnet response (field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly.

High Tc Tl–Ba–Ca–Cu–O (A) and Tl–Ba–Sr–Ca–Cu–O (B) superconducting filaments were successfully prepared using a technique in which suspension spun and pyrolyzed filaments were densified by pressing and sintering. A zero resistance state was achieved at 112 K and 106 K, and the maximum Jc at 77 K, 0 T was 1200 A/cm2 and 2300 A/cm2 for Tl–Ba–Ca–Cu–O (A) and Tl–Ba–Sr–Ca–Cu–O (B) filaments, respectively. Although the starting powder had a high Tc phase of Tl2Ba2Ca2Cu3Ox, the structure of the filament with high Jc was a high Tc phase of Tl1Ba2Ca2Cu3Ox, due to the volatility of Tl oxide from the large surface area of the filament.

Thin-films of barium titanate (BaTiO3) have been deposited onto single-crystal MgO substrates using pulsed-laser ablation. The early stages of film growth have been examined using transmission electron microscopy by deposition of very thin films onto specially prepared electron transparent thin-foil substrates. The films, which were crystalline as deposited and close to stoichiometric composition, were formed by the nucleation and growth of small islands.

YBa2Cu3Ox was deformed from 850 to 980 °C in oxygen partial pressures of 103 to 105 Pa. Steady-state creep rate, ̇, for P(O2) from 104 to 105 Pa could be expressed as ̇ = Aσ1.0 (GS)−2.8±0.6 exp −(970 ± 130 kJ/mole)/RT, where A is a constant, σ the steady-state stress, GS the average grain size, and R and T have their usual meanings, For P(O2) from 103 to 3 ⊠ 103 Pa, the activation energy decreased to about 650 kJ/mole and for a given temperature creep kinetics were much faster. The data and microscopic observations indicated that creep occurred by diffusional flow. Comparisons with diffusion data for YBa2Cu3Ox suggested that Y or Ba may be rate-controlling diffusing species.

The effect of heat treatment on microstructure development in Ba2YCu3O7−x films prepared from metal trifluoroacetate precursors is investigated. The growth of textured Ba2YCu3O7−x on BaZrO3 substrates is shown to be strongly influenced by the furnace atmosphere used during calcination. Differential thermal analysis was used to show that conditions that promote c-axis texture are also those which cause partial melting of Ba–Y–Cu–O compositions that are depleted in barium relative to Ba2YCu3O7−x.

Raman scattering experiments have been carried out on sintered pellets of YBa2Cu3−16O7−x and YBa2Cu318O7−x. The latter samples were obtained both by gas exchange and by growth with substituted oxides. Three of the observed Raman modes arise from motion of the oxygen atoms only and have nominal frequencies of 500, 435, and 340 cm−1 at room temperature in the 16O compound with x = 0. The frequencies of these modes shift significantly with oxygen isotope exchange, and these frequency shifts have been measured for several sets of samples. The results indicate that in samples prepared primarily by gas exchange the degree of exchange on the O(2) and O(3) planar sites is greater than the degree of exchange on the bridging O(4) site. Linewidth measurements have revealed that the O(4) phonon (500 cm−1) is significantly broadened by 18O exchange, and this is attributed to a random occupation of the O(4) site by 18O and 16O. The results are discussed in the context of recent measurements of oxygen diffusion in YBa2Cu3O7−x and a proposed mode for the oxygen exchange mechanism. Measurements have also been carried out on YBa263Cu316O7−x and YBa265Cu316O7−x. The results confirm that the Raman mode at 150 cm−1 arises from motion of the Cu(2) planar copper atoms.

The reactants produced at the start of the reaction of YBC with water include Y2O3, Ba(OH)2, BaCu(OH)3, and Cu2O. The compound Ba(OH)2 changes to form BaCO3, BaC2O4, and Ya(COOH)2 by reacting with CO2 present in the water. Compounds such as BaCuO2, CuO, and Y2BaCuO5 were then produced by reactions among such reactants as Y2O3, Ba(OH)2, BaCu(OH)3, and Cu2O.

Stoichiometric deviations of up to ±5% in Ba2YCu3O7−δ, thin films grown by coevaporation on LaAlO3(100) substrates are found to cause (1) a decrease of the critical current density (Jc) of up to an order of magnitude, (2) a depression of the critical temperature (Tc) and a broadening of the superconducting transition width (ΔT), (3) a deterioration of the surface morphology, and (4) a decrease in the crystallinity of the films. The data indicate that composition deviations of greater than ±1% result in degradation of film quality. These findings have significant implications for the degree of composition control required during deposition to produce films with optimized properties.

We show that magnetic flux lattice interactions are important at fields above a few thousand gauss. These interactions interfere with thermally activated current-induced flux bundle hopping and reduce the superconductor's flux creep resistance below that estimated from the standard flux creep models (which assume completely independent hopping). We find that the flux bundles can hop independently at the low fields at which, e.g., antennas and SQUID detection coils would be used, but interact very strongly at fields typical of magnet applications.

The atomic structure of liquid-quenched amorphous Al90FexCe10−x (x = 5,7) was studied by pulsed neutron and x-ray scattering. The atomic pair-density function determined by pulsed neutron diffraction indicates that a significant portion of Al–Fe distances is anomalously short, while some part of the Al–Al distances is anomalously long. Both neutron and x-ray scattering showed the presence of a prepeak in the structure factor. These results suggest that a strong interaction between A1 and Fe modifies the structure of this glass, leading to chemical and topological short-range ordering.

The effects of additions of Fe and Zn on the relative stabilities of the cubic L12 and tetragonal DO22 structures in TiAl3- and NbAl3-base alloys are evaluated using ab initio electronic band calculations. The Fe or Zn distribution on the aluminum sublattice is modeled by a periodic array which corresponds to alloying additions of 12.5 or 25 at.% Fe or Zn. Addition of 12.5 at.% Fe is sufficient to stabilize the L12 structure in both TiAl3- and NbAl3-base alloys. Interpolation of the structural energy differences suggests that the DO22 and L12 structures have the same energy at ∼4.5 at.% Fe in Ti(Al, Fe)3, in agreement with experiment,1,2 and at ∼11 at.% Fe in Nb(Al, Fe)3. The L12 stabilization effect per atom of Zn in Nb(Al, Zn)3 is approximately half as large as that of Fe. The stable structure is the one for which the Fermi energy lies in a minimum in the density-of-states (DOS) distribution, as in the binary compounds. The results are explained on the basis of a simple model involving charge transfer to alloying additions on the Al sublattice.

Cryomilling (high intensity mechanical ball milling in a liquid nitrogen bath) of the B2 crystal structure nickel aluminide leads to a NiAl composite containing about 10 vol.% of AlN particles. This is the result of a reaction milling process, where nitrogen incorporated into the matrix during cryomilling reacts with Al during subsequent thermomechanical processing to form the composite. Compressive testing at 1300 K of such materials densified by 1505 K extrusion or isostatic pressing at 1323 K or 1623 K indicated that strength at relatively fast strain rates (>10−7 s−1) is slightly dependent on the method of consolidation. At slower rates, however, no clear dependency on densification technique appears to exist, and four different consolidation methods possessed similar creep strengths. In all cases deformation at 1300 K occurred by two distinct mechanisms: at high strain rates the stress exponent is greater than 11 while at slower rates (<10−7 s−1) a much lower stress exponent (∼6) was found. Comparison of density compensated creep strengths reveals that the properties of NiAl–AlN are similar to those of the single crystal Ni-base superalloy NASAIR 100.

Fine Ni particles were directly prepared from Ni(NO3)2 and NiCl2 aqueous solutions by the spray-pyrolysis technique under an H2-N2 atmosphere. Hollow Ni particles with rough surfaces were obtained at a low reaction temperature (700–900 °C). With increasing reaction temperatures from 900 °C to 1500 °C, the particles varied gradually to solid ones with a smooth surface, and the particles obtained at 1600 °C were perfectly spherical ones whose average size was ∼0.6 μm. From the point of view that aggregation free powders are considered to be good for thick film applications, Ni(NO3)2 was preferred to NiCl2 as a starting material. The perfectly spherical particles derived from Ni(NO3)2 gave a Ni film about 3 μm in thickness having sheet resistance of 37.7 mΩ · square−1.

The chemical stability of the surface of stainless steel (SUS) 304 in acid immersion tests is greatly improved by the laser implant-deposition (LID) process, i.e., the simultaneous deposition and incorporation of silicon by KrF excimer laser irradiation. The etching depths of the treated samples in 1.32 N HCl solution are substantially zero at the laser irradiation conditions of more than 40 pulses and of more than 400 mJ/cm2 at the surface. By the quantitative verification of cathodic polarization in 1 N H2SO4, the highest polarization resistance is estimated to be 26.7 times that of the nontreated sample.

This paper reports a study of the structure and fracture mode of Pt3Ga. The results show that the structure of this compound is a tetragonal distortion of the L12 structure with lattice parameters of a = 5.47 Å and c = 7.89 Å. If the gallium concentration decreases from 22.8 at.% to 21.5 at.%, a disordered face-centered cubic phase also forms. This phase is Pt-rich and appears to form along the grain boundaries of the Pt3Ga phase. The fcc phase can also contain coherent Pt3Ga precipitates. Single phase Pt3Ga fails in a very brittle manner, and the fracture mode is intergranular. Boron additions have no effect on the fracture mode, since boron does not segregate to the grain boundaries. The fracture of an alloy containing a small amount of the disordered fcc phase is also brittle, but the fracture mode is predominantly transgranular.

The electrical resistivity of potassium-graphite intercalation compounds (K–GICs) was measured in the course of reactions with ammonia, oxygen, water, etc, The hydrogen absorption behavior at 77 K was also investigated on K–GICs before and after the reactions. The electrical resistivity of KC8 increased by reactions with ammonia, furan, and water vapor, whereas almost no change was observed in the case of the reaction with oxygen. Molecules of ammonia, furan, and water are considered to penetrate into the KC8 interlayers, while oxygen draws potassium from interlayer spaces toward the surface with resultant potassium-diluted mixed stage compounds. The hydrogen absorption isotherms of K(NH3)xC31 (0 ≤ x ≤ 2.65) at 77 K showed that the saturated amount of absorbed hydrogen, (H2/K)sat, decreased linearly with increasing ammonia content, x, When x went up to 2, (H2/K)sat became zero. Similar behavior in the degradation of the hydrogen absorption capacity of K(H2O)xC25 (0 ≤ x ≤ 1.3) was observed. Contrary to such behavior, partially oxidized KC24 could not absorb hydrogen gas. These facts are also explained by taking into account the fact that ammonia and water molecules penetrate K–GICs, while oxygen draws potassium atoms toward the surface, as predicted from the electrical resistivity measurements. Successive oxidation and heat-treatment processes made KC8 more able to absorb hydrogen, while similar processes of ammoniation and hydration followed by heat-treatment did not.

Silicide formation due to thermal treatment of thin (5–10 nm) molybdenum films on single-crystal, polycrystalline, and hydrogenated amorphous silicon substrates in the temperature range of 100 to 1000 °C was studied, with an emphasis on the initial interactions. The molybdenum deposition, annealing, and characterization using Raman scattering and Auger electron spectroscopy was carried out in UHV in order to minimize the effects of contaminants. Raman spectroscopy is used to distinguish between tetragonal (t-MoSi2) and hexagonal MoSi2 (h-MoSi2). The Raman spectrum of bulk tetragonal MoSi2 exhibits two prominent lines which are associated with the A1g (325 cm−1) and Eg (440 cm−1) modes. The only silicide phases detected in the thin film experiments were t-MoSi2 and h-MoSi2. While hexagonal MoSi2 does not appear in the bulk phase diagram, it is the first silicide phase formed in thin film reactions at a temperature between 300 and 400 °C. The nucleation temperature of h-MoSi2 was the same for Si〈100〉, Si〈111〉, and amorphous Si. Indirect evidence for disordered intermixing of silicon and molybdenum before nucleation of h-MoSi2 is found. Annealing at approximately 800 °C causes the silicide to transform from the hexagonal phase to the tetragonal phase for all substrates. Contaminants interfere with the formation of h-MoSi2 and also retard the transformation of h-MoSi2 to t-MoSi2. For the thin films considered here, the transformation to t-MoSi2 is accompanied by islanding of the silicide film. A lower interfacial energy between the silicon and silicide for h-MoSi2 has been proposed to explain the nucleation of h-MoSi2 before t-MoSi2.

The microstructures of carbon-rich regions in chemically vapor deposited SCS-6 SiC fibers have been studied by electron diffraction and high resolution transmission electron microscopy. The microstructures of the carbon in the substrate filament and the outer coating layers of the fiber are consistent with different distributions of Oberlin's model of Basic Structural Units (BSUs)1 while that of the inner substrate coating is consistent with turbostratic carbon (TC).

Results of a study of compositional, optical, electrical, and structural properties of hydrogen amorphous silicon carbide (a-SiC:H) prepared, respectively, by glow-discharge (GD) and reactive sputtering (SP) techniques at power densities varying between 1.25 · 10−2 and 1.25 · 10−1 W · cm−2 for GD samples are presented. Measurements are reported on the composition, optical and IR spectroscopy, and on the temperature dependence of electrical conductivity. All experimental observations suggest that the power density only slightly affects the physical properties of GD silicon-rich samples, whereas those of the carbon-rich SP samples depend more strongly on this deposition parameter. Finally, it is shown that the GD technique can provide films with better characteristics, whereas samples of similar composition prepared by sputtering have higher compositional disorder and are more inhomogeneous.

Auger electron spectroscopy and low energy electron diffraction have been applied to the study of the structure and thermal stability of the Pt/β–SiC(001) interface. The morphology of the interface appears to be governed by the competition among surface diffusion, intermixing, and chemical reaction. An ultrathin Pt layer (8 Å thick) deposited on a substrate at low temperature is laterally uniform with some degree of intermixing across the interface. Brief anneals at 1000 °C result in aggregation of the Pt into islands interspersed with essentially bare SiC. Higher temperatures lead to reaction of the aggregated Pt to form Pt silicide and release free C. The reaction is signaled by characteristic changes in the Si LVV and C KLL Auger line shapes and by the appearance in LEED of a (2 ⊠ 2) pattern (believed to arise from ordered PtSi) and of diffraction rings from oriented polycrystalline graphite. Subsequent deposition of Si and annealing leads to regeneration of SiC by reaction with the free C. These results contrast with those for ultrathin Pt on Si(001) and on α-SiC(0001) which are dominated by the rapid indiffusion of Pt during annealing. A detailed model is presented for the growth and annealing dependence of the Pt/β–SiC(001) interface.