Lattice Reconstruction Research Articles

Lattice reconstruction for mixed-halide blue perovskite light-emitting diodes with high brightness, outstanding color stability and low efficiency roll-off

AbstractWe report a simple, effective, and universal lattice reconstruction approach to improve the quality of perovskite films by using nonpolar solvents with high Gutmann donor numbers (DNs). We find that high-DN nonpolar solvents, for instance, ethyl acetate, can interact with perovskite precursors. Such a solvent can make the perovskite lattice more ordered and “harder” and promote the formation of heterostructures with low-dimensional perovskite impurities and residual solvent molecules. As a result, the lattice-reconstructed perovskite films exhibit reduced defect densities and suppressed ion migration. The resultant mixed-halide blue perovskite light-emitting diodes (PeLEDs) show greatly enhanced tolerance to high driving current densities and voltages, demonstrating high brightness, outstanding color stability and low efficiency roll-off. Our work provides a deep understanding of the interactions between nonpolar solvents and perovskites and offers useful guidelines for further development of high-power PeLEDs.

A new rhombohedral phase and its 48 variants in β titanium alloy

A new rhombohedral phase (termed R′) in a solution−aging-treated titanium alloy (Ti−4.5Al−6.5Mo−2Cr− 2Nb−1V−1Sn−1Zr, wt.%) was identified. Its accurate Bravais lattice parameters were determined by a novel unit cell reconstruction method based on conventional selected-area electron diffraction (SAED) technique. The orientation relationship between R′ phase and BCC phase was revealed. The results show that the R′ phase is found to have 48 crystallographically equivalent variants, resulting in rather complicated SAED patterns with high-order reflections. A series of in-situ SAED patterns were taken along both low- and high-index zone axes, and all weak and strong reflections arising from the 48 variants were properly explained and directly assigned with self-consistent Miller indices, confirming the presence of the rhombohedral phase. Additionally, some criteria were also proposed for evaluating the indexed results, which together with the Bravais lattice reconstruction method shed light on the microstructure characterization of even unknown phases in other alloys.

Unconventional Lattice Reconstruction in Twisted Multilayer CrI3

Unconventional Lattice Reconstruction in Twisted Multilayer CrI3

Relaxation effects in transition metal dichalcogenide bilayer heterostructures

While moiré structures in twisted bilayer transition metal dichalcogenides (TMDCs) have been studied for over a decade, the importance of lattice relaxation effects was pointed out only in 2021 by DiAngelo and MacDonald1, who reported the emergence of a Dirac cone upon relaxation. TMDCs of group 6 transition metals MX2 (M = Mo, W, X = S, Se) share layered structures with pronounced interlayer interactions, exhibiting a direct band gap when exfoliated to a two-dimensional (2D) monolayer. As their heterolayers are incommensurable, moiré structures are present in the bilayers even if stacked without a twist angle. This study addresses the challenge of accurately modeling and understanding the structural relaxation in twisted TMDC heterobilayers. We show that the typical experimental situation of finite-size flakes stacked upon larger flakes can reliably be modeled by fully periodic commensurate models. Our findings reveal significant lattice reconstruction in TMDC heterobilayers, which strongly depend on the twist angle. We can categorize the results in two principal cases: at or near the untwisted configurations of 0° and 60°, domains with matching lattice constants form and the two constituting layers exhibit significant in-phase corrugation—their out-of-plane displacements are oriented towards the same direction in all local stackings—while at large twist angles—deviating from the 0° and 60°—the two layers show an out-of-phase corrugation. In particular, we reveal that the lattice reconstruction results from the competition between the strain energy cost and the van der Waals energy gain. Additionally, our systematical study highlights structural disparities between heterostructures composed of different or identical chalcogen atoms. Our research not only confirms the reliability of using periodic commensurate models to predict heterostructure behavior but also enriches the understanding of TMDC bilayer heterostructures.

Defect engineering and in-situ electrochemical oxidation promote lattice reconstruction of VO2 for boosting the energy storage of aqueous zinc-ion batteries

Finding a cathode with high capacity and rate performance is very important for the large-scale application of low-cost and safe aqueous zinc-ion batteries (AZIBs). In this work, VO2 containing oxygen rich vacancies (VO) was designed through fine regulation of the hydrothermal reaction, which was mainly due to the escape of crystalline water in the material. The rich oxygen vacancies in VO will adsorb water molecules in electrolyte and have redox reaction with water molecules, thus promoting the in-situ lattice reconstruction process. On the first charge of in-situ electrochemical oxidation process, VO undergoes a complete phase transition to an oxygen-deficient V2O5/V2O5·nH2O (O-VO), allowing subsequent (de)intercalation of zinc cations on the basis of the latter structure. The electrode thus has significant rate performance (376 mAh/g at 20 A/g). The energy density/power density at 20 A/g is 274 Wh kg−1/14550 W kg−1. This work provides fundamental insights into the formation of oxygen vacancies in materials, and for the first time combines defect engineering with in-situ electrochemical oxidation strategies, providing an innovative design strategy for constructing cathodes with high-rate capacity and high energy storage.

Strengthening, strain hardening and fracture of heat-treated interstitial-free steel with massive ferrite conceptualizing the interface controlled reaction phenomena

Interstitial-free steel is extremely soft and ductile with allotriomorphic ferrite in the microstructure as a diffusional transformation product of austenite. In order to alter the mechanical property, the present work performed austenitization of the steel at 925 °C for 5 min and thereafter a rapid water quenching, resulting in massive ferrite. The yield strength (86 MPa) and ultimate tensile strength (181 MPa) increased to 362 MPa and 531 MPa, respectively, along with 18 % ductility. The statistically stored dislocation density and substructures (sub-boundaries, cells) at the grain body contributed 68 % of the yield strength. The strain hardening was observed to be lower than that with allotriomorphic ferrite, due to heterogeneous deformation of the substructures, causing an inhomogeneous distribution of geometrically necessary dislocation density at the bulk. The preferential localization of strain at cell walls initiates cracks by the de-cohesion of massive grains. The cell-substructure conceived by massive ferrite therefore has a strong role both in strain hardening and fracture. The larger the grain size is, the more the cell-substructure is, dictated by an interface-controlled growth of austenite to massive ferrite. The atomic jump at the transformation interface is usually considered to be an equilibrium process; meaning slow, not standing with the so-called faster growth kinetics of an interface-controlled reaction. In order to bridge the gap, the present work demonstrates a slip deformation at the transformation interfaces for fast-tracking the lattice reconstruction of massive ferrite from austenite, a novel.

Enhanced corrosion protection of rebars in alkaline solutions by ferroporphyrin and the mechanisms of electron consumption and lattice reconstruction

Abstract Reinforced concretes are the primary materials in coastal and offshore engineering. In alkaline environment of concrete, the anodic process is passivation of rebars and the conjugated cathodic process is oxygen reduction reaction (ORR). It is proposed that a novel approach to enhance the passivation films through catalyzed ORR by iron meso-tetra(4-carboxyphenyl)porphine (FeTCPP). The ORR catalyst FeTCPP promotes the formation of passivation film, as it accelerates the consumption of abundant electrons generated and accumulated by the anodic formation of passivation films. The passivation films of rebars are highly defective Fe3O4 semiconductor. The dissolution of interstitial ferrous ions and lattice iron ions produces defects of O ion vacancies, Fe ion vacancies and interstitial Fe ions, and they further cause the formation and accumulation of Fe atom vacancies on the metal surface, leading to the collapse of the passivation films. The FeTCPP adsorbs on the surface of passivation films, hindering the dissolution of lattice iron ions and interstitial ferrous ions, thereby inhibiting the generation and accumulation of Fe atom vacancies and improving the integrity and protective ability of the passivation films.

Molecular dynamics simulations into rolling scraping of nickel-copper bilayer film

In order to investigate the nanoscale friction mechanism and deformation behavior of nickel-copper bilayer film under rolling scraping, the effects of different factors during friction process such as the translation velocity, rotation velocity, radius of abrasive grain, contact depth, texture direction and crystallographic orientation are analyzed through molecular dynamics methods in terms of contact force, atomic lattice structure, internal substrate dislocation, kinetic energy and temperature. Results show that the contact force increases with the increase of the translation velocity or the decrease of the rotation velocity. Abrasive grains in a purely rolling state cause the most serious damage to the substrate. The contact force increases with the increase of contact depth or the decrease of abrasive grain radius. The crystallographic orientation has a significant effect on rolling scraping process and there is a crystallographic orientation with the minimum contact force. The degrees of substrate dislocation and the numbers of lattice reconstruction atoms under different factors and levels vary widely.

Multimodal learning of heat capacity based on transformers and crystallography pretraining

Thermal properties of materials are essential to many applications of thermal electronic devices. Density functional theory (DFT) has shown capability in obtaining an accurate calculation. However, the expensive computational cost limits the application of the DFT method for high-throughput screening of materials. Recently, machine learning models, especially graph neural networks (GNNs), have demonstrated high accuracy in many material properties’ prediction, such as bandgap and formation energy, but fail to accurately predict heat capacity(CV) due to the limitation in capturing crystallographic features. In our study, we have implemented the material informatics transformer (MatInFormer) framework, which has been pretrained on lattice reconstruction tasks. This approach has shown proficiency in capturing essential crystallographic features. By concatenating these features with human-designed descriptors, we achieved a mean absolute error of 4.893 and 4.505 J/(mol K) in our predictions. Our findings underscore the efficacy of the MatInFormer framework in leveraging crystallography, augmented with additional information processing capabilities.

Macroscopic low-friction via twinning assisted lattice reconstruction in magnesium

One-fourth of the global energy losses are spent to overcome friction, making it particularly important to reduce and minimize friction between contacting materials. Hexagonal close-packed (HCP) metals are an important class of structural materials. It has not been possible to reduce their friction, primarily because of friction-induced dislocation slip and twinning. Here, we find particularly low friction when sliding perpendicular to the a-axis on the basal plane in HCP Mg single crystals. This is in contrast to the common belief that friction is small along the preferred dislocation slip direction (a-axis). This macroscopic low-friction stems from twinning assisted lattice reconstruction sharing a common rotation axis, confirmed by atomistic simulations and strain energy analysis. While sliding along the a-axis and other directions, 〈c + a〉 dislocation activity accounts for high frictional resistance. By unambiguously decoupling the contributions of dislocation slip and twinning, this discovery reveals potential opportunities in mitigating the energy dissipation at tribological interfaces of HCP metals, e.g. through crystallographic texture design.

A Real Space Moiré Inversion Technique and Its Practical Applications in Real Space for Lattice Reconstruction

Distinct physical properties emerge at the nanoscale in Moiré materials, such as bilayer graphene and layered material superposition. This study explores similar structural features within a second-generation nickel-based superalloy, unveiling potential formation mechanisms. Introducing the real space Moiré inversion method (RSMIM) for nanoscale imaging, combined with the transmission electron microscopy (TEM) nano-Moiré inversion method, we reveal spatial angles between specimen and reference lattices in 3D. Simultaneously, we reconstruct the Moiré pattern region to deepen us understand the phenomenon of Moiré formation. Focused on face-centered cubic structures, the research identifies six spatial angles, shedding light on Moiré patterns in the superalloy. The RSMIM not only enhances understanding but also expands 3D structure measurement capabilities. The RSMIM served to validate TEM nano-Moiré inversion results, ascertaining the spatial relative angle between lattices, and establishing a theoretical simulation model for Moiré patterns. This study marks a substantial step toward designing high-performance nanomaterials by uncovering dynamic Moiré variations.

Dual-site segmentally synergistic catalysis mechanism: boosting CoFeSx nanocluster for sustainable water oxidation

Efficient oxygen evolution reaction electrocatalysts are essential for sustainable clean energy conversion. However, catalytic materials followed the conventional adsorbate evolution mechanism (AEM) with the inherent scaling relationship between key oxygen intermediates *OOH and *OH, or the lattice-oxygen-mediated mechanism (LOM) with the possible lattice oxygen migration and structural reconstruction, which are not favorable to the balance between high activity and stability. Herein, we propose an unconventional Co-Fe dual-site segmentally synergistic mechanism (DSSM) for single-domain ferromagnetic catalyst CoFeSx nanoclusters on carbon nanotubes (CNT) (CFS-ACs/CNT), which can effectively break the scaling relationship without sacrificing stability. Co3+ (L.S, t2g6eg0) supplies the strongest OH* adsorption energy, while Fe3+ (M.S, t2g4eg1) exposes strong O* adsorption. These dual-sites synergistically produce of Co-O-O-Fe intermediates, thereby accelerating the release of triplet-state oxygen ( ↑ O = O ↑ ). As predicted, the prepared CFS-ACs/CNT catalyst exhibits less overpotential than that of commercial IrO2, as well as approximately 633 h of stability without significant potential loss.

Raman spectroscopy of doubly aligned bilayer graphene

Graphene aligned with hexagonal boron nitride (hBN) undergoes significant structural reconstruction due to the formation of a moiré superlattice. Here, we look at the effect of such structural reconstruction on the Raman spectroscopy of bilayer graphene for both singly aligned and doubly aligned heterostructures. The G peak is found to be particularly sensitive to the hBN alignment as it broadens in doubly aligned bilayer graphene compared to that of singly aligned bilayer graphene. This broadening is attributed to the variation in the phonon frequency as a result of the lattice reconstruction of the bilayer graphene responding to the periodic potential exerted by hBNs on either side of the bilayer graphene. In addition, the position of the G-peak and 2D peak follows a slope of 2.2, which implies the formation of strain in the bilayer graphene, validating the argument of lattice reconstruction.

Impact of Polarity Mismatch in Infinite-Layer Nickelates.

The recent discovery of superconductivity in infinite-layer Sr-doped NdNiO2 grown on SrTiO3(001) provides a new platform to explore the conducting mechanism of unconventional superconductors. However, the electronic structure of infinite-layer nickelates remains controversial. In this paper, we systematically compare the structural and electronic properties of NdNiO2 films grown on SrTiO3 and LaAlO3 substrates using first-principles calculations. Our results show that the lattice reconstruction accompanied by electronic reconstruction occurs in nickelate films on both substrates. Although both heterostructures (HSs) are conducting at the interface, the SrTiO3-based HS shows distinct atomic displacement in the interfacial TiO2 layer and significant electron accumulation deep into three SrTiO3 layers below the interface, while the LaAlO3-based HS shows negligible atomic displacement and electron localization in the interfacial AlO2 layer, reflecting the impact of polarity mismatch on the electronic structure. Further, Wannier function calculations reveal that the interface stress has no obvious effect on the splitting energy and hopping integral between Ni 3d and Nd-layer orbitals. Although the hybridization between Ni 3dx2-y2 and Nd 5d orbitals is tiny, the hybridization between the Ni 3dx2-y2 orbital and an itinerant interstitial s (IIS) orbital is significantly strong in both cases, suggesting that the IIS orbital may play a critical role in the superconductivity of nickelates.

Room temperature circularly polarized emission in perovskite nanocrystals through bichiral-molecule-induced lattice reconstruction

Room temperature circularly polarized emission in perovskite nanocrystals through bichiral-molecule-induced lattice reconstruction

Strong and tunable anisotropy in monolayer graphene with broken symmetry

Low-symmetry two-dimensional materials have attracted much attention in recent years due to their exotic and incredible properties. Here, we construct Ta2NiS5-based van der Waals heterostructures to introduce in-plane polarization in monolayer graphene through symmetry engineering. Angle-dependent conductance and mobility measurement combined with theoretical calculations all verify that the pristine Ta2NiS5 possesses prominent electrical anisotropy, with anisotropic ratio (a-axis/c-axis) of about 2.1 in conductivity and 3.28 in mobility. Furthermore, we demonstrate that van der Waals interlayer coupling has induced explicit in-plane polarization in monolayer graphene according to angle-dependent Raman spectroscopy and electrical transport measurement on monolayer-graphene/Ta2NiS5 heterostructures. In polarized graphene, the conductivity and mobility ratios are up to 3.21 and 4.84, respectively. The induced polarization in monolayer graphene within heterostructures probably originates from strain, lattice reconstruction, induced symmetry reduction and charge transfer through van der Waals interfaces. These results might provide inspiration to study symmetry-related van der Waals heterostructures and pave their way to novel nano-electronic devices.

Crossover between rigid and reconstructed moiré lattice in h-BN-encapsulated twisted bilayer WSe2 with different twist angles.

A moiré lattice in a twisted-bilayer transition metal dichalcogenide (tBL-TMD) exhibits a complex atomic reconstruction effect when its twist angle is less than a few degrees. The influence of the atomic reconstruction on material properties of the tBL-TMD has been of particular interest. In this study, we performed scanning transmission electron microscopy (STEM) imaging of a moiré lattice in h-BN-encapsulated twisted bilayer WSe2 with various twist angles. Atomic-resolution imaging of the moiré lattice revealed a reconstructed moiré lattice below a crossover twist angle of ∼4° and a rigid moiré lattice above this angle. Our findings indicate that h-BN encapsulation has a considerable influence on lattice reconstruction, as the crossover twist angle was larger in h-BN-encapsulated devices compared to non-encapsulated devices. We believe that this difference is due to the improved flatness and uniformity of the twisted bilayers with h-BN encapsulation. Our results provide a foundation for a deeper understanding of the lattice reconstruction in twisted TMD materials with h-BN encapsulation.

Nonlinear Optical Response Modulated by Lattice Reconstruction in Small‐Angle Twisted Bilayer MoS2

AbstractSubtle perturbations in interlayer twist angles offer a novel investigational avenue for revealing intriguing optical characteristics within the domain of 2D materials. In this study, a homogeneous bilayer structure featuring precisely defined interlayer twist angles is meticulously engineered by stacking monolayer single‐crystal MoS2 in a controlled, layer‐by‐layer manner. Scanning tunneling microscopy (STM) reveals an unexpected lattice reconstruction, particularly at twist angles of ≤ 2°, which induces the emergence of expansive rhombohedral‐stacked large triangular domains. Furthermore, a second‐harmonic generation (SHG) is utilized as a sensitive modality to demonstrate profound transformations in the local electron band structures. By combining the linear spectra with SHG, the change in the C‐exciton optical response in the band‐nesting region of the small‐angle twisted bilayer MoS2 before and after crossing a critical twist angle of 2° is discussed. The study shows that SHG can be used as a nondestructive method to characterize the lattice structure of small‐angle twisted bilayer samples. Furthermore, determining the potential relationship between the lattice reconstruction and the linear and nonlinear spectra further demonstrates the regulatory effect of the interlayer twist angle on the nonlinear optical effects of 2D materials.

Axial and bending very high cycle fatigue of completion string

Preventing or mitigating very high cycle fatigue (VHCF) damage and failure of completion string is essential for ensuring their long-term stable operation. Therefore, a comprehensive understanding of the string's fatigue performance in tension, compression, and bending over an extended service life is necessary. This study investigated the evolution, microscopic mechanisms, fracture behavior, and life prediction of VHCF damage in completion string under axial and bending conditions. It was found that the intragranular twin structures on the critical interface of VHCF source directly participate in lattice reconstruction, enhancing the grain's strain coordination ability, and increasing the proportion of facet area on the fatigue fracture surface. Based on the fracture characteristics of VHCF, the Mayer empirical formula was improved, and a novel convolutional neural network (CNN) based VHCF life prediction model was proposed. Utilizing the CNN's powerful fracture feature extraction and nonlinear modeling capabilities, the VHCF fatigue life prediction accuracy was significantly enhanced, with prediction errors all within 2 times the experimental results' error range. Based on the axial and bending VHCF fracture mechanisms of completion string and CNN, a more advanced method for predicting axial and bending VHCF life is provided, offering theoretical supports for the engineering safety service and life assessment of completion string.

Magnetic field induced transitions probed in CrOCl flakes using dynamic cantilever magnetometry

H −T phase diagrams for chromium oxide chloride (CrOCl) are usually obtained using data from the measurements of magnetization and specific heats. Recent works suggest that magnetic anisotropy exists in CrOCl. In this work, we use dynamic cantilever magnetometry, which is sensitive to both magnetization and magnetic anisotropy, to probe phase transitions in CrOCl flakes. Together with magnetization measurements from a Superconducting Quantum Interference Device, four major regions of the CrOCl H−T phase diagram along its c-axis are obtained, which is consistent with the previously reported works. Then, we studied magnetic field induced transitions in CrOCl flakes under four different temperatures. Several transitions in antiferromagnetic state and in incommensurate state, which have not been reported before, were recognized. We believe these transitions probably originate from magnetic anisotropy due to magnetoelastic coupling and lattice reconstruction in CrOCl. Our work provides intriguing experimental results on the intricate magnetic structure of CrOCl, making progress in understanding the rich magnetic states of CrOCl.