Superior Radiation Resistance of ZrO2-Modified W Composites.

The microstructure and mechanical properties of pure W, sintered and swaged W-1.5ZrO2 composites after 1.5 × 1015 Au+/cm2 radiation at room temperature were characterized to investigate the impact of the ZrO2 phase on the irradiation resistance mechanism of tungsten materials. It can be concluded that the ZrO2 phase near the surface consists of two irradiation damage layers, including an amorphous layer and polycrystallization regions after radiation. With the addition of the ZrO2 phase, the total density and average size of dislocation loops, obviously, decrease, attributed to the reason that many more glissile 1/2<111> loops migrate to annihilate preferentially at precipitate interfaces with a higher sink strength of 7.8 × 1014 m−2. The swaged W-1.5ZrO2 alloys have a high enough density of precipitate interfaces and grain boundaries to absorb large numbers of irradiated dislocations. This leads to the smallest irradiation hardening change in hardness of 4.52 Gpa, which is far superior to pure W materials. This work has a collection of experiments and conclusions that are of crucial importance to the materials and nuclear communities.

Exceptional Photocatalytic Activities of rGO Modified (B,N) Co-Doped WO3 , Coupled with CdSe QDs for One Photon Z-Scheme System: A Joint Experimental and DFT Study.

Artificial Z-scheme, a tandem structure with two-step excitation process, has gained significant attention in energy production and environmental remediation. By effectively connecting and matching the band-gaps of two different photosystems, it is significant to utilize more photons for excellent photoactivity. Herein, a novel one-photon (same energy-two-photon) Z-scheme system is constructed between rGO modified boron-nitrogen co-doped-WO3 , and coupled CdSe quantum dots-(QDs). The coctalyst-0.5%Rhx Cr2 O3 (0.5RCr) modified amount-optimized sample 6%CdSe/1%rGO3%BN-WO3 revealed an unprecedented visible-light driven overall-water-splitting to produce ≈51 µmol h-1 g-1 H2 and 25.5 µmol h-1 g-1 O2 , and it remained unchanged for 5 runs in 30 h. This superior performance is ascribed to the one-photon Z-scheme, which simultaneously stimulates a two photocatalysts system, and enhanced charge separation as revealed by various spectroscopy techniques. The density-functional theory is further utilized to understand the origin of this performance enhancement. This work provides a feasible strategy for constructing an efficient one-photon Z-scheme for practical applications.

Theoretical Combined Experimental Study of Unique He Behaviors in High-Entropy Alloys.

Exploring new structural materials with strong He damage tolerance is one of the key tasks for the development of nuclear reactors. Helium (He), one of the most common elements in the nuclear environment, often forms undesired bubbles in metallic materials and may result in void swelling as well as high-temperature intergranular embrittlement. In this study, the behaviors of He in high-entropy alloy (HEA) TiZrHfMoNb and its constituents are systematically investigated both theoretically and experimentally. Density functional theory calculations show that the He atom prefers to occupy tetrahedral and octahedral interstitial sites in a HEA. The migration pathway for He in TiZrHfMoNb is explored and the migration energy barrier is determined. Besides, the He clustering behavior in TiZrHfMoNb is investigated. Through transmission electron microscopy analysis, a smaller He bubble size is observed in TiZrHfMoNb than in Ti, which is proposed to result from the lower tendency to form He clusters, a weaker coarsening effect, and severe lattice distortion in HEA. The current study thus provides deep insights into the He behaviors in HEAs and may help to develop structural materials with enhanced He damage tolerance in nuclear reactors.

A Density Functional Theory Study of the Hydrogen Absorption in High Entropy Alloy TiZrHfMoNb.

The high entropy alloy is promising for hydrogen storage, especially in regard to its adjustable hydrogen storage properties. Despite several experimental investigations, there still lacks a detailed atomic-level understanding of the hydrogenation process. In this study, based on first-principles calculations, the hydrogen behaviors and microstructural evolution in high entropy alloy TiZrHfMoNb during the hydrogen absorption are investigated systematically. At low hydrogen content, hydrogen atoms prefer to occupy the octahedral interstitial sites of the BCC phase, which is different from that in BCC pure metals; when the hydrogen content reaches 1.08 wt %, the BCC TiZrHfMoNb hydrides transform into FCC phase, and hydrogen atoms are more favorable to occupy the tetrahedral interstitial sites. Further radial distribution function (RDF) analysis indicates that the enhanced disorder of bonds and decreased lattice distortion of the metal structure destabilize the BCC TiZrHfMoNb hydride and eventually induce the BCC → FCC phase transformation, which is quite different from that in conventional alloys; the difference originates from the severe lattice distortion in high entropy alloy. The phonon spectra of different TiZrHfMoNb hydrides show that the hydride with a H/M ratio of 2 dynamically has a stable lattice, corresponding to a hydrogen storage capacity of 1.94 wt %. The present study demonstrates that the high entropy alloys have unique hydrogen absorption ability, which may advance the related experimental and theoretical studies.

Electronic and nanostructure engineering of bifunctional MoS2 towards exceptional visible-light photocatalytic CO2 reduction and pollutant degradation.

With recently increasing environmental issues and foreseeable energy crisis, it is desirable to design cheap, efficient, and visible-light responsive nano-photocatalyst for CO2 conversion and pollutant degradation. Herein, we report a flower-like of MoS2-based hybrid photocatalyst with high efficiency through nanostructure and electronic structure engineering. Nanostructure control is used to fabricate MoS2 in to flower-like nanosheets (NSs) with large surface active area. Then MoS2 is coupled with conduction-band edge matched tin dioxide (SnO2) and decorated with Ag nanoparticles for suitable work function to create a unique cascade band alignment electronic structure to facilitate photoexcited charge transfer. It is shown that the amount-optimized nanocomposite of SnO2/Ag/MoS2 exhibits exceptional visible-light photocatalytic activities for conversion of carbon dioxide (CO2) to methane (CH4), approximately one order of magnitude enhancement than original MoS2 with the apparent quantum efficiency 2.38% at 420 nm. Similarly, the optimized sample also shows high activities for 2,4-diclorophenol, Methylene-Blue, Rhodamine-B and Methyl-Orange degradation as compared to pure MoS2. It is clearly demonstrated through combination of hydroxyl radical evaluation, photoelectrochemical and electrochemical impedance, that the enhanced photoactivities are attributed to the increased specific surface area, optimized band alignment for charge transfer and suppressed recombination. Our current work provides feasible routes for further research.

Effects of Embedded Helium on the Microstructure and Mechanical Properties of Erbium Films.

A series of helium (He) charged nanograin-sized erbium (Er) films were deposited by direct current (DC)-magnetron sputtering with different He/Ar mixture gases. The microstructure and mechanical properties of He-charged Er films were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and nanoindentation. The helium concentrations in Er films, determined by elastic recoil detection analysis (ERDA), ranged from 0 to 49.6%, with the increase in He:Ar flow ratio up to 18:1. The XRD results show that the grain sizes of Er films decreased with and increase in He content. The embedded He atoms induced the formation of spherical nanometer He bubbles, and the diameter of the He bubbles increased with the He content. The hardness and Young's modulus increased and decreased with the decreasing grain sizes of polycrystalline Er-He films. The mechanisms of mechanical properties with respect to the grain size and He content were discussed based on the Hall-Petch formula and composite spheres model.

Revealing the Chemical and Structural Evolution of V2O5 Nanoribbons in Lithium-Ion Batteries Using in Situ Transmission Electron Microscopy.

Layer-structured vanadium oxide (V2O5) nanoribbons with efficient electron transport and short lithium ion insertion lengths are promising candidates for high-performance lithium-ion battery applications. Despite the extensive investigation of its electrochemical properties, the chemical and structural evolution during lithiation-delithiation processes has rarely been characterized in real time. Herein, the lithiation-delithiation behaviors of V2O5 nanoribbons are probed by in situ transmission electron microscopy. We reveal that the V2O5 nanoribbons exhibit high lithiation speed (0.8 nm/s) without retardation along the [010] direction and can be fully lithiated to the Li3V2O5 phase. Fully reversible retraction of lithium is observed in these V2O5 nanoribbons during delithiation. The lithiation process accompanying the coherent strain is further simulated by our phase field model. The simulation results reveal that the specific rough lithiation interface between the V2O5 and Li3V2O5 phases originates from the lithiation inhomogeneity.

Effect of Thickness of Molybdenum Nano-Interlayer on Cohesion between Molybdenum/Titanium Multilayer Film and Silicon Substrate.

Titanium (Ti) film has been used as a hydrogen storage material. The effect of the thickness of a molybdenum (Mo) nano-interlayer on the cohesive strength between a Mo/Ti multilayer film and a single crystal silicon (Si) substrate was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and nano-indenter. Four groups of Si/Mo/Ti multilayer films with different thicknesses of Mo and Ti films were fabricated. The XRD results showed that the introduction of the Mo layer suppressed the chemical reaction between the Ti film and Si substrate. The nano-indenter scratch results demonstrated that the cohesion between the Mo/Ti film and Si substrate decreased significantly with increasing Mo interlayer thickness. The XRD stress analysis indicated that the residual stress in the Si/Mo/Ti film was in-plane tensile stress which might be due to the lattice expansion at a high film growth temperature of 700 °C and the discrepancy of the thermal expansion coefficient between the Ti film and Si substrate. The tensile stress in the Si/Mo/Ti film decreased with increasing Mo interlayer thickness. During the cooling of the Si substrate, a greater decrease in tensile stress occurred for the thicker Mo interlayer sample, which became the driving force for reducing the cohesion between the Mo/Ti film and Si substrate. The results confirmed that the design of the Mo interlayer played an important role in the quality of the Ti film grown on Si substrate.

A DFT Study of Hydrogen Storage in High-Entropy Alloy TiZrHfScMo.

In recent years, high-entropy alloys have been proposed as potential hydrogen storage materials. Despite a number of experimental efforts, there is a lack of theoretical understanding regarding the hydrogen absorption behavior of high-entropy alloys. In this work, the hydrogen storage properties of a new TiZrHfScMo high-entropy alloy are investigated. This material is synthesized successfully, and its structure is characterized as body-centered cubic. Based on density functional theory, the lattice constant, formation enthalpy, binding energy, and electronic properties of hydrogenated TiZrHfScMo are all calculated. The calculations reveal that the process of hydrogenation is an exothermic process, and the bonding between the hydrogen and metal elements are of covalent character. In the hydrogenated TiZrHfScMo, the Ti and Sc atoms lose electrons and Mo atoms gain electrons. As the H content increases, the bonding is weakened, and the and bonding are strengthened. Our calculations demonstrate that the TiZrHfScMo high-entropy alloy is a promising hydrogen storage material, and different alloy elements play different roles in the hydrogen absorption process.

A Novel TiZrHfMoNb High-Entropy Alloy for Solar Thermal Energy Storage.

An equiatomic TiZrHfMoNb high-entropy alloy (HEA) was developed as a solar thermal energy storage material due to its outstanding performance of hydrogen absorption. The TiZrHfMoNb alloy transforms from a body-centered cubic (BCC) structure to a face-centered cubic (FCC) structure during hydrogen absorption and can reversibly transform back to the BCC structure after hydrogen desorption. The theoretical calculations demonstrated that before hydrogenation, the BCC structure for the alloy has more stable energy than the FCC structure while the FCC structure is preferred after hydrogenation. The outstanding hydrogen absorption of the reversible single-phase transformation during the hydrogen absorption⁻desorption cycle improves the hydrogen recycling rate and the energy efficiency, which indicates that the TiZrHfMoNb alloy could be an excellent candidate for solar thermal energy storage.