The effect of repeated melting of master alloy ingots on the bending properties of Zr55Al10Ni5Cu30 bulk metallic glass (BMG) was investigated. The bending plasticity of Zr55Al10Ni5Cu30 BMG was found to be improved with the increased remelting times. When remelted 10 times, the BMG sample cast from the master alloy ingot undergoes bending, but it does not fracture even though the bending angle increases to 100°; the maximum bending stress and elastic strain remain almost constant. The bending plasticity improvement may be attributed to the fact that the increased remelting times result in more free volume and more disorder and homogeneous microstructure in the BMG, which favors the initial nucleation of profuse shear bands and reduces the probability of catastrophic fracture.

In our previous paper [Feng et al., Acta Mater.55, 2929 (2007)], an analytical model is proposed to estimate the stress field around an elastoplastic indentation/contact, matching nicely with the finite element analysis. The model is related to an embedded center of dilatation (ECD) in a half-space. In this paper, we focus on determining the ECD strength B* and the ECD depth ξ. By matching an expanding cavity model and the ECD model, we find that B* ≈ Yc3/6 and ξ ≈ 0.4c, where Y is the yield strength and c is the plastic zone radius. We provide a method to predict Y, c, and thereby B* as well as ξ through nanoindentation data, and we also demonstrate that pileup is the physical reason for the existence of the upper limit for the ratio of hardness to Y. Thus, our ECD model is completed by combining our previous paper (the analytical expression) and this paper (the essential parameters).

The composition, structure, morphology, and optical characteristics of hydrogenated amorphous silicon-oxycarbide (a-SiCxOyHz) materials were investigated as a function of experimental processing conditions and post-deposition thermal treatment. Thermal chemical vapor deposition (TCVD) was applied to the growth of three different types of a-SiCxOyHz films, namely, SiC-like (SiC1.08O0.07H0.21), Si-C-O (SiC0.50O1.20H0.22), and SiO2-like (SiC0.20O1.70H0.24). The resulting films were subsequently annealed at temperatures ranging from 500 °C to 1100 °C for 1 h in an argon atmosphere. The composition, structure, and morphology of as-deposited and post-annealed films were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS), nuclear-reaction analysis (NRA), and scanning electron microscopy. Corresponding optical properties were assessed by spectroscopic ultraviolet-visible ellipsometry (UV-VIS-SE). These studies led to the identification of an optimized process window for the growth of Er doped silicon oxycarbide (SiC0.5O1.0:Er) thin film with strong room-temperature photoluminescence emission measured around 1540 nm within a broad (460 nm to 600 nm) wavelength band. Associated modeling studies showed that the effective cross section for Er excitation in the SiC0.5O1.0:Er matrix was approximately four orders of magnitude larger than its analog for direct optical excitation of Er ions.

The influence of the crystalline orientation of the TiO2 photoanode on the photo-electrochemical characteristics was investigated to reveal the primary factors responsible for improving the photoelectric conversion efficiency of a dye-sensitized solar cell. It was observed that the photocurrent depended on the plane orientation, whereas the dependence of the photopotential on the open circuit was almost constant. The rate of the photoanodic reaction was attributed to the dye adsorption, depending on the surface energy of each oriented plane of the TiO2. The cathodic reaction on TiO2 during open circuit is likely to determine the rate of the entire electrochemical reaction.

The deformation behavior and indentation size effect (ISE) in amorphous and crystallized Pd40Cu30Ni10P20 alloy were comparatively studied through instrumented nanoindentation. It was found that the two alloys showed different deformation behaviors, the amorphous alloy exhibited conspicuous pop-in events in the load-depth (P-h) curve, while the crystallized alloy showed a relatively smooth P-h curve. In addition, the indentation hardness was observed to decrease with increasing penetration depth in the two alloys, exhibiting a significant ISE. However, the crystallized alloy displayed a sharper reduction of hardness with indentation depth as compared to the amorphous alloy, indicating a more significant indentation size effect in the crystalline alloy. The structure difference and friction factor associated with the surface residual stress are taken into account to interpret the difference in the deformation behavior and indentation size effect of the two alloys.

We have observed ferromagnetism in dilute cobalt-doped SnO2 nanowires at room temperatures. The Co-doped SnO2 nanowires with an average diameter of ∼50 nm were synthesized by the thermal chemical vapor transport method. High-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy analyses demonstrate that the nanowires are single-crystal structures and Co is homogeneously doped into the SnO2 lattice. The ferromagnetic hysteresis curves and temperature-dependent magnetization measurement provide evidence for ferromagnetic properties with a Curie temperature above room temperature. Oxygen annealing has been performed to study the roles played by the oxygen vacancies in determining the ferromagnetic properties of the nanowires.

We examined crystalline-texture evolution during ion-beam-assisted deposition (IBAD) of MgO thin films. We have demonstrated for the first time that in-plane crystalline texturing in IBAD of MgO scales with deposition rate. At high ion currents an in-plane texture full width at half-maximum (FWHM) of 10° can be achieved in less than 1 s, and 6° in 2.2 s. MgO texture further improves with thickness of a homoepitaxial layer deposited on top. We have developed an empirical quantification of the texture evolution in both IBAD and homoepitaxial layers. The best texture attained thus far in the MgO layer on polished Hastelloy tape has an in-plane FWHM of 1.6°. The high deposition rates demonstrated here make high-throughput manufacturing of IBAD textured templates a practical and cost-effective concept.

Three solid solutions of pyrochlores in the series Nd2-yearsGdyZr2O7 (y = 0.8, 1.0, 1.2) were synthesized by the gel combustion method using citric acid as fuel. This results in a soft agglomerate powder as verified by dynamic light scattering. The single-phase nature of the products has been confirmed by x-ray diffraction. The increase in full width at half-maxima in the Raman spectra with an increase in Gd3+ content indicates that disorder increases with Gd3+ content. The morphology and particle size of the products were investigated by transmission electron microscopy. Scanning electron microscopy study reveals that the sintered pellets have a density higher than 92% of theoretical densities. The total ionic conductivity measurements in the temperature range 375–800 °C show that with the increase of disorder (Gd3+ content) in the system the activation energy of conduction increases from 0.98 to 1.06 eV and the preexponential factor, which is proportional to the number of mobile species, also follow the same trend of increase. The total conductivity measured in reducing atmosphere shows no change in electrical conductivity, which verifies a negligible contribution of electronic contribution in this system.

The influence of casting temperatures on microstructures and mechanical properties of rapidly solidified Cu50Zr45.5Ti2.5Y2 alloy was investigated. With increasing casting temperatures, the amount of the crystalline phase decreases. At a high casting temperature, i.e., 1723 K, glass-forming ability (GFA) of the present alloy is enhanced. The results imply that adjusting the casting temperature could be used for designing the microstructures of bulk metallic glass matrix composite. Nanoindentation tests indicated that CuZr phases are slightly softer and can accommodate more plastic deformation than the amorphous matrix. Compression tests confirmed that this kind of second phase (CuZr) precipitated under lower casting temperatures helps to initiate multiple shear bands, resulting in a great improvement in mechanical properties of the samples. Our work indicates that casting temperatures have a great influence on GFA, microstructures, and mechanical properties of the rapidly solidified alloy, therefore controlling the casting temperature is crucial to the production of BMGs.

Histidine is an amino acid present in proteins involved in biosilica formation and often found in peptides identified during phage display studies but its role(s) and the extent of its involvement in the silica precipitation process is not fully understood. In this contribution we describe results from an in vitro silicification study conducted using poly-histidine (P-His) and a series of different molecular weight synthetic polymers containing the imidazole functionality (polyvinylimidazole, PVI) for comparison. We show that the presence of imidazole from PVI or P-His is able to catalyze silicic acid condensation; the effect being greater for P-His. The catalytic mechanism is proposed to involve the dual features of the imidazole group—its ability to form hydrogen bonds with silicic acid and electrostatic attraction toward oligomeric silicic acid species.

Miniaturized test methods were developed and applied to measure the hoop strength of small tubular components. A diametrical loading method and an internal pressurization method using elastomeric insert were adopted in the development of testing methods. Detailed analyses to assess these testing methods were attempted by using theoretical solutions and finite element analysis for stress distributions and the characteristics of the Weibull statistics. To demonstrate the applicability of the test methods, commercially available alumina tubes and miniature silicon carbide coatings from surrogate nuclear fuel particles were tested and their fracture strength distributions were analyzed with Weibull statistics. The size scaling relationship on the fracture strength was investigated by correlating with effective surface area. Furthermore, the applicability of the testing methods was discussed in terms of multiaxial stress fields, altered stress distribution by flattened loading contact, and availability of insert, focusing on high-temperature applications.

We have fabricated La0.6Ca0.4MnO3 periodic arrays exhibiting tunable optical properties and magnetic properties using nontoxic and environmentally friendly electron beam resist made from La0.6Ca0.4MnO3 sol-gel precursor. We studied their unique optical properties by using the spectral microreflectometer and their magnetic properties using the superconducting quantum interference device and magnetic force microscopy. Additionally, the resist has the ability to demonstrate both positive and negative resist behaviors depending on the electron beam dosage. With these special characteristics, we can fabricate periodic structure on a thin film possessing controlled optical reflectance properties with one fixed design electron beam pattern without changing the structural parameters but changing the electron beam dosage only. Our approach provides an uncomplicated route for the fabrication of nanometer scale magnetic patterns, which serve as the building blocks in the search for novel properties of periodic magnetic arrays.

Ultraviolet irradiation (λ = 248 nm) was used to photocatalyze a solution of the heteroleptic titanium alkoxide (OPy)2Ti(TAP)2 [where OPy = pyridine carbinoxide and TAP = 2,4,6 tris(dimethylamino)phenoxide], leading to the deposition of a titania-based thin film only in the exposed region. The effect of water addition to the (OPy)2Ti(TAP)2 pyridine solution on the properties of the final photodeposited film structure was examined by using vibrational spectroscopy and electron microscopy. Under consistent optical exposure conditions, the amount of water added altered the nanoscale porosity of the final material produced. Films deposited from a solution with a 1:1 H2O/Ti content exhibited surface pores ∼100 nm in diameter, whereas a 4:1 ratio yielded 10-nm pores, and material produced from a 8:1 solution appeared fully condensed. In addition, the effect of postdeposition thermal treatments on the nanostructure and chemistry of the photodeposited films was examined.

This study reports the synthesis of monosized Pr nanoparticles with a controllable size ranging from 5 to 20 nm. Pr agglomerates generated by a spark generator first size-selected by a differential mobility analyzer and subsequently sintered in-flight at different temperatures result in spherical and monocrystalline Pr nanoparticles. The dependence of size and size distribution of Pr nanoparticles has been studied as a function of deposition parameters related to spark generator, differential mobility analyzer, and sintering. Transmission electron microscopy, energy-dispersive x-ray analysis, glancing angle x-ray diffraction, and x-ray photoelectron spectroscopy studies confirm that initial Pr agglomerates and the resulting nanoparticles are metallic with d-hexagonal structure and remain stable in air during post-deposition exposure. Incomplete or partially sintered nanoparticles were found to be oxidized, resulting in the formation of amorphous oxide phase due to enhanced oxidation at grain boundaries.

By optimizing the heating rate during spark-plasma-sintering (SPS) processing, a high-strength transparent spinel (MgAl2O4) can be successfully fabricated for only a 20-min soak at 1300 °C. For the heating rates of ≤10 °C/min, the spinel exhibits an excellent combination of in-line transmission (50–70%), four-point-bending strength (>400 MPa), and hardness (>15 GPa). The excellent optical and mechanical properties can be ascribed to the superimposed effects of the sub-micrograin size, fine-pore size, and low porosity, which are related closely to the heating rate during the SPS processing. The present study demonstrates that to attain a high-strength transparent spinel at low temperatures and short sintering times, the low-heating-rate SPS processing is more efficient compared with the high-heating-rate SPS processing.

FINEMET-type (Fe75Si15NbBCu) ribbons were heat treated, and their magnetic properties were analyzed. Permeability, thermal, and mechanical sensitivities were measured by commonly used industrial methods, and these properties were correlated with measured magnetic Barkhausen noise parameters. Distributions of peak area, A, and peak noise energy, E, were evaluated. Distribution functions of noise parameters, P(x), were in good agreement with the theory of self-organized criticality (SOC), satisfying power laws in the form P(x)∼x−α. It is found that the noise did not considerably depend on the temperature sensitivity parameter and on the permeability of ribbons. However, a useful correlation between the noise parameters and mechanical sensitivity has been observed. Minimal noise was detected for samples with negligible mechanical sensitivity in an amorphous-nanocrystalline composite state obtained by a heat treatment at 853 K.

This article presents an extruded Mg–Gd–Zn–Zr alloy produced by conventional ingot metallurgy, exhibiting high-strength and excellent ductility at room and elevated temperatures. The superplastic behavior was observed in the Mg–Gd–Zn (–Zr) alloy at elevated temperatures above 573 K. In the alloy, both the X phase in grain boundaries and the lamellae within matrix have the 14H-type long-period, stacking-ordered structure. It indicates that the X phase and the lamellae within matrix play important roles in the excellent mechanical properties.

High-resolution transmission electron microscopy (HRTEM) images of annealed ZnO thin films showed the domain boundaries of a (0) plane with a transition zone and a (1) plane without a transition zone. The 30° in-plane rotation domain boundaries were formed in the ZnO thin films because the angle of the c-axis was tilted 3.5° in comparison with that of neighboring 30° in-plane rotation domains to reduce the misfit strain energy. The atomic arrangement variations of 30° in-plane rotation domain boundaries in ZnO thin films grown on Si substrates due to thermal annealing are described.

Nanometric-sized nitrogen-doped titanium oxide (TiO2-xNy) powders were synthesized by the two-microemulsion technology. The dried precursor precipitate was characterized by differential thermal analysis/thermogravimetric analysis, Raman spectroscopy, transmission electron microscopy, Brunauer-Emmet-Teller, and x-ray photoelectron spectrometer (XPS), and the mechanisms for the evolution of TiO2-xNy powders in this process were proposed and discussed in the context of the microstructure. It shows that a higher pH value solution results in obtaining a small size and much more homogeneous TiO2-xNy powder after calcinations. The powder prepared from a solution of pH 10–11 and calcined at 500 °C has a particle size of ∼4–6 nm with a specific surface area of 160 m2/g and exhibits a pure phase of anatase containing ∼5 mol% of N evidenced by XPS. However, the nanometric-sized TiO2-xNy powder shows the photocatalytic degradation of methylene blue solution effectively by exposing the powders in aqueous solution under visible light.

This article presents a nanoindentation study of polycrystalline and single crystals of yttria-doped zirconia with both tetragonal and cubic phases. Analysis of the deformation mechanisms is performed by both atomic force microscopy (AFM) and micro-Raman spectroscopy. Phase transformation from tetragonal to monoclinic phase is clearly distinguished on tetragonal crystals, whereas in cubic crystals the plastic deformation seems to be controlled by dislocation nucleation and interactions. AFM observations in tetragonal zirconia grains have shown that both grain size and autocatalytic transformation strongly influence the size of the transformed zone. Furthermore, the martensitic phase transformation seems to be also strongly dependent of the indenter shape. Experimental results suggest that a critical contact pressure is necessary to induce the phase transformation.