Power compensated differential scanning calorimetry, transmission electron microscopy, and density measurements were used to characterize relaxation phenomena associated with structural transitions in electron beam evaporated amorphous silicon thin films. Two transitions were observed in the amorphous films upon heating: a broad exothermic process below 600 K and an endothermic step beginning at 600 K. The broad exothermic process is due to the relief of bond distortions. The endothermic step is related to homogenization and densification of the structure of the amorphous silicon.

The structural energy differences between cubic LI2 and tetragonal DO22 crystal structures are calculated for MAl3 compounds, where M is a group III, IV, or V transition metal. The stability of the DO22 structure relative to L12 increases rapidly as the transition-metal d-electron count increases. Typical values of E(DO22) – E(L12) are 0.1–0.15 eV/atom (9600–14500 J/g-atom) for group III,  0.05 eV/atom ( 4800 J/g-atom) for group IV, and ∼ –0.2 eV/atom (∼ –19000 J/g-atom) for group V trialuminides. Similar trends are calculated for the DO23/L12 energy difference. The calculated electronic densities of states (DOS) show that each structure has a minimum in the DOS distribution at a characteristic d-electron count. The preferred crystal structure for a given compound is the one in which the Fermi level lies in the minimum.

Thin films of Y–Ba–Cu–O and Yb–Ba–Cu–O, 0.5–1.5 μm in thickness, were deposited onto (211) and (100) SrTiO3 single crystal substrates by metalorganic deposition (MOD). After deposition the samples were annealed either by conventional furnace annealing or rapid thermal annealing (RTA). The microstructures of these films were then characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive x-ray spectrometry (EDS). Grain size of the annealed films varied from 0.25 to 1.0 μm. Improved superconducting properties were found for the RTA samples, compared to furnace annealing, and were attributed to larger grain size, little strontium diffusion into the thin films from the substrate, and highly preferred orientation of the 1:2:3 phase.

The epitactic nature of the growth of YBa2Cu3O6+x (YBCO) superconducting thin films on ceramic substrates has been studied using high-resolution electron microscopy (HREM) and selected-area diffraction (SAD) of cross-sectional specimens. The films were grown in situ on (001)-oriented MgO and (001)-oriented Y2O3-stabilized cubic ZrO2 (YSZ) single-crystal substrates by electron beam evaporation. Both of these materials have large lattice misfits with respect to YBCO. Different orientation relationships were observed for films grown on the two types of substrates. These orientation relationships are shown to provide the best matching of the oxygen sublattices across the substrate-film interfaces. A crystalline intermediate layer, 6 nm thick, between the YBCO film and YSZ substrate was observed by HREM and shown by EDS to be a Ba-enriched phase, possibly barium zirconate formed by a reaction. In contrast, the YBCO–MgO interface was found to be sharp and free of any intermediate layers.

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.

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.

Two YBa2Cu3O7−x powders were investigated: one was nearly stoichiometric, and the other, CuO-rich. After being sintered at 950 °C, samples from both powders were heat-treated in oxygen at 845, 860, and 910 °C for up to 10 days. The samples were characterized by differential thermal analysis, x-ray diffraction, optical and scanning electron microscopy, iodometric titrations, and measurement of their superconducting properties (electrical resistivity, critical temperature, and critical current density). The electrical properties of the nearly stoichiometric material improved with time at all temperatures. On the other hand, the electrical properties of the CuO-rich material deteriorated with temperature, possibly owing to problems associated with grain growth at 910 °C.

Samples of YBa2Cu3O7 were prepared by sol-gel, co-precipitation, and solid state processes. Sol-gel samples were prepared from a solution of yttrium, barium, and copper nitrates dissolved in ethylene glycol, co-precipitated samples were made by the amorphous citrate method, and solid state samples were prepared by conventional high temperature reaction of the appropriate metal oxides and carbonates. The sol-gel process was shown to yield superconducting samples of superior Meissner effect, critical current, and critical field. The co-precipitated samples contain impurities that affect the critical properties. The sol-gel and co-precipitated processes yield materials with well-formed, plate-like particles with a fairly uniform size of about 10 μm. The grains in the solid state sample are smaller but have a much wider distribution of sizes than the samples prepared by solution methods.

The superconducting properties of the system Bi1−xPbxSrCaCu2Oy have been studied as a function of lead concentration and preparation conditions. Energy dispersive x-ray analysis indicates the nominal stoichiometry is preserved up to x = 0.2 and for this concentration, zero resistance occurs at 97 K. Magnetically modulated microwave absorption measurements provide a global probe of the samples and show that resistance measurements alone can give a false impression of the quality of the materials.

Combinations of inert atmosphere sintering and oxygen atmosphere sintering have previously been reported as necessary for the synthesis of LaBa2Cu3Oy superconductors which achieve zero resistance at temperatures above 90 K. Sintering under oxygen atmosphere only is known to produce La(1+x)Ba(2−x)Cu3Oy, in which La is substituted for Ba in the crystal lattice. The latter substituted compounds achieve zero resistance at temperatures well below the boiling point of liquid nitrogen. In this work, we show that during the initial inert atmosphere sintering step, LaBa2Cu3Oy powder decomposes, in part, into several intermediate compounds. These compounds are then recombined in the subsequent oxygen atmosphere sintering step to form LaBa2Cu3Oy, which achieves zero resistance at temperatures above 90 K. We propose that the net effect of these two processing steps is to inhibit the substitution of La for Ba in the lattice of the fully processed material.

The 2223, 1223, 1324, and 1122 phases in the Tl–Ca–Ba–Cu system were prepared from sample mixtures having the same stoichiometry as the final phase. Powder x-ray diffraction analysis was used to follow the formation of these phases at 867 °C for up to 2 h. The formation of the 2223 phase is shown to occur via the sequential transformations 2021 → 2122 → 2223. For the 1–2–2–3 and 1–3–2–4 samples, the sequential transformations 1021 → 2021 → 2122 → 2223 occur before the final 1223 and 1324 phases are obtained. For the 1122 phase the formation is preceded by the 1021 → 2021 → 2122 transformations. Using scanning electron microscopy, a phase with a glassy appearance was detected in many of the reacted samples. This “glassy” phase appears to be a precursor in the formation of the Tl–Ca–Ba–Cu phases.

Uniform spherical colloidal particles of mixed internal composition were obtained by aging at 90 °C solutions containing Cu(NO3)2 + Y(NO3)3 and Cu(NO3)2 + La(NO3)3, respectively, in the presence of urea. The molar ratio of metal ions in the solids precipitated from a given solution varied with the reaction time. After sufficiently long aging, this ratio corresponded closely to that in solutions in which the particles were generated. The original precipitates consisted of basic carbonates, which on calcination converted to mixed oxides of defined composition.

It is shown that a binary alloy with an AB3 stoichiometry on a bcc lattice may develop various combinations of B2 and DO3 order along its kinetic path toward equilibrium. The temporal evolution of these two order parameters is analyzed with an activated-state rate theory. Individual vacancy jumps are treated in a master equation formalism that involves first-nearest-neighbor (1nn) and second-nearest-neighbor (2nn) interactions. In our formulation, a set of coupled differential equations is obtained describing the time-dependence of six order parameters. These equations were integrated numerically for a variety of interatomic interactions and initial conditions. It was found that the relative rates of B2 and DO3 ordering, and hence the path of the alloy through the space spanned by the B2 and DO3 order parameters, depend on the relative strengths of the interatomic interaction potentials and on the temperature. For very strong 2nn interactions, a transient B32 structure was observed to develop at early times, although this phase disappeared as equilibrium was approached.

Rapidly quenched powders of Fe3Al were subjected to thermal annealings at temperatures well below the critical temperatures for B2 and DO3 ordering. X-ray diffractometry was used to measure the subsequent evolution of B2 and DO3 long-range order. It was found that the relative rates of change of B2 and DO3 order parameters were temperature dependent; hence at different temperatures the alloy passed through different states of order en route to thermal equilibrium. These temperature dependences of “kinetic paths” can be understood in terms of a theory of kinetic paths based on the kinetic master equation. The theory indicates that the temperature dependence of the observed kinetic paths originates from having first-nearest-neighbor interactions that are stronger than second-nearest-neighbor interactions. This seems consistent with previous thermodynamic analyses of critical temperatures of Fe3Al.

CuTi was irradiated with 1-MeV Ne+, Kr+, and Xe+ in the temperature range from 150 to 563 K. The volume fraction of the amorphous phase produced during room temperature irradiation with Ne+ and Kr+ ions was determined as a function of ion dose from measurements of the integrated intensity of the diffuse ring in electron diffraction patterns. The results, analyzed by Gibbons' model, indicate that direct amorphization occurs along a single ion track with Kr+, but the overlapping of three ion tracks is necessary for amorphization with Ne+. The critical temperature for amorphization increases with increasing projectile mass from electron to Ne+ to Kr+. However, the critical temperatures for Kr+ and Xe+ irradiations were found to be identical, and very close to the thermal crystallization temperature of an amorphous zone embedded in the crystalline matrix. Using the present observations, relationships between the amorphization kinetics and the displacement density along the ion track, and between the critical temperature and the stability of the irradiation-induced damage, are discussed.

Multilayers of Mn/Bi were irrradiated with 400 keV Xe+ at temperatures from 80 to 550 K. Ferromagnetic MnBi layers oriented perpendicular to the substrate surface were formed directly at mixing temperatures from room temperature (RT) to 500 K. The measurements of Curie point and optical Faraday rotation revealed that 60–70 at. % of MnBi ion-mixed at RT is the metastable phase (QIITP: quenched high temperature phase). The fraction of QIITP is reduced with increase in mixing temperature. It was also found that ion beam mixing yields a pronounced protection effect against the deterioration of MnBi in a moist atmosphere. A detailed discussion is given on the kinetics of ion beam mixing and the growth mechanism of the metastable MnBi grains.

The effects of the addition of chromium on several properties of Fe3Al, including tensile strength and ductility, fracture behavior, and slip and dislocation characteristics, were studied. Alloying with up to 6 at. % chromium results in an increase in room temperature ductility from approximately 4% to 8–10%. Along with this increase in ductility, the addition of chromium produces a change in fracture mode from transgranular cleavage to a mixed mode of intergranular-transgranular cleavage, and a change in slip behavior from coarse straight slip to fine wavy slip. These phenomena are discussed in terms of the effect of chromium on the antiphase boundary energies and dislocation characteristics.

Since 1976 NiAl–Ni2AlTi alloys have been known to possess elevated temperature mechanical properties approaching those of Ni-base superalloys; however, due to their apparent brittleness, little additional work has been undertaken to exploit this strength. In an attempt to instill ductility in these materials, small grain size single (Ni–45Al–5Ti) and two (Ni–40Al–10Ti) phase intermetallics were fabricated by XDTM technology and tested (XDTM is a trademark of Martin Marietta Corporation). As these compositions have the potential for being the matrix material in high temperature composites, Ni–40Al–10Ti and Ni–45Al–5Ti with 20 vol.% TiB2 in the form of ∼1 μm diameter particles were also investigated. The as-fabricated materials were fully dense and polycrystalline. The grain sizes measured ∼8 μm for Ti-poor and about 15 μm for the Ti-rich unreinforced materials but could not be determined for either TiB2 containing composite. Elevated temperature compression testing was conducted to about 8% deformation between 1200 and 1400 K with strain rates varying from ∼10−4 to ∼10−7 s−1. The majority of the tests exhibited diffuse yielding over approximately 1% strain followed by negative strain hardening. However, a few experiments resulted in steady state behavior where deformation continued under a constant stress. The flow strengths on yielding of both forms of Ni–40Al–10Ti were higher than those for the Ni–45Al–5Ti versions. For each matrix composition the addition of 20 vol.% TiB2 decreased the strength at the higher strain rates in comparison to the TiB2-free forms. During slow deformation conditions, however, the particles do provide reinforcement. Light optical microscopy of tested specimens revealed that these materials are generally quite brittle as numerous longitudinal and transverse cracks were found irrespective of the type of stress-strain behavior.

Isothermal annealing studies of hillocks formed on Al–15 wt.% Cu films, vapor deposited at 25 °C on oxidized silicon wafers, were carried out in situ in a scanning electron microscope. The original hillocks formed as a result of substrate-induced thermal expansion strains which caused material to diffuse out of the film to form the hillocks when the films were heated to the isothermal annealing temperatures. During isothermal annealing the hillock density decreased and the average size of the hillocks increased. Measurements of these quantities as a function of time were made at a series of temperatures ranging from 200 to 300 °C. The activation energies for these two cases were found to be 0.29 and 0.28 eV, respectively. X-ray energy spectroscopy analysis of the films showed that the hillocks were richer in copper than the matrix. Transmission electron microscopy showed that the average hillock and grain sizes in the variously annealed films were linearly related and of the same order of magnitude. The results were also analyzed using Chakraverty's models for surface and interfacial diffusion. It was concluded that the evidence clearly shows that the observed processes could be well characterized by a typical Ostwald ripening model.

A study has been made of fatigue and fracture in zinc bicrystals. It is shown that cleavage cracks are nucleated, both under tension and as a result of fatigue, in regions of multiple slip adjacent to grain boundaries at stresses below those for crack nucleation in single crystals. The nature of crack penetration through the boundary is observed as a function of orientation across the boundary. Low angle tilt boundaries are barriers to crack propagation, increasing effective surface energies for crack propagation by 1.6–2 times. Twist boundaries, due to the tearing that accompanies penetration, can result in a twelvefold increase in effective surface energy. Nonbasal cleavage is associated with a twinning mechanism, and an even higher surface energy is required to propagate a crack into a crystal oriented for this type of cleavage. The results carry the implication that, in the absence of surface defects, fatigue, failure in polycrystalline zinc is nucleated at the first internal grain boundary and not at the surface.