Specific Crystal Planes Research Articles

Trisodium Citrate‐Assisted Synthesis of Edge‐Abundant Nickel‐Iron Layered Double Hydroxides for Efficient Oxygen Evolution Reaction

AbstractThe edges of layered double hydroxides (LDHs) display an exceptionally more efficient oxygen evolution reaction (OER) activity than the (001) basal plane as demonstrated by both theoretical calculations and experimental studies. However, a controllable synthesis method of LDHs with abundant edges has yet to be described. Herein, we report a strategy enabling the synthesis of nickel‐iron LDHs with abundant edges (NiFe LDHs‐E) based on the use of citrate anions as the structure‐directing agent. The edge density is characterized using spectroscopy techniques and its OER performance is compared with that of nickel‐iron LDHs with abundant basal planes (NiFe LDHs‐B). In alkaline electrolyte (1 M KOH), NiFe LDHs‐E exhibits excellent OER activity with very low overpotential (235 mV at 10 mA cm−2) and current densities (at η = 320 mV) up to sixfold higher than those of NiFe LDHs‐B. Density functional theory (DFT) calculations confirm the high OER activities ascribed to the abundant side‐plane edges with optimal strength of binding of OER intermediates. Overall, a comprehensive investigation, employing both experimental and computational methodologies, yields new insights to fabricate superior catalysts meticulously designed with specific crystal planes and unveils the crucial structural attributes, thus unleashing the limitless potential of the catalytic domain.

Molybdenum oxide catalyzed low temperature preparation of mullite whisker from silica-alumina gel slag

Catalyzed by MoO3, mullite whiskers were synthesized through a molten salt method. This study comprehensively explored the impact of reaction temperature, MoO3 mass fraction, and calcination temperature on the morphology of mullite whiskers. Employing analytical techniques such as XRD and SEM, the phase composition and morphology of the samples were meticulously scrutinized. The results unveiled that at a MoO3 mass fraction of 7–8% (molar fraction) and a calcination temperature of 800 °C, mullite whiskers demonstrated a heightened level of purity. Building on these observations, the study delved into the mechanistic underpinnings of MoO3 as a catalyst in mullite whisker synthesis. It is proved that the metal oxides contained in the silica-alumina glue slag can also form a local liquid phase at low temperatures, reducing the viscosity of the reaction system and liquefaction temperature. The addition of molybdenum oxide makes the reaction process of mullite whisker growth shorter. At the same time, the addition of molybdenum oxide can effectively reduce the viscosity of the reaction system, thus lowering the reaction temperature and increasing the reaction efficiency. In addition molybdenum oxide can be used as a templating agent to induce the growth of mullite whiskers along specific crystal planes. Compared with aluminum fluoride catalysis, molybdenum oxide does not produce the hazardous gas HF, the sublimated molybdenum oxide gas can be recycled, and the molybdenum oxide attached to the whiskers can also be dissolved in water. These theories provide experience in the large-scale preparation of mullite whiskers.

Effect of hydrogen on the microstructural evolution and local mechanical properties of 430 ferritic stainless steel at high-temperature conditions

The present study investigated the impact of hydrogen on the microstructural evolution and mechanical properties of 430 ferritic stainless steel at high-temperature conditions. Hydrogen trap sites were analyzed at high temperatures using thermal desorption spectrometry through high-temperature hydrogen atmosphere charging and electrolytic hydrogen charging. The microstructural evolution was characterized using scanning electron microscopy and electron backscatter diffraction. The nanoindentation technique was employed to analyze the local mechanical properties of ferrite matrix, grain boundaries, and M23C6/matrix interfaces. Hydrogen trap sites in 430 ferritic stainless steel included ferrite crystal lattice, grain boundaries, intragranular dislocations, and M23C6/matrix interfaces where hydrogen could not intrude at room temperature. At high temperatures, hydrogen caused a decrease in grain size. Furthermore, at high temperatures, hydrogen altered the crystal orientation and texture of the ferrite matrix. There was an increase in the number of ferrite grains with (001) and (101) orientation increase and the formation of a new α-fiber texture. Hydrogen inhibited the triggering of the slip system in body centered cubic crystal lattice and induced an increase in dislocation density and internal stress. While hydrogen at high temperatures had a minimal impact on the matrix strength limit, it reduced the strength limit of the near grain boundaries and (Fe, Cr)23C6 precipitates. The influence of hydrogen on the microstructural evolution and mechanical properties of 430 ferritic stainless steel could be elucidated by the mechanisms of hydrogen enhanced decohesion, hydrogen-enhanced localized plasticity, and hydrogen enhanced specific crystal plane rotation suggested in the present study.

Tailoring particle size/morphology for the stable cathode performance of polygonal-shaped Li(Ni,Mn)2O4 single crystals

We regulate the particle size and crystallographic facet of single-crystal (SC) Li(Ni,Mn)2O4 (LNMO) cathode materials via flux-selective molten salt method. By simply adjusting Li2MoO4 or LiI as sintering aids, we synthesized size controlled SC particles, both small and large, and comparatively investigated their electrochemical behavior focusing on the lithiation/delithiation reactivity in conjunction with the particle size and surface planes. Considering the growth mechanism of a SC particles with a specific crystal plane, such particle size control is not determined solely by the synthetic condition but must also consider the interfacial energy of the crystal planes in conjunction with the fluxes what we used. While the initial charge capacity is similar, the given cathode using a small SC LNMO (using LiI) with uniform particle sizes (≤5 μm) exhibits outstanding rate capability with stable capacity retention under changing current density, which indicates stable lithium transport during the repetitive electrochemical reactions. The dependency of the impedance response with change in the electrode resistances as well as the stability during the cycle reactions in conjunction with the post-mortem Li distribution by using laser-induced breakdown spectroscopy as a function of porosity change and cell degradation are thoroughly discussed from the standpoint of regulated particle property.

Controlling silver deposition morphology on aluminum surfaces: Surfactant modify anisotropy of aluminum surface energy

Faced with the challenge of uncontrollable Ag layer deposition morphology during the preparation of silver-coated aluminum particles (Al/Ag). A simple and nontoxic method involving the introduction of surfactants (PEG, PVP, and gelatin (GEL)) to alter the anisotropy of Al surface energy was proposed to achieve control over Ag deposition morphology. Theoretical calculations indicate that PEG undergoes physisorption to Al, while PVP and GEL can alter the surface energy of specific crystal planes by selectively binding to different crystal facets. This action alters the growth habit of Ag on the Al surface and modulates the Ag deposition behavior, these conclusions align with experimental results. Compared with PEG and PVP, the incorporation of GEL was beneficial for the formation of a conformal Ag layer. This can be attributed to GEL preferentially passivating the highest crystal plane Al (110) surface, forming a buffer layer at the solid-liquid interface, leveling out the Ag deposition rate on various crystal planes, and also effectively inhibiting side reactions, in addition to enhancing the wettability of reaction solution. The Al/Ag particle exhibits excellent electrical conductivity (1.03 × 10−6 Ω·cm) and electromagnetic absorption (−32.5 dB, 1.62 GHz), it is suitable for use as a highly conductive electromagnetic shielding material.

Scalable Customization of Crystallographic Plane Controllable Lithium Metal Anodes for Ultralong-Lasting Lithium Metal Batteries.

A formidable challenge to achieve the practical applications of rechargeable lithium (Li) metal batteries (RLMBs) is to suppress the uncontrollable growth of Li dendrites. One of the most effective solutions is to fabricate Li metal anodes with specific crystal plane, but still lack of a simple and high-efficient approach. Herein, a facile and controllable way for the scalable customization of polished Li metal anodes with highly preferred (110) and (200) crystallographic orientation (donating as polished Li(110) and polished Li(200), respectively) by regulating the times of accumulative roll bonding, is reported. According to the inherent characteristics of polished Li(110)/Li(200), the influence of Li atomic structure on the electrochemical performance of RLMBs is deeply elucidated by combining theoretical calculations with relative experimental proofs. In particular, a polished Li(110) crystal plane is demonstrated to induce Li+ uniform deposition, promoting the formation of flat and dense Li deposits. Impressively, the polished Li(110)||LiFePO4 full cells exhibit unprecedented cycling stability with 10000 cycles at 10 C almost without capacity degradation, indicating the great potential application prospect of such textured Li metal. More valuably, this work provides an important reference for low-cost, continued, and large-scale production of Li metal anodes with highly preferred crystal orientation through roll-to-roll manufacturability.

Enhanced flotation performance and adsorption mechanism on (0 0 2) crystal plane of fine muscovite powder

Muscovite crystal has anisotropy, the flotation performance is determined by the adsorption of collectors on its specific crystal plane. This study focused on the adsorption mechanism of sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) used as muscovite collectors on its (002) crystal plane. The flotation experiment showed that SDS has better flotation efficiency than SDBS. The adsorption behavior on the muscovite (002) crystal plane was demonstrated by contact angle, infrared spectrum tests, molecular dynamics simulation and XRD test. The results indicated that SDS had lower adsorption energy with muscovite (002) crystal plane, and was more likely to adsorb on the muscovite (002) crystal plane. What’s more, the reduction degree of the strength of the (002) crystal plane after SDS was lower than that of SDBS. It clearly proves the superiority of SDS on the adsorption of the muscovite (002) crystal plane, and provide a new idea for the muscovite flotation.

Estimation of directional single crystal elastic properties from nano-indentation by correlation with EBSD and first-principle calculations

In this study, a two-step optimisation process for the estimation of the single crystal stiffness tensor from the indentation modulus is presented. This was accomplished by using a 2-dimensional data correlation method for nano-indentation, EBSD and ab initio data, as well as EDS for phase separation in a multi-phase material. Here, a single-phase Fe-24Ni-0.4C austenitic steel and a two-phase Fe-9.5Ni-0.5Co Seymchan meteorite were used as example materials.In a first step, the combination of high-speed nano-indentation mapping data with elemental and orientation distribution maps allowed the estimation of indentation moduli along specific crystal surface planes normal directions, (001), (011) and (111) using a least squares optimisation based on starting values from DFT or experimentally determined stiffness tensors. A second global optimisation step to estimate the single crystal stiffness tensor using pre-solved solution parameters of the Vlassak-Nix equations yielded reasonable correspondence between the experimentally determined stiffness tensors from correlative nano-indentation data and other methods. The presented method demonstrates generally the possibility to derive directionally sensitive elastic properties from high-speed nano-indentation for cubic materials statistically.

Molten salt synthesis, morphology modulation, and lithiation mechanism of high entropy oxide for robust lithium storage

High entropy oxides (HEOs) with ideal element tunability and enticing entropy-driven stability have exhibited unprecedented application potential in electrochemical lithium storage. However, the general control of dimension and morphology remains a major challenge. Here, scalable HEO morphology modulation is implemented through a salt-assisted strategy, which is achieved by regulating the solubility of reactants and the selective adsorption of salt ions on specific crystal planes. The electrochemical properties, lithiation mechanism, and structure evolution of composition- and morphology-dependent HEO anode are examined in detail. More importantly, the potential advantages of HEOs as electrode materials are evaluated from both theoretical and experimental aspects. Benefiting from the high oxygen vacancy concentration, narrow band gap, and structure durability induced by the multi-element synergy, HEO anode delivers desirable reversible capacity and reaction kinetics. In particular, Mg is evidenced to serve as a structural sustainer that significantly inhibits the volume expansion and retains the rock salt lattice. These new perspectives are expected to open a window of opportunity to compositionally/morphologically engineer high-performance HEO electrodes.

High‐entropy rare earth titanates with low thermal conductivity designed by lattice distortion

AbstractHigh‐entropy single‐phase rare earth titanates (RE0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 (RE = Sm, Y, Lu) were designed and synthesized successfully, in which their lattice distortion was quantitatively described by mass disorder and size disorder. It is worth mentioning that (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 could obtain the low thermal conductivity (1.51 W·m−1·K−1, 1500°C), high thermal expansion coefficient (average, 11.69×10−6 K−1, RT ∼1500°C) and excellent high‐temperature stability. In addition, the relationship between the microstructure and thermal transport behaviors has been studied at the atomic scale. Due to the disorder of A‐site ions, severe lattice distortion occurred in specific crystal planes, and the large mass difference between Y3+ and other RE3+ further causes mass fluctuation and results in lower thermal conductivity. Compared with YSZ, the high‐entropy rare earth titanate (Y0.2Gd0.2Ho0.2Er0.2Yb0.2)2Ti2O7 has lower thermal conductivity, higher thermal expansion coefficient, and excellent high‐temperature stability, which has great potential for application in the thermal protection field.

Reaction selectivity-regulation via interfacial reconstruction for preventing hazardous slime generation: Driving mechanism of Pb-based anode with oxygen vacancy-rich MnO2

Limited selectivity in coexisted anodic reactions on lead-based anodes leads to severe lead-dissolution, anodic slime-generation and high energy-consumption. Herein, anodic reaction selectivity was regulated by phase-controlled MnO2 (MnO2-PC) on lead-based anodes which was prepared under a lower voltage and a higher Mn2+ concentration. Compared with α-MnO2 formed under normal conditions, composite phase of γ-MnO2 and ε-MnO2 was obtained from MnO2-PC with specific crystal planes exposure and rich oxygen vacancy defects enabling higher oxygen evolution reaction selectivity (OER, overpotential reduced by ∼99 mV). Meanwhile, reaction of lead corrosion and manganese oxidation, as the main reasons for generation of hazardous lead-containing slime, were synergistically suppressed by 86.8% and 91.7%, respectively. Density functional theory (DFT) calculations further clarified that the change in coordinative environment of Mn and O brought lower energy barrier of rate-determining step of OER and stronger electron delocalization ability of MnO2, beneficial for promoting the catalysis of OER. MnO2-PC also displayed excellent inhibition effects on the generation and accumulation of Mn3+, an important precursor of MnO2 slime, and changed the selectivity in the oxidative path of Mn2+. The long-term electrolysis tests proved the stable performance of Pb–Ag/MnO2-PC. This study provides an efficient, low-cost, high economic benefits and environmental-friendly strategy for designing target functional materials towards reaction selectivity regulation via phase-control and microstructure reconstruction.

Molecular Insights into the Effect of Crystal Planes on Droplet Wetting

Dynamic wetting by liquids on solid surfaces depends on several aspects such as surface energy, roughness, and interfacial tension, among many others. Copper (Cu), gold (Au), aluminum (Al), and silicon (Si) are a few of the most important metals that are used extensively as substrates in various industrial and biomedical applications. Metals are etched frequently on different crystal planes for fabrication purposes. Etching exposes distinct crystal planes that may come in contact with the liquids when used for different applications. The interaction of the crystal planes with the liquid that comes in contact with the solid dictates the wetting behavior of the surface. This necessitates the importance of understanding how various crystal planes of the same metals behave under similar conditions. Herein, three specific crystal planes, namely, (1 0 0), (1 1 0), and (1 1 1), are investigated at a molecular scale for the above-mentioned metals. The dynamic contact angle and contact diameter trends revealed that the relatively hydrophobic surfaces (Cu, Si) tend to reach their equilibrium contact angle faster compared to the hydrophilic substrates (Al, Au). Molecular kinetic theory is used to estimate the three-phase contact line friction which is found to be higher for (1 1 1) planes. Further, a consistent potential energy distribution variation is observed for the crystal lattice of (1 0 0), (1 1 0), and (1 1 1). These findings can be used as a guideline to determine the factors needed to completely describe a dynamic wetting phenomenon of the droplet over the different crystal planes. The understanding will be of great use in deciding experimental strategies where fabricated different crystal planes would be required to have a liquid contact.

Probing the interaction of calcium and magnesium ions on scheelite surface by atomic force microscopy

The presence of Ca2+/ Mg2+ could affect the surface potential of minerals during the flotation process. Still, the adsorption mechanism of these ions on specific crystal planes has yet to be fully understood. The surface potential of the scheelite (112) and (001) surfaces, under the effect of Ca2+/Mg2+ at pH 8 and 11, were determined by fitting force curve using the Derjaguin−Landau−Verwey−Overbeek (DLVO) model. It was found that increasing the Ca2+/Mg2+ concentration caused the surface potential of the (112) surface to be less negative at pH 8 and 11. The charge reversal occurred when Mg2+ concentration was only 1 mM at pH 11, indicating that MgOH+ was firmly adsorbed on the scheelite (112) surface, which is ascribed as the specific adsorption. While the (001) surface is inert regarding the adsorption of Ca2+/ Mg2+ at pH 8 and 11. The fitted potential indicated that the (001) surface was slightly affected by the increased Ca2+/ Mg2+ concentration. The understanding of adsorption mechanisms on different crystal planes may be helpful to rational design of the flotation process for scheelite.

Significant intensity dependence of anisotropic two-photon absorption in ZnSe and GaP

Using polarized femtosecond laser transmission measurements toward (100), (110), (111) ZnSe, and (100) GaP, we show that in a wide laser irradiation intensity range over two orders of magnitude before the laser damage threshold, a periodic amplitude modulation always appears clearly in the angle-dependent two-photon absorption (TPA) curves for (100), (110) ZnSe, and (100) GaP. It also exhibits a close connection between the orientation-dependent TPA and the ionic bonding symmetrical characteristics of specific crystal plane, thus revealing the origin of the orientation dependence of nonlinear absorption in the strong field laser-solid interaction. Interestingly, the modulation amplitudes of orientation-dependent TPA exhibit significant intensity dependence, with the maxima occurring around 1011 W cm−2. For the orientation-dependent nonlinear absorption in solids, such a nonmonotonic relationship between the irradiation intensity and the modulation amplitude has not been revealed previously in the near-damage-threshold regime by direct transmission measurements. In particular, with the intensity approaching the laser damage threshold, the significant descending trend of modulation amplitude confirms the consistent characteristics of saturation or even attenuation for the orientation dependence of TPA in the two crystals, which might be considered as a product of absorption saturation phenomenon of TPA at high irradiation intensity and would provide new understanding about the orientation-dependent TPA in the near-damage-threshold regime.

Influence of ammonium nitrate on the crystallisation of ammonium sulfate

ABSTRACT This study aims to explore the influence mechanism of ammonium nitrate produced by ozone denitrification on the crystallisation of ammonium sulfate, a by-product of ammonia desulfurisation. The laser method was used to study the influence of ammonium nitrate on the solubility and metastable zone width of ammonium sulfate. An experiment on the influence of ammonium nitrate on the particle size of ammonium sulfate was designed, and the influence mechanism was explored through scanning electron microscopy and X-ray diffraction. The findings showed that the addition of ammonium nitrate increased the size and aspect ratio of ammonium sulfate crystals. The addition of ammonium nitrate inhibited the dissolution of ammonium sulfate and widened its metastable zone. The addition of ammonium nitrate covered the active sites of crystal nucleus growth, which inhibited the formation of crystal nuclei to a certain extent, and crystal growth dominated the crystallisation process. Moreover, the addition of ammonium nitrate induced the preferred orientation of the specific crystal plane of ammonium sulfate, and the addition of a small concentration of ammonium nitrate decreased the crystallinity of ammonium sulfate. The research results can provide a reference for crystallisation optimisation and quality improvement of ammonium sulfate in the ammonia desulfurisation process.

Nucleation of stress corrosion cracking in aluminum alloy 6061 in sodium chloride solution: Mechanical and microstructural aspects

This study aims to elucidate the nucleation processes of transgranular stress corrosion cracking occurring in aluminum alloy 6061-T651 immersed in NaCl solution. The specimen was subjected to constant loading in the solution, and corrosion phenomena were investigated from aspects of precipitates, the site and geometry of corrosion pits and cracks, and the crystal orientation where cracking occurred. It was found that corrosion pits were formed on a smooth surface, and then stress corrosion cracks tended to occur originating from deeper pits in which the stress/strain concentration was high, along the specific crystal plane {1 1 2}.

Crystal plane-orientation dependent phase evolution from precursor to porous intermediate phase in the vapor phase dealloying of a Co-Zn alloy

Understanding phase transitions and pore formation during vapor phase dealloying (VPD) is essential to optimize the microstructure and composition of nanoporous metals for versatile applications. Nevertheless, the underlying atomic mechanisms of phase formation and pore evolution during VPD are unknown. Using a binary γ-CoZn precursor alloy as a prototype system, we found a two-step dealloying process. The microsized porous β-CoZn intermediate phase that formed at the dealloying front facilitated the subsequent growth of completely dealloyed hierarchical nanoporous α-Co with the micropore structure of the intermediate phase. Combining aberration-corrected scanning transmission electron microscopy with energy dispersion X-ray spectrometry, we found that the intermediate phase preferentially formed on specific crystal planes of the precursor, and the vacancies generated by sublimation of Zn atoms diffused dominantly on the {110} planes of the precursor close to the intermediate phase. Theoretical calculations indicated that the energy barrier to the diffusion of Zn vacancies on the low-index {110} plane was lower than on other planes. The atomic-scale phase evolution play a key role in the subsequent evolution of the porous structure and provide deep insight into the phase transition during VPD. This insight may provide a new approach to tune the pore structure and composition of nanoporous metals by designing and regulating their intermediate phases.

Directional growth of quasi-2D Cu2O monocrystals on rGO membranes in aqueous environments.

The preparation technology of unconventional low-dimensional Cu2O monocrystals, which exhibit specific crystal planes and present significantly unique interfacial and physicochemical properties, is attracting increasing attention and interest. Herein, by integrating a high-temperature oxidation process under vacuum and a pure-water incubation process under ambient conditions, we propose the self-assembled growth and synthesis of quasi-two-dimensional Cu2O monocrystals on reduced graphene oxide (rGO) membranes. The prepared Cu2O crystals have a single (110) crystal plane, regular rectangular morphology, and potentially well conductivity. Experimental and theoretical results suggest that this assembly is attributed to the pre-nucleation clusters aggregation and directional attachment of Cu and O on the rGO membranes in aqueous environment and cation-π interactions between the (110) crystal plane of Cu2O and rGO surface. Our findings offer a potential avenue for the discovery and design of advanced low-dimensional single-crystal materials with specific interfacial properties in a pure aqueous environment.

Corrosion behavior of ytterbium hafnate exposed to water-vapor with Al(OH)3 impurities

In this work, Yb4Hf3O12 ceramic, a typical rare-earth hafnate, was exposed to water vapor with Al(OH)3 impurities at 1400 ℃, and microstructural evolution and corrosion mechanisms were investigated. The long-term corrosion can be divided into initial hydration and gasification of Hf4+ and steady-state corrosion after the formation of Al5Yb3O12. In the initial stage, Hf4+ and the surrounding O2- tend to be hydrated and then volatilized in the form of Hf(OH)4, causing a metastable state of Yb4Hf3O12 on the surface. Besides, the preferential corrosion of small grains, grain boundary, and specific crystal plane on the surface and sintered and densified grains result in varied corrosion behavior from the early linear law to the later parabolic law. In the steady-state corrosion stage, due to the consumption of Hf4+, more vacancies promote bonding and diffusion of Al3+ to form corrosion product (Al5Yb3O12), and during this stage, regrowth and shedding of the corrosion layer reach a dynamic balance.

Influence of Formamidine Formate Doping on Performance and Stability of FAPbI3-Based Perovskite Solar Cells

Formamidine lead iodide (FAPbI3) perovskite material is very suitable for solar photovoltaic devices because of its ideal low band gap, theoretically high efficiency, and wide range of solar spectral absorption, coupled with its good thermal stability. A two-step spin coating method could control the crystallization process of formamidine lead iodide perovskite films better, resulting in more easily repeatable high-quality films. However, it is still difficult to avoid the formation of halide I-vacancy during the preparation of films, which will affect device performance and stability. In this paper, we added small molecular formamidine formate (FAHCOO) into the PbI2 precursor solution. Due to the high binding energy between HCOO− and I-vacancy, film defects caused by I-vacancies could be passivated. A molecular exchange process could be introduced in the two-step method with the addition of FAHCOO. The exchange process could delay the crystallization process in perovskite films and make them transform more fully; thus, ultimately improving the crystallization quality of the films. In addition, by adding FAHCOO to the PbI2 precursor solution, a small number of FAPbI3 can be pre-generated as templates. These templates could induce the growth of specific crystal planes of FAPbI3 in the second step reaction; thereby, improving the crystallinity of FAPbI3 films. The FAPbI3 of devices with optimized FAHCOO show a champion power conversion efficiency (PCE) of 19.04%, apparently higher than that of the controlled devices without FAHCOO (16.69%). For working stability tests under AM 1.5G illumination in an air environment, PSCs with FAHCOO showed nearly 100% of their initial efficiency after a 4100 s tracking test, while the original control device dropped to about 94%.