Lattice Dislocations Research Articles

Breakdown of Volterra's Elasticity Theory of Dislocations in Polar Skyrmion Lattices.

Emerging polar skyrmion crystals (SkX) have raised much interest for technological applications owing to their nontrivial topologies of electric dipoles, quasiparticle-like behaviors, and unique electrical responses. Understanding SkX defects, especially dislocations, is crucial for their unique lattice dynamics and responses; however, it still remains elusive. Here, we have not only demonstrated that a SkX dislocation exhibits an anomalously deformed core structure with over 50% elongation of skyrmions but also discovered that Volterra's elasticity theory of dislocation is broken down in SkX. Our phase-field simulation reveals that these distinct features of SkX dislocation arise from a rigid to soft quasiparticle transition of skyrmions depending on the electric field and temperature. In SkX, there exist inherent mechanics that mitigate the mismatch by both migration and deformation of skyrmions. This work provides novel insights into a new class of lattice mechanics and related functionality arising from the unique properties of quasi-particle SkX.

Growth of nanocrystalline graphite and vertically aligned graphite nanowalls thin films and their transfer on flexible substrates for applications as electrochemical sensors for anthracene detection

Plasma-enhanced chemical vapor deposition (PECVD) allows the growth of nanocrystalline graphite (NCG)-type materials, such as N-doped bulk NCG and graphite nanowalls (GNW), on different substrates (silicon and copper) to develop flexible electrochemical sensors for anthracene detection. The carbonic materials were investigated using different techniques, including X-ray diffraction, small-angle X-ray scattering, scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential pulsed voltammetry (DPV). XRD analysis revealed different crystallinity features for both graphitic materials, as the N-NCG film presented higher lattice strain (1 %) and dislocation density (5.2 × 1012 cm−2), compared to the GNW film with a lattice strain of 0.2 % and dislocation density of 7 × 1011 cm−2. We also present a successful approach for developing flexible electrodes via transfer process from Cu to polyethylene (PE) substrate. The carbonic films were transferred onto flexible substrates via thermal treatment of the Cu foils with the PE layers, followed by Cu etching to reveal the carbon material as the sensing area of the flexible sensors. Electrodes based on N-NCG and GNW grown on silicon and those transferred to PE substrates were investigated at different anthracene concentrations by DPV. The results showed greater performance for anthracene determination in the case of N-NCG/Si, showing a sensibility of 0.8 A⋅M−1 than that of GNW/Si (0.0625 A⋅M−1). However, the flexible GNW/PE electrode exhibited an increased response in DPV in the presence of anthracene, resulting in a higher sensitivity (0.23 A⋅M−1) than that of N-NCG/PE (0.19 A⋅M−1). This behavior suggests the good electrochemical compatibility of the GNW film with the flexible polymeric substrate to obtain a flexible electrochemical sensor for anthracene detection.

In-depth approach and establishment from a structural perspective of LiFePO4 cathodes for lithium-ion batteries by a two-step sintering

Most synthesis of olivine LiFePO4 (LFP) studies have emphasized the importance of a two-step sintering process for the formation of a uniform carbon coating. However, in this study, it is found that, as an advantage of the two-step sintering process, stable carbonization not only improves lithium-ion conductivity by forming a coating layer but also increases the uniformity of the internal crystal structure. In addition to basic crystallinity and structure analysis using X-ray diffraction (XRD), in-depth calculations are performed to explain the formation mechanism of crystal structure according to the two-step sintering process and the temperature of the first sintering step. In particular, lattice defects and structural uniformity are closely investigated from the crystal structure perspective by comparing lattice micro-strain and dislocation density. Improvement in lithium-ion conductivity from structural uniformity is also demonstrated through cyclic voltammetry (CV) analysis. As a result, it is confirmed that LFP, which undergoes a high-temperature two-step sintering, has high capacity and excellent cycle retention at high rates. Furthermore, ex-situ XRD analysis demonstrates the performance difference according to lithium-ion mobility by comparing the LiFePO4/FePO4 two-phase transformation reaction of two-step sintered LFP and the plateau stability during charging.

Structure, microstructure, and ESR properties of concentration-dependent Zn1-xMnxO nanoparticles

In this study, the estimated stress, strain, and crystallite sizes of different Mn-doped ZnO nanoparticles were calculated using the Williamson-Hall method and compared with the values obtained from the Debye-Scherrer formula. Moreover, defects, and magnetic properties of Mn-doped ZnO nanoparticles at different concentrations were investigated. The sol-gel method was used to synthesize nanoparticles. The X-ray diffraction and Rietveld analysis results confirm that the desired structure is formed and that no secondary phase is present up to an Mn concentration of x=0.2. In and out of plane lattice parameters, cell volumes, bond length, atomic locality, and dislocation density (δ) were clarified. The grain size of the concentration-dependent samples was provided by scanning electron microscope. Photoluminescence (PL) spectra exhibited ultraviolet emission along with a broad band encompassing violet, blue, and red regions, attributed to defect-related and excitonic emissions. These emissions were notably influenced by synthesis conditions and doping elements and ratios. Electron spin resonance properties of the concentration-dependent samples were analyzed to figure out the g-factor through line widths of pike-to-pike (ΔHPP) of ESR spectra. Mn-doped ZnO nanoparticles exhibited ferromagnetism at room temperature.

Study of the structural and optical properties of pure copper oxide and doped with zinc at fixed weight percentages

Through this research, the effect of doping with zinc ions on the structural and optical properties of copper oxide particles doped with zinc at certain weight percentages was study using Radiofrequency plasma deposition technology. X-ray diffraction (XRD) analyses and field emission scanning electron microscopy were used to ascertain the materials' characteristics. Ultraviolet and visible spectroscopy of pure and doped thin films was also perform to calculate the band gap and electrical conductivity It was discovered using the XRD readings that the pure copper particles saturated with zinc had a crystalline size. It changes as Zn concentration rises and is influenced by the CuO lattice's strain and dislocation density. The thin film samples have structures resembling irregular and cubic grains, as demonstrated by the FE-SEM pictures. After doping with Zn, their homogeneity increases and adopts a regular granular nature. The band gap was also calculated for pure CuO particles as well as those doped with certain percentages of Zn. It was note that the addition of Zn worked to reduce Band gap for CuO

Electric current-induced directional slip of dislocation and grain boundary ordering

The evolution of lattice dislocations in metals can be induced by electric current. However, the effect of electric current on the interaction between lattice dislocations and grain boundaries (GBs) remains unclear. Herein, we investigate the evolution of lattice dislocations and grain boundary dislocations (GBDs) induced by electric current in M50 steel via in-situ TEM characterization, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations. Our findings reveal that electric current induces the directional slip of lattice dislocations towards GBs, while the reduction of GB contrast is attributed to the decomposition and reorganization of GBDs. DFT calculations demonstrate that electric current enhances the force on atoms in defect regions. These in-situ TEM observations are well reproduced by MD simulations incorporating electric current, which include a virtual temperature rise at defect regions to reflect the electric current force on defect atoms. Based on these observations, we propose a novel GB accommodation model under electric current. These results provide valuable insights into the mechanisms by which electric current tailors lattice dislocation behavior and enhances GBDs ordering in metallic materials.

Atomistic insight into laser shock peening response of α-titanium: an experimentally verified simulation study

Laser shock peening (LSP) can induce severe plastic deformation in the surface zone of metallic materials, which potentially enhances their mechanical properties. Although it is widely recognized that the improvement of mechanical properties can be attributed to microstructure evolution, the microstructural characteristics and response under different LSP parameters are complex, leading to distinct mechanical behaviors of materials at the macroscale. Besides, the exceedingly brief duration of LSP also poses considerable challenges to capture the microstructure evolution within the surface layer of materials. Therefore, to grasp a first in-situ atomistic insight into LSP response of α-titanium, molecular dynamics method is applied to simulate laser incidence at the [101¯0] crystallographic orientation with various energy densities. The results show that the lattice reorientation and dislocation slip dominate the plastic deformation at low laser energy density, while stacking faults and crystal disordering are the primary microstructural features at high laser energy density. The above shock-induced microstructures are verified by transmission electron microscopy (TEM) observations. Further, varied microscale plastic deformation modes under varying shock energies are proposed based on Schmid factors and energy barriers. The findings bridge laser energy to post-processing microstructure of α-titanium, which paves the way for improving mechanical properties of materials by optimizing LSP treatment parameters.

Reconstruction and Solidification of Dion-Jacobson Perovskite Top and Buried Interfaces for Efficient and Stable Solar Cells.

Quasi-two-dimensional (Q-2D) perovskites show great potential in the field of photonic and optoelectronic device applications. However, defects and local lattice dislocation still limit performance and stability improvement by nonradiative recombination, unpreferred phase distribution, and unbonded amines. Here, a low-temperature synergistic strategy for both reconstructing and solidifying the perovskite top and buried interface is developed. By post-treating the 1,4-phenylenedimethanammonium (PDMA) based (PDMA)MA4Pb5I16 films with cesium acetate (CsAc) before thermal annealing, a condensation reaction between R-COO- and -NH2 and ion exchange between Cs+ and MA+ occur. It converts the unbonded amines to amides and passivates uncoordinated Pb2+. Meanwhile, it adjusts film composition and improves the phase distribution without changing the out-of-plane grain orientation. Consequently, performance of 18.1% and much-enhanced stability (e.g., stability for photo-oxygen increased over 10 times, light-thermal for T90 over 4 times, and reverse bias over 3 times) of (PDMA)MA4Pb5I16 perovskite solar cells are demonstrated.

Size-strain distribution analysis from XRD peak profile of (Mg, Fe) co-doped SnO2 nanoparticles fabricated using chemical co-precipitation route

In this study, we synthesize pristine and (Mg, Fe) co-doped SnO2 nanoparticles using the chemical co-precipitation method, where the Mg doping amount is fixed (2 mol%) and the amount of Fe is varied between 2 and 6 mol%. The narrow and sharp natures of intense XRD peaks notify that the crystallinity is pretty well. The formation of the single-phase tetragonal rutile type structure of all prepared compounds has been identified by Rietveld refinement, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. Moreover, the well incorporation of Fe and Mg in SnO2 and absence of any other unexpected elements are confirmed by the energy dispersive X-ray spectroscopy. How the co-doping of Mg and Fe alter the crystallite size, microstrain, and dislocation density of the prepared samples have been investigated by Scherrer method with various modified version of it, Williamson-Hall method (W–H) in three factions (UDM, USDM, and UDEDM), Size strain plot (SSP) method, Halder-Wagner (H–W) method, Wagner-Aqua (W-A) method, and Warren-Averbach (WA) method. The obtained crystallite size using the WA method is smaller than the other methods and Scherrer-based methods show much comparable (except SLMSE) sizes. Additionally, the W–H, H–W, SSP, and W-A plots show almost similar tendency of decreasing crystal size, increasing dislocation density and lattice strain with increasing doping. The scanning electron microscopy (SEM) profiles revealed that the synthesized nanoparticles are agglomerated in nature, where the agglomeration increases with decreasing crystal size. The magnetic response of the prepared samples revealed a weak ferromagnetic (or soft magnetic) nature, where saturation magnetization increased due to doping, and a reducing trend of remanent magnetization and coercivity was explored which indicates the phase transition from ferromagnetic to paramagnetic. However, this soft magnetic nature was modified with the influence of defects like changes in lattice parameters, strain, and oxygen vacancy. This phase transition at higher doping concentration makes our nanomaterial as a suitable contender for memory devices, hyperthermia treatment, and photothermal effect.

Molecular Dynamics Study on Wear Resistance of High Entropy Alloy Coatings Considering the Effect of Temperature.

High entropy alloys have excellent wear resistance, so they have great application prospects in the fields of wear resistance and surface protection. In this study, the wear resistance of the FeNiCrCoCu high entropy alloy coating was systematically analyzed by the molecular dynamics method. FeNiCrCoCu high entropy alloy was used as a coating material to adhere to the surface of a Cu matrix. The friction and nanoindentation simulation of this coating material were carried out by controlling the ambient temperature. The influence of temperature on its friction properties was analyzed on five aspects: lattice structure, dislocation evolution, friction coefficient, hardness, and elastic modulus. The results show that with the increase of temperature, the disorder of the lattice structure increases, which leads to an increase of the tangential force and friction coefficient in the friction process. At 300 K and 600 K, the ordered lattice structure of the high entropy alloy coating material is basically the same, and thus its hardness is basically the same. However, the dislocation density at 600 K is significantly reduced compared with that at 300 K, resulting in an increase of the elastic modulus of the material from 173 GPa to 219 GPa. At temperatures of 900 K and 1200 K, lattice disorder takes place rapidly, and dislocation density also decreases significantly, resulting in a significant decrease in the hardness and elastic modulus of the material. When the temperature reaches 900 K, the wear resistance of the FeNiCrCoCu high entropy alloy coating decreases sharply. This work is of great value in the analysis of wear resistance of high entropy alloys at high temperature.

Unravelling dynamic recrystallisation in a microalloyed steel during rapid high temperature deformation using synchrotron X-rays

Microstructure evolution during high-strain rate and high-temperature thermo-mechanical processing of a 44MnSiV6 microalloyed steel is investigated using in situ synchrotron high-energy powder X-ray diffraction. The conditions selected replicate a newly developed near solidus high-strain rate process designed for reducing raw material use during the hot processing of steels. High temperatures (exceeding 1300 °C) and high strain rate ε˙ = 9 s-1 processing regimes are explored. The lattice strains and dislocation activity estimated from diffraction observations reveal that the microstructure evolution is primarily driven by dynamic recrystallisation. A steady-state stress regime is observed during deformation, which develops due to intermittent and competing work hardening and recovery processes. The texture evolution during the heating, tension, shear deformation and cooling stages is systematically investigated. The direct observation of phase evolution at high-temperature and high-strain rate deformation enables a comprehensive understanding of new manufacturing processes and provides deep insights for the development of constitutive models for face-centred cubic alloys.

Deciphering ore-forming fluid evolution processes of the Yuerya gold deposit, eastern Hebei, China: Insights from pyrite texture, trace element and sulfur isotope compositions

The Yuerya gold deposit, a representative gold deposit associated with Mesozoic granites in the eastern Hebei region, is located in the eastern Hebei-western Liaoning gold ore-concentrated area, the northern margin of the North China Plate. The orebody is mainly preserved in the Yanshanian granite and its contact zone with the carbonate rocks of the Gaoyuzhuang Formation, and the main ore mineral is pyrite. Based on the pyrite texture, geochemical characteristics of the in-situ trace element analysis, and sulfur isotope, the pyrite in the mining area is classified into five generations (Py1, Py2, Py3, Py4a, and Py4b). Five generations of pyrite all have an average Te/Se ratio > 1, and their average Co/Ni ratios are 1087.27, 43.97, 4.17, 12.62, and 4.99, respectively, indicating that the ore-forming fluid predominantly originates from magmatic-hydrothermal. In-situ sulfur isotopic analysis using LA–MC–ICP–MS shows that the δ34S values of the five generations of pyrites ranged from 0.3 ‰ to 9.6 ‰; the mean values are 3.8 ‰ (Py1, n = 4), 4.2 ‰ (Py2, n = 10), 2.6 ‰ (Py3, n = 18), 4.0 ‰ (Py4a, n = 20) and 4.6 ‰ (Py4b, n = 29), respectively. Approximately 32 % of the results exceed 5.0 ‰, surpassing the values indicative of a magmatic-hydrothermal source. Thermodynamic simulations reveal that the fluctuations in the oxidation state of the ore-forming fluid is not the predominant cause of δ34S enrichment in the pyrite. Our studies suggest that sulfur is primarily derived from mantle-crust mixtures, with some contributions from the wallrock of the Gaoyuzhuang Formation. The results from LA–ICP–MS trace element analysis of pyrites reveal a significant enrichment of As-Bi-Te-Tl alongside Au in the ore-forming fluid. Additionally, the results of ore-forming elements in three typical cross sections of different wallrocks in the mining area also show that Au, Ag, As, and Pb are closely related. Therefore, it is considered that the over-enrichment of As could be an important factor leading to the precipitation of Au. Pyrite undergoes expansion of the mineral lattice parameters or lattice dislocation due to the substitution of S with As, creating space for the growth of solid-solution Au. Subsequently, some of the solid-solution Au within pyrite is liberated through internal oscillations, forming the visible gold particles.

CsPbBr3 NCs Confined and In Situ Grown in ZIF-8: A Stable, Sensitive, Reliable Fluorescent Sensor for Evaluating the Acid Value of Edible Oils.

Rapidly and sensitively evaluating the acid value (AV) of edible oils is significant to ensuring food quality and safety. Cesium lead bromide perovskite nanocrystals (CsPbBr3 NCs) are an effective candidate for AV detection; however, their instability restricts wide applications. Herein, CsPbBr3@ZIF-8 was prepared by confining and growing CsPbBr3 NCs in situ into zeolitic imidazolate framework-8 (ZIF-8) to improve the stability, and a fluorescence sensor was established to evaluate the AV of edible oils. The results present that CsPbBr3 NCs (below 5 nm) with excellent optical properties were confined and grown in situ in micropores and mesopores of ZIF-8. Meanwhile, CsPbBr3@ZIF-8 had better long-term storage, ultraviolet-irradiation, and water-exposure stabilities, compared with CsPbBr3 NCs. Given the fact that free fatty acids (the major contributor of AV) decrease the fluorescence of CsPbBr3 NCs, the fluorescence intensities of CsPbBr3@ZIF-8 were negative-linearly related to oil AV (R2 = 0.9902) in 0.04-6.00 mg of KOH/g with a 0.06 mg of KOH/g limit of detection. Besides, the practical AV recovery was 92-101% with an average relative standard deviation of 2%. Furthermore, the detection time was 20 min. The response mechanism revealed that free fatty acids could remove surface ligands and increase surface defects to prompt the aggregation of CsPbBr3 NCs and the formation of lattice fringe dislocations, inducing a decrease in the fluorescence. Thus, a stable, sensitive, reliable sensor was established to evaluate the AV of edible oils.

Synthesis of Zn0.87(Fe, Al)0.065O – MO (MO = NiO, Fe2O3, CuO, and CoO) nanocomposites: Structural, vibrational, optical and antibacterial studies

One of the most effective strategies for achieving high-performance antibacterial activity is the synthesis of nanocomposites by combining different nanoparticles. Hence, Zn0.87(Fe, Al)0.065O – MO (NiO, Fe2O3, CuO and CoO) nanocomposites (NCs) with a 7:3 molar ratio were synthesized via the solution combustion method. The produced NCs structural, vibrational, and optical characteristics were investigated using XRD, FTIR, UV–Vis, and PL spectroscopies. The standard disc diffusion method was used to evaluate the antibacterial efficacy of the NCs. The lattice constant, crystallite size, bond length, dislocation density, and other relevant parameters of the NCs were also evaluated. XRD analysis revealed a well-defined mixed-phase structure for all 0.7Zn0.87(Fe, Al)0.065O – 0.3NiO (ZFA-Ni), 0.7Zn0.87(Fe, Al)0.065O – 0.3Fe2O3 (ZFA-Fe), 0.7Zn0.87(Fe, Al)0.065O – 0.3CuO (ZFA-Cu) and 0.7Zn0.87(Fe, Al)0.065O – 0.3CoO (ZFA-Co) NCs, indicating successful mixing of each metal oxide with the ZnO matrix. The average crystallite size within the NCs ranged from 14.21 to 18.10 nm, suggesting a degree of nanocrystallinity nature of all NCs. FTIR confirmed the presence of characteristic functional groups within the NCs. Moreover, all the synthesized NCs exhibited significant optical activation in the ultraviolet radiation range but visible light absorption was also observed when the composite formed with CuO and Fe2O3 nanoparticles. The band gap energy values exhibited variation between 2.72 eV for ZFA-Co NC and 2.90 eV for ZFA-Ni NC. Photoluminescence (PL) emission in the composite formation of ZnO NPs with other metal oxide were significantly influenced by the absorption range of the composite with pn-junction formation in a notable enhancement of antibacterial efficacy against bacterial strains of Escherichia coli and Staphylococcus aureus. Particularly, ZFA-Co NC exhibited an excellent antibacterial performance against both bacterial strains.

Misorientation increase of small-angle grain boundaries during directional solidification of silicon

In situ observation of the solidification process of Si combined with ex situ characterization revealed that small-angle grain boundaries (SAGBs) increase misorientation through two paths. First, coalescence with other SAGBs leads to a boost in misorientation and SAGBs tend to coalesce during solidification. Second, the absorption of individual lattice dislocations also increases the misorientation of an SAGB. Three possible mechanisms behind dislocation absorption by SAGBs have been proposed and are discussed in this paper. Among these mechanisms, the incorporation of same-sign lattice dislocations is regarded as the prominent mechanism when misorientation increases during solidification.

Simulated TEM imaging of a heavily irradiated metal

We recast the Howie–Whelan equations for generating simulated transmission electron microscope (TEM) images, replacing the dependence on local atomic displacements with atomic positions only. This allows rapid computation of simulated TEM images for arbitrarily complex atomistic configurations of lattice defects and dislocations in the dynamical two beam approximation directly from standard atomistic simulation output files. Large-scale massively-overlapping cascade simulations, performed with molecular dynamics, are used to generate representative high-dose nanoscale defect and dislocation microstructures in tungsten at room temperature. We then compare the simulated TEM images to experimental TEM images with similar irradiation and imaging conditions. The simulated TEM shows ‘white-dot’ damage in weak-beam dark-field imaging conditions, in agreement with our experimental observations and as expected from previous studies, and in bright-field conditions a dislocation network is observed. In this work we also compare the simulated images to the nanoscale lattice defects in the original atomic structures, and find that at high dose the white spots are not only created by small dislocation loops, but rather arise from nanoscale fluctuations in strains around curved sections of dislocation lines.

Single–crystalline LiNi0.8Co0.1Mn0.1O2 stabilized by F–doping–induced superlattice for 4.8 V lithium–ion batteries

Single–crystalline Ni–rich ternary layered oxides represent the cutting–edge cathode materials for lithium–ion batteries, offering enhanced cycling stability compared to the polycrystalline counterparts by eliminating grain boundaries. However, their structural stability encounters a significant challenge when operated under high voltages (cut–off charging potential ≥ 4.6 V). Excessive extraction of Li+ ions can lead to the localized collapse of transition metal (TM) slabs and accumulation of lattice dislocations, which hinders Li+ diffusion and eventually cause capacity decay. This study demonstrate that the introduction of F dopants triggers an ordered mixing of Li+ and Ni2+ ions to form a superlattice in single–crystalline LiNi0.8Co0.1Mn0.1O2. This unique F–doping–induced superlattice stabilizes the deintercalated structure through Ni2+ (Li layer)–O2––Ni2+ (TM layer) interlayer super–exchange strong interactions, thereby facilitating the reversible H2–H3 phase transformation during cycling. Consequently, when cycled between 2.8–4.8 V at 1C, the F doped single–crystalline LiNi0.8Co0.1Mn0.1O2 exhibits unprecedented cycling stability, retaining 90.3 % of its initial capacity after 200 cycles, while achieving a high discharge capacity of 186.8 mAh/g and an impressive energy density of 706.5 Wh/kg. This work sheds light on the microstructural engineering for Ni–rich layered cathode materials.

Construction of Ferric-Oxide-Doped Nickel-Iron Hydroxide Electrocatalysts by Magnetic-Field-Assisted Chemical Corrosion toward Boosted Oxygen Evolution Reaction.

Transition-metal-based oxygen evolution reaction (OER) catalysts have attracted widespread attention due to their inexpensive prices, unique layered structures, and rich active sites. Currently, designing low-cost, sustainable, and simple synthesis methods is essential for the application of transition-metal-based catalysts. Here, magnetic field (MF)-assisted chemical corrosion, as a novel technology, is adopted to construct superior OER electrocatalysts. The produced Ni(Fe)(OH)2-Fe2O3 electrode exhibits an overpotential of 272 mV at a current density of 100 mA cm-2, presenting a 64 mV reduction compared to the electrode without an MF. The experimental results indicate that an MF can induce the directional growth of Fe2O3 rods and reduce their accumulation. In addition, an external MF is beneficial for the lattice dislocation of the obtained catalysts, which can increase the surface free energy, thus reducing the activation energy and accelerating the electrochemical reaction kinetics. This work effectively combines a magnetic field with chemical corrosion and electrochemical energy, which offers a novel strategy for the large-scale development of environmentally friendly and superior electrocatalysts.

The role of microfaceting in heteroepitaxial interfaces

We investigate the effects of microfaceting on the orientation and interface structure of fcc films on fcc substrates by molecular dynamics simulations and atomic resolution electron microscopy. For (110) substrates, the simulations reveal a misorientation between film and substrate lattices that undergoes a sudden change when interfacial facets approach the “magic size”, where a lattice dislocation minimizes the strain energy by compensating the misfit between film and substrate. For a large misfit, the angle of misorientation varies between zero and several degrees, depending on the size and sequence of microfacets. Experimental observations of interfaces in Ag/Ni near the Ni(110) orientation uncover the presence of magic-size {111} facets and show how microfaceting controls the partitioning of misfit dislocations. For facets smaller than the magic size, misfit may be compensated by partial rather than perfect dislocations. In vicinal {hhl} interfaces, made of {111} terraces separated by single-layer steps, a partial dislocation per terrace leads to film growth in the heterotwin orientation. This concept explains a range of previous results on interface structures in a variety of heteroepitaxial systems.

Transmission-scanning electron microscopy of interface fracture of ferrite deformation twins

AbstractDeformation twins in the ferrite matrix of an age-hardened duplex stainless steel have been observed using on-axis transmission Kikuchi diffraction (TKD) in a scanning electron microscope. This provided details of the lattice misorientation and dislocation arrangement, including the dislocation-free zone at the twin tip. These observations provide evidence for the link between microcracking of the irregular twin/parent interface and relaxation of the residual strains that arise from twin growth, offering new insights into fracture mechanics in these materials. Graphical abstract