YBa2Cu3O7-x was molten and resolidified by a containerless process under free-fall conditions in a drop tube. The resulting samples revealed four different microstructures originating either from a “high-temperature melt” (Tm ≥ 1550 K) or from a “low-temperature melt” (1288 K ≤ Tm ≤ 1550 K). All structures exhibited very fine, homogeneously dispersed structural constituents. One of these microstructures is not compatible with actual equilibrium phase diagrams and implies the kinetic suppression of the nucleation of both the Y2BaCuO5- and the Y2O3-phase.

A compound with the stoichiometry of Y1Ba4Cu2CO3O5.5±δ is formed in the presence of CO2 or carbonate. Analysis techniques including oxygen overpressure, wet chemical analysis, and quenching experiments establish that this material is an oxycarbonate compound. Electrical measurements indicated no superconductive properties in the 10–298 K temperature range. The ease of formation of this compound causes it to commonly appear in synthesis in this region of the phase diagram and accounts for many of the conflicting reports of properties and solid solution formation. XRD shows evidence for the existence of some solid solution in this oxycarbonate. The compound Y1Ba4Cu3O8.5±δ, formed in the absence of CO2, and Y1Ba4Cu2CO3O5.5±δ, formed in the presence of CO2, are the only barium-rich phases seen to exist.

The structures of two laser processed ternary intermetallic phases, Al16Ti6(Fe or Ni)7, have been studied by using electron diffraction and microscopy. A convergent beam electron diffraction (CBED) technique for structure determination is described based upon the principle of kinematic interpretation of large angle systematic reflections in CBED disks. The structure type of phases Al16Ti6(Fe or Ni)7 is characterized as the Mn23Th6(cF116)-type, the same as those of relevant phases Cu16Mg6Si7 and Al50Ti25Fe25 etc., by using the CBED technique. Various errors involved in the analyses are also discussed.

Ni3Fe is a compound that exhibits long-range ordering below 500 °C and a disordered structure above this temperature. Thus, Ni3Fe allows study of the effect of ordering on mechanical properties. This paper discusses the tensile properties of Ni3Fe produced via powder metallurgical routes. Some samples subsequently were densified by containerless hot isostatic compaction. Ni3Fe was consolidated with elemental nickel and iron powders that were solid state sintered. Composites of Ni3Fe with 5 vol. % Y2O3 were prepared by presintering cold isostatically pressed rods, followed by containerless hot isostatic pressing. The influence of Y2O3 particles on flow stresses of ordered and disordered Ni3Fe was determined. Ordering of Ni3Fe increased both strength and hardness with a small effect on ductility. For the Ni3Fe–Y2O3 composite, the increase in the strength in both ordered and disordered matrix conditions was accomplished by a large reduction in elongation.

A definition for structure of atomic scale systems is introduced which extends the typical crystallographic description to include elements of the total charge density. We argue that the mechanical properties of intermetallic alloys are related to this extended structure. These relationships have their origin in the nature of the charge redistribution accompanying strain. The direction of this charge redistribution is determined solely by the extended structure, while its magnitude can be correlated with a quantification of this extended structure. We demonstrate these facts by determining the extended structure and nature of the charge redistribution resulting from uniaxial strain for two alloys with the L10 structure: CuAu and TiAl. While these alloys share the same crystallographic structure, their extended structures are different, with CuAu possessing the same extended structure as the allotropic fcc metals while TiAl does not. These different extended structures give rise to different charge redistributions, which are argued to be related to the intrinsically ductile behavior of CuAu and the tendency for TiAl to fail transgranularly.

We present a description of the thermal behavior of cascades in Cu and Ag over a large energy range and irradiation temperatures. For this purpose the binary collision approximation, which gives the profile of the energy deposition, is coupled to a simplified version of the heat equation. In the present calculations, the original liquid drop model [M. Alurralde, A. Caro, and M. Victoria, J. Nucl. Mater. 183, 33 (1991)] has been extended to the case where the lattice is at finite temperatures. The resulting evolution of the liquid cascade is analyzed for PKA energies up to 1 MeV, and the results are compared to experimental observations of mixing rates. We obtain a temperature dependence that adds to the traditional Radiation Enhanced Diffusion, RED, in very good qualitative agreement with experiments on materials showing thermal spikes.

The embedded atom method (EAM) has been used to compare the stability of a series of small palladium clusters with 5–60 atoms and a variety of shapes. It is found that the 13- and 55-atom icosahedra and cubo-octahedra are stable at 0 K. However, other sized icosahedra and cubo-octahedra are unstable at 0 K. Upon annealing, the icosahedra and cubo-octahedra reconstruct into nonpolyhedral structures which are highly strained. The strained structures are much more stable than the icosahedron or cubo-octahedron except when there are 13 or 55 atoms in the cluster. Further, there are many disordered shapes which are within 0.01 eV of the minimum energy structures at all cluster sizes including 13 and 55 atoms. We observe transitions between these low energy structures in Monte Carlo calculations. These results suggest that at equilibrium one should rarely observe polyhedral palladium particles. Instead, most of the particles should be disordered. Further, there should be a wide distribution of particle shapes in agreement with experiment.

Ferromagnetic europium (EuO) films have been made by oxidizing europium (Eu) metal films deposited on glass substrates using a thermal evaporation technique. It has been found that the quality of the films is sensitive to substrate temperature. Stable EuO films were formed only if Eu metal films were annealed at temperatures of 320 to 380 °C. Both x-ray diffraction pattern (XRD) and magnetization measurements indicate that a significant amount of EuO phase has been formed in the films. These films undergo a phase transition from paramagnetic to ferromagnetic phase at temperatures between 60 and 70 K and exhibit the magneto-optical Faraday effect. The saturation magnetic moment at 10 K is about 40% of the theoretical value, and the coercive force, Hc, for slow sweeping field is about 70 Oe.

Cobalt (Co)/silicon dioxide (SiO2) reactions during rapid thermal annealing (RTA) in an N2 ambient have been investigated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that islands consisting of Co and the cobalt oxide phase, Co3O4, form during high-temperature anneals (30 s−10 min at 800 °C). After a selective wet etch to remove the islands, groove-like features are produced in the SiO2 layer. The morphologies of the islands and grooves are strikingly similar, which strongly suggest that Co and the underlying SiO2 layer have reacted, most likely to form Co3O4. We propose that small concentrations of O2 are necessary to promote Co/SiO2 interactions.

Growth defects in diamond films grown by plasma-assisted chemical vapor deposition (CVD) were studied by high resolution electron microscopy. Several features of the microstructure were resolved and their importance to the growth of the diamond film was evaluated. The observations included various twin boundaries of the type ∑ = 3, as well as ∑ = 9, ∑ = 27, and ∑ = 81, which form by an interaction of lower order twins. These higher order boundaries are loci of intersection points of growing planes on two adjacent twins and can serve as an indicator for the local crystal growth direction. The central nucleation site for the growing planes in many cases can be traced back to a quintuplet twin point. A twin quintuplet has five re-entrant angles and thus serves as a preferred nucleation site for new planes as the crystal grows.

By a Plasma Enhanced Chemical Vapor Deposition process (PECVD), we are able to prepare nitrogenated amorphous carbon materials around room temperature from methane and nitrogen gas as precursors. We have also used chlorine gas as an additive to reduce the hydrogen content of our samples. Starting from the “as-deposited” materials, we have investigated their thermal stability by successive heat treatments up to 1400 °C. These compounds suffer a weight loss mostly due to the hydrogen departure. They become nonfusible and it turns out that nitrogen, chemically bound to sp2 hybridized carbons, induces some changes in the physical properties. In order to understand the relationship between the local structural organization and the physical characteristics, we have investigated different spectroscopic techniques such as Nuclear Magnetic Resonance, IR Absorption, and X-ray Photoelectron Spectroscopy. We have also investigated several transport properties: (i) The dc electrical conductivity shows a kind of metal/insulator transition around 700 °C. The temperature dependence for the conductive samples gives evidence for a pseudogap associated with the presence of localized states, (ii) The thermal conductivity exhibits, for the as-deposited compound, a very low value varying slowly with temperature; its magnitude as well as its temperature dependence, characteristic of noncrystalline materials, are modified by the annealing process. Finally, an electronic band model is proposed, explaining the structural evolution through a kind of Mott–Anderson pseudotransition.

Because of their unusually large specific surface area (SSA), Activated Carbon Fibers (ACF's) have a huge density of micropores and defects. The Raman scattering technique and low-temperature dc electrical conductivity measurements were used as characterization tools to study the disorder in ACF's with SSA ranging from 1000 m2/g to 3000 m2/g. Two peaks were observed in every Raman spectrum for ACF's and they could be identified with the disorder-induced peak near ∼1360 cm−1 and the Breit–Wigner–Fano peak near ∼1610 cm−1 associated with the Raman-active E2g2 mode of graphite. The graphitic nature of the ACF's is shown by the presence of a well-defined graphitic structure with La values of 20–30 Å. We observed that the Raman scattering showed more sensitivity to the precursor materials than to the SSA of the ACF's. From 4 K to room temperature, the dc electrical resistivity in ACF's is observed to follow the exp [(T0/T)1/2] functional form and it can be accounted for by a charge-energy-limited tunneling conduction mechanism. Coulomb-gap conduction and n-dimensional (n ≤ 3) variable-range hopping conduction models were also considered but they were found to give unphysical values for their parameters.

The utilization of tensile strength of carbon fibers in unidirectional carbon/carbon (C/C) composites was studied for a series of four mesophase-pitch-based carbon fibers in a carbon matrix derived from a polyarylacetylene (PAA) resin. The fibers had moduli of 35, 75, 105, and 130 Mpsi. Composite processing conditions ranged from the cured-resin state to various heat-treatment temperatures (HTT's) from 1100 to 2750 °C for the C/C's. Room-temperature tensile strength and modulus were measured for the various processing conditions, and were correlated with SEM observations of fracture surfaces, fiber and matrix microstructures, and fiber/matrix interphase structures. Fiber tensile strength utilization (FSU) is defined as the ratio of apparent fiber strength in the C/C to the fiber strength in an epoxy-resin-matrix composite. Carbonization heat treatment to 1100 °C results in a brittle carbon matrix that bonds strongly with the three lower modulus fibers, resulting in matrix-dominated failure at FSU values of 24 to 35%. However, the composite with the 130-Mpsi-modulus filament had an FSU of 79%. It is attributed to a combination of tough fracture within the filament itself and a weaker fiber/matrix interface. Both factors lead to crack deflection and blunting rather than to crack propagation. The presence of a weakened interface is inferred from observations of fiber pullout. Much of the FSU of the three lower modulus fibers is recovered by HTT to 2100 or 2400 °C, principally as a result of interface weakening, which works to prevent matrix-dominated fracture. With HTT to 2750 °C, there is a drop in FSU for all the composites; it is apparently the result of a combination of fiber degradation and reduced matrix stress-transfer capability.

A digitization of the TEM pictures of fluorine-intercalated graphite fibers has been used to carry out quantitative measurements of the defect structure of this material. Emphasis is given to both the computer analysis technique and to the characterization of the defects. The amount of intercalation-induced disorder increases with increasing fluorine concentration. The fast Fourier transform of the digitized TEM image exhibits two diffuse spots, corresponding to the c-axis repeat distance of the intercalation compound. The length and width of the spots are a measure of the out-of-plane and in-plane disorder present in the fibers. From the fast Fourier transform, the distribution of interlayer repeat distances and the fraction of unintercalated graphite regions throughout the material is obtained. By selecting a small range of repeat distances and carrying out an inverse fast Fourier transform, the spatial distribution of material with a given repeat distance is determined. Regions with the same repeat distance are found to form islands. This particular feature of fluorine graphite intercalation compounds, as well as the nature of the microscopic defects and the staging behavior of fluorine-intercalated graphite fibers, are discussed in connection with the dual covalent and ionic nature of the carbon-fluorine bond in fluorine-intercalated graphite.

The structure of SIMOX wafers implanted at 180 keV with doses of 0.1 × 1018-2.0 × 101816O+ cm−2 at 550 °C, followed by annealing over the temperature range of 1050–1350 °C, has been investigated using cross-sectional transmission electron microscopy and a chemical etching. With doses of 0.35 × 1018-0.4 × 1018 cm−2, a continuous buried oxide layer having no Si island inside is formed by high-temperature annealing at 1350 °C. At a dose of 0.7 × 1018 cm−2, multilayered oxide striations appear in the as-implanted wafer. These striations grow into multiple buried oxide layers after annealing at 1150 °C. The multiple layers lead to a discontinuous buried oxide layer, resulting in the formation of a number of Si micropaths between the top Si layer and the Si substrate when the wafer is annealed at 1350 °C. These Si paths cause the breakdown electric field strength of the buried oxide layer to deteriorate. With doses of 0.2 × 1018-0.3 × 1018 cm−2 and of higher than 1.3 × 1018 cm−2, an extremely high density of threading dislocations is generated in the top Si layer after annealing at 1350 °C. The dislocation density is greatly reduced to less than 103 cm−2 when the oxygen dose falls in the range of 0.35 × 1018-1.2 × 1018 cm−2. Here we propose a mechanism that accounts for the threading dislocation generation at substoichiometric oxygen doses of less than 1.2 × 1018 cm−2.

SiC thin films grown from the reaction between acetylene (C2H2) and the Si(100) substrates in a horizontal hot-wall CVD reactor by different procedures were studied using x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The growth of the SiC films was observed from the behavior of Si2p peaks and their plasmons. A SiC thin film with a thickness of 35 Å and having a smooth surface morphology was obtained in C2H2 diluted by H2 at 1050 °C for a period of 60 min. Etch pits and hillocks were observed with increasing reaction time at 1050 °C. For the conversion conducted in C2H2, but in the absence of H2, a SiC monolayer with smooth morphology was obtained at 950 °C for 7 min and defects were observed for longer reaction times at this temperature. Defects were also observed for reaction times as short as 10 s at higher reaction temperatures (e.g., 1000 °C). H2 seems to play a key role in suppressing the formation of defects and the reaction between C2H2 and Si substrate. The formation of defects was correlated to the out-diffusion of Si in the carbonization process.

Polycrystalline CuInS2 thin films are prepared by sulfuration of Cu–In–O films. The Cu–In–O films are deposited from a sintered Cu2In2O5 target by using a pulsed laser deposition (PLD) method. Then, the Cu–In–O films are converted into CuInS2 films by means of a subsequent annealing in an H2S gas atmosphere. The characteristics of the films are determined by using an x-ray diffractometer (XRD), an energy dispersive x-ray spectrometer (EDX), and a scanning electron microscope (SEM). The effects of the deposition and sulfuration temperatures of the Cu–In–O films on the structural and microstructural properties of CuInS2 films are examined experimentally. Single-phase CuInS2 films with a chalcopyrite structure are obtained when Cu–In–O films are sulfurated at a temperature higher than 400 °C. Grain size of CuInS2 is larger when a lower deposition temperature and a higher sulfuration temperature of Cu–In–O films are employed.

Zone-melting recrystallization (ZMR) with a graphite strip heater is used to improve the material quality of thin film structures for microelectronic applications. The process takes place in a sealed chamber filled with an inert gas such as argon or helium. The effect of natural convection and conduction at the interface between the gas and film structure was studied both numerically and experimentally. Numerical simulations of the temperature profile in the film structure, and the flow pattern and temperature field in the gas were developed. Experimental observations in a scaled setup using a liquid medium verified the flow patterns calculated from the numerical model of the gas flow in the chamber. Results indicated that the gas is stagnant in the region below the strip heater; consequently, conduction from the strip heater to the wafer is prevalent. Outside the stagnant region, natural convection cools the film structure. These two effects combine to create a steeper thermal gradient across the entire wafer which can increase the thermal stresses in the film. The magnitude of this thermal gradient depends strongly on the thermal diffusivity of the gas. The configuration of the strip heater may significantly affect the amount of heat conduction in the stagnant region.

Filament formation in V2O5 gel films leading to a two-terminal switching device has been observed. In a previous paper, we have identified the switching with a metal-insulator transition within a permanent, current-induced channel between the electrical contacts. Here, we describe the reversible formation of a filament inside the channel, and obtain a static solution of the heat transport equation for this device which indicates a large temperature variation within the filament, and further reveals the failure mechanism for the reversible switching. The principle of least entropy production has been used to analyze the filament growth, which results in a successful simulation of the “on” state I-V characteristic of the switching process, including its negative resistance region.

The evaluation of the thermal stability of three different fully dense AlN materials in the temperature range of 600 °C to 1400 °C in air indicates the strong effect of the starting composition on the oxidation process. The oxidation resistance of pure AlN and Y2O3-doped AlN was found to be good up to ≍1350 °C. The kinetics are linear (1100 ≤ T ≤ 1400 °C) and the process is governed by a surface reaction that gives rise to the formation of a porous, nonprotective oxide scale, where Al2O3 and Y-aluminates (i.e., AlN–Y2O3) have been found as crystalline reaction products. For AlN-CaC2, higher oxidation rates indicate that the outward migration of Ca modifies the reaction mechanisms. Linear kinetics in the range 1100 ≤ T ≤ 1200 °C are followed by parabolic kinetics at higher temperatures (T > 1250 °C); with regard to the latter behavior, an activation energy of 160 kJ/mole could indicate the diffusion of oxygen through the oxidation scale as the rate-controlling mechanism.