Density functional theory calculations and molecular dynamics with a recently developed potential for W–He were used to evaluate the thermal stability of helium-vacancy clusters (nHe.mv) as well as pure interstitial helium clusters in tungsten. The stability of such objects results from a competitive process between thermal emission of vacancies, self interstitial atoms (SIAs), and helium, depending on the helium-to-vacancy ratio in mixed clusters or helium number in pure interstitial helium clusters. We investigated in particular the ground state configurations as well as the activation barriers of self trapping and trap mutation, i.e., the emission of one SIA along with the creation of one vacancy from a vacancy-helium or pure helium object.

Two phases of nickel sulfide (α-NiS and β-NiS) nanoarchitectures were successfully and controllably synthesized by a facile solvothermal method with two different solvents of alcohol and water, respectively. The products were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectrophotometer. The sphere-like shape for α-NiS and cross-like shape composed of nanorods for β-NiS are uniform and well distributed as well as their size. Both α-NiS and β-NiS powders were used as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). It is found that the DSSC with an α-NiS CE performs much better than the one with a β-NiS CE. The energy conversion efficiency of the former was 5.2%, whereas the latter was 4.2%, about 20% increment.

P-type Cu1.8+xSe (x = 0, 0.16, 0.20) compounds were synthesized by mechanical alloying and spark plasma sintering technique. A 100% enhancement of the Seebeck coefficient was achieved in the whole temperature interval for x = 0.16 and x = 0.20 bulks compared with that of the x = 0 bulk. The thermal conductivity was all below 1.6 W m−1 K−1 in the whole temperature interval for x = 0.16 and x = 0.20 bulks, showing a pronounced reduction compared with that of the x = 0 bulk. The lowest thermal conductivity 0.69 W m−1 K−1 was achieved in the x = 0.16 sample at 773 K, whereby a maximum ZT value of 1.23 was obtained, revealing that optimizing Cu content in Cu1.8+xSe system is an effective method to improve the thermoelectric (TE) merit and indicating a great potential for TE application along with their nontoxicity and low cost.

At room temperature (RT), Fe2Mo3O12 is stable in monoclinic structure phase and above 780 K it transforms to an orthorhombic phase. Experiment shows that in the high temperature orthorhombic phase, the material exhibits low or negative thermal expansion property. In the paper, new compounds with the formula Fe2–x(ZrMg)0.5xMo3O12 (x = 0–1.8) are reported. The compounds are designed and synthesized to reduce the phase transition temperature of the Fe2Mo3O12 by substitutional co-incorporation of Zr4+ and Mg2+ in it. It is found that the monoclinic-to-orthorhombic phase transition temperature can be lowered effectively by the co-incorporation. The orthorhombic phase of Fe0.4(ZrMg)0.8Mo3O12 may be obtained at RT and it may keep the orthorhombic structure as low as 103 K. Meanwhile, the co-incorporation of Zr4+ and Mg2+ may tailor the coefficient of thermal expansion (CTE) of the Fe2Mo3O12 and the near-zero CTEs are obtained for the compound around x = 1.7 (Fe0.3(ZrMg)0.85Mo3O12). This work paves the way toward developing low-cost and near-zero thermal expansion materials over wide temperature ranges.

Magnesium aluminate (MgAl2O4) spinel nanoparticles with an average crystalline size of 35 nm were synthesized by polymer-gel and isolation-medium-assisted calcination. In the process, a large excess of MgO, 40 times the stoichiometric amount of spinel, is added to the precursor mixture to separate the spinel particles as they are nucleated to prevent their agglomeration and coarsening during calcination. Well-dispersed MgAl2O4 nanoparticles with a single-crystal structure were obtained after acid washing of calcined product. The microstructures of the as-prepared samples were characterized by differential thermal and thermogravimetric analysis, x-ray diffractometry, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and transmission electron microscopy. The results indicate that MgO acting as the isolation medium is effective in preventing the agglomeration of MgAl2O4 nanoparticles, and it also prevents their contamination by introducing an isolation medium during the preparation process. The nanopowder was sintered up to 95% of the theoretical density but with parallel grain growth.

Multilayer stereo micro/nanometer-sized porous surface structures were prepared by selective chemical etching of biphasic calcium phosphate (BCP) scaffolds with hydroxyapatite (HAP)/β-tricalcium phosphate (β-TCP) weight ratios of 90/10, 80/20, 70/30, 60/40, and 50/50 in phosphoric acid solution. The porous surface structures revealed periodic fluctuations in the observed heights of micro/nanometer-sized needles. And the average height increased from 0.59 ± 0.02 to 12.09 ± 0.03 μm when the β-TCP content in BCP scaffolds rose from 10 to 50%. In vivo cell tests using MG-63 cells (belonging to the human osteosarcoma cell line) revealed that micro/nanometer-sized pores on the scaffold surface could provide location for cell adhesion and migration and facilitate the formation of gap junction between cells. The BCP scaffold with 40% β-TCP exhibited the optimal surface structure for cell seeding and growth due to the largest number of micro/nanometer-sized pores on the surface. However, excessive β-TCP led to the damage of micro/nanometer-sized porous surface structure, which further impeded the cell interaction.

Three-dimensional transmission electron microscopy (3D-TEM) is a powerful technology that provides 3D characterization of the internal details of a material. In this work, for the first time, 3D-TEM was used to characterize a laser-sintered polymer nanocomposite. The dispersion of carbon nanotubes (CNTs) in the laser-sintered polyamide 12 (PA12)-CNT nanocomposite parts was evaluated. At first, to prepare 3D-TEM samples at specific locations, a focused ion beam technique was used. Then, high quality two-dimensional (2D)-TEM images were achieved at various scanning angles for the PA12-CNT laser-sintered sample. After that, 3D-TEM images were reconstructed by combining all the 2D-TEM images. Results revealed that the CNTs were agglomerate-free in the PA12-CNT parts after laser sintering, which helps to explain previously reported improvement in mechanical properties of laser-sintered PA12-CNT parts.

In this work, mechanical stability, thermodynamic and elastic properties of rhodium (Rh), rhodium monohydride (RhH), and the newly discovered rhodium dihydride (RhH2) under high temperature and pressure are studied by ab initio method together with quasiharmonic Debye model. Mechanical stability test indicates that RhH2 is no longer mechanically stable when pressure is higher than 22.7 GPa, which is quite less than the dynamically stable pressure (90 GPa). The heat capacity at constant volume (Cv) of Rh, RhH, or RhH2 increases proportional to T3 at low temperature, and tends to Dulong–Petit limit (about 241.67, 478.47, and 706.15 J/(kg·K), respectively). The thermal expansion coefficient (α) of Rh, RhH, and RhH2 increases acutely when temperature is not more than 300 K. And then, the increase of α slows down. The α reduces with pressure transiently. H atom's entering in fcc-Rh lattice would greatly change the electron density distribution, which would cause obvious difference in thermodynamic and elastic properties between Rh, RhH, and RhH2.

Ordered 30-nm Co1−xSnx (0 ≤ x ≤ 0.78) nanowire arrays have been prepared by co-electrodeposition of Co and Sn into pores of homemade anodized aluminum oxide (AAO). The magnetic properties of the Co1−xSnx nanowires are presented as a function of Sn content (x), annealing, electrolyte pH, electrodeposition frequency, and wave form. The result of energy-dispersive x-ray spectroscopy (EDX) showed anomalous co-deposition for Co and Sn. The nanowires have uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axis due to the large shape anisotropy. As-deposited and annealed alloy nanowires, determined by x-ray diffraction (XRD), have amorphous phase. The nanowires electrodeposited at different pH and the electrodeposition frequencies have significantly different magnetic properties. Magnetization measurement showed that variation in magnetic properties of the nanowire arrays rooted in surface formation of Co(OH)2 and Sn(OH)2 in upper pH. The XRD patterns of Co and Co0.97Sn0.03 of nanowires obtained at pH = 2 and 4 obviously illustrated that pH affects the crystal structure of Co nanowires but has no effect on alloy nanowires. Moreover, the precipitation process was affected by raising the electrodepositing frequency via changing the rate of reduction of solute ions. The electrodeposition wave form has no significant effect on nanowire magnetic properties. The considerable enhanced coercivity has been measured in annealed nanowires. Experimental data demonstrate that the optimized composition for annealed Co1−xSnx nanowire is around Co0.93Sn0.07 in which the coercivity (Hc) has a maximum value of 2030 Oe.

Amorphous Ta–O nanotubes (NTs) prepared by anodization in a sulfuric-acid-based solution have been found to contain considerable amounts of extra oxygen and sulfur. Their structural and thermal stability has been studied by combining x-ray diffractometry, transmission electron microscopy, and thermal analysis. The amorphous Ta–O, whose composition was estimated to be Ta2O6.6S0.7, crystallizes into orthorhombic β-Ta2O5 at temperatures around 1073 K by an endothermic reaction, at which excess oxygen and impurity sulfur are released. The amorphous NTs were found to be thermally more stable than stoichiometric amorphous Ta2O5, whose crystallization temperature is around 973 K. Excess oxygen and impurity sulfur, which form chemical bonds with Ta atoms in the amorphous solid, must be the origin of the stability. The crystallization follows the out-diffusion of oxygen and sulfur from the solid at temperatures where the mobility of atoms is high enough, indicating that the crystallization is kinetically arrested.

An electro-acoustic method for measuring volume charge distributions in dielectric films (50 μm–0.2 mm thick) is described. A high voltage (>1 kV) sinusoidal signal (frequency ∼ 2 kHz) is applied across the dielectric sample. The charges inside the dielectric material will mechanically respond to the input electric signal and excite acoustic waves. The acoustic waves can be detected and measured using a piezoelectric sensor. By analyzing the received acoustic signal, we are able to compare the amount of charge in various samples.

Oxide membranes are the foundation of several electrochemical devices and sensors, where functionality is related to selective transport of electrons and ions through a membrane or physical responses from an external perturbation. The ability to engineer power sources and sensors for the rapidly growing field of autonomous systems requires high power density and specific energy. Clamped free-standing nanoscale membranes provide an experimentally tunable platform to explore the limits of dimensionality reduction for such purposes. This review addresses the following: (i) advancing experimental methods to fabricate nanoscale oxide membranes that can sustain a chemical potential gradient, thermomechanically stable under large thermal cycles, and can be electrically interrogated with negligible parasitic loss; (ii) a representative example of high performance energy devices, solid oxide fuel cells, utilizing such membranes; and (iii) a brief discussion on emerging research directions broadly in the areas of condensed matter sciences and energy conversion and storage intersecting low-dimensional complex oxide materials.

A strategy for identifying the preferred sites and overall propensity of a Sn film to form whiskers has been developed based on film textures, local grain orientations, and elastic strain energy densities (ESEDs), with preferred sites predicted to be grains with local high ESEDs. Using β-Sn films with various textures, ESED distributions were simulated for elastic and thermoelastic stresses depending on isothermal aging or thermal cycling conditions. Local high ESEDs are preferentially induced in (110) or (100) oriented grains with c-axes nearly parallel to the film plane; films with overall low ESEDs have strong (100) textures for elastic stresses and strong (001) textures for thermoelastic stresses, suggesting low propensities to form whiskers. This work establishes a model for understanding the effect of the β-Sn anisotropy on whisker formation and provides guidelines for testing whether engineering specific film textures will reduce a film's propensity to form whiskers.

BaTiO3–SnO solid solutions have been investigated from the viewpoints of synthesis and Sn ion valence. First-principles calculations show that the solution energy of Sn2+ into the Ba sites in BaTiO3 is less than that into the Ti sites under high pressure. The BaTiO3–SnO solid solutions have been synthesized under high pressure (∼20 GPa) and temperatures using a laser-heated diamond anvil cell. The synthesized materials have been characterized using x-ray diffractometry, scanning transmission electron microscopy, and energy-dispersive x-ray spectroscopy. It is found from these various methods that we have successfully synthesized uniform solid solutions of BaTiO3–SnO. Furthermore, it is also clarified by the Sn L3-edge electron energy loss spectra measurements that the valences of the Sn ions in the BaTiO3–SnO solid solution are 2+. These results indicate that the Sn2+ ions are substituted into the Ba sites, according to the ion size. Consequently, the Sn ions can be substituted into the Ba sites of the shrinking BaTiO3 lattice under high pressure, which is similar to the Ca and Sn co-substitution into Ba sites under ambient pressure as reported previously.

High energy laser (HEL) systems are currently being evaluated for various land, sea, and air based platforms. Some of these systems operate in or have to withstand harsh environment of sand storm, hurricane, and rain. The exit aperture on a HEL system operating in harsh environment can become the single point of failure. Current HEL systems operating in 1–2 µm wavelength use fused silica windows which are at risk of damage in the theater. Rugged window materials such as sapphire, ALON, and spinel are currently being evaluated as a potential replacement. One of the major parameters in window selection apart from its ruggedness is its absorption loss coefficient at laser wavelength. This paper reports on 3 different methods to reduce absorption loss in spinel ceramic from 100,000 ppm/cm down to 75 ppm/cm. The results are compared with ALON and sapphire.

Au nanoparticles (Au NPs) have attracted much interest owing to their unique optical properties. In this paper, a facile process has been successfully developed to synthesize the SiO2/Au hybrid microspheres with a diameter of 200 nm via the galvanic replacement of SiO2/Ag hybrid microspheres and chlorauric acid (HAuCl4) solution. The as-prepared products were investigated by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM, JEOL-6700F), and transmission electron microscopy (TEM, JEOL 3010), respectively. As expected, the as-prepared SiO2/Au hybrid microspheres show strong chemical stability and superior catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The SiO2/Au hybrid microspheres would be found widely used in wastewater treatment, catalytic reaction, bacteriostatic and bactericidal applications.

Atomically thin films, such as graphene, graphene oxide, hexagonal-boron nitride (h-BN), and molybdenum disulfide (MoS2), have attracted intensive studies to explore their properties and potential applications as next generation materials due to their outstanding mechanical, electrical, thermal, and optical properties. The study of the mechanical behavior of this class of materials is in particular interesting as it not only physically determines the potential application fields where these materials can be utilized but also has revealed unique mechanical size effects and phenomena. Researchers have been studying the mechanical properties such as elastic modulus, strength, friction, and fracture behavior of atomically thin films for over a decade now. Here, we review recent results of the mechanical characterization and understanding of this class of materials.

A novel thermosensitive core/shell microgel with carbon microspheres (CMSs) cores was prepared by three steps. First, oxidized-carbon microspheres were obtained by mixed-acid oxidization. Second, the silane agent of 3-(trimethoxysilyl)-propyl methacrylate was used to functionalize the oxidized-carbon microspheres so as to generate the vinyl groups on the microspheres. Thereafter, the as-synthesized particles were used as seeds in the precipitation polymerization of N-isopropylacrylamide to introduce a thermosensitive polymer microgel shell onto the surfaces of the silanized-CMSs in the presence of an initiator and a crosslinker. The morphology and thermosensitive properties of the composite microspheres were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transformation infrared spectroscopy, thermogravimetry, and dynamic light scattering. Results indicate that the thickness of polymer layer could be adjusted by the crosslinking agent's concentration. The composite microgels had a low critical solution temperature at about 30 °C and exhibited strong thermosensitivity. The controlled release of a drug molecule (a model drug, acetosalicylic acid) was also investigated.

The conjugated polymer poly(2,5-dihexyl-1,4-phenylene-alt-2-amino-4,6-pyrimidine) was synthesized and used in the supramolecular functionalization of single-walled carbon nanotubes (SWNTs). It was found that this polymer can form strong supramolecular polymer–nanotube assembly and produce a stable composite in solution. The resulting polymerized nanotubes were analyzed by UV–Vis absorption and emission spectroscopy, thermogravimetry, transmission electron microscopy and scanning electron microscopy. It was found that the noncovalent functionalization did not damage the nanotube structure. The polymer content in the polymer–nanotube composite could be calculated to be 41% by thermogravimetry analysis. The composite exhibited certain solubility in dimethylacetamide (DMAc), where the solubility in the absence of excess free polymer solution is 78.7 mg L−1. The composite exhibited a conductivity of 0.005 S cm−1 and the anodic and cathodic peaks were observed at 0.47 and 0.37 V. Galvanostatical charge/discharge tests give good cycling behavior of maintaining a stable capacitance value of 66.7 F g−1 over 1000 cycles at a current load of 1 mA cm−2 without distinct drop.

Graphene is currently one of the most extensively studied materials because it displays a number of unique structural and electronic properties. A variety of methods are currently available for the growth of graphene; however, few are viable for large scale, cost-effective production of high quality graphene. Here, a novel growth process for few layer graphene using chemical vapor deposition (CVD) and a commercial iron nanopowder catalyst is described. This method is readily scalable so it can be used to produce a large volume of graphene sheets. Graphene sheets made from this process were characterized by Raman spectroscopy, and scanning and transmission electron microscopy. Raman spectroscopy shows that the product consists of few layer graphene sheets. This is the first reported method of utilizing nanoparticles to synthesize graphene by a CVD process, which typically produces multiwalled carbon nanotubes. A possible mechanism for the formation of graphene by this modified CVD process is discussed.