Nickel-based superalloys have been coated with magnesium oxide (MgO) using ion-beam-assisted deposition (IBAD). This technique produced a well-oriented bi-axially textured MgO template layer with a Ф scan full width half maximum of 6.4°. The layer architecture for these samples was as follows: polished hastelloy C276/amorphous Si3N4/IBAD MgO/ pulsed laser deposited (PLD) Y2O3–ZrO2/PLD CeO2/PLD YBa2Cu3O7?δ. The subsequent heteroepitaxial PLD of 1.5-mm-thick YBCO showed a nominal critical current density of over 1 MA/cm2 (75 K, self-field) along a microbridge and had an in-plane mosaic spread of 4.8° and an out-of-plane spread of 1.3°. These results compare well with our earlier work using IBAD yttria-stabilized zirconia (YSZ) as a template layer and indicate that IBAD MgO is a suitable substitute. Furthermore, these results suggest that IBAD MgO could be adapted to and increase the feasibility of a continuous process to fabricate longer lengths of coated conductors at speeds 100 times faster than that previously realized with IBAD YSZ.

A cubic silicon nitride embedded in amorphous SiO2 compound has been characterized by means of high-resolution analytical electron microscopy. The specimen was prepared from β–Si3N4 powders at a high pressure and temperature by shock wave compression. The typical high-resolution electron microscopy image from one small crystallite together with its diffractodiagram pattern indicated that the Si3N4 crystallites had a cubic symmetry. The electron energy loss spectrum from the small crystallite is very different from those of outside amorphous SiO2 phase and raw β–Si3N4 particles, and there are more N elements that were detected in this small crystallite than those in standard Si3N4.

Tensile creep behavior of silicon nitride with aligned rodlike grains (anisotropic silicon nitride), fabricated by superplastic forging, was investigated at elevated temperatures. Creep rate of the anisotropic silicon nitride was about 1 order of magnitude lower than that of the isotropic one (without forging). The stress sensitivities for the isotropic and anisotropic specimens at 1200 °C were 2.1 and 2.6, respectively, and that for the anisotropic specimen at 1250 °C was 3.6. The grain alignment should cause a remarkable improvement in the creep resistance when a tensile stress is applied along the alignment direction.

Sol-gel technology was used to fabricate two types of near-infrared absorbing dye-doped polyceram coatings for eye protection purposes against laser radiation. Tolerance of polycarbonate visors against mechanical and chemical stresses may be enhanced by using these coatings. The visible light transmission maxima of high-quality 35 and 25 μm-thick spray-coated polyceram coatings were 70% and 90% for methacrylic and propyl functionalities, respectively. Optical densities at 1064 nm were 4 and 2.

Using a pure α–SiC starting powder and an oxynitride glass composition from the Y–Mg–Si–Al–O–N system as a sintering additive, a powder mixture was hot-pressed at 1850 °C for 1 h under a pressure of 20 MPa and further annealed at 2000 °C for 4 h in a nitrogen atmosphere of 0.1 MPa. High-resolution electron microscopy and x-ray diffraction studies confirmed that a small amount of β–SiC was observed in the liquid-phase-sintered α–SiC with this oxynitride glass, indicating stability of β–SiC even at high annealing temperature, due to the nitrogen-containing liquid phase.

Highly (111)-oriented and conformal iridium (Ir) films were deposited by a liquid source metalorganic-chemical-vapor-deposition process on various substrates. An oxygen-assisted pyrolysis of (methylcyclopentadienyl) (1,5-cyclooctadiene) Ir precursor at a wide range of substrate temperatures (Tsub) between 300 and 700 °C was used. At a low Tsub of 350 °C, the randomly oriented polycrystalline films exhibited an I111/I200 x-ray intensity ratio of 6. However, the films deposited at Tsub = 700 °C on native SiO2 and amorphous SiO2 surfaces were highly oriented with the I111/I200 ratios of 277 and 186, respectively. The transmission electron microscopy study revealed continuous, dense, and faceted microstructures of Ir films. Also, the step coverage of Ir on TiN (64%) was higher than that on amorphous SiO2 (50%) surfaces.

Photoluminescence (PL) measurements were performed on p-Cd0.96Zn0.04Te single crystals to investigate the dependence of the excitons on temperature. The activation energies and the longitudinal acoustic parameters of the excitons were determined from the temperature dependence of the PL spectra and were in reasonable agreement with the theoretical calculations. These results can help improve understanding for the application of p-CdxZn1–xTe single crystals in optoelectronic devices.

Aluminum nitride powder was synthesized by a combustion synthesis method using various additives. Each additive was mixed with Al powder, and the powder mixture was then pressed into a compact. The combustion reaction was ignited by heating the compact under N2 atmosphere of 0.4 MPa. Additives containing halogens were found to have a catalytic effect on the combustion reaction. High product yields were obtained when using additives of NH4X, CO(NH2)2, CH3(CH2)16COOH, and CO2H(CH2)2CO2H. In all these cases, eggshell-like skins were observed to form on the Al particles at the early stage of combustion. The catalytic effect, formation of the eggshell-like skins, and their effects on the combustion process were investigated and discussed.

The exothermic process that occurs around 700 K during calcination of ZrO2−x(OH)2x, associated with the crystallization of the low-temperature tetragonal metastable phase of ZrO2, was analyzed using x-ray diffraction, high-resolution thermogravimetric analysis (TGA), nitrogen adsorption, and modulated differential scanning calorimetry (MDSC). High-resolution TGA allowed us to determine the water loss, resulting from condensation of OH− groups. The amount was 0.137 wt% in our case, equivalent to 1.7 × 10−2 mol of H2O/mol of ZrO2. That corresponds to about one −OH group per nm2 being lost in that process. By using MDSC we determined that the change in enthalpy (∆Hglobal = −15.49 kJ/mol of ZrO2) was the result of two parallel contributions. One of them was reversible and endothermic (∆Hrev = 0.11 kJ/mol of ZrO2), whereas the other was irreversible and exothermic (∆Hirrev = −15.60 kJ/mol of ZrO2). The variability and magnitude of the exotherm, as well as the fact that the accompanying weight loss is so small, are consistent with a mechanism involving the formation of tetragonal nuclei, rather than global crystallization, and hence depend on the number of nuclei so formed.

Multilayers of tungsten carbide/carbon (WC/C) deposited by physical vapor deposition onto steel substrates were subjected to depth-sensing indentation testing. The investigation aimed at probing the influence of dissimilarities between the microstructure of the multilayers and substrate on the system mechanical properties. The resultant load-displacement data were analyzed both by conventional load-displacement (P-δ) and load-displacement squared (P-δ2) plots. Furthermore, it was demonstrated that the occurrence of annular through-thickness cracks around the indentation sites can be identified from the load-displacement curve. Also, analysis of the lower part of the unloading curve permitted us to identify whether the coating had popped up by localized fracture. The cracking mechanism was characterized using a new technique for cross-sectional electron microscopy of the nanoindentations. The information retrieved with this technique eliminates the problems, inherent in assessing at this small contact scales, whether the fracture is by coating decohesion or by interfacial failure. In our case, it was demonstrated that the failure mechanism was decohesion of the carbon lamellae within the multilayers. The mechanical properties (hardness and effective Young's modulus) were also assessed by nanoindentation. The hysteresis loops were analyzed and discussed in terms of the method developed by Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)].

A new microtensile test device using a magnetic-solenoid force actuator was developed to evaluate the mechanical properties of microfabricated polysilicon thin films that were 100–660 mm long, 20–200 μm wide, and 2.4-μm thick. It was found that the measured average value of Young's modulus, 164 GPa ± 1.2 GPa, falls within the theoretical bounds. The average fracture strength is 1.36 GPa with a standard deviation of 0.14 GPa, and the Weibull modulus is 10.4–11.7. Statistical analysis of the specimen size effects on the tensile strength predicated the size effects on the length, the surface area, and the volume of the specimens. The fracture strength increases with an increase of the ratio of surface area to volume. In such cases, the size effect can be corrected to the ratio of the surface area to volume as the governing parameter. The test data accounts for the uncertainties in mechanical properties and may be used to enhance the reliability and design of polysilicon microelectromechanical systems devices.

Non-steady-state solidification of YBa2Cu3O6+δ (Y-123) superconducting oxides was observed by the isothermal undercooling experiment. A sudden decrease in crystal growth rate was found for all the Y-123 samples processed at the different temperatures and from the different Y2BaCuO5 (Y-211) contents in the initial composition. Quantitative analysis revealed that the Y-211 particles are pushed by the Y-123 crystal and accumulate in the liquid during solidification. It is also found that the particle volume fraction increased and reached a constant value of about 0.6, when the growth rate decreased abruptly, regardless of a variety of growth conditions. A simple solidification model is developed to interpret the experimental observation. This model shows that particle accumulation, as a result of the particle-pushing behavior, causes less connectivity of the liquid and thereby decreases the liquid diffusion flux, which is responsible for the non-steady-state solidification of Y-123.

The resistance change with applied stress was measured for ruthenium-based metal–insulator–metal thick films under tensile and hydrostatic pressures over the temperature range −25 to +135 °C. The derived longitudinal, transverse, and hydrostatic piezoresistivity coefficients were corrected for elastic effects to yield the corresponding piezoresistivity coefficients and their temperature dependencies. The results clearly demonstrate for the first time a hydrostatic piezoresistivity coefficient that is sevenfold larger than the longitudinal component. Symmetry analysis is used to explain this phenomenon and to deduce additional piezoresistivity matrix elements and their degeneracy. In addition, pressure effects on electrical transport support a tunneling mechanism.

Depth-sensing indentation testing has proven extremely useful in the determination of mechanical properties of thin films and small volumes of material. However, the validity of the results obtained depend largely on the corrections made to the experimentally recorded data to account for initial penetration depth, nonuniformities in indenter shape, and compliance of the loading frame. The present work examines each of these issues and presents potential methods of correction for them. The present work also highlights limitations inherent in the data analysis methods and the significance of these in terms of experimental test parameters.

The linear thermal-expansion coefficients of yttrium silicate Y2SiO5, [Y2(SiO4)O] were measured in the temperature range from 20 to 1400 °C using x-ray diffraction. The anomalous behavior of thermal expansion was observed above Tc = 850 °C and was attributed to the displacive phase transformation. The transformation was reversible and resulted from the local order °C the compositional disorder and local fluctuation in the elastic free energy constrained a secondary transformation related to the polymorphic twin transformation. This created an additional peak in x-ray diffraction patterns at 2 's intensity. The characteristic of phase transformation both on heating and on cooling of the sample was also investigated using the differential thermal analysis method. The thermogravimetric technique did not indicate on a change of weight at Tc.

A series of photochromic sol-gel films are prepared through entrapping tungsten heteropolyoxometallates (PW12O403−, SiW12O404−) and molybdenum heteropolyoxometallate (PMo12O403−) into a kind of inorganic–organic matrix cohydrolyzed from tetraethylorthosilicate and 3-aminopropyltriethoxysilane. The films show reversible photochromicity. Irradiated with ultraviolet light, the transparent films change from colorless to blue. Then, bleaching occurs when the films are in contact with air or O2 in the dark. The Keggin-type polyanions interact with R–NH3+ cations strongly, and thus disperse uniformly in the sol-gel matrix, as proved by Fourier transform infrared spectra and x-ray diffraction. The molybdenum heteropolyoxometallate sol-gel film has higher photochromic efficiency and much slower bleaching than its counterparts of tungsten heteropolyoxometallate. A charge-transfer model which is supported by electron spin resonance and related literature [T. Yamase, Chem. Rev. 98, 307, (1998)] is put forth to explain the above experimental results.

Highly densed silicon nitride ceramics with various α/β phase ratios were produced by pulse electric current sintering process. The β-phase content of Si3N4 in sintered materials varied from 20 to 100 wt% depending on the sintering condition. The microstructure was observed by scanning electron microscopy and investigated by image analysis. Young's modulus, hardness, fracture toughness, and strength were strongly dependent on the α/β phase ratio. The fracture toughness increased from 4.6 MPa m1/2 for 20-wt% b-phase content to 8.2 MPa m1/2 for 95-wt% β-phase content, and the fracture strength showed a maximum value of about 1.6 GPa at 60-to-80-wt% β-phase content.

The structure and the crystallography of lithium niobate and lithium niobate–tantalate thin films (0.2–1.0 μm in thickness) with the tantalum composition range of 0 ≤ x ≤ 0.5 grown on (0001) sapphire substrate by thermal plasma spray chemical vapor deposition have been studied by means of cross-sectional high-resolution transmission electron microscopy and x-ray diffraction. The tantalum composition in the films shows a minor effect on the rocking curve full width at half maximum values. The narrowest rocking curve width was obtained for the LiNb0.5Ta0.5O3 film to be as low as 0.25° θ. The films are under compressive strain along the c direction; c- and a-axis lattice parameters are correspondingly smaller and higher than those of the bulk single crystal. Under optimized growth conditions, the LiNbO3 and LiNb1−xTaxO3 films are 97% c-axis oriented. The film out-of-plane orientation changes from the [0001] to the [0112] direction by either decreasing the growth rate or increasing the substrate temperature. Particular attention has been paid to the orientation of individual grains in the partly c-axis-oriented films. The results demonstrate that their orientations are not random and specific orientation relationships are preferred for the film nucleation. The surface of as-received sapphire substrate reveals polishing defects with the well-defined surface ledges of 1–2 nm in height with smooth terraces of 25 nm in width. In the case of columnar growth, the terrace width becomes a limiting factor controlling the lateral crystallite size in the film. Finally, the film growth mechanism is discussed.

Electromagnetic theory is used to characterize the magnetization processes in metals and alloys. The analysis shows that the free energy of a phase transformation may be reduced or enhanced by the magnetic field depending on the ratio of the permeability of the old and new phases. This means that the magnetic field can either stimulate or inhibit the nucleation process. The theory is in accord with the experimental results by others and us.

This paper describes a novel technique for determining the constitutive equation of elastic–plastic materials by the indentation technique using plural indenters with different apex angles. Finite element method (FEM) analyses were carried out to evaluate the effects of yield stress, work hardening coefficient, work hardening exponent, and the apex angle of indenter on the load–depth curve obtained from the indentation test. As a result, the characterized curves describing the relationship among the yield stress, work hardening coefficient, and the work hardening exponent were established. Identification of the constants of a constitutive equation was made on the basis of the relationship between the characterized curves and the hardness given by the load–depth curve. This technique was validated through experiments on Inconel 600 and aluminum alloy. The determined constitutive equation was applied to the FEM analyses to simulate the deformation including necking behavior under uniaxial tension. The analytical results are in good agreement with experimental results.