Plastic instabilities were observed to appear during dynamic ultramicrohardness testing of a solid solution Al–3.3 wt.% Mg alloy. The tests were carried out at room temperature with a Vickers hardness indenter in a computer-controlled dynamic ultramicrohardness testing machine. During the tests the applied load was increased from 0 to 2000 mN at constant loading rate. The instabilities appear as characteristic steps in the continuously recorded load-indentation depth curves. The physical basis for the occurrence of the instabilities is the interaction between moving dislocations and solute atoms, a phenomenon termed in the literature as serrated yielding, jerky flow, or Portevin-Le Châtelier effect. The instabilities start at a critical load, Fc, in the depth-load curve. Varying the loading rate, μ, by two orders of magnitude Fc was found to increase linearly with the loading rate.

Thin films of wurtzitic AlN have been deposited by molecular-beam epitaxy onto (001) oriented MgO substrates. The films are epitactic and align with the and the , as evidenced by transmission electron microscopy. This configuration, which matches a close-packed direction of the film and substrate, allows for growth of two symmetrically equivalent orientation variants of the AlN film. These variants are distinguished by a 90° rotation about the direction that is normal to the substrate surface. Each variant also aligns the and the to within 5° of being parallel to the (200)MgO. The microstructure of the AlN films and origins of these novel alignments are discussed.

Epitaxial films of (100) Ag were deposited onto (100) MgO substrates to a thickness of 4 μm with no evidence of (111) nucleation. Deposited films were smooth and had large areas, 50 × 50 microns square, free of morphological defects. Films were deposited using a two-step process. First, pulsed laser deposition was used to grow a 1000 Å Ag (100) seed layer on the MgO substrate. Second, e−beam evaporation was used to grow the film to the desired thickness. The high quality of the resulting films will allow them to be used as templates for further epitaxial deposition of other applied materials.

Epitaxial SrTiO3(STO) thin films have been grown successfully on Si(001) buffered with single and double buffer layers by pulsed laser deposition. Depending on the buffer structure and under appropriate substrate temperature and oxygen pressure values, epitaxial films are grown with single orientations. Epitaxial STO films with (0hh), (00h), and (hhh) out-of-plane orientation have been obtained for the first time on yttria-stabilized zirconia (YSZ)ySi(001), CeO2/YSZ/Si(001), and TiN/YSZ/Si(001), respectively. Secondary ion mass spectrometry analyses show sharp interfaces and good uniformity of the elements in each layer. The films are practically free of droplets, and the rms value of roughness is smaller than 0.5 nm.

We report a dendritic crystallization of ionic melt of lead molybdate (PbMoO4) under a concentric thermal field. The solidified melt is a PbMoO4 single crystal with [001] axis normal to surface. The dendrite arms propagate and branch along 〈310〉 and 〈130〉, forming a well-organized surface structure. It is evident that the interaction between a cation to its second-nearest anions determines the dendrite development and meltsolidification.

A temperature programmed method for determining diffusivities has been previously applied to oxygen diffusivity in V2O5. In this communication we extend the method to the case of oxygen diffusivity in MoO3. The reduction of MoO3 to MoO2 using NH3 is utilized to obtain experimental parameters such as the temperature of reduction and the activation energy for oxygen diffusion. These parameters are in turn used to solve Fick's equation for the oxygen diffusivity D0. The utility of this temperature programmed method for obtaining diffusivities has now been clearly established by extension to MoO3.

This review provides a comprehensive evaluation of the state-of-knowledge of radiation effects in crystalline ceramics that may be used for the immobilization of high-level nuclear waste and plutonium. The current understanding of radiation damage processes, defect generation, microstructure development, theoretical methods, and experimental methods are reviewed. Fundamental scientific and technological issues that offer opportunities for research are identified. The most important issue is the need for an understanding of the radiation-induced structural changes at the atomic, microscopic, and macroscopic levels, and the effect of these changes on the release rates of radionuclides during corrosion.

The detailed structure and interfacial reaction of epitaxial Yba2Cu3O7/Y-ZrO2 (YBCO/YSZ) films grown by chemical vapor deposition (CVD) on LaAlO3 (LAO) substrates are investigated by means of high-resolution electron microscopy (HREM), analytical transmission electron microscopy, and scanning transmission electron microscopy (STEM). The epitaxial relations of YBCO/YSZ/LAO are [100]YBCO // [110]YSZ // [100]LAO and (001)YBCO // (001)YSZ // (001)LAO. The optimum atomic configuration at the YSZ/LAO interface, in which oxygen is the first atomic layer on LAO, is proposed by using HREM combined with image simulation based on the atomic structure models of the interface. Near the YBCO/YSZ interface, two localized interfacial reaction products are formed: (i) a Y-rich modulated ZrO2 structure at the surface of the YSZ film, which may be caused by the diffusion of Y into the YSZ grains; (ii) an intergranular BaZrO3 phase formed by the diffusion of Ba along the columnar grain boundaries of the YSZ film during YBCO growth.

A self-assembly technique was used for fabrication of a Si/metal interface in nanometer scale. Fine particles of gold of nanometer-order diameter were generated by a gas-phase condensation method and deposited on a Si substrate. Through a heat treatment and a cooling process, a nanoscopic Si–Au composite structure was formed on the surface of the Si substrate. Then, surface diffusing Si atoms played an important role for fabrication of the Si–Au structure which were epitaxially grown projecting onto the substrate. Furthermore, the Si/Au interface was atomically flat with no mixed-layer formation, and the Au nanoparticles also had the same crystal orientation as that of the Si dots in spite of a large lattice constant mismatch between them. This structure was considered to be fabricated as a result of minimization of the total surface and interface energy of the Si/Au system.

The processes of rapid solidification from liquid to solid and heating from glass to crystalline for Ni3Al are simulated using molecular dynamics method. An amorphous state can be obtained by rapid solidification as long as the cooling rate is sufficiently large, which is very difficult to get in experiment. An fcc-type crystalline is obtained by heating the amorphous with a small heating rate. Based on the pair analysis technique, the microstructures of liquid, supercooled liquid, amorphous, and crystalline states of Ni3Al have been analyzed. Furthermore, the effects of cooling rate and heating rate on microstructures of Ni3Al during rapid solidification and heating processes have been discussed.

Kinetics of congruent ordering in Cu3Au at 350 °C was investigated by means of a three-dimensional atom probe. This instrument, called a Tomographic Atom Probe (TAP), enables atomic resolution images of a small volume (10 × 10 × 100 nm3) of the material reconstructed in the three dimensions of space. The time evolution of ordered domains at 350 °C shows that a t1/2 law is followed as soon as 5 min. For this aging time, the nucleus diameter is close to 1.7 nm. This scaling law was observed even before domains came into contact (t = 50 min). Competitive growth was observed to start as soon as 5 min. The number density was observed to decrease rapidly up to t = 50 min. A slower decrease was observed when domains begin to impinge. Experimental conditions and requirements as well as advantages of TAP as compared to HREM for the study of ordering are discussed in detail.

Recently, a new method, i.e., a plasma jet method, was developed in our lab for the production of ultrafine powders. In the present work, we investigated the formation of binary Al–Fe, Al–Si, Fe–Si, Al–Cu, Al–Ni, Ni–Ti, Fe–Cu, and Fe–Ti ultrafine powders using this method. Premixed pure elemental powders of various compositions of Al–Fe, Al–Si, Fe–Si, Al–Cu, Al–Ni, Ni–Ti, Fe–Cu, and Fe–Ti were used as starting materials. These premixed powders were injected into the plasma jet of Ar–N2 working gas to form ultrafine powders. The obtained ultrafine powders were characterized by x-ray diffraction and transmission electron microscope to check the microstructures of ultrafine particles.

X-ray powder diffraction was used to characterize a Pt–Si sputtering target and subsequent films. The powder patterns of each sample indicated lines due to diffraction from different phases. We have initiated a preliminary study through which we have analyzed and characterized these films. The results presented for these samples corroborate with results observed for this system in the planar configuration.

A systematic structural characterization has been conducted on combustion synthesized MoSi2–Si3N4 powders and plasma sprayed composites by transmission electron microscopy (TEM). The powders are cleaner and with little surface oxide contamination than most commercial powders. The distribution of the two phases can be tailored by modifying the synthesis conditions, which has resulted in improved retention of Si3N4 after plasma spraying. TEM studies performed on deformed composites indicate a strong link between even dispersion of second phases and enhanced dislocation plasticity in the plasma sprayed composites.

Unidirectional celsian matrix composites having 42–45 vol% of uncoated or BN-SiC coated Hi-Nicalon fibers were tested in three-point bend at room temperature. The uncoated fiber-reinforced composites showed catastrophic failure with strength of 210 ± 35 MPa and a flat fracture surface. In contrast, composites reinforced with coated fibers exhibited graceful failure with extensive fiber pullout. Values of first matrix cracking stress and strain were 435 ± 35 MPa and 0.27 ± 0.01%, respectively, with ultimate strength as high as 960 MPa. The elastic Young modulus of the uncoated and coated fiber-reinforced composites were 184 ± 4 GPa and 165 ± 5 GPa, respectively. Fiber push-through tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interface. The low strength of composite with uncoated fibers is due to degradation of the fiber strength from mechanical damage during processing. Because both the coated- and uncoated-fiber-reinforced composites exhibited weak interfaces, the beneficial effect of the BN-SiC dual layer is primarily the protection of fibers from mechanical damage during processing.

A simple model of the elastic stress in a composite hydrogen absorbing material is developed to account for the hydrogen storage properties of nanocrystalline FeTi with a network of intergranular phase having a wide storage site energy distribution. The model accounts for the equilibrium properties of nanocrystalline FeTi hydrogen absorbers made by ball-milling such as the narrowing of the miscibility gap and changes in plateau pressure. A second model is proposed for disconnected inclusions of the second phase. The effect of chemical disorder is also briefly examined.

Metallo-organic thin film decomposition (MOD) was used in forming barium strontium titanate (BST) thin film capacitors on phosphorus doped polysilicon films deposited on 4 in. silicon wafers. A single step deposition process yielded highly uniform, crack-free BST films ranging up to 0.25 εm in thickness and having various step heights and dimensional area. Scanning electron microscopy (SEM) showed very good step coverage and planarization of the BST. The capacitors had capacitance densities above 200 nF/cm2, leakage current densities less than 1.55 εA/cm2 at a bias voltage of 10 V, and a dielectric breakdown field above 1 MVycm. Small temperature coefficients of capacitance and dissipation (tan δ) were also observed. Frequency response measurements were made using the BST capacitors and on-chip resistors in low pass and high pass circuit configurations. A plot of relative gain and phase angle versus frequency showed excellent agreement with predicted results.

Phosphate ceramics were synthesized using sol-gel technique of direct reaction of P2O5 with tetraethoxy silane (TEOS) or titanium tetraethoxide (Ti(OEt)4). The reaction mechanism of P2O5 and TEOS was deduced using liquid and solid-state NMR. Hexacoordinated silicon in phosphosilicate gels was observed. A specially structured titanium phosphate-layered Ti(HPO4)2 · 2H2O was synthesized for the first time through the sol-gel method. The gelation process and phase transformations were investigated.

The microwave sintering process not only densified the ZnO materials in a higher rate, but also resulted in significantly better varistor characteristics. Large nonlinear coefficient and low leakage current density were attained by cooling the samples under a rate of 80 °C/min after sintering, followed by 600 °C postannealing for 60 min under oxygen atmosphere. Inappropriate annealing deteriorated the varistor characteristics that can either be attributed to the insufficient reoxidation along grain boundaries when annealed in N2 (or air) or loss of Zn species in these regions when annealed at 750 °C (900 °C). By contrast, the degradation behavior of these materials can be improved by the annealing process regardless of the annealing atmosphere or temperature.

The kinetics of phase transitions and phase segregation induced by annealing temperature on the Ti–W–O gas-sensing layer was studied by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The main goal was to identify, on the basis of kinetics studies, structurally stable Ti–WO3 thin film phases and compare their response to polluting gases in order to determine possible correlations between structural and electrical properties of the sensing layers.