A new acentric protonated garnet Li6−xHxCaLa2Nb2O12 has been synthesized and structurally characterized from Rietveld refinement of high-resolution neutron diffraction data. This phase can be prepared by Li+/H+ exchange on the mother garnet Li6CaLa2Nb2O12 in acetic acid heated at reflux for 4 days, conditions determined after several tests varying acid solution, time, and temperature. Li6−xHxCaLa2Nb2O12 crystallizes in the noncentrosymmetric cubic space group I$\overline 4$3d (no. 220) with the cell parameter a = 12.8040(3) Å. The noncentrosymmetry has been confirmed from unambiguous results obtained by second harmonic generation test as well as from transmission electron microscopy study (selected area electron diffraction). The Li+/H+ exchange corresponds to a topotactic reaction since this new protonated phase is built from the garnet framework [CaLa2Nb2O12]6− like its mother form Li6CaLa2Nb2O12 with lithium and proton cations distributed on different sites.

We have fabricated Ag-decorated ZnO nanoplate arrays by combining water-bath heating toward ZnO hexagonal nanoplate arrays and subsequent decoration of Ag films or nanoparticles on the ZnO surfaces by magnetron sputtering or photoreduction. Experimental surface-enhanced Raman scattering (SERS) results show that Ag-film–ZnO hybrid substrates with different Ag sputtering times exhibit a large difference in enhanced SERS signals for Rhodamine 6G (10−7 M). Atomic force microscope analysis reveals that two kinds of positions create abundant “hot spots” in this SERS substrate: one is located at the gap between adjacent separate Ag-film–ZnO hybrid nanoplates, and the other is located at the V-grooves formed by two adjacent interlaced Ag-film–ZnO hybrid nanoplates. The effects of simultaneous changes in interplate spacing and groove wall angle are considered to be the key factors affecting the SERS of our prepared Ag-film–ZnO hybrid substrates, which have also been evaluated by finite-difference time-domain simulation.

There have been efforts to develop alternative transparent conductors to replace indium tin oxide (ITO). A hybrid transparent conductor that integrates a metallic Cu grid and graphene film promises to be a suitable candidate. Flexibility, sheet resistance, and transmittance comparable to ITO have been demonstrated. Here, we show that the optical and electrical properties of the hybrid transparent conductor can be easily tuned by clever design of the metal grid. The outcome of our study provides unprecedented guidelines for future design of metal grids integrated in transparent conductors. We also find that the graphene film forms an effective barrier to retard the degradation of the copper grid when the hybrid transparent conductor is heated in air up to high temperatures for an extended period of time. Hence, a superior hybrid transparent conductor, which can be carefully engineered to display desirable properties, has been demonstrated.

Interfacial reactions at 100 and 150 °C in the Sn–20.48 at.% In–3.05 at.% Ag (Sn–20.0 wt% In–2.8 wt% Ag)/Ni couples are studied. Three unusual phenomena are observed. First, liquation is found in Sn–20.48 at.% In–3.05 at.% Ag (Sn–In–Ag)/Ni couples that are reacted at 150 °C, which is lower than the melting points of both the solder and the Ni substrate. In addition to the Ni3Sn4 phase, liquid phase is formed in the reaction layer. Second, the liquid phase disappears and isothermal solidification occurs when there is prolonged isothermal heat treatment at 150 °C. The results are similar to those for transient liquid phase bonding. Third, the thickness of the reaction layer in Sn–In–Ag/Ni couples that are reacted for 1440 h at 150 °C is 40 times thicker than that of those reacted at 100 °C. The reaction mechanisms for these three unusual phenomena: liquation, isothermal solidification, and an extraordinary increase in the reaction rate for only 50 °C difference in temperature are elaborated and are related to each other.

Deformation mechanisms of a ZrTiAlV alloy with two ductile phases including a hexagonal close-packed (hcp) structure phase were investigated. A ZrTiAlV alloy was prepared via smelting, breakdown, forging, and suitable heat treatments. X-ray diffraction results show that the proposed ZrTiAlV alloy has two ductile phase structures, namely, hcp structure α-phase and bcc (body-centered cubic) structure β-phase. Scanning electron microscopy (SEM) results show that the plastic deformation of the examined ZrTiAlV alloy starts from the α-phase. Transmission electron microscopy (TEM) analysis shows that only dislocation slips can be found near fractured areas, and the main slip plane in the α-phase is the (0001) lattice plane. Both of the SEM and TEM results show the inexistence of deformation twin in the examined ZrTiAlV alloy including a hcp structure α-phase. Reasons for the abnormal deformation behavior of the hcp structure α-phase are also discussed.

Uniform ytterbium ion and erbium ion codoped gadolinium oxyfluoride (GdOF: Yb3+, Er3+) hollow nanospheres of 100-nm diameter were synthesized via the nanoscale Kirkendall approach, using colloidal nanospheres of ytterbium ion and erbium ion codoped gadolinium hydroxide [Gd(OH)3: Yb3+, Er3+] as sacrificial templates and titanium tetrafluoride as fluorine source under hydrothermal condition. The shell thickness of the as-synthesized GdOF: Yb3+, Er3+ hollow nanospheres can be facilely tuned from 31 to 13 nm by controlling reaction temperature and reaction time. The upconversion emission color could be adjusted from red to yellow to green when the host lattices variedfrom gadolinium (III) oxide to gadolinium oxyfluoride to gadolinium fluoride. Furthermore, the formation mechanism of the hollow GdOF: Yb3+, Er3+ nanospheres was found to depend on the fluorine source.

In this work, the relationship between the substrate crystallinity and the on-state resistances of silicon carbide (SiC) photoconductive semiconductor switches (PCSSs) was investigated. PCSSs with different channel lengths were fabricated on semi insulating 6H–SiC having different crystal qualities. A method was introduced for determining the photoconductive capacity of the SiC PCSSs. The experimental data suggest that the photoconductive capacity decreases sharply with the degradation of the full width at half maximum of the rocking curve of the 6H–SiC substrates. It is found that increasing the carrier mobility is a key factor for reducing the on-state resistance of the 6H–SiC PCSSs. Moreover, the results in this work present reference for the selection of 6H–SiC substrates for the fabrication of PCSSs and some other photoelectric devices.

An experimental study on the indentation hardness of NiTi shape memory alloys (SMAs) by using a spherical indenter tip and a finite element investigation to understand the experimental results are presented in this paper. It is shown that the spherical indentation hardness of NiTi SMAs increases with the indentation depth. The finding is contrary to the recent study on the hardness of NiTi SMAs using a sharp Berkovich indenter tip, where the interfacial energy plays a dominant role at small indentation depths. Our numerical investigation indicates that the influence of the interfacial energy is not significant on the spherical indentation hardness of SMAs. Furthermore, the depth dependency of SMA hardness under a spherical indenter is explained by the elastic spherical contact theory incorporating the deformation effect of phase transformation of SMAs. Hertz theory for purely elastic contact shows that the spherical hardness increases with the square root of the indentation depth. The phase transformation beneath the spherical tip weakens the depth effect of a purely elastic spherical hardness. This study enriches our knowledge on the basic concept of hardness for SMAs under spherical indentation at micro- and nanoscales.

High purity anatase titanium dioxide (TiO2) and iron (Fe)-doped TiO2 nanocrystals were prepared by a continuous flow synthesis method using isopropanol-water mixtures as solvent in supercritical or near-critical conditions. The method allows complete control of size (5–20 nm) and crystallinity (10–100%) of the nanoparticles and provides quick synthesis with a residence time of ∼10 s that can be scaled up to commercial production. It is found that the average crystallite size can be easily controlled by adjusting the ratio between isopropanol and water in the solvent, whereas the crystallinity is mainly controlled by the reaction temperature. As-prepared Fe-doped TiO2 nanoparticles appear to be single phase, but Fe3+ ions most likely do not occupy the Ti4+ sites in the anatase TiO2 crystal structure.

The ternary Cu–Co–Fe alloy was rapidly solidified by using the high pressure gas atomization technique. Powders with a well-dispersed microstructure resulting from the liquid–liquid phase transformation were obtained. A model describing the microstructure evolution in an atomized drop during the liquid–liquid phase transformation was developed. The kinetic details of the liquid–liquid phase transformation were discussed. The numerical results show a favorable agreement with the experimental ones. They demonstrate that under the rapid cooling conditions of gas atomization, the spatial phase separation due to the Marangoni migration of the minority phase droplets is very weak. Also, the effect of Ostwald coarsening of the minority phase droplets on the microstructure is negligible. For Cu-10 wt% Co-10 wt% Fe alloy, the average radius and number density of the Fe–Co-rich particles depend exponentially on the cooling rate of the melt during the nucleation period of the Fe–Co-rich droplets.

Nanosized oxides of barium strontium zirconate of general formula Ba1-xSrxZrO3 (0 ≤ x ≤ 1) have been prepared over the entire range of x for the first time by polymeric precursor route using citric acid and ethylene glycol. These solid solutions were investigated by means of powder x-ray diffraction, transmission electron microscopy, scanning electron microscope and Brunauer, Emmett and Teller surface area studies. X-ray diffraction studies reveal the monophasic nature of the powders at 1000 °C. The grain size was found to be in the range of 17–52 nm for all the oxides at 1000 °C. Specific surface area of these solid solutions comes out to be in the range of 49.1–94.4 m2/g. Smallest particle size with highest surface area has been achieved for x = 0.25 and comes out to be 17 nm and 94.4 m2/g respectively. Dielectric constant (ε) and dissipation factor (D) were investigated as a function of frequency and temperature. The room temperature dielectric constant of Ba1-xSrxZrO3 was found to be maximum 105 for x = 0.20 at 1 MHz.

Buffer leakage in aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure transistors is recognized as an issue that has deleterious consequences on device performance for high-power, high-frequency transistors and has been related to the presence of uncharged threading screw dislocations. In this study, we demonstrate that measurements of buffer leakage in AlGaN/GaN heterostructures grown on bulk gallium nitride (GaN) substrates are consistent with a mechanism based on the concept of dislocations acting as quantum wires in series with unintentional silicon (Si) impurity incorporation at the bulk GaN substrate/GaN buffer interface. The number of electronic channels N deduced from the leakage data using Landauer’s formula for the quantum resistance of N electronic channels is consistent with the number of dislocations along the ohmic contact pads determined from panchromatic cathodoluminescence and x-ray diffraction measurements of the dislocation density. This mechanism is consistent with Shockley’s suggestion that dislocations can act as one-dimensional conductors due to the presence of edge states along the dislocation core.

Resistance degradation of zirconium (Zr)-doped barium titanate (BaTiO3) was investigated. A series of Ba(Ti1−yZry)O3 powders and coarse-grained ceramics ranging y from 0 to 0.1 were prepared. The increase of Zr concentration systematically increased the time to as well as electric field to degradation. Such behaviors directly corresponded to those of ionic conduction contribution as evaluated by the Warburg impedance. The magnitude of Warburg impedance decreased with the increase of Zr concentration, which demonstrates that the Zr incorporation inhibits the ionic conduction caused by oxygen vacancies. The prototype multilayer ceramic capacitor (MLCC) samples were also prepared by applying these Ba(Ti1−yZry)O3 base powders and formulated X5R additives of commercial application. In this case, however, such distinct difference in degradation behavior with the variation of Zr concentration did not appear. It is supposed that the influence of additives far outweighs the effect of relative difference in the ionic conduction of Ba(Ti1−yZry)O3 under the MLCC test condition where the applied electric field strength is much higher than those for the coarse-grained bulk ceramics. Resistance degradation of MLCC under such high field might not be explained by only oxygen vacancy-related behavior alone.

The structural properties, the formation enthalpies, and the mechanical properties of Co–Al compounds (CoAl, CoAl3, Co3Al, Co2Al5, Co2Al9, and Co4Al13) are studied by using Chen's lattice inversion embedded-atom method. The potential is transferable and therefore does well for studying different Co–Al compounds. The calculated lattice parameters and cohesive energies are consistent with the experimental and theoretical results. The formation enthalpies of all the Co–Al compounds are negative; therefore, the chemical bonding between Co and Al atoms increases the stability of compounds. According to elastic constant restrictions, all the six Co–Al compounds are mechanically stable. CoAl alloy with the larger moduli and lower Poisson's ratio is the hard or brittle phase. Moreover, CoAl3, Co3Al, Co2Al5, and Co2Al9 alloys are considered to be ductile materials, which have lower ratio of shear modulus to bulk modulus.

The influence of calcium fluoride (CaF2) on combustion characteristics of Na2WO4 + 3 Mg system and microstructure of the produced W and WO3/W crystals is investigated. The results of thermodynamic analysis and experimental investigations show that CaF2 simultaneously enhances the conversion of Na2WO4 toward tungsten and binds sodium through the formation of NaF phase. The examination of the microstructure of quenched combustion products and differential scanning calorimetry analysis indicate that at early stages of combustion, a part of Na2WO4 is reduced by Mg to tungsten, whereas another part reacts with CaF2 forming CaWO4 and NaF. Subsequent magnesium reduction of CaWO4 significantly increases the overall temperature of the combustion process. Such modification in reaction mechanism coupled with postcombustion processing (e.g., acid/basic treatment) of the product allows us to produce either pure tungsten nanocrystals or tungsten oxide—tungsten nanostructures consisting of two-dimensional WO3 nanoflakes assembled on a W core. It is found that CaF2 does not influence the sizes of tungsten nanocrystals. However, since the addition of CaF2 leads to the increase of overall reaction temperature, it facilitates the formation of W particles with equilibrium crystal shape by faceting process.

The relationship between morphology and crystallography of an entangled lathy ferrite during directional solidification in Fe–Cr–Ni alloy has been investigated. During solidification, morphology of the lathy ferrite depends on the orientation relationship between the lathy ferrite and austenite. When the plane in the austenite substrate is ${(1\bar 11)_{\rm{\gamma }}}$, “Y-shaped” lathy ferrite grows in an entangled cluster and the orientation relationship between the lathy ferrite and austenite is the Nishiyama–Wassermann relationship. Lathy ferrite is preferentially elongated along ${\langle 211\rangle _{\rm{\gamma }}}$ and ${\langle 011\rangle _{\rm{\gamma }}}$ directions on ${(1\bar 11)_{\rm{\gamma }}}$ plane due to lower misfit. The included angle among the “Y-shaped” lathy ferrite is about 120° because the angle between each pair of ${[21\bar 1]_{\rm{\gamma }}}$, ${[\bar 112]_{\rm{\gamma }}}$, and ${[\bar 1\bar 2\bar 1]_{\rm{\gamma }}}$ crystal directions is equal to 120°. Formation mechanism of the perpendicular lathy ferrite has also been analyzed according to the relationship between ${\langle 211\rangle _{\rm{\gamma }}}$ and ${\langle 011\rangle _{\rm{\gamma }}}$ on ${(1\bar 11)_{\rm{\gamma }}}$ plane. This indicates that required crystal morphology of the lathy ferrite in the solidified microstructure can be obtained by controlling the crystal plane of austenite.

Branched core–shell hybrids of tin nanowires and carbon nanotubes have been successfully obtained on silicon substrate via a self-assembly process by chemical vapor deposition. Structure characterization unveiled that the nanostructures are the hybrids of branched single-crystalline β-Sn nanowires coated with amorphous carbon nanotubes. Detailed investigation demonstrates that the amount of introduced ethylene plays a crucial role in triggering the morphology change of the product from freestanding core–shell hybrids to branched hybrids accompanying with a thickness and surface morphology change of carbon shell. Architecture of the branched core–shell hybrids has been categorized and the mechanism has been discussed. This kind of branched hybrids may find great potential applications in building multipath nanoelectronic components, lithium-ion battery electrodes, and enhanced superconducting nanodevices as well.

In this work, we report on the optoelectronic and photocatalytic features of europium (Eu3+)-doped TiO2 nanoscale particles synthesized via a sol-gel mediated rapid-condensation technique. X-ray diffraction studies have revealed the mixed phases of the synthesized systems. In particular, a mixture of anatase, brookite, and rutile phases was found to coexist beyond a sintering temperature of 600 °C while a pure anatase phase was witnessed below 500 °C. The photoluminescence spectra of ∼7 nm sized anatase TiO2 nanoparticles have exhibited different intra 4f (Eu3+ ion related) transitions with the most intense red emission (5D0→7F2) peak located at ∼613 nm. The emissions due to color centers and oxygen vacancies of TiO2 were also evident in the PL spectra. The Brunauer-Emmett-Teller surface area analysis has revealed a significant increment of surface area and pore volume owing to the enhanced interfacial region introduced by point defects and dislocations due to Eu doping. The photocatalytic activity of the Eu3+ doped TiO2 nanoscale system was found to be ∼12% stronger than its un-doped counterpart, as assessed from the degradation of methyl orange (MO) solution under UV light irradiation. The percentage of degradation was found to be strongly dependent on the duration of the UV exposure and Eu doping concentration. As an efficient photosensitive candidate, rare earth sensitized TiO2 systems would bring new insights while displaying both optoelectronic and photocatalytic characteristics through use of the localized states present in the band gap of the host.

Visible light emitting ZnO quantum dots (QDs) were synthesized by a modified sol–gel method and in situ coated with the amino acid cysteine to modify their surface chemistry and govern the crystal growth process. Surface chelation by a hydrophilic thiol such as cysteine offered a fine control over the particle size and modulated the optical emission and its stability by reducing the density of surfacial oxygen deficiencies and also induced the formation of hierarchical nanostructures in the solution. TEM and XRD results confirmed the formation of mono-dispersed and spherical ZnO QDs in the size range 2.5–3.8 nm. The modulation of band gap energies was manifested in the visible emission of cysteine modified QDs, which was found to be remarkably stable for cell labeling applications, when compared to the photoluminescence of conventional ZnO QDs.

Stable, aqueous, red-to-near infrared emission is critical for the use of silicon nanoparticles (Si NPs) in biological fluorescence assays, but such Si NPs have been difficult to attain. We report a synthesis and surface modification strategy that protects Si NPs and preserves red photoluminescence (PL) in water for more than 6 mo. The Si NPs were synthesized via high temperature reaction, liberated from an oxide matrix, and functionalized via hydrosilylation to yield hydrophobic particles. The hydrophobic Si NPs were phase transferred to water using the surfactant cetyltrimethylammonium bromide (CTAB) with retention of red PL. CTAB apparently serves a double role in providing stable, aqueous, red-emitting Si NPs by (i) forming a hydrophobic barrier between the Si NPs and water and (ii) providing aqueous colloidal stability via the polar head group. We demonstrate preservation of the aqueous red emission of these Si NPs in biological media and examine the effects of pH on emission color.