Uniform α–Fe2O3 particles of varying axial ratios have been prepared from hydrolyzed ferric chloride solutions at 100 °C. In the absence of phosphate anions, spherical particles were obtained by a mechanism that follows the classical LaMer and Dinegar scheme. However, in the presence of phosphates ellipsoidal particles were observed, with their formation taking place through an aggregation process from smaller primary particles of α–Fe2O3. It is also shown that all particles are monocrystalline irrespective of their formation mechanism.

The photoelastic stress-freezing technique is applied to observe the stress distribution inside two spheres of different sizes compressed together elastically. After the stress is frozen in, thin slices of the material containing the symmetry axis are prepared for observation through a polariscope. The stress distribution is compared with both the finite element numerical analysis and the Hertz analytical theory which is limited to small deformations. Among the three, the agreement between the experimental results and the finite element analysis is the best. The deviation from the Hertz theory is less in the larger sphere contacting a smaller one than in the smaller sphere contacting a larger one.

Models for nonthermal effects on ionic motion during microwave heating of crystalline solids are considered to explain the anomolous reductions of activation energy for diffusion and the overall faster kinetics noted in microwave sintering experiments and other microwave processing studies. We propose that radiation energy couples into low (microwave) frequency elastic lattice oscillations, generating a nonthermal phonon distribution that enhances ion mobility and thus diffusion rates. Viewed in this manner, it is argued that the effect of the microwaves would not be to reduce the activation energy, but rather to make the use of a Boltzmann thermal model inappropriate for the inference of activation energy from sintering-rate or tracer-diffusion data. A highly simplified linear oscillator lattice model is used to qualitatively explore coupling from microwave photons to lattice oscillations. The linear mechanism possibilities include resonant coupling to weak-bond surface and point defect modes, and nonresonant coupling to zero-frequency displacement modes. Nonlinear mechanisms such as inverse Brillouin scattering are suggested for resonant coupling of electromagnetic and elastic traveling waves in crystalline solids. The models suggest that nonthermal effects should be more pronounced in polycrystalline (rather than single crystal) forms, and at elevated bulk temperatures.

Scanning tunneling microscope observations of gold-coated polymer fracture surfaces are reported. We compare nm-scale surface features of poly(methyl methacrylate) (PMMA) fractured under three different loading conditions: in tension at room temperature, in tension at liquid nitrogen temperature, and in the double torsion geometry at room temperature (slow crack growth). Fracture surfaces of polystyrene and polycarbonate loaded in tension at room temperature are also described. Each of these surfaces shows distinctive nm-scale features which we interpret in terms of the interaction between craze growth (fibril formation) and crack growth along the craze boundary. The resolution of these images is sufficient to greatly complement other fractographic studies.

Experiments on thin mica sheets are used to demonstrate that coplanar cracks in double-cantilever beam specimens do not universally attract each other, as conventionally portrayed, but, at long range, actually repel. An elasticity analysis explains the repulsion in terms of a compression zone, ≍0.35 times the beam half-thickness ahead of the crack tip, generated by bending moments from the cantilever arms on the remaining specimen section.

An extensive investigation of twin structures in lanthanum aluminate single crystals at room temperature has been undertaken using White Beam Synchrotron X-Ray Topography (WBSXRT). Twin configurations, directly observable via orientation contrast, were found to comprise both large-volume, macroscopic twins and thick twin lamellae. Positional shifts of twin domain images with respect to matrix images, arising from the mutual misorientation of diffraction vectors, were measured on x-ray topographic images recorded from the (220)rhom planes approximately parallel to the specimen surface and compared to calculated values in order to solve the twin laws in this system. The dominant twin operations were found to be (101)rhom, (011)rhom, and (112)rhom mirror reflections. The potential influence of the twins on the growth of epitaxial Ba2YCu3O7−δ thin films is discussed.

X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were employed to investigate the effects of the ion beam implantation upon the chemical bonding and the final microstructure in the irradiated polyimide layer. XPS results show an increase of graphite cells with irradiation dose until a threshold is reached. A decomposing approach of data analysis for the experimental Raman spectra further discloses that the implantation parameters, i.e., dose, beam current density, and target temperature, play important but different roles in the formation of the final structure. By the current spectroscopic investigation, a deeper insight has been achieved into the origin of the enhanced conductivity, which shows the conductivity of modified layers are partly, even mainly, determined by their inner established order. This conclusion may serve as a guide in conductive polymer preparations.

Optical, electron microprobe, and x-ray diffraction analysis of 88 samples of various compositions between Ag2S and Ag2Se synthesized at high temperature in sealed quartz tubing indicates the presence of two solid-solution series in this system at ambient (room) conditions. One series extends from Ag2S to approximately Ag2S0.4Se0.7 and has the Ag2S-III-type structure (monoclinic). The second series ranges from Ag2S0.3Se0.7 to Ag2Se and is characterized by the Ag2Se-II-type structure (orthorhombic). Members of both series, in appropriate proportions, characterize the apparent compositional gap between the two solid solutions. Gradual shifts in the locations of the x-ray diffraction peaks along the compositional gradient of each solid solution revealed an expansion of the d-spacing as the larger Se ion was substituted for S in the Ag2S-III-type structure and a contraction as S was substituted for Se in the Ag2Se-II-type structure. The reported discrete phase, Ag4SSe (aguilarite, orthorhombic), appears to be simply a member of the monoclinic Ag2S-III-type solid solution.

In this paper, the techniques of SQUID magnetometry and line broadening in x-ray diffraction are employed for determining an important parameter for catalysts, viz. the particle size distribution. Magnetization versus temperature (5 K–400 K) and magnetization versus field (up to 55 kOe) data are reported for an α–Fe2O3 based catalyst. After determining the region of superparamagnetism, the distribution function f(r) is determined assuming a log normal distribution and Langevin paramagnetism of superparamagnetic particles. The distribution is found to be fairly symmetric with center near 65 Å and range of 35 to 115 Å. From line-broadening of Bragg peaks in x-ray diffraction, particle radii varying between 75 Å and 110 Å are obtained. These results are compared with the reported Mössbauer measurements of Huffman et al. on the same sample.

Diamond, silicon carbide, gallium nitride, aluminum nitride, and boron nitride are currently under development for both electronic and optoelectronic semiconductor devices. Predictions based on their physical properties indicate that devices made from these materials should be far superior to currently available devices in high power, high frequency, and short wavelength applications. Yet actual device implementation requires that adequate materials processing technology exists. In this review, the current state of the art for producing semiconductor devices from these materials is evaluated, and recommendations for areas needing further research are outlined.

An aqueous, metallo-organic precursor for PbTiO3 (PT), Pb(Zr, Ti)O3 (PZT), and (Pb1−x, Lax) (Zry, Ti1−y)1−x/4O3 (PLZT) ceramic powders has been developed employing the acetate complexes of Pb2+, La3+, Zr4+, and Ti4+. The crystallization behavior (e.g., degree of crystallization and crystallite size) was examined over the temperature range of 400–700 °C with concentrations of excess lead varying from 0–5% using x-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy techniques. It was found that PT, PZT, and PLZT crystallize at temperatures as low as 450 °C, 500 °C, and 500 °C, respectively, and the excess lead required for crystallization of the perovskite phase is ⋚1%. Intermolecular mixing among acetate precursors via chelating and bridging structures was evident and appeared to be responsible for the low crystallization temperatures. The process is compared to the current sol-gel methods for its possible use in thin film ferroelectric manufacture.

The microstructure of LaB6-base thick film resistors was investigated by cross-sectional transmission electron microscopy. The specimens were prepared by a technique that polished them to a thin wedge, thus avoiding ion-milling and permitting imaging over a distance of tens of microns. The resistor microstructure contained a finely divided electrically conductive phase of TaB2 and nonconducting crystals of CaTa4O11, formed during high temperature processing of glass and LaB6 ingredients of the thick film ink. Using higher surface area ingredients virtually suppressed the formation of CaTa4O11 crystals, and the microstructure became more uniform. Resistors made with higher surface area intermediates also had better voltage withstanding properties.

The formation of a polyester between citric acid (CA) and ethylene glycol (EG) was found to be a decisive factor for the foaming of resin intermediates in a Pechini-type powder process. This process was modified by changing the organic mass ratio of CA/EG which results in ceramic powders with different morphologies. The most porous resin intermediate (with or without chelated cations) was prepared using a polymeric gel made of equimolar citric acid and ethylene glycol. It was also found that a premixing of organic components, prior to adding constituent nitrate solutions, makes the whole process more controllable.

A method for calculating lattice statics Green's function is described for a bimaterial lattice or a bicrystal containing a plane interface. The method involves creation of two half space lattices containing free surfaces and then joining them to form a bicrystal. The two half space lattices may have different structures as in a two-phase bicrystal or may be of the same type but joined at different orientations to form a grain boundary interface. The method is quite general but, in this paper, has been applied only to a simple model bicrystal formed by two simple cubic lattices with nearest neighbor interactions. The bimaterial Green's function is modified to account for an interfacial crack that is used to calculate the displacement field due to an applied external force. It is found that the displacement field, as calculated by using the lattice theory, does not have the unphysical oscillations predicted by the continuum theory.

The equilibrium shapes of stress free inclusions with a small mismatch and possibly a small rotation from the matrix phase are studied. The model used includes both bond-breaking and elastic contributions to the interface energy. The unrotated shape contains only facets. Rotated inclusions sometimes contain smoothly curved parts as well. Interface phase diagrams are used to characterize the stable phase behavior of flat interfaces of fixed orientation.

The evolution of microstructure as a function of firing temperature in sol-gel derived porous titania xerogels was investigated by small-angle x-ray scattering (SAXS). SAXS curves for xerogels fired below 550 °C exhibit a well-defined structure peak. This peak indicates the presence of a high degree of order in the electron density correlations associated with the interparticle structure factor. Results from electron microscopy and SAXS give a primary particle mean diameter of 50 Å, while scaling analysis of the scattered intensity at large momentum transfer values yields the Porod exponent 4, indicating a sharp transition zone between the solid and void phases. The pore volume fraction of the unfired xerogel is consistent with random close-packing of spheres. The internal surface area decreases almost linearly with increasing firing temperature. Rapid grain growth and pore coarsening begin near 90% of theoretical density, and lead to a breakdown in pore interconnectedness and the development of isolated pores. Observed enhanced sintering properties may be attributed primarily to the large surface-to-mass ratio of the sol-gel particles. The SAXS curves were adequately fit using a bicontinuous phase model developed for late-stage spinodal decomposition structures. Alternatively, the microstructure can be described by a hierarchical close-packing of spheres model. SAXS results are compared with data from gas adsorption and electron microscopy.

Sol-gel solutions prepared from tetraethylorthosilicate (TEOS) hydrolyzed in acidic conditions were used to make thin films on Si wafers via spin coating. Solutions with H2O/TEOS ratios of 2, 5, and 10 were prepared and aged at room temperature in sealed containers for times ranging from <2.5 h to 1 month. Transmission Fourier transform infrared spectra acquired around 1 min after spinning showed peaks characteristic of both SiO2 and SiOH. Additional features at ≍580, 1093, and 1130 cm−1 were observed and possible origins are discussed. Peaks at ≍580 and 1130 cm−1, which increased in intensity with solution age time, are attributed to cyclic Si–O, e.g., 4-member rings. When films were exposed to room air, ring concentration decreased significantly within 30 min. Rings were stable for hours, however, when films were kept in N2. The feature at 1093 cm−1, most sensitive to H2O/TEOS, is attributed to residual Si–O–C.

Nonagglomerated ceramic precursor for Sr-doped lanthanum chromite powder was prepared by a modified resin–intermediate process using equimolar citric acid, ethylene glycol, and metallic nitrates. Pure and well-crystallized submicron powders with a narrow particle-size distribution were calcined from an optimally pulverized resin at a temperature of 750 °C for 2 h in flowing air. The material cost for organics used in the investigated process was considerably lower than the original Pechini process.

Mixed oxide powders, e.g., Al2O3−TiO2, SiO2−GeO2, and TiO2−SiO2, are used in industry to produce ceramics, optical fibers, catalysts, and paint opacifiers. The properties of these products depend upon the morphology of the powders. Ceramics and optical fibers are produced using either a uniform mixture of multicomponent particles or a uniform solution. The desired morphology for catalysts is a high surface area and many active sites. TiO2 coated with a layer of SiO2 is the desired structure for use as a paint opacifier. In this paper, TiO2−SiO2 mixed oxide powders were synthesized using a counterflow diffusion flame burner. TiCl4 and SiCl4 were used as source materials for the formation of oxide particles in hydrogen-oxygen flames. In situ particle sizes were determined using dynamic light scattering. A thermophoretic sampling method also was used to collect particles directly onto carbon coated grids, and their size, morphology, and crystalline form examined using a transmission electron microscope. A photomultiplier at 90° to the argon ion laser beam was used to measure the light-scattering intensity. The effect of temperature and of Si to Ti concentration ratio on particle morphology was investigated. Strong temperature dependence was observed. At high temperatures, TiO2 particles were covered with discrete SiO2 particles. At low temperatures, the structure changes to TiO2 particles encapsulated by SiO2. TEM diffraction pattern measurements showed that the TiO2 is rutile and the SiO2 is amorphous silica. At high Si to Ti ratios, SiO2-encapsulated TiO2 particles form. At low Si to Ti ratios, one obtains TiO2 particles covered with discrete SiO2 particles.