A promising n-type thermoelectric oxide, based on the tungsten bronze-structured ferroelectric SrxBa1–xNb2O6–δ (SBN, x~0.61), was investigated to enhance the thermoelectric power factor through templated grain growth (textured polycrystalline). In the reduced SBN textured, both the electrical conductivity (σ) and the magnitude of thermopower (S) are increased in the c axis: σ33 > σ11 and |S33| > |S11|, and consequently, the thermoelectric power factor (PF) increased significantly due to crystal anisotropy and grain boundary density reduction. It was found in randomly oriented polycrystalline ceramics that the thermoelectric properties are dominated by a-axis properties. A ferroelectric–thermoelectric anomaly is observed at 4mm–4/mmm phase transition temperature (TC) and depends on temperature and reduction degree, consistent with our earlier observations in single crystal SBN. Above TC, the carrier transport mechanism is controlled by polaron hopping conduction, and below TC the behavior depends on the degree of reduction. However, the magnitude of the Seebeck coefficient is dependent on the crystal anisotropy.

A catalytic technique to enhance graphite formation in nongraphitizing carbons was adapted to work with three-dimensional wood-derived scaffolds. Unlike many synthetic graphite precursors, wood and other cellulosic carbons remain largely disordered after high temperature pyrolysis. Using a nickel nitrate liquid catalyst and controlled pyrolysis conditions, wood-derived scaffolds were produced showing similar graphitic content to traditional pitch-based graphite while retaining the high-aspect ratio pores of the precursor wood microstructure. Graphite formation was studied as a function of processing time and pyrolysis temperature, and the resulting carbons were analyzed using x-ray diffraction, Raman spectroscopy, x-ray photoelectron spectroscopy, and electron microscopy techniques.

We report on the electrochromic response of as-deposited and annealed nanostructured molybdenum trioxide films prepared with the glancing angle deposition (GLAD) technique. Morphology of the as-deposited films, obtained with an atomic force microscope (AFM), showed a typical grain size of 10 to 50 nm diameter. After annealing, the AFM images clearly showed the dominant presence of a layered structure, characteristic of the orthorhombic (α) phase of molybdenum trioxide, with typical grain dimensions of a few micrometers. The annealed samples showed pronounced coloration in the visible and near-infrared regions of the electromagnetic spectrum, while the as-deposited samples showed significant coloration only in the visible region.

Hafnium dioxide (HfO2) thin films were synthesized on silicon and quartz substrates by thermal oxidation of metallic hafnium films in oxygen. The crystalline structure and optical properties of the HfO2 films were systematically investigated using x-ray diffraction, ultraviolet (UV)-Raman, and UV-visible spectrophotometer techniques. All the films thermally oxidized at 450 to 800 °C were mostly monoclinic. Interestingly, cubic phase coexisted with monoclinic phase in the films thermally oxidized at 500 to 600 °C. The corresponding optical band gap (Eg) varied from 5.92 to 6.08 eV for the films with a different phase ratio (cubic to monoclinic one) ranging between 0 and 1:3. These results imply that the mixed phase could have a certain effect on the increase of the Eg of HfO2 films.

The poly (vinylidene difluoride) (PVDF) has been of great interest for energy conversion of microelectromechanical system devices. A semicrystalline polymer, the PVDF has five crystallographic forms, α, β, γ, δ, and ε. The latter four structures exhibit a permanent dipole moment. In this research, we investigated effects of microstructures of the PVDF on its piezoelectricity for energy harvesting. Using various experimental techniques, we observed the power density generated by a mechanical force that was correlated with the phase transformation between amorphous, α, β, and γ phases. The transformation was time-dependent in a nonlinear manner. Such transformation influences the energy transition and storage of small devices.

We report on the enhanced dielectric constant and electrical resistivity of the Co-ferrite (CoO.Fe2O3) by partially substituting Fe with La. Structural characteristics of La-doped Co ferrite namely CoO.Fe1.925La0.075O3 indicate the cubic inverse spinel phase with a small amount of LaFeO3 additional phase. The lattice parameter obtained is 8.401 Å (±0.001 Å), which is higher than that reported for Co ferrite (8.387 Å, ±0.001 Å). The dielectric constant and electrical resistivity of CoO.Fe1.925La0.075O3 are higher compared with pure Co ferrite. The dielectric constant dispersion of CoO.Fe1.925La0.075O3 in the frequency range of 100 Hz to 1 MHz fits to the modified Debye’s function with more than one ion contributing to the relaxation. Temperature-dependent electrical resistivity curves exhibit two distinct regions indicative of two different types of conduction mechanisms. Analysis of the data indicates that the small polaron and variable-range hopping mechanisms are operative in the 220 to 300 K and 160 to 220 K temperature regions, respectively.

Tin oxide (SnO2) nanotubes have been synthesized using carbon nanotubes (CNTs) as removable templates. The entire synthesis takes place on the microscale on a micromachined hotplate, without the use of photolithography, taking advantage of the device’s built-in heater. Well-aligned multiwalled CNT forests were grown directly on microhotplates at 600 °C using a bimetallic iron/alumina composite catalyst and acetylene as precursor. Thin films of anhydrous SnO2 were then deposited onto the CNT forests through chemical vapor deposition of tin nitrate at 375 °C. The CNTs were then removed through a simple anneal process in air at temperatures above 450 °C, resulting in SnO2 nanotubes. Gas sensing measurements indicated a substantial improvement in sensitivity to trace concentrations of methanol from the SnO2 nanotubes in comparison with a SnO2 thin film. The synthesis technique is generic and may be used to create any metal oxide nanotube structure directly on microscale substrates.

This work uses a method based on indentation to characterize a polydimethylsiloxane (PDMS) elastomer submerged in an organic solvent (decane, heptane, pentane, or cyclohexane). An indenter is pressed into a disk of a swollen elastomer to a fixed depth, and the force on the indenter is recorded as a function of time. By examining how the relaxation time scales with the radius of contact, one can differentiate the poroelastic behavior from the viscoelastic behavior. By matching the relaxation curve measured experimentally to that derived from the theory of poroelasticity, one can identify elastic constants and permeability. The measured elastic constants are interpreted within the Flory–Huggins theory. The measured permeability indicates that the solvent migrates in PDMS by diffusion, rather than by convection. This work confirms that indentation is a reliable and convenient method to characterize swollen elastomers.

The interplay of large strain and large strain rate during high-rate severe plastic deformation (HR-SPD) lead to dynamic temperature rise in situ that engenders a recovered microstructure whose characteristics are not just a function of the strain, but also of the strain rate and the coupled temperature rise during the deformation. In this work, we identify three classes of microstructures characterized by multistage recovery phenomena that take place during the high strain rate SPD of Cu. It is found that the first stage of this recovery is similar to the first stage of static recovery, which is characterized mainly by annihilation of dislocations. The second stage starts around 360 K and was characterized by dislocations getting arranged in tight cell boundaries and eventually into subgrain. Recovery stages were found to be followed by a stage of grain growth and recrystallization when the temperature in the deformation zone approaches 480 K.

Theoretically dense ZrB2–SiC two-phase microstructures were isothermally oxidized for ∼90 min in flowing air in the range 1500–1900 °C. Specimens with 30 mol% SiC formed distinctive reaction product layers that were highly protective; 28 mol% SiC–6 mol% TaB2 performed similarly. At and above 1700 °C, the composition with only 15 mol% SiC oxidized extensively because of deficient silicate liquid formation. Specimens with 60 mol% SiC were resistant to oxidation up to 1800 °C; at 1900 °C, this composition displayed periodic ruptures of the passivating layer by emerging gas bubbles. Oxide coating thicknesses calculated from weight loss data were consistent with those measured from scanning electron microscopy micrographs. A layer of ZrB2 devoid of SiC was argued to be from preferential removal of SiC by reaction of a silica oxidation product with adjacent unreacted SiC to form escaping gases.

Effects of stacking fault energy (SFE) on the thermal stability and mechanical properties of nanostructured (NS) Cu–Al alloys during thermal annealing were investigated in this study. Compared with NS Cu–5at.%Al alloy with the higher SFE, NS Cu–8at.%Al alloy exhibits the lower critical temperatures for the initiation of recrystallization and the transition from recovery-dominated to recrystallization-dominated process, which significantly signals its low thermal stability. This may be attributed to the large microstructural heterogeneities resulting from severe plastic deformation. With increasing the annealing temperatures, both Cu–Al alloys present the similar trend of decreased strength and improved ductility. Meanwhile, the remarkable enhancement of uniform elongation is achieved when the volume fraction of Static recrystallization (SRX) grains exceeds ~80%. Moreover, the better strength–ductility combination was achieved in the Cu–8at.%Al alloy with lower SFE.