Based on dimensional analysis and finite element computations, an energy-based representative strain for conical indentation in elastoplastic materials has been proposed to establish an explicitly one-to-one relationship between the representative stress σr, the indentation loading curvature C, and the ratio of reversible work We to total work Wt performed by the indenter, i.e., σr/C = F0(We/Wt), where σr is the flow stress corresponding to the representative strain. The relationship provides a very simple method to evaluate the representative stress σr from the three directly measurable quantities We, Wt, and C. Numerical examples and further theoretical analysis reveal that a unique, stable solution can be obtained from the present method for a wide range of material properties, including both highly plastic materials (e.g., Ni for which E/σy = 1070) and highly elastic materials (e.g., materials for which E/σy = 25 and n = 0.5), using indenters with different tip apex angles. Based on the representative strains and stresses given by two indenters with different tip apex angles, e.g., (σr,80, ϵr,80) and (σr,65, ϵr,65), the plastic properties of materials, i.e., the yield strength σy and strain hardening exponent n can be further determined.

A meso-porous anodic alumina capillary tube (MAAC) having highly oriented radial meso-pore channels with a minimum diameter of 3 nm has been successfully synthesized using a novel pulse sequential anodic oxidation technique at 100 Hz of pulse frequency. A value resulting in a high channel-pore formation rate at 1 V of the pulse sequential voltage was determined to be the optimum pulse frequency for the anodization. Transmission electron microscopy observation and N2 sorption analysis revealed that controlling the minimum pore channel diameter at 3 nm was possible by the voltage of 1 V. The gas permeance according to Knudsen’s diffusion mechanism was demonstrated at 500 °C, by evaluating gas permeation properties through the meso-porous anodic alumina capillary tube with radial meso-pore channels with minimum diameter of 3 nm, achieving hydrogen permeance of 1.8 × 10−6 mol/m2 s Pa.

Electrical conductivity of electronic interconnects made with Sn-based solders undergo a significant amount of deterioration during service. Several factors, such as anisotropy of Sn, coefficient of thermal expansion mismatches between the entities that make up the joint, and growth of intermetallic compounds present within the solder and solder/substrate interface, may contribute to the damage accumulation during thermal excursions and cause deterioration of properties. This study dealing with effects of aging and thermal shock on electrical conductivity, carried out with bulk Sn, and eutectic Sn–Ag in bulk and joint configurations, is aimed at evaluating the roles of the above factors on the deterioration of electrical conductivity from these thermal excursions.

Nanoindentation tests of Pd40Cu30Ni10P20 bulk metallic glass were performed over a wide range of indentation rates (from 0.04 up to 6.4 mN s−1) under the standard load control mode. New results using the feedback displacement control mode are also presented. The dependence of the pop-in formation on the loading rate is investigated. Variations in hardness and reduced elastic modulus as a function of the indentation rate are observed. A softening effect occurs when increasing the loading rate. This is explained by the differences in plastic deformation achieved at different indentation rates. The displacement control mode was used to avoid the shear localization of the free volume, leading to the almost complete absence of pop-ins along the loading curve. The obtained results suggest that plastic flow in bulk metallic glasses is governed by the rate of creation of free volume, which depends on the strain rate and its localization into shear bands.

The concentration of hydroxyl (–OH) groups in epitaxial barium titanate (BaTiO3) films (thickness ∼ 200 nm), deposited on single-crystal strontium titanate (SrTiO3) at 150 °C by a hydrothermal technique, was investigated using x-ray photoelectron spectroscopy and Fourier transform infrared (FTIR) spectroscopy. After hydrothermal treatment, a broad FTIR resonance for the hydroxyl groups indicated a significant concentration of surface –OH groups in the films. The as-deposited films were subsequently treated hydrothermally with D2O, and the kinetics of the exchange reaction between –OH incorporated into the film and –OD from the D2O were studied using FTIR. For reactions carried out intermittently, the kinetics of the exchange reaction between –OH by –OD depended not only on the total reaction time, but also on the duration of each treatment. The broad FTIR hydroxyl resonance in the as-deposited hydrothermal film was significantly reduced only after heating for 1 h at 600–800 °C.

The mechanical properties of thermally grown oxide films on various aluminum substrates were tested using nanoindentation. A sudden discontinuity, indicative of film fracture, was observed upon loading portion of the load–depth curve. The 63-nm-thick films were determined to have ultimate strengths between 4.8 and 8.9 GPa. The ultimate stress is a superposition of the bending and membrane stress. The stress intensity at fracture for each of the films was developed by approximating the resulting bending moment and various cracks sizes. At a constant ratio of crack size to oxide thickness of 0.3, the applied stress intensity at fracture of these aluminum oxide films were between 0.46 and 1.20 MPa m1/2. The residual stress in the film was assumed to be negligible in the stress intensity calculation.

Several bismuth layer-structured compounds An−3Bi4TinO3n+3 (A = Ba, Sr, Ca) with n > 4 were synthesized and investigated. The average radius of A-site cations was found to be closely related to the lattice parameters in the a–b plane and, therefore, closely related to the stability of the layer structure. For Ba2Bi4Ti5O18 ceramics, there was a diffused phase transition centered at approximately 330 °C, which should be due to the cation redistribution of A-site Ba2+ and Bi3+ in the (Bi2O2)2+ layer. For Sr2Bi4Ti5O18 ceramics, a sharp dielectric constant peak was found at 325 °C. Ceramics of five-layered Ca2Bi4Ti5O18 and six-layered Ca3Bi4Ti6O21 showed temperature-stable dielectric constants up to 800 °C, and ferroelectricity was observed. In addition, as ferroelectrics, these Ca-containing bismuth layer-structured compounds showed frequency-independent dielectric constants >150 and small tan δ on the order of 10−3–10−4 in the frequency range of 1 kHz to 1 MHz.

The early dissolution behavior of Cu in a molten Sn–Zn–Ag solder was studied at 250 °C by fast quenching the dissolving specimen in liquid nitrogen. The atomic level dissolution behavior of Cu in the molten solder was revealed by high-resolution transmission electron microscopy. The dissolution of Cu occurs through channel dissolution and thermal vibrational dissolution. The dissolution channel has a dimension of less than 0.5 nm. The formation of channels, and thus the channel zone, is initiated by preferential removal of Cu atoms from the surface vacant site of Cu lattice. Relict strips of lattice between channels subsequently dissolve into the molten solder with the aid of thermal vibration and the interaction with liquid Zn atoms. The dissolved atoms form an atomic cluster zone. These clusters are the intermediate state of the dissolution of Cu from the channel zone into the molten Sn–Zn–Ag solder. The clusters convert into an amorphous structure prior to further formation of compound.

The fundamental processes controlling the high-temperature interaction of dislocations with precipitates in Al-alloys were investigated in real time by deforming specimens in situ in the transmission electron microscope at elevated temperature. The observations support a bypass mechanism involving the interaction of lattice dislocations with the precipitate–matrix interface dislocations, where the rate-limiting step in the interaction is the release of the dislocation from the particle. These observations are discussed in relation to high-temperature deformation processes and models.

A method for applying conductive inorganic tungsten bronze (NaxWO3) coatings over ceramic foams is presented. The general basis of bronze coating involves an intermediate layer between the ceramic surface and the redox external agent (liquid or gas phase). The intermediate layer is a multifunctional element and its function depends on the agents involved in redox reaction. The bronze film is formed either on the intermediate layer or in place of it. The initial melt included Na2WO4, WO3, and NaCl. The reticulated ceramic foams, made from pure alumina (Al2O3), were prepared by a standard impregnation method. In all depositions, the temperature was above the melting point of the Na2WO4/WO3 system. The effect of NaCl content on the final coating properties was investigated in the 10–40 mol% range. The best results were obtained with hydrogen reduction of 40% NaCl in the melt. The bronze crystals size in the coating was 0.8–1.6 μm. The bronze layer was continuous throughout the foam. The obtained coating has a bright yellow-gold color, consistent with a stoichiometric parameter value (x) of 0.85–0.95. The resistivity of coated foams decreased from above 12 Ω mm to below 1 Ω mm when the NaCl concentration in the melts increased from 10% to 40%, respectively, due to improved continuity of the bronze crystals. These highly conductive, bronze-coated alumina foams, can potentially serve as high-temperature electrodes in aggressive conditions.

A (Bi,Sb)2Te3 alloy powder was sintered via a pulse discharge sintering process followed by a rotary-die equal channel angular pressing (ECAP) process. It was found by x-ray diffraction analysis that the as-sintered material shows preferentially orientated microstructure, which were considerably eliminated by following ECAP processes. Generally, the Seebeck coefficient of the material was reduced by ECAP processing, which was attributed to the increased carrier concentration after the severe plastic deformation. Electrical conductivity increases after ECAP, which was also originated from the increased carrier concentration. The figure of merit of the material in different conditions shows higher value in the transverse direction. In the transverse samples, those after ECAP processing showed increased figures of merit, which reached 3.85 × 10−3/K in the material after 4 passes of ECAP.

Ti–Al–Si–C powder mixtures of two different compositions, namely, 58Ti–30Al–6Si–6C (at.%) and 50Ti–15Al–20Si–15C (at.%), were mechanically alloyed to investigate the solid-state reactions during such a process. The mechanically alloyed powders were characterized as a function of milling time by x-ray diffraction (XRD), scanning electron microscopy, energy-dispersive spectrometry, and transmission electron microscopy (TEM). XRD results showed that solid solutions of Ti were formed for a powder mixture of 58Ti–30Al–6Si–6C in about 20 h of milling, whereas Ti5(Al,Si)3 and Ti(Al,Si)C compounds started to form in the powder mixture of 50Ti–15Al–20Si–15C within just 5 h of milling. TEM observations demonstrated that the particle sizes were of nano and submicron scale in both cases. This investigation indicated that in mechanically alloyed Ti–Al–Si–C powder mixtures, the main solid-state reactions are due to interdiffusion and mechanically induced self-propagating reaction.

Multilayered titanium dioxide thin films with a spinodal phase separation structure were prepared by the sol-gel process from sols containing polyoxyethylene(20) nonylphenyl ether (NPE-20), and their photoelectrochemical and photocatalytic properties were investigated. The obtained films showed much higher anodic photocurrent and photocatalytic activity than the dense TiO2 thin film electrodes. We explained these phenomena by the large specific surface area inherent in the spinodal phase separation structure and the higher concentration of Ti3+ species, which were produced by the reducing action of the incorporated organic polymers at sintering temperatures. Ti3+ species in the bulk raise the donor density, and those at the surface provide a larger number of active sites available for photoelectrochemical reaction and photocatalytic reaction.

Boron sub-arsenide, B12As2, is based on twelve-atom clusters of boron atoms and two-atom As–As chains. By contrast, SiC is a tetrahedrally bonded covalent semiconductor. Despite these fundamental differences, the basal plane hexagonal lattice constant of boron sub-arsenide is twice that of SiC. This coincidence suggests the possibility of heteroepitaxial growth of boron sub-arsenide films on properly aligned SiC. However, there are a variety of incommensurate alignments by which heteroepitaxial growth of B12As2 on (0001) 6H–SiC can occur. In this study, we first used geometrical crystallographic considerations to describe the possible arrangements of B12As2 on (0001) 6H–SiC. We identified four translational and two rotational variants. We then analyzed electron backscattered diffraction and transmission electron microscopy images for evidence of distinct domains of such structural variants. Micron-scale regions with each of the two possible rotational alignments of B12As2 icosahedra with the SiC surface were seen. On a finer length scale (100–300 nm) within these regions, boron-rich boundaries were found, consistent with those between pairs of the four equivalent translational variants associated with a two-to-one lattice match. Boron-carbide reaction layers were also observed at interfaces between SiC and B12As2.

In situ transmission electron microscopy was used to study, in real time, the sub-surface deformation taking place in Cu–Be alloy during nanoindentation. A twinned region of the material was indented with a sharp tungsten tip in a specially developed transmission electron microscopy (TEM) holder. A flexible hinge-based force sensor was used to measure the force on the indenter, and the force–displacement curve for the tip was obtained by tracking the tip in the sequential images of a TEM video of the indentation process. Step-like structures ∼50 nm in size resulting from the tip surface roughness were observed to generate clusters of dislocations in the sample when they come in contact with the softer Cu–Be. With this setup, the forces and the mean pressure associated with such an individual deformation event in a nanostructured TEM sample were measured.

Piezoelectric ceramics with TC > 500 °C were projected in the perovskite BiInO3–PbTiO3 (BIPT) system based on their low tolerance factor (∼0.884). However, a stable perovskite phase could be synthesized only when the PbTiO3 (PT) content was greater than 75%. Furthermore, the large tetragonality (c/a > 1.08) and low electrical resistivity made the ceramics difficult to pole. Niobium-modified BIPT ceramics with PT contents of 80% and 85% were found to possess significantly lower dielectric loss at elevated temperatures, making it possible to polarize the materials. Piezoelectric properties were measured for a BIPT85–1.5 mol% Nb composition with a Curie temperature of 542 °C; the longitudinal piezoelectric coefficient and coercive field were found to be 60 pC/N and 125 kV/cm, respectively.

High-purity, mesoporous titania was prepared by reaction of dimethylaminotitanatrane, [NMe2–Ti(OCH2CH2)3N] in the presence of micellar aggregates as templating agents followed by thermal treatments in the temperature range 350–450 °C. The powders were characterized by nitrogen adsorption–desorption isotherms, thermogravimetry–differential thermal analysis, Fourier transform infrared, field-emission scanning electron microscopy, and x-ray diffraction. Analysis of the morphological characteristics of titanium oxide powders calcined at 350 °C for 120 h and at 450 °C for 6 h showed the presence of a mesoporous structure, with an average pore size of about 3.5 nm. Firing temperatures above 450 °C caused the collapse of the mesoporous structure. Composite Nafion-based membranes, containing 5 wt% mesoporous titania fired at 450 °C as a filler were successfully prepared. Preliminary tests in a prototype direct methanol fuel cell demonstrated that the composite membrane allowed cell operation up to 145 °C, thus showing a significant performance improvement over pure Nafion.

The carburization process of nanocrystalline iron in a flow of CH4/H2 mixture under atmospheric pressure at 580 °C in a differential reactor–thermobalance was studied. The course of reaction was followed by thermogravimetry, and the phase composition of the samples carburized to different degrees was determined by x-ray diffraction (XRD) and Mössbauer spectroscopy techniques. The XRD method was also used for calculating the mean crystallite size of unconverted iron after reaction at different time intervals. An unexpected relation between the average size of iron crystallites and the degree of conversion was found. The nucleation mechanism of the nanocrystalline iron carbide in the kinetic area of the reaction, limited by the dissociative adsorption of methane, has been suggested. According to this mechanism, iron crystallites are carburized successively, from the smallest to the largest.

YBa2Cu3Oy (YBCO) films produced by the ex situ conversion of BaF2-based precursors deposited by physical vapor deposition on ion-beam assisted deposited (IBAD) yttrium-stabilized zirconia (YSZ) and rolling-assisted biaxially textured substrates (RABiTS) templates are characterized by a bi-axially aligned, laminar grain structure that results from the anisotropic growth characteristics of the YBCO phase and its precipitation from a transient liquid phase during the conversion process. A bimodal microstructure characterizes these films and is defined by large, well-formed YBCO grains with Y2O3 precipitates in the bottom region of the film and small YBCO grains with a high density of stacking faults in the upper half. Ba2Cu3Oy or Ba–O–F/CuO second phase layers were often found between large YBCO grains in the bottom half of the films. YBCO grain sizes exceeded 50 μm within the plane of the film in some cases. Conversely, discrete secondary phases of Y2Cu2O5, Y2O3, and Ba2Cu3Oy/Ba–O–F could be found among the much smaller YBCO grains in the top portion of the bimodal structure. The dividing line of the bimodal structure was generally at one half of the film thickness, although exceptions to this trend were found. The highest critical current densities (Jc) and best film alignments for a given film thickness were found in samples where the layers of Ba2Cu3Oy or Ba–O–F were minimized or eliminated from the films. Samples quenched after partial conversion show the segregation of CuO to the top region of the film and the lateral growth of large YBCO grains from a precursor mix of Y2Cu2O5 and Ba–O–F. The data demonstrate that transient liquid phases are part of the conversion process of BaF2-based YBCO films. The control of both CuO segregation and the amount of liquid phases generated during the initial stages of phase formation is needed for optimizing the ex situ conversion process for high-Jc coated conductors.

Epitaxial films of rare-earth (RE) niobates, RE3NbO7 with pyrochlore structures, were grown on biaxially textured nickel–3 at.% tungsten (Ni–W) substrates using a chemical solution deposition process. A precursor solution of 0.3–0.50 M concentration of total cations was spin coated on to short samples of Ni–W substrates, and the films were crystallized at 1050–1100 °C in a gas mixture of Ar–4% H2 for 15 min. Detailed studies revealed that RE-niobates with ionic radius ratio RRE/RNb (R = ionic radius) from 1.23 to 1.40 (i.e., Sm, Eu, Gd, Ho, Y, and Yb) grow epitaxially with the pyrochlore structure. X-ray studies showed that the films of pyrochlore RE niobate films were highly textured with cube-on-cube epitaxy. Scanning electron and atomic force microscopy investigations of RE3NbO7 films revealed a fairly dense and smooth microstructure without cracks and porosity. The rare-earth niobate layers may be potentially used as buffer layers for YBa2Cu3O7−δ coated conductors.