The deformation behavior of melt-textured Y1Ba2Cu3O7-x (YBCO) prepared by the vertical gradient freeze (VGF) method was investigated by high temperature deformation experiments at temperatures ranging from 850 to 950 °C. The experiments were performed in an atmosphere of pure oxygen under uniaxial pressure with constant strain rates in the range from 1 × 10−5 to 5 − 10−4 s−1. An analysis of the dependence of the steady state flow stress on the strain rate and the deformation temperature reveals that the predominant deformation mechanism is dislocation glide and climb controlled by climb at Y-211 particles and that no significant grain boundary sliding occurs. Furthermore, transmission electron microscopy observations of deformed and undeformed samples support a deformation mechanism based on dislocation movement. The total fracture strain, however, does not depend on the temperature or strain rate. Scanning electron microscopy investigations of the fracture faces of samples deformed until fracture reveal that fracture does not occur within the Y-123 matrix but along platelet boundaries. An improvement of the fracture behavior is expected by introducing large Y-211 particles interconnecting neighboring platelets.

This paper presents the results of a systematic investigation of structure and formation of the interface between gold and trimethylcyclohexane polycarbonate, particularly concerning interface evolvement during gold evaporation and the influence of evaporation rate, substrate temperature, and subsequent annealing. The means of investigation were cross-sectional transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. Extensive metal diffusion into the polymer and cluster formation near the interface were observed at deposition rates of the order of one monolayer per minute and below. The penetration depth is strongly temperature dependent. At high evaporation rates metal aggregation at the surface prevents cluster formation inside the polymer. No diffusion into the polymer was observed from metal films deposited at room temperature after extensive annealing at elevated temperatures.

A 100-nm CuFeS2 ultrafine powder was prepared through a solvothermal reaction at 200–250 °C. X-ray powder diffraction and transmission electron microscopy results revealed that chalcopyrite-phase CuFeS2 was crystallized with single-crystalline nature and preferential orientation growth. Mössbauer spectrum exhibited a six-peak hyperfine magnetic spectrum and a single nonmagnetic peak. Elemental analysis gave the atomic ratio of Cu:Fe:S of 1:1.02:2.10. The influence factors on the formation of CuFeS2 ultrafine powder are discussed.

Both the thermoelectric power and the resistivity of the oxygen deficient YBa2Cu3O6+x samples were measured. The rare-earth-doped samples, such as Sm and Dy, whose magnetic moments in the +3 valence state are different, were studied. Then the power factor of the thermoelectric ability was calculated. The power factor of the Dy-doped samples is smaller than those of the other samples, especially at high temperature. This smallness of the power factor is the main reason why the Dy-doped samples have larger resistivity. We try to analyze the data by the theoretical expression under the variable range hopping conduction model. The expression of the thermoelectric power could be fit for the nondoped and Sm-doped samples, except at low temperature. In this situation, the thermoelectric power increases as temperature increases, and this temperature dependence is good for the thermoelectric materials at high temperature where the resistivity decreases with temperature increasing.

Porosity depth profiles in porous silicon were realized by time modulation of the applied current density during electrochemical etching of crystalline silicon. The samples were investigated by variable angle spectroscopic ellipsometry. Using a basic optical model based on isotropy assumptions and the Bruggeman effective medium approximation, deviations from an ideal profile in terms of an interface roughness between the silicon substrate and the porous silicon layer and a compositional gradient normal to the surface were revealed. Furthermore, optical anisotropy of the sample was investigated by generalized ellipsometry. The anisotropy was found to be uniaxial with the optic axis tilted from surface normal by about 25°. The material was also found to exhibit positive birefringence.

Polycrystalline silicon thin films (polysilicon) have been deposited on single crystalline silicon substrates, and square and rectangular windows have been etched into these substrates using standard micromachining techniques. Pressure-displacement curves of the resulting polysilicon membranes have been obtained for these geometries, and this data has been used to determine the elastic constants E and v. The microstructural features of the films have been investigated by transmission electron microscopy (TEM) and x-ray diffraction. The grains were observed to be columnar and were found to have a 〈011〉 out-of-plane texture and a random in-plane grain orientation. A probabilistic model of the texture has been used to calculate the bounds of the elastic constants in the thin films. The results obtained from bulge testing (E = 162 ± 4 GPa and v = 0.20 ± 0.03) fall in the wide range of values previously reported for polysilicon and are in good agreement with the microsample tensile measurements conducted on films deposited in the same run as the present study (168 ± 2 GPa and 0.22 ± 0.01) and the calculated values of the in-plane moduli for 〈1103〉 textured films (E = 163.0–165.5 GPa and v = 0.221–0.239).

A theoretical model is proposed to explain the degree of texture achieved in high-Tc superconductors during melt-processing under an elevated magnetic field. The degree of grain alignment is quantified through a factor F which is defined as ranging from 0 (random alignment) to 1 (completely oriented). Intermediate values of F clearly characterize intermediate states of alignment in which there is still some tendency for the grains to align their c axes with the magnetic field. The model suggests that the enhancement in texture is primarily obtained through grain rotation during the early stages of grain growth from the liquid. At the later stages of growth, grains interact with each other, which hinders the phenomena of magnetic-field–induced grain alignment.

Two experiments that probe the nature of the rapid transition from elastic to plastic deformation are described. The load, and therefore stress, at which this yield point occurs is shown to be relatively independent of temperature in an iron alloy. When stresses lower than those required to generate a yield point during loading are applied for times between seconds and minutes, yielding occurs while the sample is under an applied stress. The time to generate a yield point increases as the applied stress is decreased. The possibilities of dislocation glide loop nucleation, double kink nucleation, and dislocation breakaway from pinning points are examined. Only glide loop nucleation appears to match the experimental observations. Criteria based on the stress-volume requirements of glide loop nucleation and the stress field underneath an indenter are presented which qualitatively describe the experimental data.

Titanium dioxide thin films prepared with and without lithium and niobium were as follows: uniform, crack-free, and stoichiometric, amorphous as-deposited at 300 °C and below; polycrystalline anatase when deposited at 400 °C or annealed at 500−800 °C; and rutile when annealed at 900 °C. Films prepared around 200 °C were very porous, but the porosity decreased as the substrate temperature increased. Optical absorption spectra revealed an indirect bandgap of 3.0 eV for amorphous and anatase films, and a direct bandgap of the same value in rutile. Dark dc conductivity of undoped films was lower than 10−10 (Ω · cm)−1; Hall effect measurements indicated that effective electron mobility was below 1 cm2/(V · s). The presence of Nb and Li increased the conductivity by 2–3 orders of magnitude, similar to the effect of hydrogen annealing. Illumination increased the conductivity by several orders of magnitude, and the decay followed a multiexponential law extending into the 106 second range after irradiation was stopped. The electronic properties of the films were determined by oxygen-related surface states at grain boundaries. Samples containing Li exhibited considerable sensitivity to water vapor.

Two very different pulsed laser deposition rates, 192 and 6 Å/s, were used to produce 1 μm thick superconducting YBa2Cu3Ox (YBCO) films on (001) SrTiO3 single-crystal substrates at 790 °C. Transmission electron microscopy (TEM) was used to characterize and compare microstructures between the two films. It has been found that the high deposition rate led to a slight deviation from the expected epitaxial orientations, and extra stress was induced in the films by increased lattice mismatch between the films and the substrates. In addition, misoriented YBCO grains were formed in the high-rate films after a thickness of about 150 nm. Postannealing in oxygen had no visible influence on these defects, although superconducting properties were improved significantly. In contrast to the high-rate films, overall epitaxial orientations have been formed in the low-rate films, and no misoriented YBCO grains were found. However, variations in lattice parameters and columnar voids were observed, although their existence apparently does not have considerable influence on superconducting current density (Jc). Cation disorder was observed in both films. A two-step film growth mechanism is concluded which is responsible for the formation of some defects in the high-deposition rate films.

Ceramic compacts of spinel-type ZnIn2S4 and IIIa-ZnIn2S4 polytype with a layer structure were synthesized by the reaction-sintering of mixed powders of ZnS and In2S3 at 723 K and 1073 K in Ar (containing 1° H2) atmosphere, respectively. The thermoelectric properties were investigated in the temperature range from 473 to 873 K. Thermoelectric figure of merit of the IIIa type was much larger than that of the spinel type, and it was slightly higher than the figure of merit of (ZnO)9In2O3, which is known to show the largest value among the oxide homologous compounds. To improve the thermoelectric properties, a c-plane-oriented sintered body of the IIIa polytype was successfully fabricated by a usual ceramic process. The figure of merit in the direction on the c plane was larger than on the ab plane due to higher electrical conductivity on the c plane and increased with increasing temperature showing the largest value of 1.3 × 10−4 K−1 at 873 K.

A new material system for applications involving thermal shock is proposed. The system consists of thin layers of ceramics and thinner metallic interlayers. In this study, a ceramic/metal laminate was constructed from Coor's ADS96R thin plates alternating with thinner Wesgo Cusil Active Braze Alloy interlayer foils and joined in active brazing. The maximum brazing temperature was 845 °C. Square laminated plates were quenched in room-temperature distilled water, where a very large heat transfer coefficient exists, and therefore, severe conditions of thermal shock occur. The laminated plates, initially at temperatures of 600 and 800 °C, were quenched at their bottom surface only in a specially designed apparatus. The temperatures at the top and the bottom surfaces of the specimens were measured by means of two thermocouples during quenching. The basic features of this architecture are described. The dominant behavior was the absence of interaction between the biaxial cracking mechanisms in a ceramic layer with those in an adjacent ceramic layer, and localization of the damage to those layers that experienced sufficient tensile stresses. The result was a dramatic increase of the residual strength after thermal shock. In addition, R-curve behavior upon mechanical loading caused by plastic deformation of the metallic interlayer was observed.

The effect of solidification rate on the precipitation and microstructure of directional solidification IN792 + Hf alloy was studied. The solidification sequence and the initial precipitation temperature of different phases were determined by the observation of the quenched microstructure combined with the differential thermal analysis measurement. The script carbide was turned into faceted carbide with the drop of solidification rate. It was concluded by microstructure analysis that the faceted carbide was pushed by the γ solid front before it was captured. The incorporation of γ phase into the faceted carbide was due to the dendrite growth of the carbide toward one point and the mergence of the dendrites. Some long carbide bars were formed along the grain boundaries by continual reaction of eutectic (γ + MC carbide) at a solidification rate of 0.5 μm/s. Two zones, the γ′ forming elements enriched zone and depleted zone, were found in the residual liquid area. Eutectic γ/γ′ nucleated in the γ′ forming elements enriched zone. The η-phase precipitation was controlled by the ratio of (Ti + Hf + Ta + W)/Al in the residual liquid. The growth of eutectic γ/γ′ increased the ratio and induced the η-phase precipitation. A lower solidification rate decreased the ratio by sufficient diffusion and hence efficiently suppressed the η-phase precipitation.

This paper is concerned with the effective piezoelectric moduli of a special class of dispersions called matrix laminates composites that are known to possess extremal elastic and dielectric moduli. It is assumed that the matrix material is an isotropic dielectric, and the inclusions and composites are transversely isotropic piezoelectrics that share the same axis of symmetry. The exact expressions for the effective coefficients of such structures are obtained. They can be used to approximate the effective properties of any transversely isotropic dispersion. The advantages of our approximations are that they are (i) realizable, i.e., correspond to specific microstructures; (ii) analytical and easy to compute even in nondegenerate cases; (iii) valid for the entire range of phase volume fractions; and (iv) characterized by two free parameters that allow one to “tune” the approximation and describe a variety of microstructures. The new approximations are compared with known ones.

Phase transformation and physical characteristics of the spray-pyrolyzed Tl–Ba–Ca–Cu–O superconducting films with 3 mol% silver dopant have been studied using electrical resistivity, x-ray diffraction, and scanning electron microscopy. The major phase formed in the resultant film, annealed at a temperature of 885 °C for 3 min, was found to be the nearly single-phase, high-Tc Tl2Ba2Ca2Cu3Oy (Tl-2223). The multiple phase of Tl2Ba2Ca2Cu3Oy and TlBa2Ca2Cu3Oy (Tl-1223) appeared at annealing temperatures lower and higher than 885 °C. It was also observed that Ag dopant effectively reduces normal resistivity at 300 K and enhances the phase transformation of single-Tl-layer Tl-1223 to double-Tl-layer Tl-2223 phases and further helps to form the nearly single-phase Tl-2223 within a short duration. Critical transition temperature (Tc,zero) and current density (Jc, 77 K, 0 Tesla) of the best resultant film were shown to be 123 K and 5.7 × 104 A/cm2, respectively.

The size distributions of Si and ZnTe nanoparticles produced by low energy density ArF (193 nm) pulsed laser ablation into ambient gases were measured as a function of the gas pressure, P, and target-substrate separation, Dts. For both Si and ZnTe, the largest nanoparticles were found closest to the ablation target, and the mean nanoparticle size decreased with increasing Dts. For Si ablation into He, the mean nanoparticle diameter did not increase monotonically with gas pressure but reached a maximum near P = 6 Torr. High resolution Z-contrast transmission electron microscopy and energy loss spectroscopy revealed that ZnTe nanoparticles consist of a crystalline core surrounded by an amorphous ZnO shell; growth defects and surface steps are clearly visible in the crystalline core. A pronounced narrowing of the ZnTe nanocrystal size distribution with increasing Dts also was found. The results demonstrate that the size of laser-ablated nanoparticles can be controlled by varying the molecular weight and pressure of an ambient gas and that nanometer-scale particles can be synthesized. Larger aggregates of both ZnTe and Si having a “flakelike” or “weblike” structure were formed at the higher ambient gas pressures; for ZnTe these appear to be open agglomerates of much smaller (∼10 nm) particles.

Using direct carbon ion beam deposition, in situ surface modification was performed by an energetic C- beam (400 and 500 eV) prior to amorphous carbon film growth to enhance adhesion of the film. It has been found from high-resolution electron microscopy that the C and Si mixing layer at the interface causes strong adhesion of the film. Electron energy loss spectroscopy was used to investigate chemical states of the C and Si mixing layer at the interface. The carbon composition profile in silicon showed that the thickness of the mixing layer was about 30 nm for 500 eV modification (at 200 °C). Silicon L-edge study at the C/Si interface found C–Si bond formation only at the surface of silicon over 2–3-nm-thick layers. The C–Si bond formation is a function of C- ion impingement energy. The thickness of the bonding layer decreased to less than 1 nm for 400 eV surface modification. When the substrate was modified by a 500-eV C- beam at 800 °C, the thickness of the SiC layer was about 10 nm. C–Si bond formation was enhanced by the supplemental thermal energy.

Grain boundaries in laser-deposited YBa2Cu3O7−δ (YBCO)/MgO thin films have been investigated by high-resolution transmission electron microscopy. The films exhibit perfect texturing with YBCO(001)/MgO(001) giving rise to low-angle [001] tilt grain boundaries resulting from the grains with the c axis normal to the substrate surface and with misorientation in the a-b plane. The atomic structure of the grain boundaries was analyzed by using a dislocation model. Low-angle grain boundaries have been found to be aligned along (100) and (110) interface planes. For the (110) boundary plane, the low-energy dislocation configuration was found to consist of an array of alternating [100] and [010] dislocations. We have calculated the energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of the (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary. We have also modeled critical current transport through grain boundaries with various structures and found that the low-energy (110) grain boundary with dissociated dislocation array is expected to transport a lower superconducting current (by 25% for 6° misorientation) than (100) boundaries.

The current method of analysis for hardness measurements by indentation is examined. Although the method is based on Sneddon's solution for an elastic stress field within a homogeneous half space indented by an elastically deformable indenter, it implicitly assumes a fixed indenter geometry. Therefore, if indentations are made on materials whose hardness or elastic modulus are close to those of the indenter, this method underestimates the contact area and, thus, overestimates the hardness and modulus values of the indented materials. A new method, based on the Hertz contact theory, is proposed that accounts for the elastic deformation of the indenter and provides a simple way to calculate the tip radius. The restrictions of this method are also indicated and discussed. Finally, the hardness and modulus for two recently developed films are measured by this method, and the results are compared with published finite element method (FEM) results.

Highly pure, ultralong, and uniform-sized semiconductor nanowires in bulk quantity were synthesized by thermal evaporation or laser ablation of semiconductor powders mixed with oxides. Transmission electron microscopy study shows that decomposition of semiconductor suboxides and defect structures play important roles in enhancing the formation and growth of high-quality nanowires. A new growth mechanism is proposed on the basis of microstructure and different morphologies of the nanowires observed.