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.

Mechanisms and magnitudes of the large piezoelectric response observed in lead-free (1–x)BiFeO3–xBaTiO3 (BFBT) ceramics are investigated. Preceding studies reported significant strain hysteresis and hard ferroelectric behavior in BFBT leading to a small low-field piezoelectric coefficient, instability of the poled domain state, and rapid degradation of piezoelectric properties. The current investigation shows that under application of a suitable direct current (dc) bias to stabilize the ferroelectric phase low- and high-field piezoelectric coefficients (d33) of 150 pC/N and 250 pC/N are observed for the composition 0.67BiFeO3–0.33BaTiO3 + 0.1 wt% MnO with a Curie temperature of 605 °C. Such enhancement of electromechanical properties under dc bias is in contrast to the expected behavior in traditional piezoelectric materials such as soft lead zirconate titanate (PZT). The large piezoelectric coefficients confirm strong intrinsic and extrinsic contributions to the piezoelectric response in BFBT, which coupled with high ferroelectric Curie temperature TC > 500 °C, suggests BFBT-based materials as promising lead-free alternatives to PZT piezoceramics.

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.

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 〈110〉 oriented Tb0.3Dy0.7Fe1.95 alloy rod was annealed at 500 °C under a magnetic field of 0.3 T, which was applied 35° away from the rod axis. X-ray diffraction characterization and optical microscopy observation showed that both the crystal orientation and morphologies were retained after magnetic annealing. Magnetic force microscopy images exhibited obvious change of the magnetic domain configurations. The magnetostrictive performance was changed drastically. Saturation axial magnetostriction λ‖s increased from 1023 to 1650 ppm by the ratio of 61.3%, but saturation perpendicular magnetostriction λ⊥s decreased from −802 to −624 ppm. Maximum magnetostrictive strain coefficients d33 and d31 were found to be enhanced by 29.3% and 32.6%, respectively. In addition, the fields for obtaining both optimum d33 and d31 decreased, which indicates that better magnetostrictive performance can be achieved at lower external fields after magnetic annealing.

The temperature dependence of the various electric relaxation times in the perovskite oxide CaCu3Ti4O12 (CCTO) is determined (i) by trap state spectroscopy and (ii) by the dielectric loss function. A similarity in both number and properties of the (i) and (ii) relaxation times was found, suggesting that the dielectric response is strongly correlated with the trap state relaxation, although some differences remain. One or more dipoles developing charged trap states are considered responsible, and the experimental dielectric response of CCTO and Mn substituted CCTO are explored.

Both low and high resistance states (which were written by voltage application in a local region of NiO/Pt films using conducting atomic force microscopy [C-AFM]) were observed with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The writing regions are distinguishable as dark areas in a secondary electron image and thus can be specified without using a complicated sample fabrication process to narrow down the writing regions such as the photolithography technique. In addition, the writing regions were analyzed using energy-dispersive x-ray spectroscopy (EDS) mapping. No difference between the inside and outside of the writing regions is observed for all the mapped elements including C and Rh. Here, C and Rh are the most probable candidates for contamination that affect the secondary electron image. Therefore, our results suggested that the observed change in the contrast of the secondary electron image is related to the intrinsic change in the electronic state of the NiO film and a secondary electron yield is correlated to the physical properties of the film.

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.

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.

As deposited amorphous and crystallized thin films of Ti 37.5% Si alloy deposited by pulsed laser ablation technique were irradiated with 100 keV Xe+ ion beam to an ion fluence of about 1016 ions-cm−2. Transmission electron microscopy revealed that the implanted Xe formed amorphous nanosized clusters in both cases. The Xe ion-irradiation favors nucleation of a fcc-Ti(Si) phase in amorphous films. However, in crystalline films, irradiation leads to dissolution of the Ti5Si3 intermetallic phase. In both cases, Xe irradiation leads to the evolution of similar microstructures. Our results point to the pivotal role of nucleation in the evolution of the microstructure under the condition of ion implantation.

Hollow nanoparticles of hexagonal close-packed (hcp)-NaYF4:Yb,Er were synthesized by thermal decomposition of trifluoroacetate precursors at 340 °C via vacancy diffusion, likely due to the Kirkendall effect and Ostwald ripening mechanism. The average outer diameter, inner diameter, and shell thickness of these hollow particles were 14 ± 3 nm, 7 ± 2 nm, and 4 ± 1 nm, respectively. The surface effects on the fluorescence properties of these hollow particles were studied by comparing with that of solid NaYF4:Yb,Er (average size ∼15 ± 3 nm) and solid NaYF4 core/NaYF4:Yb,Er shell (NaYF4 core ∼10 ± 1 nm and NaYF4:Yb,Er shell ∼3 ± 2 nm) nanoparticles containing similar composition of Yb and Er ions. The green, red, and total emission intensities decreased with increasing upconversion active volume-normalized surface area. Surface coatings of undoped NaYF4 on both inner and outer surfaces of the hollow nanoparticles enhanced the total emission intensity by ∼19 and ∼5 times compared with those of the hollow and solid NaYF4:Yb,Er nanoparticles, respectively.

Here we present a microemulsion route to prepare core–shell structured NaGdF4:Yb,Er@Carbon nanoparticles, in which a thin layer of hydrophilic carbon was covered on hydrophobic NaGdF4:Yb,Er nanocrystals. The prepared NaGdF4:Yb,Er@Carbon nanoparticles were uniform in a size of 25 nm, water-dispersible, and displayed good biocompatibility and strong upconversion fluorescence. Their potential for use as efficient cell-imaging probes is also demonstrated.

Three-dimensional (3D) sphere-like Eu3+-doped white light lutetium tungstate phosphors have been fabricated by the cationic surfactant cetyltrimethyl ammonium bromide (CTAB)-assisted hydrothermal method, which presents a diameter of ∼2-μm morphology assembled by nanoflakes with a length of 100 to ∼200 nm. The results demonstrate that CTAB, suitable pH values, reaction time, and reaction temperature are all essential for the formation of lutetium tungstate microspheres. Photoluminescence measurement indicates that lutetium tungstate microspheres show a broad O–W Charge transfer state (CTS) transition and the characteristic emission of Eu3+ at ∼591 and ∼611 nm.

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.