The dielectric properties and tunability with external magnetic and electric fields for LuFe2-xMnxO4 (0 ≤ x ≤ 1) are systematically studied. It was found that the dielectric loss, the ferrimagnetic Curie temperature, and the conductivity reduce with increasing Mn doping. One of the most important results is that the room temperature dielectric tunability with low magnetic and electric fields can be achieved in these samples. The analysis demonstrates that the electron transfer between Fe2+ and Fe3+ is efficiently suppressed with Mn doping and thus results in the decreases of the leaky conductivity and the dielectric loss. Furthermore, from the studies on the combination of impedance and modulus complex planes for the samples with different electrodes, the tunability is found to be more closely related to the extrinsic effect than the intrinsic bulk effect.

A strategic scheme for controlling the shape of titania nanorods while maintaining their highly crystallized state was investigated in terms of the effects of reactant concentration and temperature change on the formation mechanism. Lowering the temperature from 433 to 413 K markedly slowed down the reaction rate and resulted in the coexistence of amorphous-like films and crystalline titania nanorods due to the concurrence of nucleation out of the amorphous phase and particle growth by crystallization. Based on these findings, a strategy for shape control was proposed and long, high aspect ratio titania nanorods in a highly crystallized state were successfully synthesized.

A combined dislocation–cohesive zone model was proposed to describe the fracture toughness of nanocrystalline (nc) materials. In the framework of the model, cohesive stress near crack tip initiates edge dislocations, which move to the opposite grain boundaries. The emitted dislocations provide a shielding effect of the crack. The dependence of both the maximum number of dislocations, emitted by a crack, and the critical stress intensity factor on grain size d (ranging from 20 to100 nm) for Cu was calculated. The calculated results show that (i) nc materials have low fracture toughness, (ii) the critical stress intensity factor decreases with decreased grain size, and (iii) the grain size effect is not high; for instance, increasing the grain size from 20 to 100 nm increases the value of critical stress intensity factor only by 0.035 MPa/m1/2.

Flowerlike hierarchical Bi2MoO6 and Bi2MoO6:Er3+ microspheres were synthesized by a hydrothermal method. The crystalline size of microspheres decreases with increasing Er3+ concentration. The incorporation of Er3+ has no evident influence on the morphology of Bi2MoO6. The photocatalytic activity of microspheres was evaluated by the degradation of rhodamine B (RhB) aqueous solution under simulated solar light. The best photocatalytic performance was observed when the Er3+ concentration was 0.5%. In addition to the aforementioned high photocatalytic activity, the Bi2MoO6:Er3+ microspheres can emit pure green upconversion (UC) luminescence (2H11/2/4S3/2 → 4I15/2) under 980 nm excitation. We suggest that the enhancement of photocatalytic activity of Bi2MoO6:Er3+(0.5%) is related to the UC luminescence of Er3+ ions. In addition, the BET surface areas of samples increased with increasing Er3+ concentration, which is also benefit for RhB adsorption.

The elastic anisotropy of cementite (Fe3C) is still under discussion. Recent theoretical (ab initio) calculations predict a very high elastic anisotropy for this iron carbide, and a few published experiments suggest that prediction could be true. This work presents a first attempt of using nanoindentation for assessing the elastic anisotropy of such an important component of steels. Our nanoindentation results show that the elastic anisotropy of Fe3C is high but smaller than predicted by ab initio calculations. The elastic modulus is obtained from the load–penetration curves before the first pop-in indicative of plasticity nucleation is detected. The tests thus provide information on the plastic anisotropy of cementite. Surprisingly, the mean indentation pressure or the maximum shear stress under the indenter at the onset of plasticity has been observed to be nearly independent of the crystalline orientation of the indented surface.

Phosphonated polysulfones in the acid form (PPSU-As) with degree of phosphonation (DP) = 0.4, 0.75, and 0.96 were successfully synthesized and utilized for the preparation of polymer blend with sulfonated poly(ether ether ketone) (SPEEK) having a degree of sulfonation (DS) = 75. The resulted blend membranes were characterized and investigated as new polyelectrolyte membrane for fuel cells applications. SPEEK/PPSU-A blend membranes formed ionic networks through hydrogen bonding bridges between the strong sulfonic acid groups and the amphoteric phosphonic acid groups. These ionic interactions resulted in enhanced membrane properties in terms of water swelling, methanol uptake, methanol permeability, mechanical strength, and thermal stability, without significant loss of proton conductivity. All the blend membranes were transparent to visible light with presence of microphases in the order of 10–20 nm. When compared to parent SPEEK membranes, the new SPEEK/PPSU-A blend membranes showed slightly lower methanol permeability compared to neat SPEEK membrane. Membranes with 30 wt% phosphonic acid content with DP = 0.75 and 0.96, exhibited slightly higher proton conductivities at temperatures above 50 °C in comparison with Nafion membrane.

The piezoelectric β-phase of poly(vinylidene fluoride) (PVDF) has been synthesized through solution route in presence of varying percentage of silicon carbide (SiC). Various measurements were conducted to analyze the effect of SiC addition on structural, mechanical, and dielectric properties, as also the properties affecting hydrophilicity and morphology of PVDF. The x-ray diffraction, Fourier transform infrared spectroscopic and differential scanning calorimetry analyses confirm the presence of β-phase of PVDF on addition of SiC. The Young’s modulus of the composites increases as compared with pristine PVDF. The hydrophilic nature of the composites improves with increasing SiC content. Dielectric constant increases in composites, especially at lower frequency range and the relaxation pattern in the crystalline phase changes significantly causing reduction of relaxation frequency with increasing SiC concentration.

Nanocomposite Zr0.52Al0.48N1.11 thin films consisting of crystalline grains surrounded by an amorphous matrix were deposited using cathodic arc evaporation. The structure evolution after annealing of the films was studied using high-energy x-ray scattering and transmission electron microscopy. The mechanical properties were characterized by nanoindentation on as-deposited and annealed films. After annealing in temperatures of 1050–1400 °C, nucleation and grain growth of cubic ZrN takes place in the film. This increases the hardness, which reaches a maximum, while parts of the film remain amorphous. Grain growth of the hexagonal AlN phase occurs above 1300 °C.

NbN thin films grown on Nb using pulsed laser deposition (PLD) were investigated for film crystal structures. The nanomechanical properties of NbN on Nb were examined as a function of the film/substrate crystal structure. X-ray diffraction (XRD) reveals peaks that correspond to δ-NbN cubic and β-Nb2N hexagonal phases in addition to δ′-NbN phase. Samples of various crystal structures were tested for phase characterization, microstructure, and surface morphology using XRD analysis, scanning electron microscopy, and atomic force microscopy. The nanomechanical properties were investigated using nanoindentation. The results indicate that there are clear effects of the crystal structure on the hardness of the PLD-grown NbNx films.

A new approach has been proposed to determine the interfacial toughness of soft-film hard-substrate systems based on wedge indentation experiments. In this approach, a comprehensive finite element study was undertaken to correct de Boer’s solutions, which were used to measure the wedge-indented interfacial toughness. Two-dimensional indentation simulations were first performed to systematically study the effects of the plastic properties of the films and the interfacial toughness itself on the correction factor for de Boer’s equations, which were used as closed-form solutions to evaluate the interfacial toughness. Further, three-dimensional simulations were used to investigate the effects of stress states on the interfacial toughness, which depends on the ratio of the indenter length to the film thickness. A universal correction expression for de Boer’s equations was obtained using a regression method. With this expression, a reverse algorithm was proposed to determine the interfacial toughness, and extensive numerical calculations were performed to verify that the present approach accurately evaluates the interfacial toughness. Finally, this new approach was applied to analyze the wedge indentation of low-k dielectric films, namely, methylsilsesquioxane and black diamond (BDTM) films, on a Si substrate.

In this study, we have developed and characterized two previously unstudied alkoxysilane surface chemistries for use with superparamagnetic iron oxide (SPIO) nanoparticles as a magnetic resonance imaging contrast agent. We modified superparamagnetic iron oxide nanoparticles (SPIO) using aminopropyl triethoxysilane and two analogous alkoxysilanes, aminopropyl dimethylethoxysilane and aminopropyl methyldiethoxysilane, to compare a mono- and dialkoxysilane, respectively, to a more commonly used trialkoxysilane as two new SPIO surface chemistries capable of forming ultrathin functional surface coatings. The ligand densities of the mono- and dialkoxysilane-modified SPIO produced in this study are consistent with near monolayers of ligands on the SPIO surface. We studied the chemical stability of the mono-, di-, and trialkoxysilane-modified SPIO in neutral and acidic media to evaluate the viability of these surface chemistries for use in long-term intracellular applications. The mono- and dialkoxysilane-modified SPIO demonstrate comparable chemical stability to the trialkoxysilane-modified SPIO, indicating that the mono- and dialkoxysilane are both viable new SPIO surface chemistries for future applications requiring minimally thick alkoxysilane surface coatings.

All the existing theories presuppose the continuity of oxygen chemical potential at interfaces between contiguous layers, in calculating steady-state chemical potential profiles across a multilayer composite of mixed conductor oxides that is subjected to an oxygen chemical potential gradient of whatsoever origin, but they have never been tested experimentally. We have observed that this continuity hypothesis appears to break down in yttria-stabilized zirconia/gadolinia-doped ceria bilayer electrolytes under an electric tension in ion-blocking condition (Hebb–Wagner polarization). It is suggested that all the continuity hypothesis-based existing theories to calculate the steady-state chemical potential distributions may not always be true depending on boundary conditions.

NiMn2−xMgxO4 (0 ≤ x ≤ 0.4) ceramics have been studied by powder x-ray diffraction (XRD), infrared (IR) spectroscopy, and thermogravimetric analysis. NiMn2−xMgxO4 ceramics are all single-phase with spinel structure. XRD and IR spectroscopy results indicate that Mg2+ ions occupy A- and B-site of spinel lattice, which inhibits the formation of cation vacancies. Moreover, Mg2+ substitution enhances the tolerance of the oxidation in air. As a result, Mg substitution leads to a significant increase in ρ25, temperature coefficient of resistivity B25/85, and activation energy, which improves the aging property of NiMn2−xMgxO4 negative temperature coefficient thermistors.

In this work, the ultrafine nanoporous Ag ribbons were achieved through addition of 2 at.%–6 at.% Ce into the melt-spun Cu-Ag alloys and applying different electrochemical dealloying potentials. The dendritic morphology of the ligaments in the dealloyed Cu80Ag20 alloy varied to be equiaxial due to the addition of Ce, and the pore size reduced from 200 nm to less than 60 nm. The nanoporous Ag with an average pore size of ∼15 nm was obtained from the Cu74Ag20Ce6 alloy. The pore and ligament sizes of the nanoporous Ag prepared from the Cu76Ag20Ce4 alloy exhibited an increasing tendency with the increase of applied potentials, while the dealloyed Cu78Ag20Ce2 had an opposite variation. Moreover, the addition of Ce into the Cu-Ag alloys also promoted the dealloying. Nanoporous Ag exhibited the stronger enhancement of the surface enhanced Raman scattering effects with the increase of Ce contents in the precursory alloys.

Thick (>150 μm) beryllium coatings are studied as an ablator material of interest for fusion fuel capsules for the National Ignition Facility. DC magnetron sputtering is used because of the relative controllability of the processing temperature and energy of the deposits. However, coatings produced by DC magnetron sputtering leak the fuel gas D2. By using ion-assisted DC magnetron, sputtered coatings can be made that are leak-tight. Transmission electron microscopy (TEM) studies revealed microstructural changes that lead to leak-tight coating. Ultrasmall angle x-ray spectroscopy is used to characterize the void distribution and volume along the spherical surface along with a combination of focused ion beam, scanning electron microscope, and TEM. An in situ multibeam optical stress sensor was used to measure the stress behavior of thick beryllium coatings on flat substrates as the material was being deposited.

We have grown VO2/NiO epitaxial thin films by pulsed laser deposition where integration with Si(001) substrates was achieved by cubic yttria-stabilized zirconia (YSZ) buffer layer. The most interesting aspect of this work is that a complete relaxation along c-axis of VO2 is achieved in these large misfit systems through the domain matching epitaxy paradigm, which is critical for controlling the semiconductor to metal transition (SMT) characteristics. Regarding x-ray diffraction and cross-sectional transmission electron microscopy results, the epitaxial relationship across the YSZ/Si(001) interface was (001)[100]YSZ‖(001)[100]Si. In the case of YSZ/NiO interface, the epitaxial relationship was $(001)[010]_{{\rm{YSZ}}} \parallel (111)[00\overline 1 ]_{{\rm{NiO}}} $. The epitaxial relationship at the NiO/VO2 interface was determined to be $(010)[001]_{{\rm{VO2}}} \parallel (111)[00\overline 1 ]_{{\rm{NiO}}} $. The SMT characteristics of these fully relaxed films were determined, and a transition temperature of 341 K with amplitude over four orders of magnitude and the hysteresis of 3.4 K hysteresis were obtained, which are close to those of the bulk high quality single crystals.

Nature and mechanism of interfacial reactions between boron nitride nanotubes (BNNTs) and aluminum matrix at high temperature (650 °C) are studied using high-resolution transmission electron microscopy (HRTEM). This study analyzes the feasibility of the use of BNNTs as reinforcement in aluminum matrix composites for structural application, for which interface plays a critical role. Thermodynamic comparison of aluminum (Al)-BNNT with analogous Al-carbon nanotube (Al-CNT) system reveals lesser amount of reaction in the former. Experimental observation also reveals thin (∼7 nm) reaction-product formation at Al-BNNT interface even after 120 min of exposure at 650 °C. The spatial distribution of the reaction-product species at the interface is governed by the competitive diffusion of N, Al, and B. Morphology of the reaction products are influenced by their orientation relationship with BNNT walls. A theoretical prediction on Al-BNNT interface in macroscale composite suggests the formation of strong bond between the matrix and reinforcement phase.

Vanadium (V)–aluminum (Al)–carbon (C) thin films were deposited on Al2O3$(11\mathop 2\limits^ - 0)$ substrates at 500 °C by direct current magnetron sputtering using a powder metallurgical composite target with 2:1:1 MAX phase stoichiometry. Transmission electron microscopy (TEM) and x-ray diffraction results suggest that a hexagonal Al-containing vanadium carbide solid solution (V,Al)2Cx was formed. The films exhibited a strong basal plane texture. The lattice parameter of the hexagonal solid solution was dependent on the annealing temperature: the c lattice parameter decreased by 3.45% after annealing for 1 h at 750 °C compared to the as-deposited film. Based on the comparison between experimental and theoretical lattice parameter data, it is reasonable to assume that this annealing-induced change in lattice parameter is a consequence of atomic ordering. Meanwhile, the formation of V2AlC MAX phase was observed at 650 °C and phase-pure V2AlC was obtained at 850 °C. TEM images support the notion that V2AlC forms by nucleation and growth.

Mechanisms leading to correlation between structural phase transitions in functional oxides and consequent insulator–metal transitions driven by band gap closure are an active area of research. In cases where large volume changes are present, structural stability considerations become important. Here, we present in situ studies of mechanical instability of VO2 grown on self-supported Si3N4 membranes spanning the structural phase transition boundary of vanadium dioxide. We observe film cracking across the phase transition, and the transition-induced cracks correlate with the symmetry change and the corresponding changes in the optical/electrical response arising from the insulator–metal transition. Transmission electron microscopy studies revealed twinned platelets proximal to crack regions. Interestingly, the membranes are mechanically stable until a large fraction of resistance change occurs across the phase transition. The ability to manipulate the stability and controlled rupture of self-supported membranes through temperature or other stimuli could be of interest to microelectromechanical systems and sensor devices.

A bismuth telluride alloy-based thermoelectric generator with high-aspect ratio, free-standing legs was fabricated. Such legs are desirable for efficient generator performance from low-grade heat sources but are difficult to assemble because they are fragile and difficult to handle and position. Plunge and wire electro-discharge machining (EDM) were used to produce 150 μm × 300 μm legs, approximately 6-mm long, with high fidelity. Removal of recast material from EDM was necessary for good adhesion of metallization, but sputter etching was found to deteriorate the mechanical strength of the contacts. A wet chemical cleaning process was developed instead that resulted in good adhesion under test conditions. Au was preferred for designs where interconnects could be patterned directly on the module. Module figure of merit (ZT) was 0.72, close to the 0.85 value expected from bulk material property measurements. Impedance spectroscopy and the Harman technique were shown to significantly underestimate module ZT in the present test configuration. Shear and fatigue testing were performed on arrays of high-aspect ratio legs. Legs survived over 104 cycles of shear loading at 90% of the load to failure.