The modulated structure in solid solution Bi2+xSr2−xCu1+yO6+δ (0.1 < x < 0.6, y ∼ x/4) has been investigated by means of powder x-ray diffraction, electron diffraction, and transmission electron microscopy. The [010] component of the modulation vector decreases almost linearly with increasing x, from 5.2b (x = 0.1) to 4.2b (x = 0.5), where b is the unit length of the average structure along the [010] direction, and is little sensitive to excess oxygen content δ. A structure model of the modulation based on a periodic substitution of Sr for Bi and formation of Bi blocks whose size varies with x is proposed. Relations among various modulations appearing in other related phases such as the Pb-substituted 105 K Tc phase are discussed.

We have measured x-ray diffraction patterns and Meissner flux exclusion of YBa2Cu3Oσ containing indium. All samples were synthesized at temperatures near 940 °C, and the data indicate the indium atomic solubility to be approximately 3% per formula unit. At the solubility limit Tc is reduced from 92.7 K to 91.3 K relative to undoped samples, and the total magnetic flux excluded is reduced from approximately 40% to about 10%. For samples of formula InxY1−xBa2Cu3Oσ concentrations of other Y–Ba–Cu oxide phases are low and do not depend systematically on x. These results indicate that indium substitutes predominantly for yttrium when x is small.

The phase diagram of the Y2O3–CuO–Cu2O system was constructed as a function of temperature in air by means of thermal analysis and x-ray diffraction. The phase Y2Cu2O5 was found to be stoichiometric and melted peritectically at about 1110 °C. A new intermediate phase with the composition YCu2O2.5 was discovered. It exists between 990 and 1105 °C in air and quenching did not preserve it to room temperature. High temperature x-ray diffraction established its pattern and confirmed its peritectic decomposition. Above 1110 °C YCu2O2.5 consists of Y2O3 and liquid. The results of this system are shown on a ternary system as well as on a pseudo-binary phase diagram. The solid state reactions were established. Melting occurs with isothermal oxygen loss or gain, depending on the initial composition.

The effect of silver additions and excess copper on the sinterability and weak link behavior has been studied in the nominal composition Bi1.72Pb0.32Sr2Ca2Cu3Ox (Ag = 1−4 wt. %) and Bi1.72Pb0.32Sr2Cu3+yOx where y = 0.2−0.5, using magnetic susceptibility, XRD, and SEM methods. Ag additions enhance the weak link behavior, giving a magnetic susceptibility shoulder at 103 K. This shoulder became more prominent at high fields (35 Oe), and a low Tc phase became evident with 4 wt. % Ag additions. In contrast to stoichiometric compositions, samples containing excess copper demonstrated an enhancement of the sinterability and a large volume of 2223 phase even in calcined samples. XRD data and SEM analysis failed to detect any Cu-rich phase up to copper contents y = 0.4. However, in copper samples with y = 0.5, a small x-ray peak at 2θ = 48.5°has been observed corresponding to CuO.

A metallo-organic deposition technique was employed to grow Bi2Sr2CaCu2O8+x flexible films on unpolished metal foils (stainless steel and silver). Since strong interactions occurred at elevated temperatures between stainless steel and superconducting oxides, HfO2 buffer layers prepared by ion-assisted deposition were used to stabilize the system and Na additions were used to reduce processing temperature and enhance grain growth. The transition of superconducting films on stainless steel was complete around 70–73 K, and the critical current density was about 1000 A/cm2 at 10 K. Silver appears to be an attractive metal support due to its chemical stability and mechanical ductility. The film on silver showed the onset to superconductivity at 77 K, attaining zero resistance at 73 K. The critical current density in zero magnetic field was approximately 27000 A/cm2 at 20 K, comparable to that obtained from MOD films on MgO (100).

Magnetic shields for SQUID applications were successfully fabricated using high Tc superconducting Bi–Sr–Ca–Cu–O (BSCCO). In order to produce shields with adequate superconducting properties and close dimensional control, it was necessary to develop several new processing techniques. Shields were produced by casting liquid BSCCO into molds, heat treating, and machining. A series of BSCCO alloys with different compositions were cast from the molten state into metal molds and subsequently heat treated to render the castings superconducting. The heat-treating cycles were studied with the aid of thermogravimetric analysis (TGA), differential thermal analysis (DTA), and dilatometer measurements. The phases and microstructures after various heat-treating cycles were monitored by x-ray diffraction (XRD), optical microscopy, and scanning electron microscopy (SEM). Superconducting properties were measured after various stages of heat treatment and machining. Prototype magnetic shields were machined from bulk castings and found to perform successfully. The most significant factor in shield quality was the nominal composition of the shield, which was shown by transmission electron microscopy (TEM) to affect the grain boundary chemistry.

The energies and configurations of interstitials and vacancies in the ordered compounds CuTi and CuTi2 were determined using atomistic simulation with realistic embedded-atom potentials. The formation energy of an antisite pair was found to be 0.385 and 0.460 eV in CuTi and CuTi2, respectively. In both compounds, the creation of a vacancy by the removal of either a Cu or Ti atom resulted in a vacant Cu site, with an adjacent antisite defect in the case of the Ti vacancy. The vacant Cu site in CuTi was found to be very mobile within two adjacent (001) Cu planes, with a migration energy of 0.19 eV, giving rise to two-dimensional migration. The vacancy migration energy across (001) Ti planes, however, was 1.32 eV, which could be lowered to 0.75 or 0.60 eV if one or two Cu antisite defects were initially present in these planes. In CuTi2, the vacancy migration energy of 0.92 eV along the (001) Cu plane was significantly higher than in CuTi. The effective vacancy formation energies were calculated to be 1.09 eV and 0.90 eV in CuTi and CuTi2, respectively. Interstitials created by inserting either a Cu or Ti atom had complicated configurations in which a Cu 〈111〉 split interstitial was surrounded by two or three Ti antisite defects. The interstitial formation energy was estimated to be 1.7 eV in CuTi and 1.9 eV in CuTi2.

We present results of a molecular dynamics simulation study of the effect of electron-ion interactions on the dynamics of the thermal spike in Cu. Interatomic forces are described with a modified embedded atom method potential. We show that the electron-ion interaction acts to reduce the lifetime of the thermal spike and therefore the amount of atomic rearrangement that takes place in energetic displacement cascades in Cu. The results point toward the important effect that inelastic energy losses might have on the dynamics of displacement cascades in the subcascade energy regime where the lifetime of the thermal spike is expected to exceed the electron-phonon coupling time.

A continuous annealing, using the Joule effect, is performed during the fabrication of a tinned copper wire. During this operation, which lasts between 1/10 and 1/100 of a second, the wire is brought in air to a temperature which exceeds the melting point of tin. The influence of the continuous annealing on the nature of the surface layer of the tin coating is studied using XPS. The thickness of the tin oxide film covering the metallic tin is shown to be reduced after the annealing. This result is confirmed by measurements of the electrical contact resistance using the crossed rods method.

Solid state reactions between Ni and Sn at two compositions, Ni75Sn25 and Ni60Sn40, have been induced by means of near room temperature cold rolling and mechanical alloying. The reaction steps have been monitored by x-ray diffraction and differential scanning calorimetry. At both compositions, the first effect of plastic deformation is the formation of two metastable phases which, by further milling or low temperature thermal treatment, transform into the Ni3Sn4 compound. The chemical composition of the metastable phases has been determined to be close to that of Ni3Sn4 and the crystal structure of one of them appears to be related to that of β–Sn. Differential scanning calorimetry and thermal treatment of samples containing the metastable phases have shown that these phases transform into Ni3Sn4 at about 150 °C and that no other reaction takes place up to this temperature. Upon prolonged milling, a different behavior has been observed for the two compositions. While the Ni60Sn40 mixture eventually forms the Ni3Sn2 compound in agreement with previous results, the final product of mechanically alloying the Ni75Sn25 mixture is a phase whose structure, rather than amorphous as previously hypothesized, in our case can be described as based on that of the disordered high temperature form of the Ni3Sn compound. Differential scanning calorimetry and x-ray diffraction analysis of this sample have shown the formation, at 380 °C, of ordered Ni3Sn with an associated heat release of about 10 kJ/mole.

MoSi2-based composites reinforced with particles, whiskers, and continuous fibers were fabricated using hot pressing and hot isostatic pressing techniques. The microstructure, interface compatability, and interfacial properties between the reinforcements and matrix are discussed. The microstructural parameters which control the mechanical behavior of the MoSi2 composites were characterized. The need for developing a satisfactory reinforced MoSi2 composite for high-temperature structural applications is also addressed.

The microstructural changes and the tensile behavior of laser processed A356-Al alloy matrix composites reinforced with 10 and 20 vol.% SiC particulates are characterized. The autogenous bead-on-plate welds were made using a pulsed CO2 laser operating at a peak power level of 3.2 kW. The pulse on-time was constant at 20 ms and the off-time was varied from 20 to 2 ms (duty cycles of 50–91%). The microstructure of the laser melted region was investigated by optical, scanning, and transmission electron microscopy, and x-ray microchemical analysis techniques. The extent of microstructural changes varied directly with duty cycle, i.e., being a maximum for the longest (91%) duty cycles. Pulsed laser processing produced partial to complete dissolution of SiC particles and sometimes resulted in the formation of aluminum carbide. The associated rapid cooling also produced a fine distribution of nonequilibrium complex precipitates. In addition, the laser energy modified the SiC surface both physically and chemically. The results of tensile tests indicated that the modified SiC and the distribution of fine nonequilibrium precipitates enhance the mechanical properties of the laser processed composites. Optimum changes in microstructure and mechanical properties were obtained in the composites processed with intermediate (67 and 74%) duty cycles; therefore pulsed processing appears to be a strong candidate for successful joining of these MMCs.

The compression behavior of both the monolithic L12 compound Al22Fe3Ti8 and discontinuous composites obtained by incorporating ∼1 μm TiB2 particles was studied for various volume percent reinforcements as a function of temperature and at high temperatures as a function of strain rate. In this study, by varying the Fe and Ti contents, the nature and volume fraction of the minor phases coexisting with the dominant L12 phase were changed and were examined with and without TiB2 reinforcement. At high strain rates (10−4 s−1), the TiB2 reinforcements significantly enhance ambient and warm-temperature strength, although a crossover is observed at ∼1000 K, above which the monolithic material is stronger than the composite. At slow strain rates (10−7 s−1), representative of creep conditions, however, the TiB2-containing composites retain their superiority at least up to 1200 K. Power law fits of compressive flow stress at 1% strain versus strain rate yielded a stress exponent of ∼3.0 with an activation energy of 310 kJ/mol for the monolithic material. For the particulate composites (20 vol. % TiB2), the corresponding values were ∼5.0 and 465 kJ/mol, suggesting a change in the dominant deformation mechanism.

Fracture mechanics and mechanisms of a carbon fiber reinforced carbon matrix lamina composite are studied. The importance of microfracture processes of first matrix cracking, fiber bridging, and fiber pullout processes for toughening C/C-composites is emphasized, and then, the fiber bridging process of the composite is mainly focused through the measurement of the R-curve. The fiber bridging tractions are estimated by the Dugdale approach from which the superb stress shielding and excellent notch tolerance of the composite are demonstrated.

A simple and practical method is described for determining the residual stress in vapor deposited thin films that are less than 1000 Å in thickness. The method relies on the evaporation of thin films onto prefabricated micro-cantilever beams of SiO2. The vertical deflection at the end of the beam is measured using an optical microscope to determine the average film stress with a resolution of 25 MPa. Calculations show that the vapor deposition of metal films onto these beams does not induce significant heating, so the thermal component of residual film stress is minimal. The micro-cantilever technique is used to measure the film stress in 500 Å films of Al, Ti, Pt, Au, Ni, and Ge. These measured values are compared to similar measurements reported in the literature.

As part of the investigation of the use of Pd-based ohmic contacts to p-type GaAs, cross-sectional transmission electron microscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy were used to explore the uniformity at the metal/GaAs interface and its composition profile after ohmic contact formation. Comparisons were made among Au:Be, Au:Be/Pd, and Au/Pd contacts. Regions of p+ were formed in n-type GaAs by a spin-on source which was rapid diffused at 950 °C for 6 s or by ion implantation at a dose of 3 × 1014 atoms/cm2 at 150 keV for 15 min. Metallizations were accomplished by evaporation with a base pressure of 3 × 10−6 Torr. Sintering of the metallizations was done in a furnace at 350 °C for 15 min. Cross-sectional transmission electron microscope studies revealed an absence of spiking when Be is present in the metallization scheme but a broad band diffused into GaAs. An improper metal/GaAs adhesion was observed when Pd is absent. Be assists in confining the reaction of Pd with GaAs and acts as a diffusion barrier to the p+ dopant. Electrical measurements, taken from transmission line and cross bridge Kelvin resistors, were best for the Pd/Au:Be, which yielded a contact resistance of 0.3 μΩ-cm2.

“Tracks” of alpha-recoil nuclei have been observed directly in titanite (CaTiSiO5). Recoil tracks in titanite are 4 to 6 nm in diameter and consist of a central aperiodic zone surrounded by a narrow (0–2 nm) outer zone that is essentially crystalline, but which exhibits modulated image contrast due to interstitial defects. Previous work has suggested that titanite is 2 to 3 times more sensitive to alpha-decay damage than other ceramic phases (e.g., zircon, ZrSiO4). We find, however, that track diameters in titanite are essentially the same as reported for other phases, including zircon (ZrSiO4), pyrochlore (NaCaTa2O6F), and zirconolite (CaZrTi2O7). An annealing study of titanite (300 to 700 °C, N2) shows a two-stage recovery process. Track diameter decreases at 400 °C. An intermediate phase develops at 500 °C, and nearly all tracks are epitaxially recrystallized. At 700 °C, all tracks and the intermediate phase are gone.

Structures of some phases in the SrMnO3−x system accompanied by planar defect were studied using a high resolution electron microscope. A four-layer structure with a hexagonal unit cell was found to have an oxygen deficiency in some degree followed by planar defects normal to the c-axis which are classified into several types. On the basis of observed images showing an irregular stacking along the c-axis in the hexagonal unit, the distribution and the origin of the planar defect are discussed. A structure image showed the transformation of the four-layer phase into a nonstoichiometric state and a shear structure with a displacement vector of occurring between the face-sharing octahedra. Experiment by in situ observation during beam irradiation in an electron microscope indicates the process of the formation of the planar defect. A mechanism for the formation of the planar defect is proposed by which oxygen deficiency in face-sharing octahedra induces the displacement of SrO3 layers and oxygen octahedra which reduce the coordination number of Mn ions and the disruption of face-sharing octahedra.

In situ gravimetric measurements and microscopic examinations were used to determine the mechanisms of oxygen removal from synthetic ilmenite disks between 823 and 1353 K. Under a hydrogen atmosphere, iron was observed to form a layer of low porosity on the surface of samples early in the reduction. This created diffusion limitations for hydrogen to the reaction front and for the escape of water vapor. A shrinking core reduction model, modified to include the growth of this iron film, was capable of predicting the conversion-time relationships of ilmenite samples. An activation energy of 43.2 ± 2.6 kcal/gmole was determined to be representative of reaction control over the temperature range 823–1023 K.

Reaction sintering in the Na2O–MgO–Al2O3 system was studied with α–alumina green compacts containing Na2O and MgO in the pores of a controlled structure to produce β, β″–alumina polycrystalline at low temperatures. HCOONa and (CH3COO)2Mg were infiltrated into the alumina powder compacts (average particle size 0.2 μm) with relative densities of 51 to 66% at the compositions of Na2O/MgO/Al2O3 = 1/0.10/4.0–7.6. The alumina powder compacts were formed by filtration of the aqueous colloidal suspensions through gypsum molds. Phase change from α to β, β″–alumina proceeded fast at low temperatures in the samples with high Na2O/Al2O3 ratios. However, no significant densification occurred below 1500 °C owing to the volume increase of powder compacts associated with the phase change of α to β, β″–alumina. At 1600 °C, the green compacts were rapidly densified to relative densities above 99%. This densification was related to the liquid phase sintering based on the partial decomposition of β″–alumina. The dense β, β″–alumina polycrystalline consisted of needle-like grains of 2–5 μm in length and 1–2 μm in width.