Contact-induced fracture modes in trilayers consisting of a brittle bilayer coating on a soft substrate were investigated. Experiments were performed on model transparent glass/sapphire/polycarbonate structures bonded with epoxy adhesive, to enable in situ observation during the contact. Individual layer surfaces were preferentially abraded to introduce uniform flaw states and so allowed each crack type to be studied separately and controllably. Fracture occurred by cone cracking at the glass top surface or by radial cracking at the glass or sapphire bottom surfaces. Critical loads for each crack type were measured, for fixed glass thickness and several specified sapphire thicknesses. Finite element modeling (FEM) was used to evaluate the critical load data for radial cracking, using as essential input material parameters evaluated from characterization tests on constituent materials and supplemental glass/polymer and sapphirse/polymer bilayer structures. The FEM calculations demonstrated pronounced stress transfer from the applied contact to the underlying sapphire layer, explaining a tendency for preferred fracture of this relatively stiff component. Factors affecting the design of optimal trilayer structures for maximum fracture resistance of practical layer systems were considered.

The magnetic properties of the substitutional iron and aluminum impurity centers in a sintered Vycor silica glass were studied before and after 1.1–1.3 MeV γ irradiation. Observation of two overlapping spin resonances (g ∼ 4.20–4.28) in the spectra of both the irradiated and preirradiated glasses indicated the existence of two types of tetra coordinated substitutional iron centers of the [FeO4−/Na+]0 type. The intensity of these electron-paramagnetic resonance (EPR) signals decreased upon g irradiation of the glass with concomitant generation of aluminum hole center [AlO4]0, which was manifested by the occurrence of a new six-line EPR signal with g 4 2.009, while thermal annealing of these aluminum oxygen hole centers restores the intensity of the iron centers almost to their preirradiation level. This result suggests that if not the whole, a major fraction of the electrons released in the process of g-ray-induced hole trapping at the Al site are captured by the substitutional iron centers. The electron traps, thus formed, are quite stable and can be deactivated by thermal stimulation.

To improve the oxidation resistance of TiB2 material, dense silica (SiO2) layer was caused to form on the surface. The coating layer was formed on the surface by exposing the specimens next to a bed of SiC powder in a flowing H2 containing 0.1% H2O at 1450 °C. Part of SiO2 “smoke”, generated by a reaction between the SiC powder and H2O in the H2 gas stream, was deposited on the sample surface to form a dense and uniform SiO2 layer. Beneath the SiO2 layer, an interfacial layer composed of Ti2O3 and B2O3was formed. Oxidation resistance of the specimen was improved markedly by the coating layers. The coating layers enhanced the oxidation resistance through the retardation of oxygen transport and also through the consumption of oxygen by a reaction with Ti2O3 to form TiO2.

Small spherical samples (diameter approximately 2 mm) of NdBa2Cu3O7−δ (Nd123) were fully melted in Ar gas flow in an aero-acoustic levitation device and subsequently rapidly cooled by splat quenching. For samples quenched above the liquidus, the microstructual and x-ray-diffraction (XRD) observations suggested the existence of the amorphous phase with small quantities of the BaCuO2 and BaCu2Ox. The high-temperature XRD results indicated that the decomposition of the amorphous phase, probably assisted by atmospheric CO2 and H2O, led to formation of the BaCO3 phase at 400 °C and, subsequently, the Nd123 phase was formed by the solid diffusion above 800 °C. Another set of Nd123 samples was fully melted in O2 gas flow, undercooled while levitated, and then splat quenched at a temperature below the peritectic temperature (TP). These samples possessed a microcrystalline microstructure of the Nd123 phase that was confirmed by XRD. This indicated that the Nd123 phase was solidified directly from the undercooled melt quenched below TP.

Y2-xLnxO3 (Ln 4 Ce, Pr, Nd, Eu, Gd, Ho, and Er) powders obtained by propellant synthesis have been characterized using small-angle x-ray scattering, wide-angle x-ray scattering, and transmission and scanning electron microscopy. All the samples showed a very porous, open microstructure with fractal scaling properties. The building blocks of the fractal aggregates are nanocrystallites of lanthanide-doped Y2O3, with variations in the cubic lattice constant proportional to the composition of the solid solution and to the lanthanide ionic radius. The particles had a narrow distribution of sizes with an average value in the 20–50 nm range. They are made of a core of 10–20 nm, consisting of almost perfectly ordered crystals and a “fuzzy” layer, characterized by either a growing lattice disorder or by a compositional gradient. From this dimension, up to at least 200 nm, the particle aggregate is a mass fractal with a fractal dimension, DMf, in the 1.6–2.0 range.

Coordination structures of implanted Fe, Co, and Ni ions were studied in 1.78–2.00-MeV 5 × 1016 ions/cm2-implanted silica glasses by x-ray absorption and optical absorption spectroscopies. It was found from x-ray absorption spectra that the implanted Fe, Co, and Ni ions are coordinated by ca.3 oxygen atoms. The implanted ions dispersed in glass matrix and did not form crystals. The valence of the implanted ions was about 1.5. The Fe–O, Co–O, and Ni–O interatomic distances were 190, 191, and 192 pm, respectively. In addition, it was found from optical absorption spectra that one-fifth of implanted Co ions were present as Co2+ ions in tetrahedral symmetry.

The sponge impregnation of water-based suspensions of hydroxyapatite powders synthesized by the coprecipitation method was investigated. The powder characteristics and slurry properties were correlated with the porosity and mechanical properties of the porous bodies obtained. The rheological characterization in the continuous flow condition revealed a strong dependence of the rheological behavior on the solid loadings particularly with high specific surface area powder. The behavior changed from newtonian to plastic, with pronounced hysteresis effects due to time dependency, by increasing the solids loading from 10 to 18 vol%. The morphology and distribution of the macropores could be related to the starting powder crystallinity and morphology as well as to the rheological properties of the suspensions. The compressive strength of the materials was strongly influenced by the porosity, while there was almost no dependence on the crystallinity of the powder. From a statistical viewpoint, the microporosity better explained the behavior of the mechanical strength than the total porosity.

A new route, based on the use of ionic calcium phosphate cements, has been developed to synthesize hydroxyapatite. Cements were prepared from tetracalcium phosphate, α–tricalcium phosphate, phosphoric acid, strontium nitrate, and water. They were then mixed and shaped. Cements with various amounts of strontium and different (Ca + Sr)/P atomic ratios were prepared. All the materials obtained were coherent and solid. When the amount of strontium was low, mixed hydroxyapatite was obtained at low temperatures. Mixed calcium strontium apatite was obtained after heating. This original method can be of interest in various fields such as biomaterials or the storage of radioactive waste.

Polycrystalline Ce0.77Nd0.23O1.885 having a relative density in excess of 98% was prepared. Oxygen diffusion experiments were performed for the temperature range from 750 to 1100 °C, in an oxygen partial pressure of 6.6 kPa. The concentration profile of 18O in the specimens following diffusion annealing was measured by secondary ion mass spectroscopy (SIMS). The oxygen self-diffusion coefficient obtained using secondary ion mass spectrometry was expressed by D = 6.31 × 10−9 exp(−53 kJ mol−1/RT) m2 s−1 and was in the extrinsic region. The oxygen diffusion coefficient of Ce0.77Nd0.23O1.885 was larger than that of Ce0.8Y0.2O1.90; it was close to those of Ce0.6Y0.4O1.80 and Ce0.69Gd0.31O2−δ. The oxygen diffusion coefficient obtained by the tracer method at 700 °C agreed with that calculated from the electrical conductivity in Ce0.77Nd0.23O1.885. The activation energy of the surface exchange coefficient was 94 kJ mol−1, and the values of the surface exchange coefficient were similar to those of stoichiometric CeO2 and ThO2.

The diffusion of oxygen in silicon was modeled to result from the diffusion of dissolved silicon monoxide. The SiO molecule dissolved in the largest space in the diamond lattice of silicon, oriented in a 〈111〉 direction, with the oxygen lightly bonded to a network silicon atom. This configuration is consistent with infrared spectra, dichroism of infrared spectral lines, and internal friction of oxygen in silicon. The anomalous rapid diffusion of oxygen below 700 °C could result from the diffusion of molecular water or oxygen in silicon, but more evidence is needed to test these possibilities. Diffusion and exchange of silicon tracer in SiO with lattice silicon can possibly explain tracer diffusion of silicon in silicon.

The thermal activation energies for conduction of Nb-doped SrTiO3 grains and grain boundaries have been investigated by impedance spectroscopy. First, to observe the effect of electrode/SrTiO3 bulk interface, the varied impedances of SrTiO3 single crystal were measured with temperatures. The activation energy of an electrode/bulk interface was determined to be 1.3 eV, whereas that of bulk was 0.8 eV. When the impedances of Nb-doped SrTiO3 ceramics were measured, it was suggested that the more precise impedance values of a single grain and a single grain to grain junction be obtained using a microelectrode method. The activation energies for a grain, a grain boundary, and an electrode/bulk interface were determined to be about 0.8, 1.3, and 1.5 eV, respectively. From these measured results, it was suggested that the activation energy, 0.8 eV, measured in grain was originated from oxygen vacancies and the activation energy, 1.3 eV, in grain boundary was from strontium vacancies.

Barium titanate nanosized powders were prepared by a slightly modified Pechini method. The obtained polymerized resin was used as the precursor for BaTiO3 powder production. DTA TG thermal analysis indicated that thermal decomposition of the precursors proceeds through four major step processes: (i) dehydration reaction; (ii) combustion reactions; (iii) intermediate phases formation; (iv) decarbonation of the intermediate to give BaTiO3. X-ray diffractometry (XRD) and Raman spectroscopy results indicated that, depending on the heating rate, the BaTiO3 formation took place via a predominant solid-state reaction between nanosized BaCO3 and amorphous TiO2 (TiO2−x) when crystallized by a low-heating rate (1.5 °C/min), although a small amount of a quasi-amorphous intermediate phase was also present. BaTiO3 crystallization by rapid heating rate (5 °C/min) took place through a quasi-amorphous intermediate phase formation as the main rate-controlling factor for the crystallization process. The fact that the low heating rate minimizes the intermediate phase content indicates the strong influence of the thermal heating on the kinetics of the involved transformation or in the mechanism. Although XRD results seem to indicate the formation of pseudocubic BaTiO3 as the final reaction product, the Raman spectra indicated as more probable the formation of a mixture of an oxygen-deficient hexagonal and tetragonal BaTiO3 phases below 700 °C. Above that temperature the tetragonal BaTiO3 was the only phase present. As-prepared BaTiO3 strongly agglomerated powders were relatively sinter active, leading to dense ceramic bodies (≥95% of the theoretical value). Microstructural (grain size approximately 1 mm) and room-temperature dielectric properties (ετ ≈ 2000 and tan δ ≤ 2%) at 10 kHz indicated that the obtained powders have to be optimized.

Complete control of the texture of a film during growth requires the ability to determine the in-plane and out-of-plane texture simultaneously. We present both computer simulation and experimental evidence for the simultaneous establishment of out-of-plane and in-plane texture during ion beam assisted deposition of aluminum. Channeling along 〈110〉 directions (60° from the normal) creates a {220} out-of-plane orientation rather than the thermodynamically preferred {111} orientation. The ion beam also aligned 〈220〉 directions within the plane of the film. Measured x-ray pole figures confirmed the presence of a strong out-of-plane texture and the presence of two main, twin-related, in-plane texture components. We theoretically demonstrated that it is impossible to completely control both the in-plane and out-of-plane texture with a single ion beam in high-symmetry crystals and two ion beams must be employed to ensure complete texture control.

This article describes a convenient, noncontacting technique for determining the flexural rigidity and residual stress in thin membranes. The method was based on transient grating photoacoustics, also known as impulsive stimulated thermal scattering. Crossed laser pulses provided a coherent source of wavelength tunable acoustic modes in the membranes. Diffraction of a probe laser revealed the time dependence of these motions. The measured dispersion of the lowest-order Lamb mode at small acoustic wavevectors, coupled with classical plate theory, allowed the flexural rigidity and the residual stress to be determined. The technique, its accuracy, and spatial mapping capabilities were demonstrated through analysis of membranes designed for masks in next-generation lithography systems based on projected beams of electrons.

An experimental and theoretical approach has been described for the determination of the strength of partially aligned discontinuous fiber-reinforced composites. The fiber alignment information was obtained as a Gaussian or normal distribution function by using an x-ray-diffraction technique. The distribution function was then used in the composite strength equation to calculate the theoretical strength. This approach was applied to a composite of vapor grown carbon fiber (VGCF) in a polypropylene matrix, and the experimental and theoretical results were compared. As expected, the composite strength increased with increase in fiber volume fraction and the degree of fiber alignment. It was also observed that the composite strength was sensitive to variation in fiber length when the average fiber length was less than the critical fiber length. At higher fiber volume fractions the composite strength was much lower than predicted by theory. This is most likely due to incomplete wetting and infiltration of the VGCF.

The effect of fiber texture on the x-ray residual stress analysis in thin films of cubic materials is discussed according to different mechanical models. The x-ray elastic constants (XECs) were calculated from single-crystal elastic constants for Cu, cubic ZrO2, and TiN, in the case of a typical [111] fiber texture with different spread of orientations [expressed by the half-width at half-maximum of the (111) pole figure]. Calculations were performed according to Reuss, Voigt, and Hill models, considering different crystallographic directions in cubic structures, in order to underline the effect of the mechanical anisotropy and fiber texture. The results clearly indicated the dependence of the XECs on the sample tilting angle, with the notable exception of [111] and [200], which were texture oscillation-free directions. Profiting from this condition the residual stress gradient in a fiber-textured TiN thin film deposited on stainless steel was determined by the simultaneous analysis of texture and residual strain for the (111) and (200) reflections. Advantages and limits of the procedure are discussed together with the experimental results.

Adhesion and subcritical debonding at interfaces between a silica-filled epoxy underfill and a silicon die passivated by silicon nitride and benzocyclobutene (BCB) layers were investigated. Adhesion was measured in terms of a critical value of the applied strain energy release rate, G (J/m2 ). Subcritical debond-growth rates in the range of 10−9 to 10−3 m/s were characterized as a function of applied G. Adhesion and subcritical debonding were affected by changes in interfacial chemistry and environment. The surprisingly large effect of adjacent layer elastic properties on interfacial adhesion was demonstrated with simulations of interfacial fracture using a mechanics of materials approach. Interfacial chemistry was modified by using different adhesion promoters, by varying the BCB cure state, and by using different epoxy underfill resins. The effects of environmental variables were studied with temperature- and humidity-controlled environments in order to determine the separate roles of moisture activity and temperature.

c-Axis-oriented (Hg0.9Re0.1)Ba2CaCu2Oy thin films were grown on the (100) plane of SrTiO3 substrates by a so-called two-step process. Transmission electron microscopic observation revealed that, in the film annealed under a higher temperature, some steplike regions appeared at the top layer of SrTiO3 substrate. High-resolution transmission electron microscopic images showed that the lattice parameters in these regions are about 4.05–4.15 Å, being longer than the lattice parameter of SrTiO3. It is supposed that a chemical reaction occurred in these regions, and a phase of (Bax,Sr1−x)(Cuy,Ti1−y)O3δs was formed by partially substituted Ba for Sr and Cu for Ti.

GaN grown on sapphire (α–Al2O3) was characterized by laser-induced molecular beam epitaxy. Threading dislocations with Burgers vectors of 1/3〈1120〉, 1/3〈1123〉 and [0001] were observed with a predominance of the first type. Additionally, inversion domains with Ga-polarity existed with respect to the adjacent matrix, which was of N-polarity. The dislocation densities and coherence lengths were deduced from x-ray diffraction and found to be in accordance with those measured by transmission electron microscopy. Both displacement fringe contrast analysis and high-resolution transmission electron microscopy results indicated that the inversion domain boundaries had Ga–N bonds between domains and the adjacent matrix.

Fiber textured {100}-oriented lead magnesium niobate–lead titanate (PMN–PT) (70/30) films with thicknesses between 0.35 and 2.1 mm were prepared using chemical solution processing. The degree of preferred orientation changed little with increasing thickness. However, the measured dielectric constant, remanent polarization, and piezoelectric coefficients (d31) increased with increasing film thickness. The effective d31 coefficients of highly {100}-oriented PMN–PT films on Pt-coated Si substrates were found to range from −16 to −96 pC/N. Ultraviolet illumination during poling resulted in abnormal aging behaviors and lower overall aging rates for the films. The initial nonlinear aging behavior was attributed to the presence of an internal space-charge field that developed from photoinduced charge carriers. As the space-charge field decays over time, the magnitude of d31 increased until 450–500 min after poling, at which time d31 remained either constant or declined slightly. Thus, the changes in d31 were limited to 1–2%/decade 500–600 min after poling.