Effect of Strain Rate on Deformation Mechanisms of a Mg Alloy

The effect of strain rate on dislocation slip and deformation twinning in a Mg–3wt.pctAl alloy was investigated by three-dimensional X-ray diffraction (3DXRD). In situ tensile tests were performed at strain rates of 10−4, 10−3, and 10−2 s−1. In each tested sample, more than 500 grains were indexed by 3DXRD, and their deformation was tracked. By measuring diffraction peak broadening, plastic deformation can be quantitatively analyzed in individual grains. Basal slip, prismatic slip, and pyramidal I  slips were identified in various grains during deformation, and their critical resolved shear stress (CRSS) values were systematically evaluated. At higher strain rates, non-basal slip systems exhibited increased activity, although basal slip remained dominant. Twin nucleation was observed in a limited number of grains, including some with orientations unfavorable for twinning. Interestingly, in certain cases, the resolved shear stress on the activated twinning systems was negative, indicating a deviation from the generalized Schmid law. This phenomenon is likely associated with prior dislocation activity in the matrix grains, which could create localized conditions conducive to twin formation

Observation of X-ray transition radiation from a relativistic electron passing a stack of plates

The results of experimental observations of resonant transition radiation (RTR) with energies ranging from 8 to 200 keV using stacks of thin aluminium foils (thickness a = 10 μm) separated by layers of either air (radiator no. 1) or Teflon (radiator no. 2) (thickness b = 100 μm). Period of both radiators was fixed (d = a + b = 110 μm). For the studied energy interval, a radiation formation length was larger than period for radiator 1 and was less for radiator 2. For the previous one we observed a reasonable agreement between experiment and theory, but for the latter one we observed some discrepancy

Atomic level mechanism of nanoripple formation on silicon by oblique angle irradiation with molecular nitrogen ions

Reactive ion beam sputtering is an efficient tool to produce modifications in the surface topography in the form of periodic nanoripples with controlled modulation period and amplitude. In the present work, the atomic level processes responsible for nanoripple formation on silicon surface by oblique angle irradiation with molecular nitrogen ions have been studied. A variety of complementary techniques have been used to elucidate the structural and compositional changes occurring in the surface and sub-surface regions with irradiation fluence. It is shown that the implanted nitrogen ions react with the Si substrate to form Si$_3$N$_4$ phase in the subsurface region. GI-SAXS measurements suggest that the buried nitride layer gets phase separated to generate periodic variation in the density at nanometer length scale. With increasing fluence, the surface layer of Si gets sputtered out and the nitride layer reaches the surface. At this stage an unequal sputtering of nitride-rich and nitride-depleted regions results in development of surface instability which is already periodic in nature. Further irradiation results in development of well-defined surface ripples as a combined effect of composition-dependent and curvature-dependent sputtering. A direct chemical evidence for the phase separation of the nitride layer comes from the Auger electron scanning microscopy

Interface-driven electrocatalysis: Highlighting the role of NdNiO₃-NiO heterointerface in urea electro-oxidation

Enhancing the activity of Ni-based catalysts for the electrochemical urea oxidation reaction (UOR) through the construction of heterojunctions or by heteroatom doping primarily involves the generation of polarized and/or high-valent Ni sites. However, systematic investigations of the impact of this strategy on the formation of UOR-active NiOOH species and its influence on UOR activity are scarce. Herein, we have chosen NdNiO$_3$-NiO catalysts to systematically vary the average oxidation of Ni from + 2 to + 3 by adjusting the stoichiometric ratio of NdNiO$_3$ to NiO. Detailed electrochemical analysis and in situ X-ray absorption spectroscopy have revealed that the catalyst systems rich in NdNiO$_3$-NiO heterointerfaces exhibit more favourable formation of NiOOH species and, subsequently, better UOR activity. Interestingly, this enhanced UOR activity does not show an obvious positive correlation with the increase in the average oxidation state of Ni. The UOR current density follows the trend NNO$_2$NO$_8$ (20 % NdNiO$_3$ and 80 % NiO) > NNO$_2$NO$_8$ > NNO$_6$NO$_4$ > NNO$_4$NO$_6$ > NiO > NdNiO$_3$. The higher UOR activity of NNO$_2$NO$_8$ and NNO$_2$NO$_8$ is attributed to the more effective formation of surface-exposed heterointerfaces, thereby establishing the dependence of UOR activity on these active heterointerfaces. In situ Raman spectroscopy substantiates the formation and sustained presence of NiOOH in NdNiO$_3$-NiO heterointerface during UOR. Theoretical studies indicate that the modulation of electronic structure through charge redistribution at the heterointerface optimizes hydroxylation, urea adsorption, and CO₂ desorption, consequently leading to enhanced UOR performance. These insights bring attention to the importance of heterointerface engineering in enhancing Ni-based UOR electrocatalysts

The synergistic strength-ductility mechanism of the in-situ constructed interfacial/intragranular hierarchical structure in nano particulate reinforced (TiB+La2_2O3_3)/Ti composites

The strength-ductility trade-off has hindered the widespread application of powder metallurgy (PM) titanium matrix composites (TMCs). In-situ planting nano-particles as ultra-fine networks into the TMCs powder and constructing the interfacial/intragranular hierarchical microstructure have emerged as a promising strategy to overcome the strength-ductility trade-off. In the present work, we precisely controlled the distribution of the network nano-particles by adjusting the sintering temperatures and successfully transformed the ultrafine network into the interfacial/intragranular structure. The well-designed (TiB + La$_2$O$_3$)/IMI834 TMCs demonstrated exceptional mechanical properties, achieving a tensile strength of 1158 MPa while maintaining an elongation exceeding 8.6 %—performance comparable to wrought TMCs without requiring thermo-mechanical processing. The dislocation evolution and the slip activation behavior were investigated by in-situ synchrotron X-ray diffraction experiments and interrupted in-situ SEM-EBSD observations, which provided new insights into the strength-ductility synergy mechanism of the interfacial/intragranular nano-particles. These studies revealed that the hierarchical structure enhanced the dislocation storage capacity while simultaneously promoting slip activation. This dual effect facilitated multi-system sliding, which effectively optimized dislocation distribution and reduced stress concentration. This study visually elucidates the synergistic strength-ductility mechanism of the interfacial/intragranular hierarchical structure and establishes a straightforward and reliable approach for manufacturing high-performance PM TMCs

Laser-induced alignment of nanoparticles and macromolecules for single-particle-imaging applications

Laser-induced alignment of particles and molecules was long envisioned to support three-dimensional structure determination using “single-molecule diffraction” with X-ray free-electron lasers [PRL 92, 198102 (2004)]. However, the alignment of isolated macromolecules has not yet been demonstrated also because quantitative modeling is very expensive. We computationally demonstrated that the alignment of nanorods and proteins is possible with a standard laser technology. We performed a comprehensive analysis on the dependence of the degree of alignment on molecular properties and experimental details, e.g., particle temperature and laser-pulse energy. Considering the polarizability anisotropy of about 150,000 proteins, our analysis revealed that most of these proteins can be aligned using realistic experimental parameters

Effect of particle reinforcements on the texture and dislocation activities of magnesium matrix composites

The introduction of ceramic particles into magnesium (Mg) alloys not only leads to a grain refinement effect but also influences their texture. However, dislocation activities within the Mg matrix resulting from these effects remain unclear. In this study, in-situ tensile testing combined with synchrotron radiation techniques was utilized to investigate the microstructure, load partitioning, and dislocation density evolution of SiCp/Mg–5Zn and Mg–5Zn samples under different tensile strain conditions. It was found that more dislocation slip systems were involved in the SiCp/Mg–5Zn composite during deformation, whereas the Mg–5Zn alloy exhibited a higher capacity for dislocation accumulation. By an elasto-plastic self-consistent (EPSC) model and a full-field crystal plasticity finite element method (CPFEM) simulation, the pyramidal dislocation activity was identified after a 2 % strain in the SiCp/Mg–5Zn composite. This was accompanied by the load transfer between α-Mg grains as well as regions with different SiCp volume fractions. Additionally, a novel texture formation mechanism was proposed to explain the texture characteristics of Mg matrix composites (MMCs). The strengthening mechanisms induced by reinforcements were also quantified

Regulating Electronic Structure and Coordination Environment of Transition Metal Selenides through the High-Entropy Strategy for Expedited Lithium–Sulfur Chemistry

Transition metal diselenides (TMSe$_2$) have proven as promising catalysts able to promote the conversion kinetics of lithium polysulfides (LiPSs) in lithium–sulfur batteries (LSBs). However, the limited number of catalytically active edge sites in TMSe$_2$ severely hinders the realization of their full potential for boosting LSB’s performance. Herein, we report the synthesis of high-entropy NiCoMnCrVSe$_2$ nanoflakes anchored on graphene supports (NiCoMnCrVSe$_2$/G) through a microwave-assisted solvothermal method. We systematically investigate how the high-entropy strategy enables the regulation of the electronic structure and coordination of various metal species in TMSe$_2$ through comprehensive experimental studies and theoretical calculations. Our results show that as the number of transition metals in TMSe$_2$ increases, the d-band center of metal active sites upshifts toward the Fermi level and the difference among d-band centers of various metal species diminishes, which facilitates the adsorption of LiPSs and lowers the energy barriers to nucleation/decomposition of Li$_2$S. Consequently, LSBs containing NiCoMnCrVSe$_2$/G as sulfur hosts deliver a high specific discharge capacity of 1453 mAh g$^{–1}$ at 0.1 C and excellent stability at 1 C for 500 cycles with a low decay rate of merely 0.016% per cycle. More importantly, we fabricate a ∼2.18 Ah multilayer pouch cell that can deliver an energy density of 435 Wh kg$^{–1}$ (based on the whole pouch cell weight), demonstrating the great potential of NiCoMnCrVSe$_2$/G for practical applications. This work provides important guidelines for the rational design of efficient high-entropy catalysts for bidirectional LiPSs conversion and other reactions beyond

Stress-induced orthorhombic O phase in TiAl alloys

The orthorhombic O phase precipitation within the D0$_{19}-\alpha_2$ phase has attracted increasing attention recently inhigh Nb containing TiAl (high Nb-TiAl) alloys since the precipitation temperature is close to the expected servicetemperature of the alloys. In this study, in-situ synchrotron high energy X-ray diffraction (HEXRD) reveals thatthe O phase precipitates at 550 ◦C while it dissolves into the $\alpha_2$ phase at 750 ◦C during heat treatments. However,under external stress the O phase unexpectedly precipitates from $\alpha_2$ phase at 800 ◦C and even 900 ◦C. The Ophase formation proceeds further in the presence of a critical stress promoted by internal stress accumulation inthe $\alpha_2$ phase, whereas the reverse O → $\alpha_2$ phase transformation takes place when the internal stresses are relaxed.Additionally, it has been revealed that the O phase preferentially precipitates from specifically oriented $\alpha_2$ grainswith one of their directions aligned perpendicular and their 〈0001〉directions rotated by an angle of 120◦ out of the external load axis. This $\alpha_2$ phase orientation facilitates the $\alpha_2$ → O crystal transition during uniaxialcompression. Transmission electron microscopy (TEM) study shows that stress-induced $\alpha_2$ → O transformation isgoverned by small atomic shifts in the $\alpha_2$ lattice. In addition, the selective growth of certain O variants viashuffling along an [11$\bar{2}$0]$\alpha_2$ direction is found to accommodate the external strain component in this direction

Modulating Local Oxygen Coordination to Achieve Highly Reversible Anionic Redox and Negligible Voltage Decay in O2O_2‐Type Layered Cathodes for Li‐Ion Batteries

O2-type layered oxides have emerged as promising cathode materials for high-energy lithium-ion batteries, offering a solution to mitigate voltage decay through reversible transition metal (TM) migration between TM and Li layers during cycling. However, achieving a fully reversible oxygen redox remains a significant challenge. Here, this is addressed by introducing Li─O─Li configurations in the layered structure of Li0.85□0.15[Li0.08□0.04Ni0.22Mn0.66]O2 (O2-LLNMO), where □ represents vacancies. This adjustment alters the redox-active oxygen environment and increases the energy gap between the O 2p nonbonding and TM─O antibonding bands. As a result, the contribution of lattice oxygen to capacity is significantly enhanced, improving the reversibility of oxygen redox processes. The O2-LLNMO cathode demonstrates minimal voltage decay (0.13 mV per cycle) and excellent cycling stability, retaining 95.8% of its capacity after 100 cycles. A novel strategy is presented to design high-performance layered oxides with stable anionic redox activity, advancing the development of next-generation lithium-ion batteries