A new elpasolite-type (NH4,K)3VO2F4 compound was prepared and characterized by x-ray diffraction, differential scanning calorimeter (DSC), impedance analysis, and electrical polarization measurements. It crystallizes in an orthorhombic lattice with unit-cell parameters: a = 8.9584(4), b = 18.6910(14), c = 6.2174(4) Å, V = 1041.04(11) Å3, Z = 6. NH4+, and K+ ions are distributed statistically over crystallographically four equivalent sites. There are two distinguishable vanadium atoms forming cis- and trans-VO2F4 octahedra present in the unit cell. High-temperature studies by DSC and in situ x-ray diffraction revealed a first-order structural transformation from orthorhombic to cubic lattice around 343 K. Impedance measurements show two different kinds of conductivity behaviors for the two phases. In orthorhombic phase a significant conductivity resulting from involvement of protonic species is observed. In the orthorhombic phase, a clear ferroelectric hysteresis loop is observed.

The AlGaN-based ultraviolet (UV) light-emitting diode (LED) structures with AlN as buffer were grown on sapphire substrate by metalorganic vapor-phase epitaxy (MOVPE). A series of cathodoluminescence (CL) spectra were measured from the cross section of the UV-LED structure using point-by-point sampling to investigate the origins of the broad parasitic emissions between 300 and 400 nm, and they were found to come from the n-type AlGaN and AlN layers rather than p-type AlGaN. The parasitic emissions were effectively suppressed by adding an n-type AlN as the hole-blocking layer. Electroluminescence (EL) and atomic force microscopy (AFM) measurements have revealed that the interface abruptness and crystalline quality of the UV-LED structure are essential for the achievement of the EL emissions from the multiple quantum wells (MQWs).

The cooperative self-assembly of organic–inorganic siliceous composite structures has been studied from the aspect of inorganic precursors. We reveal that the vesicular or mesostructured materials can be obtained selectively by just changing the silica sources in one templating system. For poly(ethylene oxide)-type block copolymers with either poly(propylene oxide) or poly(butylene oxide) as the hydrophobic moieties, when the other synthesis parameters are exactly the same, the use of tetramethyl orthosilicate (TMOS) as a silica source gives rise to highly ordered mesostructures, while the use of tetraethyl orthosilicate (TEOS) leads to vesicles or foams. The attenuated total reflection Fourier transform infrared (ATR-FTIR) technique is used to monitor the silicate species derived from the hydrolysis and condensation of TMOS and TEOS as a function of the reaction time. On the basis of the ATR-FTIR results, we propose a “differentiating effect” at relatively high pH (4.7) to interpret the influence of different silica sources on the self-organized composite structures. For comparison, a “leveling effect” at relatively low pH (strong acidic conditions) is revealed to explain that both TMOS and TEOS lead to the same mesostructures. Our contribution provides a feasible and designable method to synthesize from conventional ordered mesostructures to novel vesicular structures, which are significant for their future practical applications.

The engineering stress–strain curve is one of the most convenient characterizations of the constitutive behavior of materials that can be obtained directly from uniaxial experiments. We propose that the engineering stress–strain curve may also be directly converted from the load–depth curve of a deep spherical indentation test via new phenomenological formulations of the effective indentation strain and stress. From extensive forward analyses, explicit relationships are established between the indentation constraint factors and material elastoplastic parameters, and verified numerically by a large set of engineering materials as well as experimentally by parallel laboratory tests and data available in the literature. An iterative reverse analysis procedure is proposed such that the uniaxial engineering stress–strain curve of an unknown material (assuming that its elastic modulus is obtained in advance via a separate shallow spherical indentation test or other established methods) can be deduced phenomenologically and approximately from the load–displacement curve of a deep spherical indentation test.

We report a novel method of growing silver nanostructures by cathodic sputtering onto an ionic liquid (IL) and our visualization by transmission cryo-electron microscopy to avoid beam-induced motion of the nanoparticles. By freezing the IL suspension and controlling electron dose, we can assess properties of particle size, morphology, crystallinity, and aggregation in situ and at high detail. We observed round silver nanoparticles with a well-defined diameter of 7.0 ± 1.5 nm that are faceted with crystalline cubic structures and ˜80% of the particles have multiply twinned faults. We also applied cryo-electron tomography to investigate the structure of the nanoparticles and to directly visualize the IL wetting around them. In addition to particles, we observed nanorods that appear to have assembled from individual nanoparticles. Reexamination of the samples after 4–5 days from initial preparation showed significant changes in morphology, and potential mechanisms for this are discussed.

Layer-structured polypyrrole/montmorillonite (PPy/MMT) naoncomposite films were synthesized by the electrodeposition method. The fabricated free-standing films consist of about 0∼2 wt% Na+-montmorillonite (NMMT). The thickness of films could be controlled by deposition time. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to observe the microstructure of the films. After MMT was introduced into the PPy matrix, the interspace between PPy chains decreased, according to the XRD results. The layered structure of the films was observed from the SEM images. Tensile and nanoindentation test results showed that the mechanical properties of the composite films were improved at low clay loading. The electrical conductivity of the films with 1.2 wt% MMT loading was increased from 3.6 to 51 S/cm, probably because of the restricted growth of PPy chains in the interspace of MMT layers.

Low energy metal ion implantation has been used to combine an easy “bottom-up” way of creating and tuning different topographic structures on submicron to micrometer scales with the embedding of a metallic element-rich functionalized layer at the surface for a variety of scientific and technological applications. The self-organizing and complex patterns of functionalized topographic structures are highly dependent on the implanted metal ion species, variations in the geometric confinement of the buckled areas on the larger unmodified elastomer film, and the boundary conditions of the buckled regions. Systematic investigations of these dependencies have been carried out via optical and atomic force microscopy, and confirmed with cross-sectional transmission electron microscopy.

Eu3+ ion-doped BaY2ZnO5 phosphors were synthesized using a vibrating milled solid-state reaction. The phosphors exhibit a series of Eu3+ ion intra-4f excited state 5DJ (J = 3, 2, 1, 0) transitions under an excitation of 395 nm. The maximum photoluminescence intensity for 5D0 → 7F2 transition (625 nm) was obtained at a Eu3+ ion concentration of 40 mol%; quenching occurred at higher concentrations. The critical distance (Rc) for the 5DJ (J = 3, 2, 1) → 7F1 transition was 18.1 Å, which is longer than that of 6.67 Å for the 5D0 → 7F2 transition, indicating that 5DJ (J = 3, 2, 1) is easier for concentration quench because of the cross-relaxation mechanism. The red emission of the BaY1.6Eu0.4ZnO5 phosphor has CIE chromaticity coordinates of (0.66, 0.34), which are close to the NTSC system standard red chromaticity (0.67, 0.33). BaY1.6Eu0.4ZnO5 may thus be potentially applicable as a red phosphor for ultraviolet light-emitting diodes converted in solid-state lighting technology.

Thornlike Tb-doped SiC (SiC:Tb) nanostructures were synthesized through a carbothermal reduction of electrospun Tb-doped SiO2 nanofibers (SiO2:Tb). The synthesized SiC nanostructures annealed at a high temperature of 1300 °C displayed a unique morphology and a high crystalline quality with the β-SiC phase. Strong green-light emissions were detected from the SiC:Tb samples. Photoluminescence excitation results show that, besides a small amount of energy coming from the SiC cores (464 nm), most of the energy needed for the excitation of Tb3+ ions comes from the light absorption of the SiO2–Tb surface layers (295 nm) and near-interface regions in the samples (388 nm). Transmission electron microscopy, energy dispersive spectrometry, and Raman analyses suggested that the formations of Tb clusters and SiO2 surface layers are very important to the enhancement of the luminescence behaviors of Tb3+ ions. Finally, we have constructed an excitation model and further proposed an energy transfer mechanism for these thornlike SiC:Tb nanostructures.

The asymmetrical hysteresis loops were observed for the annealed Fe65Co15Si5B15 amorphous ribbons. The curves, which shift from the zero point of H axis with a unilateral step magnetization, exhibit the special magnetic features of the ribbons. A few magnetic crystalline phases were identified in the amorphous matrix of annealed ribbons by microstructure measurement. It was also found that the Z-oriented local magnetic domains emerge in the surface of ribbons with the loops shift behavior. Subsequent magnetic torque measurement indicated that the unidirectional magnetic anisotropy was induced in the amorphous ribbons with proper thermomagnetic annealing. These obtained evidences support our understanding that the magnetic history caused by thermomagnetic treatment plays a main role in promoting the formation of the asymmetrical loops.

Al8B4C7 was used as a sintering additive for the densification of nano-SiC powder. The average grain size was approximately 70 nm after sintering SiC-12.5wt% Al8B4C7 at 1550 °C. The densification rate strongly depended on the sintering temperature and the applied pressure. The rearrangement of SiC particles occurred at the initial shrinkage, while viscous flow and liquid phase sintering became important at the middle and final stage of densification.

Nanoindentation methods are well suited for probing the mechanical properties of a heterogeneous surface, since the probe size and contact volumes are small and localized. However, the nanoindentation method may introduce errors in the computed mechanical properties when indenting near the interface between two materials having significantly different mechanical properties. Here we examine the case where a soft material is loaded in close proximity to an interface of higher modulus, such as the case when indenting bone near a metallic implant. The results are derived from both an approximate analytical quarter space solution and a finite element model, and used to estimate the error in indentation-determined elastic modulus as a function of the distance from the apex of contact to the dissimilar interface, for both Berkovich and spherical indenter geometries. Sample data reveal the potential errors in mechanical property determination that can occur when indenting near an interface having higher stiffness, or when characterizing strongly heterogeneous materials. The results suggest that caution should be used when interpreting results in the near-interfacial region.

A combustion synthesis technique was used to prepare nanoparticulate LiMgxMn1−xPO4 (x = 0, 0.1, 0.2)/carbon composites. Powders consisted of carbon-coated particles about 30 nm in diameter, which were partly agglomerated into larger secondary particles. The utilization of the active materials in lithium cells depended most strongly on the post-treatment and the Mg content and was not influenced by the amount of carbon. Best results were achieved with a hydrothermally treated LiMg0.2Mn0.8PO4/C composite, which exhibited close to 50% utilization of the theoretical capacity at a C/2 discharge rate.

There is a concerted effort to develop lead-free piezoelectric ceramics. (Na0.5K0.5)NbO3-based ceramics have good electrical properties, and are a potential replacement material for lead zirconate titanate piezoelectric ceramics. In this work a commercial powder based on (Na0.5K0.5)NbO3 with an initial particle size of ∼260 nm was consolidated by spark plasma sintering (SPS). To avoid volatilization, high mechanical pressures were used to minimize the densification temperature. It was found that under a uniaxial pressure of 100 MPa, fully densified compacts can be prepared at 850 °C. Ceramics densified at such a low temperature demonstrate an unusually high remanent polarization (30 μC/cm2) and high d33 (146 pC/N). The improved ferroelectric properties are ascribed to the homogeneous, dense, and submicron grained microstructure achieved.

Semiconducting KTaO3 single crystals were investigated as a model potential photoanode for hydrogen production using photoelectrochemical cells. To modify the electronic properties of KTaO3 by reducing the band gap and thereby increasing the absorption of light at longer wavelengths, the crystals were doped during growth. A wide range of dopant elements was used that consisted primarily of transition metal atoms. Most of the crystals exhibited n-type behavior with carrier concentrations from 4 × 1018 to 2.6 × 1020 cm–3. The position of the band edges indicated that the crystals were thermodynamically capable of water dissociation. External quantum yield measurements revealed that the samples were photoactive up to a wavelength of ∼350 nm. The indirect band gap and a parameter denoted as E1 that is related to the direct band edge of the semiconductor, were found to be essentially the same for all of the samples. These results indicate that the various dopants and treatments did not produce changes in the KTaO3 electronic structure that were sufficient to significantly modify the behavior of KTaO3 in a PEC cell.

SrY2O4:Eu3+ phosphors were synthesized by both the solid-state reaction method and the sol-gel method, and their photoluminescence in vacuum ultraviolet (VUV) and the ultraviolet (UV) region were evaluated. The excitation spectra of SrY2O4:Eu3+ phosphors prepared by solid-state reaction show another excitation band centered at 324 nm except for the charge-transfer bands (CTB) of Eu3+ when monitored at 610 nm, and a blue emission band around 406 nm is observed when excited at 324 nm, which could be associated with defects. Both the excitation and emission bands mentioned above disappear when the samples were prepared by the sol-gel method. SrY1.98O4:0.02Eu3+ phosphors synthesized by the sol-gel method exhibit a higher emission intensity under 147 nm excitation compared with solid-state reaction technology. The main reason could be that the samples prepared by the solution-based route have more regular and uniform morphologies.

A novel colloidal co-casting process was developed to fabricate laser quality, multisegment composite ceramic laser gain materials. The approach was demonstrated for a three segment transparent composite rod 62 mm long by 3 mm diameter consisting of undoped yttrium aluminus garnet (YAG), 0.25% Er:YAG, and 0.5% Er:YAG. The Er concentration profile in the composite has steep, controllable gradients at the segment interfaces, while maintaining constant dopant concentrations within each segment. The composite rod has 84% transmittance at 1645 nm (the lasing wavelength) with a scatter loss of 0.4% cm−1. Laser operation of such a composite Er:YAG ceramic rod was demonstrated for the first time, with nearly equivalent lasing behavior to an Er:YAG single crystal rod.

An effective way to prepare a robust CuInSe2 (CIS) target for subsequent vapor depositions of thin films is suggested in this work. The technique involves addition of excess Se to presynthesized CIS powder followed by cold pressing and sintering at a temperature as low as 300 °C. Phase-pure chalcopyrite CIS films were prepared at a substrate temperature of 300 °C from targets that contained different amounts of excess Se. The average size of particulates, typical of the pulsed laser deposition process, and their surface coverage decreased with increasing Se content up to 50 wt% in the targets. Films grown from the target with 50 wt% excess Se exhibited a hole concentration of ˜3 × 1019 cm−3 and a Hall mobility of ˜2 cm2/Vs. With the decrease of substrate temperature to room temperature, the resistivity increased from 1.1 × 10−1 to ˜7.5 × 108 Ω·cm, which is attributed to the potential contributions of Se interstitials, CuIn, and VIn defects.

Two laser processes, flat plate ablation (FPA) and laser ablation of microparticle aerosols (LAMA), capable of producing nanoparticles and nanoparticulate thick films of Terfenol-D (Fe1.92Tb0.3Dy0.7) were investigated. The influence of processing parameters on the sizes, compositions, and morphologies of the nanoparticles produced using these processes were studied by transmission electron microscopy. The nanoparticles were used to deposit nanoparticulate films by supersonic impaction with thicknesses ranging from 4 to 50 μm, depending on processing conditions. The microstructures and properties of the films were studied using scanning electron microscopy and magnetometry. The LAMA process produced nanoparticles with a mean size and standard deviation (SD) of 8 to 10 nm ± 5 nm, depending on the type of gas used during synthesis. In contrast, nanoparticles produced using the FPA process exhibited a much broader size distribution varying from 5 to 150 nm and a much greater variation in compositions compared to the LAMA process. Films produced using LAMA also had lower levels of porosity compared to those produced using FPA as a result of the smaller, more uniform nanoparticles from which they were produced and the resulting higher impaction velocities. Compared to the FPA-produced films, the LAMA-produced films exhibited greater resistance to oxidation, higher magnetizations (13–15 emu/g versus 9–11 emu/g, depending on processing conditions) and lower coercivities (versus 41–59 Oe versus 80–110 Oe).

The formation enthalpy, electronic structures, and elastic moduli of the intermetallic compound Ti5Si3 with substitutions Zr, V, Nb, and Cr are investigated by using first-principles methods based on the density-functional theory. Our calculation shows that the site occupancy behaviors of alloying elements in Ti5Si3, determined by their atom radius, are consistent with the available experimental observations. Furthermore, using the Voigt–Reuss–Hill (VRH) approximation method, we obtained the bulk modulus B, shear modulus G, and the Young’s modulus E. Among these four substitutions, the V, Nb, and Cr substitutions can improve the ductility of Ti5Si3 effectively, while Zr substitution has little effect on the elastic properties of Ti5Si3. The elastic property variations of Ti5Si3 due to different substitutions are found to be correlated with the Me4d–Me4d antibonding and the strengthened Me4d–Si bonding in the solids.