Using the lattice Green's function approach and LCAO (linear combination of atomic orbitals) electron theory, we investigate the atomistic configuration and lattice trapping of cracks in Si. The LCAO electron theory coupled to second order perturbation theory (SOP) has been used to derive explicit expressions for the bond breaking nonlinear forces between Si atoms. We calculate the cracked lattice Green's functions for a crack on the (111) plane and lying in the (110) direction. With the nonlinear forces acting in a cohesive region near the crack tips, the crack structure is then calculated. The calculated structure possesses a crack opening at the Griffith load which should allow penetration of typical external molecules to the crack tip at the Griffith loading. Other consequences for chemical reactions at the crack tip are discussed in the light of these results. The lattice trapping is low, only a few percent of the Griffith load.

Controlled chemical polymerization of tantalum ethoxide in the presence of glacial acetic acid (HOAc/Alk. = 16) and solubilized lithium acetate (Li/Ta = 1.00, H2O/Alk. = 55.55) was used for the preparation of an amorphous gel precursor to LiTaO3. Although additional investigations are required, the results suggest that successful formation of amorphous gel network, as opposed to that of colloidal tantalum (hydrous) oxide, may be due to the generation of a new organotantalum precursor via a structural modification reaction between the tantalum ethoxide and glacial acetic acid. The evolution of LiTaO3 ceramics from pre-ceramic gels was investigated using thermal analysis, electron microscopy, and x-ray diffraction. The results indicate that after the completion of gel pyrolysis (200–400 °C) and crystallization (Tc = 590 °C), ultrafine (average particle size 100–300 nm), single phase, crystalline (a = 5.243, c = 13.812 Å) LiTaO3 powders can be prepared at low processing temperatures.

Phosphor packages for a laser-heat thermoluminescence radiation-dosimetry system have been analyzed with Rutherford Backscattering Spectrometry and X-ray Photoelectron Spectroscopy. Samples consist of 20–50 μm diameter powder grains of CaSO4: Tm and LiF: (Mg, Ti) phosphor embedded in a transparent silicone matrix about 60 μm thick. Our principal finding with regard to layer morphology indicates an inhomogeneous outer layer of areal density at least ∼300 μg/cm2 depleted of phosphor and contaminated with boron.

The tensile properties, fracture behavior, and surface chemical composition of the rigid-rod heterocyclic aromatic polymer fiber poly-(p-phenylene benzobisthiazole), PBT, have been measured as a function of contact with nominally zero valent aluminum overlayers. The samples were produced by immersion of suitable fiber or film specimens in a molten aluminum-12.7 wt. % silicon alloy or by aluminum-vapor deposition followed by heat treatment. The strength of uncoated PBT fiber was 3.0 GPa. After 5 min immersion in the molten aluminum alloy, strengths drop to 80% and 25% of the uncoated fiber values for 600°and 700 °C immersion, respectively. Fiber strengths after aluminum immersion are from zero to 20% lower than the strength for corresponding uncoated fibers heated at an equivalent temperature in argon. Coated fibers exhibit tensile strengths after heating intermediate to similarly heated uncoated or immersed fibers. For all types of samples, the fiber fracture mode changes from fibrillar at failure strengths >1.9 GPa (independent of the environment) to planar at failure strengths <1.9 GPa. X-ray photoelectron spectroscopy of PBT fiber and film surfaces indicates oxidation of the polymer surface has occurred, most likely during fabrication of the fiber or film. The oxygen content of the surface layer is decreased when the film is immersed in molten aluminum-silicon alloy. The lack of corresponding changes in the relative intensities of the polymer C, S, or N photoemission peaks after this immersion suggests that the surface oxidized layer plays some role in protecting the polymer from degradation by molten aluminum. These results strongly suggest that it is possible to fabricate low-density, high-strength PBT/metal composites by liquid aluminum alloy infiltration if the melt temperature is kept below 680 °C and the contact time with molten aluminum kept below 3 min.

Basic thin film deposition processes for controlled deposition of the high-Tc superconductors of the Bi-systems are described. The layered structures of Bi-oxide superconductors are fabricated by a multitarget sputtering process. The multitarget sputtering process realizes the controlled deposition of single phase Bi-oxide superconductors, Bi2O2 · 2SrO · (n −1)CaO · nCuO2 for n = 1 to 5. The minimum thickness controlled by the multitarget sputtering is a half crystal unit-cell of around 15 Å, and the superlattices comprising (AkBk) · m, where A and B denote the Bi-oxide superconductors with different numbers of Cu–O layers, could be fabricated for k > 1, although ion mixing takes place during the sputtering deposition due to the bombardment of the highly energetic sputtered adatoms. Multitarget sputtering will be available for the fabrication of the artificially-made layered oxide superconductors (ALOS).