The mixed-valence oxide Co3O4 nanoparticles, having the normal spinel structure, possess large surface area, active-site surface adsorption properties, and fast ion diffusivities. Consequently, they are widely used in lithium-ion batteries, as well as for gas sensing and heterogeneous catalysis applications. In our research, we use a two-step method to synthesize Co3O4–based core-shell nanoparticles (CSNs). Cobalt oxide (Co3O4) nanoparticles were successfully synthesized using a wet synthesis method employing KOH and cobalt acetate. Manganese was incorporated into the Co3O4 structure to synthesize inverted Co3O4@MnxCo3-xO4 CSNs using a hydrothermal method. By adjustment of pH value, we obtained two different morphologies of CSNs, one resulting in pseudo-spherical and octahedron-shaped nanoparticles (PS type) whereas the second type predominantly have a nanoplate (NP type) morphology. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS) have been performed in order to determine the morphological and structural properties of our CSNs, whereas the magnetic properties have been characterized using a superconducting quantum interference device (SQUID) magnetometer. XRD and TEM results show that the CSNs have the same spinel crystal structure throughout the core and shell with an average particle size of ∼19.8 nm. Our Co3O4 nanoparticles, as measured prior to CSN formation, are shown to be antiferromagnetic (AFM) in nature as shown by the magnetization data. Our SQUID data indicate that the core-shell nanoparticles have both AFM (due to the Co3O4 core) and ferrimagnetic properties (of the shell) with a coercivity field of 300 Oe and 150 Oe at 5 K for the PS and NP samples, respectively. The magnetization vs temperature data show a spin order-disorder transition at ∼33 K and a superparamagnetic blocking temperature of ∼90 K for both batches.

The use of waste is rapidly becoming a supra-disciplinary field in most parts of the world where the use of industrial wastes like fly ash, granulated steel slag, silica fume, and waste fibers in construction has become very popular since the last half of the 20th century. Other forms of industrial wastes are also re-used even for more sensitive applications on soils to upgrade soil texture. For example, waste from bauxite refining (red mud) is known to be extensively re-utilised. These concepts are yet to take tangible hold in Africa, despite the huge resources available. Electric-Arc Furnace Steel slag is a major waste product from the steel industry involving the melting of scrap to make steel in an electric arc furnace. Use of such waste materials in construction alleviates the huge environmental pollution problem which often exists in areas where they are produced and/or dumped. Currently, the material is mainly used in construction works as unbound aggregate for asphalt concrete pavements, or as road base in many countries. However, it consists predominantly of oxides and silicates of magnesium, calcium, aluminium, iron and thus can be used as substitute for cement. This paper compares the effect of utilising this type of Steel slag and Granulated Blast Furness Slag, as partial replacement for Portland cement. The influence of the physical and chemical characteristics of the two materials on the setting time, compressive strength, total porosity and pore-size distribution of cement pastes have been evaluated. For the experimental conditions studied, the result reveal adequate properties for high levels of replacement but suggests that superior qualities, compared with Portland cement concrete is possible only if replacement levels do not exceed about 10%.

Second-order diffraction (SOD) of x-rays refers to all diffraction processes where the photons reaching the detector have been diffracted twice within a crystal lattice. By measuring the two dimensional intensity profile of SOD, it is possible to distinguishing rescattering processes taking place inside each grain (perfect crystal domain) or in between grains. These two SOD regimes, usually called dynamical and kinematical, respectively, are ruled by size and relative orientation of the grains. In this work, we demonstrate how to explore SOD phenomena to understand the micro scale grain structure in plastically deformed silicon single crystal.

Tunable plasmonic resonances across the visible and near infrared spectra have provided novel ways to develop next-generation nanophotonic devices. Here, by utilizing optothermally controllable phase-changing material (PCM), we studied highly tunable charge transfer plasmon (CTP) resonance modes. To this end, we have designed a two-member dimer assembly including gold cores and Ge2Sb2Te5 (GST) shells in distant, touching, and overlapping conditions. We successfully demonstrated that toggling between amorphous (dielectric) and crystalline (conductive) phases of GST allows for achieving tunable dipolar and CTP resonances along the near-infrared spectrum. The proposed dimer structures can help forming optothermally controlled devices without further morphological variations in the geometry of the design, and having strong potential for advanced plasmon modulation and fast data routing.

A synthesis method to form foams consisting of a shell of metals conformally coated on carbon nanotube (CNT) arrays by electroplating from a single bath electrolyte is demonstrated in this work. A triple cyclic pulse electrodeposition technique was used to deposit Ni and Cu layers on the CNT arrays, and electron microscopy was then used to identify conditions amenable to semi-conformal and island growth morphologies. Nanoindentation of the resulting metallic-CNT composite foam structure, using a flat punch/compression geometry, demonstrates that adding metallic shells to the CNT turf to create a metallic low density foam increases both the hardness and elastic modulus; however, once island growth initiates there is no significant subsequent increase in mechanical properties with increases in deposited metals.

Motivated by an experimental finding on the density of supercooled water at high pressure [O. Mishima, J. Chem. Phys. 133, 144503 (2010)] we performed atomistic molecular dynamics simulations study of bulk water in the isothermal-isobaric ensemble. Cooling and heating cycles at different isobars and isothermal compression at different temperatures are performed on the water sample with pressures that range from 0 to 1.0 GPa. The cooling simulations are done at temperatures that range from 40 K to 380 K using two different cooling rates, 10 K/ns and 10 K/5 ns. For the heating simulations we used the slowest heating rate (10 K/5 ns) by applying the same range of isobars. Our analysis of the variation of the volume of the bulk water sample with temperature at different pressures from both isobaric cooling/heating and isothermal compression cycles indicates a concave-downward curvature at high pressures that is consistent with the experiment for emulsified water. In particular, a strong concave down curvature is observed between the temperatures 180 K and 220 K. Below the glass transition temperature, which is around 180 K at 1GPa, the volume turns to concave upward curvature. No crystallization of the supercooled liquid state was observed below 180 K even after running the system for an additional microsecond.

The recently discovered orthorhombic allotrope of silicon, Si24, is an exciting prospective material for the future of solar energy due to a quasi-direct bandgap near 1.3 eV, coupled with the abundance and environmental stability of silicon. Synthesized via precursor Na4Si24 at high temperature and pressure (∼850 °C, 9 GPa), typical synthesis results have yielded polycrystalline samples with crystallites on the order of 20 μm. Several approaches to increase the crystal size have yielded success, including in-situ thermal spikes and refined selection of the starting materials. Microstructural analysis suggests that coherency exists between diamond silicon (d-Si) and Na4Si24. This hypothesis has led to the successful attempts at single crystal synthesis by selecting large crystals of d-Si along with metallic Na as the precursors rather than powdered and mixed precursor material. The new synthesis approach has yielded single crystals of Na4Si24 greater than 100 μm. These results represent a breakthrough in synthesis that enables further characterization and utility. The promise of Si24 for the future of solar energy generation and efficient electronics is strengthened through these advances in synthesis.

In the safety assessment of a radioactive waste disposal, it is extremely important to assess the migration behavior of long-half-life radionuclides in the disposal environment. The migration behavior in the disposal environment for a radionuclide varies with the chemical form of the nuclide. In particular, C-14 has various chemical forms, and its migration behavior in the disposal environment substantially varies with the chemical forms. It has been reported that hardly soluble C-14 is generated in PWRs. However, the chemical form of this hardly soluble C-14 is little known. In this study, the thermal decomposition behavior of particles containing C-14 and the mass spectra of gases released through thermal decomposition were analyzed in order to examine the chemical form of C-14 generated in PWRs. In this study, the gases released during the thermogravimetric (TG) analysis were partially oxidized to CO2, trapped in an alkaline solution and analysed for C-14. Another part of the gas was analysed directly by mass spectrometry (MS). The residues obtained after TG analysis were also analysed for C-14 by oxidizing the residue to CO2, trapping the CO2 in alkaline solutions and analysing C-14 by LSC. During TG-analysis in inert gas (He) atmosphere, about 90% of C-14 was found in residue, while when air was used during TG-analysis, no C-14 could be detected in residue. From the MS-analysis of species released during TG-analysis in inert gas, fragments regarded as originating from ion-exchange resins were detected in released gases. Based on this result, it was found that while substances originating from ion-exchange resin were present in radioactive particles generated in a PWR, the main part of C-14 was contained in the residue after heating in the form of thermally stable substances, easy to be oxidized by air at high temperature. It was not possible to determine their exact chemical composition in this work but also, In addition, sorption of insoluble C-14 to cementitious materials was preliminarily examined. As a results, the concentration of insoluble C-14 decreased greatly in 7 days. That means insoluble C-14 tended not to stay in water. Elucidation of the sorption mechanism in the disposal environment of these C-14 is also a future task.

Schwarzites are crystalline, 3D porous structures with a stable negative curvature formed of sp2-hybridized carbon atoms. These structures present topologies with tunable porous size and shape and unusual mechanical properties. In this work, we have investigated the mechanical behavior under compressive strain and energy absorption of four different Schwarzites. We considered two Schwarzites families, the so-called Gyroid and Primitive and two structures from each family. We carried out reactive molecular dynamics simulations, using the ReaxFF force field as available in the LAMMPS code. Our results also show they exhibit remarkable resilience under mechanical compression. They can be reduced to half of their original size before structural failure (fracture) occurs.

Rapid transitions between semiconducting and metallic phases of transition-metal dichalcogenides are of interest for 2D electronics applications. Theoretical investigations have been limited to using thermal energy, lattice strain and charge doping to induce the phase transition, but have not identified mechanisms for rapid phase transition. Here, we use density functional theory to show how optical excitation leads to the formation of a low-energy intermediate crystal structure along the semiconductor-metal phase transition pathway. This metastable crystal structure results in significantly reduced barriers for the semiconducting-metal phase transition pathway leading to rapid transition in optically excited crystals.

This work shows a part of a theoretical study of Polymer-Clay Nanocomposites (PCN) formed by an acetylated amylose segment and fatty acids present in the Pequi oil, a fruit from the Brazilian Cerrado, in aqueous medium, including or not, organophilized montmorillonite (MMT-O). The simulated systems aim to provide qualitative information about the molecular movement among diverse chemical species; their structural and behavioral correlations and essential intermolecular forces. The calculations were carried out by Molecular Mechanics and Dynamics methods with the Polymer Consistent Force Field-interface. Simulation results had shown behavioral differences between systems. Without MMT-O, the acetyl amylose residues quickly became coiled, most of the fatty acids cover its surface, and water molecules are stabilized over the polysaccharide portions free of fatty acids. With MMT-O the fatty acids show a potential plasticizing effect due to the greater compatibility between the components of the studied system, since the organic assemblage is strongly attracted by the electrostatic force of the clay. Besides, water molecules flow to the clay layer, while the non polar portion of fatty acids increase their flexibility, in spite to stay attached to acetyl amylose, progressively coiled, through hydrogen bonds. This behavior is interpreted as an improvement in the miscibility of the oil. The new knowledge acquired about these molecular systems encourages us to increase the models complexity, and undertake further studies in the design of PCNs with biopolymers.

The ground state structure, optical properties and charge carrier dynamics of silicon nanowire (SiNW) grown in <211> crystallographic direction is studied as a function of wavevector using density functional theory. This nanowire can be used as fundamental unit of nanoelectronic devices. The optical properties are computed under assumption of momentum conservation$\Delta \vec{k} = 0$. The on-the-fly non-adiabatic couplings for electronic degrees of freedom are obtained along the ab initio molecular dynamics nuclear trajectories, which are used as parameters for Redfield density matrix equation of motion. By investigating the photo-induced process on this nanowire, it is shown that high-energy photoexcitation relaxes to the band gap edge within 75 ps. The results of these calculations help to understand the mechanism of electron transfer process on the Si nanowire.

Physical and chemical properties of graphene-metal interfaces have been largely examined with the objective of producing nanostructured carbon-based electronic devices. Although electronic properties are key to such devices, appropriate structural, thermal and mechanical properties are important for device performance as well. One of the most studied is the graphene-titanium (G-Ti) interface. Titanium is a low density, high strength versatile metal that can form alloys with desirable properties for applications ranging from aerospace to medicine. Small clusters and thin films of titanium deposited on graphene have also been examined. However, while some experiments show that thin films of titanium on graphene can be removed without damaging graphene hexagonal structure, others reported the formation of titanium-carbide (TiC) at G-Ti interfaces. In a previous work [ACS Appl. Mater. Interfaces, 2017, 9 (38), pp 33288-33297], we have shown that pristine G-Ti interfaces are resilient to large thermal fluctuations even when G-Ti structures lie on curved or kinked substrates. Here, using classical molecular dynamics with the third-generation Charge Optimized Many Body (COMB3) potential, we show that di-interstitial defective G-Ti structures on a copper substrate with a relatively large curvature kink, present signs of TiC formation. This result might help explain the different experimental results mentioned above.

Recently, low-density steels have received increased attention as promising alternatives for automotive applications of the next generation of Advanced High-Strength Steels (AHSS), considering that vehicle´s weight decrease has been the subject of intense interest. It is well-known that the addition of rare earth metals (REM) has a remarkable effect on shape control and the modification of inclusions. Also, REM additions affect the grain size refinement as well as the tendency to form oxides and sulfides. The aim of this research work was to determine the effect of REM (Ce, La) addition on the microstructure and mechanical properties of the Fe-30Mn-8Al-1.8C low-density steel in as-cast condition. In order to clarify the REM effect on the Fe-Mn-Al-C system, non-microalloyed (LD-NM) and REM microalloyed (LD-REM) specimens were examined in detail by means of light optical and scanning electron microscopy for microstructural characterization. In the same way, the primary and secondary phases founded in the studied steels were identified by X-ray diffraction (XRD). Meanwhile, in order to evaluate the mechanical properties, ten microhardness measurements were carried out on the overall bulk by the Vickers hardness testing. In general, the results showed a dendritic refinement effect due to the addition of REM to low-density steel. REM acted as effective inoculants agents which reduced the primary and secondary arm spacing. Also, the strong segregation tendency at the grain boundaries in the liquid phase was limited. XRD profiles revealed the presence of austenite, ferrite, κ and DO3 phases. Low density steel microalloyed with REM showed a moderate increase in hardness compared to the non-microalloyed steel in the as-cast condition.