Bulk Structures Research Articles

Coalescence of Porous Coordination Cages into Crystalline and Amorphous Bulk Solids.

Discrete porous coordination cages are attractive as a solution processable material whose porosity is not predicated on a network structure. Here, we leverage the peripheral functionalization of these cage structures to obtain 12 novel, solution processable, porous coordination cages that afford crystalline and amorphous single-phase millimeter-scale monolithic bulk structures (six of each) upon solidification. These structures are based upon prototypal metal-organic polyhedra [Cu24(5-x-isophthalate)24] (where x = NH2, OH), wherein meta-substitution of linker ligands with acyl chloride or isocyanate moieties afforded amide and urethane functional groups, respectively. These porous cage structures were obtainable via direct synthesis between a metal salt and a ligand as well as postsynthetic modification of the cage and formed monoliths following centrifugation and drying of the product. We rationalize their self-assembly as colloidal packing of nanoscale cuboctahedral cages through weak interactions between their hydrophobic alkyl/aromatic surfaces. In general, amorphous solids were obtained via rapid precipitation from the mother liquor upon methanol addition, while crystalline solids could be obtained only following further chloroform and pyridine additions. The structure of the materials is confirmed via gas sorption and spectroscopic methods, while powder X-ray diffraction and transmission electron microscopy are used to determine the nature of these bulk solids.

Linking Bulk and Surface Structures in Complex Mixed Oxides

Linking Bulk and Surface Structures in Complex Mixed Oxides

From Bulk to one-dimensional MoS2 nanochains: evolution of electronic, mechanical, and optical properties

We theoretically investigate the stability of a MoS2 nanochain, reporting its electronic, mechanical, and optical properties. The nanochain presents a semiconductor structure with a minute band gap of 67m eV compared to the larger gap bulk and monolayer structures. It is more malleable, enduring a maximum compressive (tensile) strain of 6% (6.5%). It is dynamically stable, showing no negative frequencies along its Brillouin zone (BZ) path. The nanochain is thermally stable at 300K, making it possible to synthesize as a freestanding structure. The optical properties of the bulk, monolayer, and 1D MoS2 materials are evaluated using the time-dependent density functional perturbation theory (TDDFPT) and compared to those determined via the independent particle approximation (IPA). Along the nanochain’s periodic x direction, the reflectivity retains a maximum value of ∼68% in the infrared (IR) region. Furthermore, its optical conductivity also exhibits a peak within the IR regime. These two features make such nanochains suitable as coating materials in applications involving infrared radiation or can even be exploited as conductive substrates in near-IR devices.

Enhancing the Cycling and Rate Performance of Ni-Rich Cathodes for Lithium-Ion Batteries by Bulk-Phase Engineering and Surface Reconstruction.

The structural and interfacial instability of Ni-rich layered cathodes LiNi0.9Co0.05Mn0.05O2 (NCM9055) severely hinders their commercial application. In this work, straightforward high-temperature solid-state methods are utilized to successfully synthesize Nb-doped and Li3PO4-coated LiNi0.9Co0.05Mn0.05O2 by combining two niobium sources, NbOPO4·3H2O and Nb2O5, for the first time. Studies indicate that Nb doping enhanced the integrity of the layered structure, and the Li3PO4 coating reduced water absorption on the surface and considerably boosted the durability of the interface. The dual-modified cathode Li(Ni0.9Co0.05Mn0.05)0.985Nb0.015O2@Li3PO4 (NCM-2) exhibits remarkable cycling and rate performance. The initial discharge specific capacity of NCM-2 is 203.33 mAh g-1 at 0.1 C and 196.04 mAh g-1 at 1 C, while the capacity retention after 200 cycles is 91.38% at 1 C, which is much higher than that of pristine NCM9055 (49.96%). In addition, it also provides a superior discharge specific capacity of about 175.63 mAh g-1 even at 5 C. This study emphasizes a feasible approach to enhancing the stability of Ni-rich cathodes at the interfaces and bulk structures.

Overcoming poisoning issues in hydrogen fuel cells with face-centered tetragonal FePt bimetallic catalysts

Hydrogen fuel cells are expected to play a central role in the next-generation energy paradigm. However, owing to practical limitations, hydrogen is supplied in the form of refined hydrocarbons or alcohols in industrial applications. Among them, methanol is widely used as a hydrogen source, and CO is inevitably generated during its oxidation process. Even a small amount of CO (∼20 ppm) strongly binds to Pt used as a catalyst, and deactivates it. In addition to CO, surface adsorption of organic cations by binder or ionomer use in alkaline fuel cells is also one of the poisoning issues to be overcome. Herein, we propose FePt bimetallic catalysts that can resist unavoidable CO and organic cation poisoning. Our synthetic strategy, including annealing and acid treatment, allows the catalysts to possess different alloying degrees and surface structures, which in turn induce different levels of resistance to CO and organic-cation poisonings. The correlation between the surface and bulk structures of the catalysts and poisoning resistance was elucidated through X-ray photoemission spectroscopy and electrochemical analysis. The results revealed that an FePt catalyst having an ordered atomic arrangement displayed a better poisoning resistance than that having a disordered arrangement.

Additive Manufacturing of cryogenic materials

The use of pure copper and Inconel 718 as cryogenic materials has been well known in the cryogenic materials space. Despite their potential, little is known about the use of these materials in cryogenic environments regarding their ability to withstand these conditions when manufactured using Additive Manufacturing (AM) methods. AM has emerged as a promising production method due to its ability to produce complex geometries and near net-shape parts. Copper and Inconel 718 offer a wide range of uses in cryogenic applications, as Copper being highly conductive makes it ideal for electrical applications, whilst Inconel 718 serves well as an engineering material.In this paper, we demonstrate the Coldgas Spraying (CS) of copper and the Selective Laser Melting (SLM) of Inconel 718 and Scalmalloy as the AM processes of choice for each respective material. The main distinction between both processes is that CS is useful for rapid deposition of material in the range of several kg/h whereas SLM is limited to a range of several hundred g/h. However, CS can only yield bulk structures while SLM allows the production of fine and intricate structures due to the nature of their approaches.The work presented here was performed in the framework of a research project named AdHyBau. It is funded by the German government in which several partners from industry and academia seek to jointly develop a 500 kW output power electric drive for aviation applications which employs liquid hydrogen as a propellant for a fuel cell but also for advanced cooling to obtain very high power densities in the range of above 10 kW/kg.

Significant improvement in structural, electronic, optical and thermoelectric properties of PdTe2 in bulk and monolayer phase: A G0W0+BSE approach

Using first principles calculations structural, electronic, thermoelectric and optical properties of PdTe2 in bulk and monolayer were investigated. The calculated lattice parameters with different exchange correlation functionals show that the results obtained with addition of van der Waals corrections (vdW-DFC09x) are very well matched with the results obtained experimental. For correct prediction of electronic band gap, G0W0 approximation is used and the calculated band structure reveal that PdTe2 in bulk form has metallic nature as attained in experimental studies. In addition, the electronic band gap results with G0W0 approximation depicted that PdTe2 in monolayer phase is a semiconductor material with a direct band gap of 1.12 eV. The optical spectra have been calculated via many-body perturbation theory (MBPT) by solving Bethe-Salpeter equation (BSE) (G0W0+BSE). Ultimately, the results of optical spectra demonstrated that PdTe2 in monolayer phase has strong optical absorption within visible light wavelengths than the bulk phase which is good for solar cell applications. Thermoelectric (TE) properties of PdTe2 in bulk and monolayer structures have been studied using BoltzTraP code. The TE properties calculations indicated that better performance can be obtained by reducing the dimensionality of materials. The figure of merit was found to be above unity for monolayer phase. This paper successfully exploited the enhancement of the figure of merit values with the monolayer structure of PdTe2 material.

Laser ultrasonic frequency-domain imaging and phase weighted optimization based on full matrix capture

Far-field laser technology has greatly promoted the progress of nondestructive ultrasonic imaging of bulk structures. However, under thermoelastic excitation, the body waves exhibit a relatively low signal-to-noise ratio, resulting in images with low resolution and contrast. Based on the motivation, this paper developed a frequency-domain phase weighted imaging method to improve the quality of laser ultrasonic defect imaging. Firstly, laser ultrasonic scanning was performed on the sample with artificial transverse hole defects. The cylindrical lens focused line source was used to improve the intensity of the body wave signals, and ensure that there was no damage on the material surface under high laser energies. Then, the frequency-domain phase shift migration (PSM) algorithm was used to perform multimode imaging of defects, achieving frequency-domain synthetic aperture focusing technique (F-SAFT) and total focused method (F-TFM) imaging based on full matrix capture. Furthermore, the phase circular statistical vector (PCSV) was proposed for weighted optimization, which improved the image quality, suppressed the background noise and multimode artifacts. Finally, the imaging quality of several algorithms were discussed. The results indicate that frequency-domain images were superior to time-domain results. After phase weighting, the imaging quality can be further improved, and the detection blind zone was significantly reduced. This work will contribute to the rapid and high-quality defect imaging of laser ultrasonic.

Anion Architecture Controls Structure and Electroresponsivity of Anhalogenous Ionic Liquids in a Sustainable Fluid.

Three nonhalogenated ionic liquids (ILs) dissolved in 2-ethylhexyl laurate (2-EHL), a biodegradable oil, are investigated in terms of their bulk and electro-interfacial nanoscale structures using small-angle neutron scattering (SANS) and neutron reflectivity (NR). The ILs share the same trihexyl(tetradecyl)phosphonium ([P6,6,6,14]+) cation paired with different anions, bis(mandelato)borate ([BMB]-), bis(oxalato)borate ([BOB]-), and bis(salicylato)borate ([BScB]-). SANS shows a high aspect ratio tubular self-assembly structure characterized by an IL core of alternating cations and anions with a 2-EHL-rich shell or corona in the bulk, the geometry of which depends upon the anion structure and concentration. NR also reveals a solvent-rich interfacial corona layer. Their electro-responsive behavior, pertaining to the structuring and composition of the interfacial layers, is also influenced by the anion identity. [P6,6,6,14][BOB] exhibits distinct electroresponsiveness to applied potentials, suggesting an ion exchange behavior from cation-dominated to anion-rich. Conversely, [P6,6,6,14][BMB] and [P6,6,6,14][BScB] demonstrate minimal electroresponses across all studied potentials, related to their different dissociative and diffusive behavior. A mixed system is dominated by the least soluble IL but exhibits an increase in disorder. This work reveals the subtlety of anion architecture in tuning bulk and electro-interfacial properties, offering valuable molecular insights for deploying nonhalogenated ILs as additives in biodegradable lubricants and supercapacitors.

Titanium Substitution Facilitating Oxygen and Manganese Redox in Sodium Layered Oxide Cathode

AbstractSodium layered oxide with anion redox activity (SLO‐A) stands out as a promising cathode material for sodium‐ion batteries due to its impressive capacity and high voltage resulting from Mn‐ and O‐redox processes. However, the SLO‐A faces significant challenges in cycling stability and rate performance, primarily due to the poor reversibility and sluggish kinetics of the O‐redox. In this study,a novel Ti‐doped material, Na2/3Li2/9Mn53/72Ti1/24O2 (NLMTO), exhibiting remarkable characteristics such as a notable rate capacity (130 mAh g−1 at 3C, where 1C equals 200 mA g−1) and excellent cycling retention (85.4% after 100 cycles at 0.5C) is introduced. Employing electrochemical differential analyses, the contributions to the superior performance arising from the Mn‐ and O‐redox processes are quantitatively delineated. The optimized performance of NLMTO is attributed, in part, to the enhanced stability of both bulk and interface structures. The introduction of Ti through substitution not only contributes to this stability but also allows for the fine‐tuning of the material's electron configurations. This is achieved by augmenting the density of states near the Fermi energy level, as well as elevating the O 2p and Mn 3d orbits. This research advances sodium‐ion battery technology.

Fabrication and Characterization of a Magnetic 3D‐printed Microactuator

AbstractConventional MEMS microactuators have, in recent years, been complemented by 3D‐printed actuatable microstructures fabricated via two‐Photon‐Polymerization (2PP). Herein, a novel compact 3D‐printed magnetically actuatable microactuator with a diameter of 500µm is demonstrated, originally designed for micro‐optical systems. It is fabricated by incorporating a composite of NdFeB microparticles and epoxy resin into a designated reservoir of the printed mechanical structure within a simple post‐processing step. The microactuator structure features mechanical springs, allowing for continuous positioning with large displacement. Mechanical studies by nanoindentation of IP‐S bulk structures reveal a viscoelastic material behavior, described by a two‐element General Kelvin‐Voigt viscoelasticity model. The obtained material parameters are then used to simulate and characterize the spring behavior of the microactuator. Actuation experiments are conducted using an external microcoil. The actuator displacement is measured for triangular current pulses with a peak current of 106 mA and durations of 1 to 100 s, resulting in displacements of 69.1 to 88.9 µm. Hysteretic behavior of the actuator is observed, attributable to viscoelasticity and magnetic properties of the core material. Numerical simulations of the experiment demonstrate this behavior as well. On‐the‐fly demagnetization and the implementation of closed‐loop control allow for both high repeatability and precise positioning.

Abundance of Low-Energy Oxygen Vacancy Pairs Dictates the Catalytic Performance of Cerium-Stabilized Zirconia.

Cerium-stabilized zirconia (Ce1-xZrxOy, CZO) is renowned for its superior oxygen storage capacity (OSC), a key property long believed to be beneficial to catalytic oxidation reactions. However, 50% Ce-containing CZO recorded with the highest OSC has disappointingly poor performance in catalytic oxidation reactions compared to those with higher Ce contents but lower OSC ability. Here, we employ global neural network (G-NN)-based potential energy surface exploration methods to establish the first ternary phase diagram for bulk structures of CZO, which identifies three critical compositions of CZO, namely, 50, 60, and 80% Ce-containing CZO that are thermodynamically stable under typical synthetic conditions. 50% Ce-containing CZO, although having the highest OSC, exhibits the lowest O vacancy (Ov) diffusion rate. By contrast, 60% Ce-containing CZO, despite lower OSC (33.3% OSC compared to that of 50% Ce-containing CZO), reaches the highest Ov diffusion ability and thus offers the highest CO oxidation catalytic performance. The physical origin of the high performance of 60% Ce-containing CZO is the abundance of energetically favorable Ov pairs along the ⟨110⟩ direction, which reduces the energy barrier of Ov diffusion in the bulk and promotes O2 activation on the surface. Our results clarify the long-standing puzzles on CZO and point out that 60% Ce-containing CZO is the most desirable composition for typical CZO applications.

Топар МАЭС бөгетінің жай-күйін бағалау кезіндегі ғылыми зерттеулердің нәтижелері

The article considers the development of a methodology for conducting research on the stability of bulk structures. Software complexes have been implemented based on the use of the latest achievements in the field of geodetic instrumentation and new technologies in geophysics, hydrogeology and soil geomechanics research. The purpose of the work is to study the design features of bulk structures, the stages of their construction during the construction of roads, railways. As well as a variety of enclosing dams of tailings dumps, ash dumps of HRPP, determination of their category of responsibility, requirements during operation and timely selection of the method of geodetic control. Scientific research was carried out on hydrotechnical bulk structures of the Topar HRPP. The analysis of the current regulatory documents in Kazakhstan is carried out. The analytical review of scientific works of famous scientists of Kazakhstan, Russia and far abroad is carried out.

Band Alignment of Oxides by Learnable Structural-Descriptor-Aided Neural Network and Transfer Learning.

The band alignment of semiconductors, insulators, and dielectrics is relevant to diverse material properties and device structures utilizing their surfaces and interfaces. In particular, the ionization potential and electron affinity are fundamental quantities that describe surface-dependent band-edge positions with respect to the vacuum level. Their accurate and systematic determination, however, demands elaborate experiments or simulations for well-characterized surfaces. Here, we report machine learning for the band alignment of nonmetallic oxides using a high-throughput first-principles calculation data set containing about 3000 oxide surfaces. Our neural network accurately predicts the band positions for relaxed surfaces of binary oxides simply by using the information on bulk structures and surface termination planes. Moreover, we extend the model to naturally include multiple-cation effects and transfer it to ternary oxides. The present approach enables the band alignment of a vast number of solid surfaces, thereby opening the way to a systematic understanding and materials screening.

Directionally assembled FeCO3 nanoparticles wrapped with rGO enabled by the synergy of tartaric and ascorbic acids for lithium/sodium storage

Ferrous carbonate (FeCO3) particles synthesized by conventional routes generally possess large-size bulk structures with the drawbacks of low conductivity and easy pulverization, thereby limiting their promising application as high-capacity anodes for lithium/sodium ion batteries (LIBs/SIBs). Herein, a robust strategy via the synergy of tartaric and ascorbic acids (TA/AA) is developed to craft FeCO3 dumbbells that are directionally assembled by ultrafine nanoparticles and uniformly encapsulated in reduced graphene oxide matrixes (denoted FeCO3 NADs-rGO). It is noteworthy that TA serves as a capping agent to inhibit the overgrowth of FeCO3 nanoparticles and guide their directional assembly into dumbbells. Concurrently, AA functions as a reductant to prevent the oxidation of Fe2+ and initiate the reduction of GO. Remarkably, benefiting from the efficient synergy of hierarchical architecture and rGO encapsulation, FeCO3 NADs-rGO delivers highly-reversible lithium and sodium storage capacities of 1853 and 641 mAh/g in the 1200th and 100th cycles at 100 and 20 mA g−1, respectively, which are 2.1 and 3.9-fold over FeCO3 micron peanut kernels-rGO (884 and 163 mAh/g) fabricated without introducing TA. As revealed by experimental investigations and theoretical calculations, FeCO3 nanoparticles shorten the ion transfer distance and rGO accelerates the electron conduction to boost the electrochemical kinetics for high-rate capability. More importantly, the ample mesopores of FeCO3 NADs accommodate the inward stress and the rGO buffer the outward expansion of lithiated/sodiated FeCO3 NADs to strengthen the electrode durability. As such, FeCO3 NADs-rGO may stand out as a superior LIB/SIB anode, and the implementation of facile capping and reductant co-regulators (e.g., TA and AA) could synergistically render the creation of various rGO-based nanocomposites with outstanding mechanical flexibility and electrochemical activity for advanced energy storage.

Explainable AI for optimizing oxygen reduction on Pt monolayer core–shell catalysts

AbstractAs a subfield of artificial intelligence (AI), machine learning (ML) has emerged as a versatile tool in accelerating catalytic materials discovery because of its ability to find complex patterns in high‐dimensional data. While the intricacy of cutting‐edge ML models, such as deep learning, makes them powerful, it also renders decision‐making processes challenging to explain. Recent advances in explainable AI technologies, which aim to make the inner workings of ML models understandable to humans, have considerably increased our capacity to gain insights from data. In this study, taking the oxygen reduction reaction (ORR) on {111}‐oriented Pt monolayer core–shell catalysts as an example, we show how the recently developed theory‐infused neural network (TinNet) algorithm enables a rapid search for optimal site motifs with the chemisorption energy of hydroxyl (OH) as a single descriptor, revealing the underlying physical factors that govern the variations in site reactivity. By exploring a broad design space of Pt monolayer core–shell alloys ( candidates) that were generated from thermodynamically stable bulk structures in existing material databases, we identified novel alloy systems along with previously known catalysts in the goldilocks zone of reactivity properties. SHAP (SHapley Additive exPlanations) analysis reveals the important role of adsorbate resonance energies that originate from ‐band interactions in chemical bonding at metal surfaces. Extracting physical insights into surface reactivity with explainable AI opens up new design pathways for optimizing catalytic performance beyond active sites.

A reactive molecular dynamics model for uranium/hydrogen containing systems.

Uranium-based materials are valuable assets in the energy, medical, and military industries. However, understanding their sensitivity to hydrogen embrittlement is particularly challenging due to the toxicity of uranium and the computationally expensive nature of quantum-based methods generally required to study such processes. In this regard, we have developed a Chebyshev Interaction Model for Efficient Simulation (ChIMES) that can be employed to compute energies and forces of U and UH3 bulk structures with vacancies and hydrogen interstitials with accuracy similar to that of Density Functional Theory (DFT) while yielding linear scaling and orders of magnitude improvement in computational efficiency. We show that the bulk structural parameters, uranium and hydrogen vacancy formation energies, and diffusion barriers predicted by the ChIMES potential are in strong agreement with the reference DFT data. We then use ChIMES to conduct molecular dynamics simulations of the temperature-dependent diffusion of a hydrogen interstitial and determine the corresponding diffusion activation energy. Our model has particular significance in studies of actinides and other high-Z materials, where there is a strong need for computationally efficient methods to bridge length and time scales between experiments and quantum theory.

Atomic Imaging of Multi-Dimensional Ruddlesden-Popper Interfaces in Lead-Halide Perovskites.

Ruddlesden-Popper (RP) interface with defined stacking structure will fundamentally influence the optoelectronic performances of lead-halide perovskite (LHP) materials and devices. However, it remains challenging to observe the atomic local structures in LHPs, especially for multi-dimensional RP interface hidden inside the nanocrystal. In this work, the advantages of two imaging modes in scanning transmission electron microscopy (STEM), including high-angle annular dark field (HAADF) and integrated differential phase contrast (iDPC) STEM, are successfully combined to study the bulk and local structures of inorganic and organic/inorganic hybrid LHP nanocrystals. Then, the multi-dimensional RP interfaces in these LHPs are atomically resolved with clear gap and blurred transition region, respectively. In particular, the complex interface by the RP stacking in 3D directions can be analyzed in 2D projected image. Finally, the phase transition, ion missing, and electronic structures related to this interface are investigated. These results provide real-space evidence for observing and analyzing atomic multi-dimensional RP interfaces, which may help to better understand the structure-property relation of LHPs, especially their complex local structures.

Overlap and rotate - a simple method for predicting out-of-plane and in-plane orientations of heteroepitaxial thin films

The production of heteroepitaxial thin films is increasingly important due to their considerable utility in technical practice. This usability is determined by their specific physical and chemical properties influenced by the mutual crystallographic substrate-film orientation, both the out-of-plane and the in-plane. The possibility of predicting these orientations would reduce the time and financial burden of their experimental determination. This study shows how the out-of-plane and the in-plane orientation of heteroepitaxial film can be predicted by simply calculating number of overlapping atoms in a system of two overlapping crystallographic planes, one of which rotates relatively to the other. Coordinates of atoms in the crystallographic planes are taken from bulk structures, which contributes to the simplicity of the method. The average number of overlapping atoms (calculated from a 360° rotation) and the maximum number of overlapping atoms (including a corresponding angle) indicate the out-of-plane and the in-plane orientation, respectively. The method is tested on various substrate/film systems (SrTiO3/ZnO, Al2MgO4/ZnO, MgO/ZnO, MgO/CuO, Si/Al, MoS2/Au) and the results are compared with experimental data obtained from the literature. The good agreement with the experimental data shows this method to be reliable and sufficiently accurate for heteroepitaxial thin films.

Composition-driven Mott transition within SrTi 1−x V x O3

The last few decades has seen the rapid growth of interest in the bulk perovskite-type transition metal oxides SrVO3 and SrTiO3. The electronic configuration of these perovskites differs by one electron associated to the transition metal species which gives rise to the drastically different electronic properties. Therefore, it is natural to look into how the electronic structure transitions between these bulk structures by using doping. Measurements of the substitutional doped SrTi 1−x V x O3 shows an metal–insulator transition (MIT) as a function of doping. By using supercell density functional theory with dynamical mean field theory (DFT+DMFT), we show that the MIT is indeed the result of the combination of local electron correlation effects (Mott physics) within the t2g orbitals and the atomic site configuration of the transition metals which may indicate dependence on site disorder. SrTi 1−x V x O3 may be an ideal candidate for benchmarking cutting-edge Mott–Anderson models of real systems. We show that applying an effective external perturbation on SrTi 1−x V x O3 can switch the system between the insulating and metallic phase, meaning this is a bulk system with the potential use in Mott electronic devices.