We have modeled plasma-assisted diamond growth on substrates placed in a high velocity 1-dimensional flow. The gas consisted of methane or acetylene injected into a flow of partially dissociated hydrogen gas at 800 °C. Diamond is formed only near the injector. More diamond is formed when methane is the additive, and Raman spectra show that the quality of the diamond films is also higher when methane is the additive. The model, which includes detailed chemistry, convection, concentration diffusion, and thermal diffusion, shows that with this experimental arrangement only methane and methyl radicals are present in significant quantities when methane is added, while only acetylene is present when acetylene is added. We conclude that (1) Diamond films can be grown directly from methyl radicals (or, possibly, from methane) and from acetylene. This suggests that a variety of hydrocarbons could act as growth species. (2) An environment containing methane and methyl is much more effective for growing diamond films than one containing acetylene. (3) The quality of the diamond film depends on the identity of the growth species, with acetylene producing lower quality films than methyl (or methane). (4) The fall-off in diamond formation with distance from the injector is due to destruction of species crucial to diamond growth on the silicon substrates.

We report the infrared reflection and absorption spectra of the high Tc superconductor Tl2Ba2CaCu2O8 in the temperature range from 10 K to 300 K. For temperatures above 100 K, the reflection spectra show only small changes with temperature. Just below 100 K, the reflectance suddenly increases for energies below 210 cm−1 with very little change as the temperature is further decreased. Several peaks corresponding to normal modes of the material are observed in both reflection and absorption spectra.

The surface morphology and near-surface chemical composition of high temperature superconducting Y–Ba–Cu–O thin films have been studied by Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. These films were fabricated on SrTiO3 substrates by RF diode sputter deposition and subsequent furnace annealing in oxygen. The chemical composition at and near the surface of thin films was found to differ from the bulk composition. At about 500 Å below the surface the Y, Ba, and Cu stoichiometry, as determined by AES, gradually approach that of the film interior. These results suggest that, for furnace annealed films, there may exist a minimum deposited Y–Ba–Cu–O film thickness in which superconductivity is possible. It was also found that the calculated copper concentration determined by AES during depth profiling is significantly lower than its actual value.

The preparation of multicomponent chalcogenide glassy thin films from bulk targets by laser ablation is described. The film stoichiometries are characterized by proton-induced x-ray emission (PIXE). Compared to single source thermal evaporation, laser ablation is found to preserve starting stoichiometries in the resulting thin films far more accurately. Thermally evaporated films were studied both by PIXE and by energy dispersed x rays (EDX) produced in a scanning electron microscope, and the results of these two analytical techniques compare well.

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.

As-deposited superconducting Y-Ba-Cu-O films have been grown on stainless steel substrates by the plasma assisted laser deposition technique. Low interfacial diffusion of iron at the 550°C growth temperature enables us to produce superconducting films with critical temperatures up to 83 K and critical currents up to ∼4 × 103 A/cm2 (40 K). Dependence of the superconducting properties of the Y-Ba-Cu-O films on the surface condition of the mirror finished stainless steel substrate has been studied. Critical temperature and critical current of the films have been improved by heat-treating the substrate and incorporating buffer layers. Variation of the critical current with the bend radii of the film is discussed.

By monitoring the electrical resistivity of single phase polycrystalline Y1Ba2Cu3O7-δ samples while changing their oxygen content in both ozone and ordinary oxygen environments, we were able to investigate the correlation between their average oxygen content and the diffusion time for oxygen inside the grains. We model the resistivity time dependence as a two-step process and find that this explains our experimental results satisfactorily. From this model we are able to estimate a value of the oxygen diffusion coefficient from our data that agrees well with other measurements. We also conclude that while ozone and ordinary oxygen may have different effects in oxidizing the surface of grains, they show no observable differences in the oxygen diffusion process in the bulk Y1Ba2Cu3O7-δ material.

NiTi was irradiated with Ni ions at various temperatures in order to study the temperature dependence of the irradiation-induced crystalline-to-amorphous transition. The irradiations were conducted above the Af temperature, and thus the specimens contained only the ordered B2 (CsC1) phase. The irradiations to similar doses at 150, 200, and 250°C showed that the amorphization kinetics slow down appreciably as the temperature is increased in this range. No amorphization was detected at irradiation temperatures of 350°C or higher, even after doses of 4 dpa. The small volume fraction of amorphous material observed after irradiation to 0.67 dpa at 250°C indicates that the cutoff temperature for amorphization is in the vicinity of this temperature. The amorphous regions of partly amorphous samples are distributed in a nonuniform manner and exhibit a morphology similar to the martensitic microstructure that existed in the specimens before heating to the irradiation temperature. Large amorphous regions in these samples exhibit some very fine crystalline debris which tends to disappear with increasing irradiation dose. Post-irradiation annealing experiments indicated that no thermally activated crystallization occurred during irradiation at temperatures up to 250°C.

Comparison of superconducting thin films of Bi–Sr–Ca–Cu–O deposited by laser ablation from a melt-quenched, amorphous, nonsuperconducting target and a polycrystalline sintered superconducting target shows that they have similar superconducting properties, but the melt-quenched target yields a much smoother film. Additionally, the melt-quenched target is much easier to prepare with target preparation time reduced by a factor of twenty-five.

An attempt has been made to improve the high temperature mechanical strength of the B2 cubic crystal structure intermetallic NiAl by dispersion strengthening. Prealloyed Ni–51 (at.%) Al was cryomilled with a Y2O3 addition to form an yttria dispersoid within the intermetallic matrix. Following milling, the powder was hot extruded to full density and machined into test coupons. Compression testing between 1200 and 1400 K indicated that the cryogenic process yielded the strongest NiAl based material tested to date: creep resistance was six times better than NiAl and twice that of a NiAl particulate composite containing 10 vol.% TiB2. Surprisingly, transmission electron microscopy revealed that the second phase was inhomogeneously distributed. Furthermore, x-ray analysis indicated that the second phase was not Y2O3 but rather AIN.

The microstructural development and grain growth of YBa2Cu3O7−y ceramics at 925, 950, and 975 °C were studied. Densification occurred quite rapidly at temperatures below 925 °C. The grain growth of YBa2Cu3O7−y followed a D5 − D50 = Kt relation when sintered at 925 and 950 °C. At 975 °C, the kinetics changed to cubic (D3) behavior, which can be attributed to the formation of a liquid phase at grain boundaries. A trend of decreasing Jc with increasing sintering temperature was observed. Other properties including Tc and the width of the transition were virtually unaffected by the change in microstructure. Without prolonged annealing, a relatively homogeneous oxygen stoichiometry of 6.8 was obtained for fairly dense samples (>93% of theoretical). These results suggest that the oxygenation rate of YBa2Cu3O7−y was quite rapid between the tetragonal phase and the orthorhombic composition of YBa2Cu3O6.8.

A wide variety of cation substitutions have been tried in the 1-2-3 compound, YBa2Cu3Ox, in the hope that its superconducting properties can be improved. While significant improvement has not been achieved, the response of the material to such substitutions can still be helpful in understanding its defect chemistry. In this paper, we report on measurements of the equilibrium oxygen content, by thermogravimetry, and the electrical conductivity of YBa2−zLazCu3Ox, with z = 0, 0.1, and 0.2. The results are consistent with the view that the stoichiometric composition for this system, YBa2Cu3O6, is a highly acceptor-doped material.

Several high Tc compounds containing Tl (thallium) were prepared starting from different initial compositions. Superconducting properties and the structure were determined for each sample. Electron diffraction and transmission electron microscopy showed the existence of polytypic high Tc compounds with the same a- and b-axes but different c-axis values. The c-axis appears to increase approximately in integral multiples of 0.15 nm with varying composition and is associated with the insertion of Cu–Ca or Cu–Tl layers in each unit cell. Several random stacking faults were also noted, which give rise to diffuse streaking in the electron diffraction pattern.

A relationship between continuum mechanical internal stress variables, kinetic back stress, isotropic drag stress, and microscopic local stresses in the dislocation cell interior and cell walls, is developed based upon Mughrabi's composite model of deformation of heterogeneous microstructure during cyclic deformation in cell forming metals. The experimental data on the evolution of kinematic back stress and isotropic drag stress during cyclic deformation of Cu along with TEM measurements of cell diameter and cell width are utilized to determine the evolution of mobile and immobile dislocation densities in the cell interior and cell walls, respectively, as a function of the number of cycles. The range of values obtained is in agreement with the available experimental data.

The effects of internal electrodes on the fracture properties of relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 multilayer structures were studied. It was observed that the position of the first electrode layer from the surface is critical to the strength and toughness of the multilayer structure. Positioning the electrode close to the surface was found to enhance interaction with cracks which initiate on the multilayer surface. This interaction limits the effective crack length and therefore increases the fracture strength and effective toughness of the composite. Samples indented parallel to the electrodes exhibited higher fracture strengths and toughness than those indented perpendicular to the conducting layers. Both parallel and perpendicular orientations gave higher strength and toughness than the control specimens (without electrodes).

Experimental results are presented on efforts to maximize the content of the phase responsible for the 110 K superconducting transition, Bi2Ca2Sr2Cu3O2 or (2223), in the system Bi–Ca–Sr–Cu–O. It was found that the content of this phase depends not only on the initial composition of the reacting mixture, but also on the presence of PbO, the temperature of reaction, and the duration of the reaction.

Diamond films grown by microwave plasma assisted chemical vapor deposition (CVD) were studied by thermogravimetric analysis under an air atmosphere. Oxidation rates were measured between 600 and 750 °C to determine an activation energy of 213 kJ/mol which is similar to that reported for natural diamond. The rate of oxidation increases with increasing surface area and decreases with increasing humidity. The oxidation proceeds by etching pits into the film, creating a highly porous structure. Graphitization was not detected in partially oxidized samples by Raman or Auger electron spectroscopy. A film that was heated to 1170 °C under nitrogen remained IR transmissive.

The microstructure and mechanical properties of several Ni–Al–Hf alloys in the composition range between NiAl (β) and Ni2AlHf (Heusler phase) have been studied. The volume fraction of Heusler phase, Vf, in these alloys varies from about 15 to 96%. The lattice misfit between the β and Heusler phases in two-phase alloys is larger than 5%, indicating no coherency between them. The yield strength increases with increasing Vf at all temperatures to 1000°C. Compressive ductilities of 4 and 7% were obtained for the alloy with Vf of 15% at room temperature and 500°C, respectively, but they decreased to 0% with increasing Vf to 96%. The corresponding fracture mode is basically transgranular cleavage. However, all the alloys can be deformed extensively without fracture at 1000°C. The hardness of the Heusler alloy is very high (8.3 GPa) at room temperature, and it decreases gently with temperature to 600°C, followed by a rapid decrease to 1000°C. The brittleness and high hardness of the Ni2AlHf Heusler phase at low temperatures are interpreted in terms of internal lattice distortion resulting from its crystal structure. The thermally activated process of deformation takes place above 600°C, which is responsible for the rapid drop of the hardness of the alloys.

Samples of Y-Ba-Cu-O materials with the formulation Y:Ba:Cu = x:2:3 and values of x ranging between 1 and 3 were prepared by partial melting at a maximum temperature of 1045 °C. Measurements of magnetic susceptibility and maximum (low-field) as well as remanent magnetization show highest values for x = 2. XRD and SEM/EDX analyses show that the corresponding structure involves numerous small crystals of Y2BaCuO5 (211) embedded in highly ordered assemblages of continuous YBa2Cu3O7−y (123) layers. The presence of these impurity sites is correlated with flux pinning capacity. Other impurity phases include CuO, a minor phase which shows an increase in amount when x increases, BaCuO3, a possibly detrimental minor phase which vanishes when x is raised from 1 to 2, and zones of intermediate composition between the 211 grains and the 123 layers, which are formed from the residual liquid upon cooling. These intermediate regions, like the 211 grains themselves, become gradually more important when x is increased from 1 to 3.

In order to obtain essential information on the formation process of the high-Tc phase in the Bi, Pb–Sr–Ca–Cu–O system, subsolidus phase equilibrium in the systems PbO(PbO2)–SrO–CuO and PbO(PbO2)–CaO–SrO has been studied, mainly by XRD analysis. A pseudoternary Pb–Sr–Cu–O solid solution was newly found. This solid solution has a wide solubility range including its typical composition Pb2.03Sr3Cu0.73O7.70. It has a hexagonal structure with lattice parameters a = 10.11 and c = 7.11 in AU. Composition dependences of the lattice parameters and the decomposition (incongruent melting) temperature of (Ca1−xSrx)2PbO4 solid solution are also reported.