Mesoscopic structures of SiC fibers produced from polycarbosilane by different methods were studied by diffraction and small-angle scattering of neutrons and x-rays. Microvoids of a size of 4–10 Å in diameter have been observed for the first time by neutron scattering in a medium momentum transfer range (Q = 0.1–1.0 Å−1). The size and the volume fraction of β–SiC particles were determined for fibers prepared at different heat-treatment temperatures. The results show that wide-angle neutron scattering measurements are especially useful for the study of the mesoscopic structure of multicomponent materials.

We report the microstructure of magnetically melt-textured Dy-123 samples, as observed by polarized light metallography. The phase dimensions, morphology, orientation, nature, and distribution are outlined. Grain, twin structure pattern, and grain boundary are characterized. The relationship among cracking, secondary phases, and tetragonal-orthorhombic phase transformation is discussed. The results are obtained by observing a “not-too-well-ordered” region. This leads to definite conclusions on the relationship between crack spacing and 211 distribution, and to some confirmation of the growth mechanism and on macro- and microcrack origins. From the present observations, the effect of the oxygenation process and the quantification of the tensile stress in the materials can also be obtained.

Thin films of NiFe2O4 were deposited on SrTiO3 (001) and Y0.15Zr0.85O2 (yttria-stabilized zirconia) (001) and (011) substrates by 90°-off-axis sputtering. Ion channeling, x-ray diffraction, and transmission electron microscopy studies reveal that films grown at 600 °C consist of ∼300 Å diameter grains separated by thin regions of highly defective or amorphous material. The development of this microstructure is attributed to the presence of rotated or displaced crystallographic domains and is comparable to that observed in other materials grown on mismatched substrates (e.g., GaAs/Si or Ba2YCu3O7/MgO). Postdeposition annealing at 1000 °C yields films that are essentially single crystal. The magnetic properties of the films are strongly affected by the structural changes; unannealed films are not magnetically saturated even in an applied field of 55 kOe, while the annealed films have properties comparable to those of bulk, single crystal NiFe2O4. Homoepitaxial films grown at 400 °C also are essentially single crystal.

An aqueous, all nitrate, solution-based preparation of BaTiO3 is reported here. Rapid freezing of a barium and titanyl nitrate solution, followed by low temperature sublimitation of the solvent, yielded a freeze-dried nitrate precursor which was thermally processed to produce BaTiO3. XRD revealed that 10 min at temperatures ≧600 °C resulted in the formation of phase pure nanocrystalline BaTiO3. TEM revealed that the material was uniform and nanocrystalline (10–15 nm). The high surface to volume ratio inherent in these small particles stabilized the cubic phase of BaTiO3 at room temperature. It was also found that the average particle size of the BaTiO3 produced was highly dependent upon calcination temperature and only slightly dependent upon annealing time. This result suggests a means of selection of particle size of the product through judicious choice of calcination temperature. The experimental details of the freeze-dried precursor preparation, thermal processing of the precursor, product formation, and product morphology are discussed.

Lead-based relaxor ferroelectrics such as Pb(Mg1/3Nb2/3)O3 (PMN), Pb(Zn1/3Nb2/3)O3 (PZN), and their solid solutions with BaTiO3 and PbTiO3 have been prepared by a solution combustion process which involves metal nitrates/oxalate and tetraformal trisazine (TFTA) at 350 °C. Thermal evolution of perovskite relaxors has been investigated at different temperatures of calcination using the powder x-ray diffraction method. Particles are fine and sinter-active at low temperature (1050 °C). Both particulate and dielectric properties are compared.

The formation process of Ba(Mg1/3Ta2/3)O3 was confirmed to be a direct reaction between constituent compounds without the presence of intermediate compounds. Isothermal analysis of reaction kinetics indicated the controlling reaction to be a three-dimensional diffusion process. Based on the Ginstling–Brounshtein model, the activation energy of the formation process was estimated to be 257 kJ/mol. A new definition of the ordering parameter for Ba(Mg1/3Ta2/3)O3 was deduced to quantitatively evaluate the ordering degree. Raising sintering temperatures resulted in an increase in the ordering degree and bulk density of Ba(Mg1/3Ta2/3)O3. Reducing the barium content in Ba(Mg1/3Ta2/3)O3 substantially resulted in improved densification and enhanced ordering structure. On the other hand, an excess barium content in specimens hindered the progress of sintering, and also induced the disordering structure.

Si(100) wafers were prepared by both diamond turning and standard lapping and polishing techniques. For single-point diamond machining, characterization of subsurface damage resulting from ductile-regime machining identified a plastic-yield zone consisting of slip planes and dislocation networks extending 1 to 3 μm deep despite surface root-mean-square roughness values as low as 5 nm. For conventional lapping and polishing using alumina grit, a transition from brittle to ductile yield was observed for grit sizes less than 300 nm. Subsurface damage depth correlated to surface roughness in a more straightforward manner than for the diamond point machining. Completely damage-free material removal was obtained only when a chemical component to the polishing was present.

Multivariable screening and response surface experiments have been performed to model ohmic contact resistance (Rc) of a Ni–Ge–Au ohmic metal process for n+ GaAs-based high electron mobility transistors (HEMTs). Seven variables were examined via a fractional factorial screening experiment to rank the effects of each process variable. The results of the screening experiment indicated that the most significant variables were total Ge and Au evaporated thickness, Ge-to-Au ratio, and the post-alloy cooling time. Response surface experiments were designed around these three variables to examine the first- and second-order effects. The results enabled the development of an empirical model of ohmic contact resistance from which a new low value of 0.03 ± 0.03 Ω · mm (one-sigma) was predicted. Twenty confirmation runs on the new process indicated an average Rc of 0.06 ± 0.02 Ω · mm (one-sigma), with a range of 0.02 Ω · mm to 0.11 Ω · mm, a reduction from the previous average process value of 0.14 ± 0.07 Ω · mm (one-sigma).

A process for the formation of low-resistance Ni–Ge–Au ohmic contacts to n+ GaAs has been refined using multivariable screening and response surface experiments. Samples from the refined, low-resistance process (which measure 0.05 ± 0.02 Ω · mm) and the unrefined, higher resistance process (0.17 ± 0.02 Ω · mm) were characterized using analytical electron microscopy (AEM), transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and x-ray photoemission spectroscopy (XPS) depth profiling methods. This approach was used to identify microstructural differences and compare them with electrical resistance measurements. Analytical results of the unrefined ohmic process sample reveal a heterogeneous, multiphase microstructure with a rough alloy-GaAs interface. The sample from the refined ohmic process exhibits an alloy which is homogeneous, smooth, and has a fine-grained microstructure with two uniformly distributed phases. XPS analysis for the refined ohmic process sample indicates that the Ge content is relatively depleted in the alloy (relative to the deposited Ge amount) and enriched in the GaAs. This is not evidenced in the unrefined ohmic process sample. Our data lead us to conclude that a smooth, uniform, two-phase microstructure, coupled with a shift in Ge content from the post-alloy metal to the GaAs, is important in forming low-resistance ohmic contacts.

The Nb/α−Al2O3 system has been used as a model study for investigating the stability of different MBE grown epitaxial Nb films on α−Al2O3 substrates. The films were grown at 800 °C in ultrahigh vacuum. The growth process was monitored in situ by reflection high energy electron diffraction (RHEED). After deposition the structure of the film was investigated by x-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) which encompasses also selected area diffraction (SAD). Both techniques revealed the following orientation relationship between the Nb film and the α–Al2O3 substrate: (0001)α–Al2O3‖ (111)Nb; [2110]α–Al2O3‖ [110]Nb. The stability of the niobium films was investigated by annealing the Nb-film/α–Al2O3 system to temperatures up to 1500 °C for different periods of time. Surprisingly, the orientation relationship between the Nb film and the substrate changed to (0001)α–Al2O3‖ (110)Nb; [0110]α–Al2O3‖ [001]Nb. A model will be developed which shows that above a critical film thickness the growth orientation is metastable with respect to its crystallographic orientation. Furthermore, high resolution transmission electron microscopy (HREM) was performed to investigate the defect structure of the annealed Nb/α–Al2O3 interface.

The chemical interaction between two β′–O′ Si–Al–O–N ceramics and a number of iron-based alloys is studied by means of static interaction couple experiments at 1100 and 1200 °C. The onset temperature of reaction of Si3N4 with pure iron was found to be at 1095 °C, which is in good agreement with a calculated temperature of 1033 °C. During the interaction, silicon and nitrogen from the ceramic dissolve and diffuse into the iron alloy, whereas the remaining aluminum and oxygen form Al2O3 particles. The interaction between ceramic and iron alloy is reaction controlled. In the initial stage of the interaction, the dissociation rate of the ceramic is the rate-controlling step. After the ceramic/metal interface is isolated from the furnace atmosphere, the nitrogen solution rate into the iron alloy becomes rate controlling. The influence of alloying elements on the reactivity could be related to their effect on the nitrogen solubility in the iron alloy. Ni, Si, and C decrease the nitrogen solubility and decrease the reactivity with the sialon ceramic. Cr and Mo have the opposite effect. The thickness of the interaction layer on the ceramic side of the interaction couple was found to be a function of the calculated nitrogen solubility in the iron alloy at 1 atm nitrogen pressure, making it possible to predict the relative chemical reactivity of a number of iron-based alloys with the same sialon ceramic.

Ion beam mixing, diffusion properties, and phase stability have been investigated in Cu/Al2O3 bilayer samples. Specimens were prepared by vapor deposition and irradiated with 150 keV Ar+ ions up to a fluence of 1.5 · 1017 Ar+/cm2. Sample temperature under irradiation was varied between 77 K and 673 K. The mixing behavior was studied by analyzing the concentration depth profiles, determined by Rutherford Backscattering Spectroscopy. It was found that mixing efficiencies of Cu, Al, and O scale with Ar+ fluence. Radiation enhanced diffusion (RED), observed above room temperature, is separated from ballistic mixing and high temperature diffusion. The migration enthalpy for interdiffusion in the RED region (between RT and 300 °C) was estimated to be approximately 0.3 eV. Sputtering yields depending on temperature gradient near to sample and phase stability versus ion dose and temperature are also discussed.

The effects of Si additions on the behavior of high modulus carbon fiber reinforced aluminum matrix (CF/Al) composites during thermal exposure at 773 K for different times have been investigated. The composites were fabricated via hybridization with a small volume fraction of SiC particles using a pressure-casting process. The change of longitudinal tensile strength, the strength degradation of carbon fibers, and the microstructural observations on the interfaces of CF/pure Al composites and CF/Al-Si composites after thermal exposure undoubtedly indicate that the alloying element Si in an aluminum matrix can effectively prohibit the interfacial reactions at the fiber/aluminum interface and has positive effects on the characteristics of CF/Al composites.

Silane-coated glass microspheres randomly embedded in an epoxy polymer matrix have been employed as a model system to investigate the degradation of disordered composite materials by water, and to test various models of deformation and fracture. Numerous composites containing sodalime (A) glass in the range 0 to 25% by volume were tested dry and immersed in saturated NaCl at 40 °C for periods up to 70 days before testing. Enhanced osmotic water uptake due to percolating interface damage was observed for composites containing more than 15% glass. The electrical resistance of similar composites filled with conducting spheres confirmed the existence of a percolation transition, though with high resistance values implying no direct contact of the spheres. Tensile measurements conducted on dry material at a nominal strain rate of about 10−3 s−1 showed an increase in elastic modulus and a decrease in the fracture strength with increasing glass content. New detail was apparent in these curves and confirmed by statistical analyses. For wet specimens, in addition to a general embrittlement effect of water absorption, there was a distinct plateau or small peak in fracture strength in the range 9 to 12% glass, and an abrupt drop between 12 and 15%. The plateau can be related to favorable crack interaction effects between disconnected clusters of interfaces just below the percolation threshold. The steep increase in elastic modulus with glass content seen in the dry material vanished entirely in wet material, which behaved like a porous polymer above 6% glass, owing to osmotic interface damage within particle clusters.

The process of complex formation has been studied during milling a powder mixture of metallic Al and titania hydrogel, TiO2 · H2O. Solid state 27Al NMR and ESR are employed together with conventional x-ray diffractometry and thermal analyses. Al atoms partly changed from metallic to oxide state. 27Al NMR analyses indicate that two metallic Al states are allotted to distorted and undistorted lattices, while the other to AlOx units in the oxide state, where x is 4, 5, or 6. As detected by ESR, Ti4+ was partly reduced to Ti31, suggesting a redox reaction during milling. A vigorous thermit reaction was detected during subsequent heating of the mixture after prolonged milling. These results indicate the formation of Al–O–Ti bonds during milling, leading to Al2TiO5 on subsequent heating.