Anisotropic Strain Research Articles

Enhancing the stability of Li-Rich Mn-based oxide cathodes through surface high-entropy strategy

Li-rich Mn-based layered oxides (LMR) hold promise as cathode materials for lithium-ion batteries (LIBs) due to their high reversible capacity. However, issues such as oxygen release and structural degradation associated with oxygen redox cause voltage decay and capacity decline during cycling. In this study, a monodisperse Li1.2Ni0.13Co0.13Mn0.54O2 cathode material with surface high-entropy architecture (MZCN-LMR) was synthesized to enhance the overlap between the non-bonding orbitals of oxygen (|O2p) and the (TM-O)* occupied band. This enhancement enables regulation of the depth of oxygen oxidation, improving reversible oxygen redox and creating highly flexible structures, with mitigated anisotropic modulus and lattice strain evolution during (de)intercalation. Consequently, the developed MZCN-LMR cathode exhibits impressive capacity retention of 80.5 % after 400 cycles and minimal voltage decay of 0.7 mV per cycle with the voltage range of 2.1–4.6 V. This surface high-entropy strategy offers a universal approach to enhancing the redox stability of anions, contributing to the application of LMR.

Interplay between anisotropic strain, ferroelectric, and antiferromagnetic textures in highly compressed BiFeO3 epitaxial thin films

Interplay between anisotropic strain, ferroelectric, and antiferromagnetic textures in highly compressed BiFeO3 epitaxial thin films

Influence of GaN substrate miscut on the XRD quantification of plastic relaxation in InGaN

In the epitaxy of semiconducting materials, substrate miscut is introduced to improve the morphology of deposited layers. However, in the mismatched epitaxial system, the substrate miscut also changes the stress geometry in the deposited layer, thus influencing the relaxation processes. In this paper, we show that InGaN layers grown on misoriented (0001)-GaN substrates relax by preferential activation of certain glide planes for misfit dislocation formation. Substrate misorientation changes resolved shear stresses, affecting the distribution of misfit dislocations within each dislocation set. We demonstrate that this mechanism leads to an anisotropic strain as well as a tilt of the InGaN layer with respect to the GaN substrate. It appears that these phenomena are more pronounced in structures grown on substrates misoriented toward 〈112¯0〉 direction than corresponding structures with 〈1¯100〉 misorientation. We reveal that the lattice of partially relaxed InGaN has a triclinic deformation, thus requiring advanced XRD analysis. The presentation of just a single asymmetric reciprocal space map commonly practiced in the literature can lead to misleading information regarding the relaxation state of partially relaxed wurtzite structures.

Mechanochemically Robust LiCoO2 with Ultrahigh Capacity and Prolonged Cyclability.

Pushing intercalation-type cathode materials to their theoretical capacity often suffers from fragile Li-deficient frameworks and severe lattice strain, leading to mechanical failure issues within the crystal structure and fast capacity fading. This is particularly pronounced in layered oxide cathodes because the intrinsic nature of their structures is susceptible to structural degradation with excessive Li extraction, which remains unsolved yet despite attempts involving elemental doping and surface coating strategies. Herein, a mechanochemical strengthening strategy is developed through a gradient disordering structure to address these challenges and push the LiCoO2 (LCO) layered cathode approaching the capacity limit (256mAhg-1, up to 93% of Li utilization). This innovative approach also demonstrates exceptional cyclability and rate capability, as validated in practical Ah-level pouch full cells, surpassing the current performance benchmarks. Comprehensive characterizations with multiscale X-ray, electron diffraction, and imaging techniques unveil that the gradient disordering structure notably diminishes the anisotropic lattice strain and exhibits high fatigue resistance, even under extreme delithiation states and harsh operating voltages. Consequently, this designed LCO cathode impedes the growth and propagation of particle cracks, and mitigates irreversible phase transitions. This work sheds light on promising directions toward next-generation high-energy-density battery materials through structural chemistry design.

Full electrical manipulation of perpendicular exchange bias in ultrathin antiferromagnetic film with epitaxial strain

Achieving effective manipulation of perpendicular exchange bias effect remains an intricate endeavor, yet it stands a significance for the evolution of ultra-high capacity and energy-efficient magnetic memory and logic devices. A persistent impediment to its practical applications is the reliance on external magnetic fields during the current-induced switching of exchange bias in perpendicularly magnetized structures. This study elucidates the achievement of a full electrical manipulation of the perpendicular exchange bias in the multilayers with an ultrathin antiferromagnetic layer. Owing to the anisotropic epitaxial strain in the 2-nm-thick IrMn3 layer, the considerable exchange bias effect is clearly achieved at room temperature. Concomitantly, a specific global uncompensated magnetization manifests in the IrMn3 layer, facilitating the switching of the irreversible portion of the uncompensated magnetization. Consequently, the perpendicular exchange bias can be manipulated by only applying pulsed current, notably independent of the presence of any external magnetic fields.

Emergent tetragonality in a fundamentally orthorhombic material.

Symmetry plays a key role in determining the physical properties of materials. By Neumann's principle, the properties of a material remain invariant under the symmetry operations of the space group to which the material belongs. Continuous phase transitions are associated with a spontaneous reduction in symmetry. Less common are examples where proximity to a continuous phase transition leads to an increase in symmetry. We find signatures of an emergent tetragonal symmetry close to a charge density wave (CDW) bicritical point in a fundamentally orthorhombic material, ErTe3, for which the two distinct CDW phase transitions are tuned via anisotropic strain. We first establish that tension along the a axis favors an abrupt rotation of the CDW wave vector from the c to a axis and infer the presence of a bicritical point where the two continuous phase transitions meet. We then observe a divergence of the nematic elastoresistivity approaching this putative bicritical point, indicating an emergent tetragonality in the critical behavior.

Pre-introducing Li4NiWO6 defect phase by tungsten modification enables highly stabilized Ni-rich cathode

Tungsten (W) has attracted considerable attention as a promising dopant capable of enhancing the structural stability of Ni-rich cathode materials. However, investigations into W modification remain highly debated due to the elusive mechanisms involved, particularly in determining whether W is doped into the lattice structure or exists as a distinct phase on the surface of the particles. In this work, we systematically observe the effects induced by the introduction of W into LiNi0.9Co0.05Mn0.05O2 (NCM). We discovered that during high-temperature solid-state reactions, W-containing substances tend to react preferentially with surface Li, creating a lithium-deficient state on the NCM surface, resulting in the generation of Li4NiWO6. Molecular dynamics simulations tracking Li, W, and Ni elemental changes at the interface confirm the initial creation of Li6WO6, succeeded by diffusion of Ni to replace Li, forming Li4NiWO6. The pre-introducing Li4NiWO6 defect phase can effectively absorb anisotropic lattice strain, preserving the mechanical integrity of the secondary particles. Furthermore, the Li4NiWO6 phase, combined with the amorphous LixWyOz coating layer, effectively acts as a guard against undesirable interfacial side reactions, ultimately imparting excellent electrochemical performance to NCM. Understanding the dynamic processes of interfacial reactions is crucial for tailoring surface properties of Ni-rich cathodes towards long-life lithium-ion batteries.

Ultrahigh-temperature capacitors realized by controlling polarization behavior in relaxor ferroelectric

Dielectric film capacitors have drawn much attention in recent years due to the fast charge–discharge rate, while the energy storage performance at ultra-high temperature needs to be satisfied for the increasing demand of the market. Here, we develop an ultrahigh-temperature capacitor of relaxor ferroelectric (RFE) films via controlling polarization behavior. The (110) oriented 0.85BaTiO3-0.15Bi(Mg0.5Zr0.5)O3 (BT-BMZ) thin film, with anisotropic strain and the optimal ratio of extrinsic/intrinsic polarization, exhibits minimized hysteresis loss and maintains maximum polarization. The (110) oriented film capacitor shows giant energy storage density 104.94 J/cm3, with energy storage efficiency 75.83 % BT-BMZ at room temperature. Moreover, the BT-BMZ capacitor achieves excellent thermal stability, from −100 °C to 400 °C, with an energy density 51.61 J/cm3 at an efficiency 79.36 % due to the low leakage current and hysteresis loss. This work demonstrates that the energy storage performance can be enhanced by adjusting the ratio of intrinsic/extrinsic polarization and provides a feasible method for improving high-temperature performance of capacitors.

Symmetry Engineering of Epitaxial Hf0.5Zr0.5O2 Ultrathin Films.

Robust ferroelectricity in HfO2-based ultrathin films has the potential to revolutionize nonvolatile memory applications in nanoscale electronic devices because of their compatibility with the existing Si technology. However, to fully exploit the potential of ferroelectric HfO2-based thin films, it is crucial to develop strategies for the controlled stabilization of various HfO2-based polymorphs in nanoscale heterostructures. This study demonstrates how substrate-orientation-induced anisotropic strain can engineer the crystal symmetry, structural domain morphology, and growth orientation of ultrathin Hf0.5Zr0.5O2 (HZO) films. Epitaxial ultrathin HZO films were grown on the heterostructures of (001)- and (110)-oriented La2/3Sr1/3MnO3/SrTiO3 (LSMO/STO) substrate. Various structural analyses revealed that the (110)-oriented substrate promotes a higher degree of structural order (crystallinity) with improved stability of the (111)-oriented orthorhombic phase (Pca21) of HZO. Conversely, the (001)-oriented substrate not only induces a distorted orthorhombic structure but also facilitates the partial stabilization of nonpolar phases. Electrical measurements revealed robust ferroelectric properties in epitaxial thin films without any wake-up effect, where the well-ordered crystal symmetry stabilized by STO(110) facilitated better ferroelectric characteristics. This study suggests that tuning the epitaxial growth of ferroelectric HZO through substrate orientation can improve the stability of the metastable ferroelectric orthorhombic phase and thereby offer a better understanding of device applications.

Investigation of the magnetic and structural properties in the non‐stoichiometric Heusler alloy Ni50Mn25+xSn25‐x; x = 13, 14

AbstractMemory shape magnetic alloys, especially Heusler alloys, are important materials in replacing conventional cooling with magnetic systems. In the present study off stoichiometric Heusler alloys with nominal composition Χ50Υ25+xΖ25‐x (X = Ni; Y = Mn; Z = Sn; x = 13, 14) were prepared by arc melting followed by thermal treatment. Structural properties were analyzed with X‐ray diffraction at room temperature (RT) and at elevated temperatures, above the martensite—austenite transition area, to determine the relevant crystallographic parameters and observe the transition. Martensite stabilization at RT appears to be a challenge, coexistence of martensite—austenite phases were observed and calculated for both 38–12 and 39–11 (16% and 12% austenite, respectively). Magnetization measurements versus temperature and field were recorded in the areas of interest where 1st order transitions were expected (355 K for x = 13 and 408 K for x = 14), and the magnetic entropy's changes (ΔSm) were determined [0.4 (J/kgK) for x = 13 and 0.3 J/(kgK) for x = 14; Hmax = 1 T]. The complex character of the magnetic properties and their dependence on Mn‐Sn ratio and on the distance between Mn atoms is discussed. The structure and the lattice parameters were determined using an anisotropic strain broadening model; stress and strain were detected in the structure due to crystal phase coexistence.

Highly sensitive and selective flexible anisotropic strain sensor based on liquid metal/conductive ink for wearable applications

Although many high-performance wearable strain sensors have been developed, they are limited to uniaxial strain monitoring, which makes it challenging to meet the monitoring needs of complex multidimensional motion in practical applications. This study effectively constructed an anisotropic strain sensor by combining two materials that exhibit different responses to external stimuli (strain): liquid metal and conductive ink. In particular, the maximum gauge factors of this anisotropic strain sensor in conductive ink direction and liquid metal direction are 158.9 and 1.9, respectively. Both directions display outstanding dynamic stability, frequency independence, and durability over 3000 cycles. Furthermore, the integrated sensor formed by the orthogonal stack of two anisotropic strain sensors can distinguish the strain magnitude and direction (an outstanding selectivity of 3.7). The mechanism of the sensor's selective sensing ability is analyzed, and the broad application of the sensor in complex motion monitoring, human-computer interaction, and multi-component control is demonstrated. This research discovery provides new ideas and methods for constructing anisotropic wearable strain sensors. It creates conditions for the development and practical application of multifunctional wearable devices.

Tuning superconductivity and spin-vortex instabilities in CaKFe4As4 through in-plane antisymmetric strains

Lattice strains of appropriate symmetry have served as an excellent tool to explore the interaction of superconductivity in the iron-based superconductors with orthorhombic-nematic and stripe spin-density-wave (SSDW) order. In this Letter, we contribute to a broader understanding of the coupling of strain to superconductivity and competing normal-state orders by studying CaKFe4As4 under large, in-plane strains of B1g and B2g symmetry. In contrast to the majority of iron-based superconductors, pure CaKFe4As4 exhibits superconductivity with a relatively high transition temperature of Tc∼35K in proximity of a noncollinear, tetragonal, hedgehog spin-vortex crystal (SVC) order. Through experiments and calculations, we demonstrate an anisotropic in-plane strain response of Tc and the favored SVC configuration in CaKFe4As4. This supports a scenario, in which the change in spin fluctuations dominates the strain response of superconducting Tc. Overall, by suggesting moderate B2g strains as an effective parameter to change the stability of SVC and SSDW, we outline a pathway to a unified phase diagram of iron-based superconductivity. Published by the American Physical Society 2024

Practical fracture limit function considering data flexibility under plane-stress conditions in Lagrangian formulation

Ductile fracture limits have been extensively studied from the perspectives of material science and mechanics. While these studies have provided scientifically significant insights into ductile fracture limits, the influence of the evolution of anisotropy observed in actual experimental data suggests a need to account for diversity in the experimental data. To address this, it may be possible to further develop the model by investigating more influences from the field of materials science. However, from an engineering perspective, it can be effective to represent the diversity of acquired experimental data as practical functions for use, rather than solely focusing on the material science aspect. This paper presents mathematical formulations representing the strain- and stress-based fracture limit surfaces of ductile materials, to consider diverse data set for the evolution of anisotropy, under plane-stress conditions within the framework of the Lagrangian formulation. The model introduces a strain-based fracture limit surface (FLS), which has an additional anisotropic profile function based on the commonly used two-dimensional strain-based fracture limit curve (FLC). The anisotropic profile function is capable of capturing the evolving anisotropic profile based on the deformation mode and principal loading direction to represent more flexible shapes. With this function, a three-dimensional strain-based FLS, which can present the variation in fracture strains in the space of the deformation mode and principal loading direction, can be constructed. Then, the proposed model transformed this strain-based FLS into a stress-based FLS by converting the presented state vector in the former into the corresponding vector in the latter in the Lagrangian formulation. To achieve this, this study developed a formulation that considers the nonlinear evolution of stress anisotropy independent of the strain anisotropy during stress evolution. The two proposed models were validated by experimental results on a dual-phase steel. These models provide flexible fracture limit functions for ductile materials under varying stress and strain conditions in engineering applications.

Precision engineering of high-performance Ni-rich layered cathodes with radially aligned microstructure through architectural regulation of precursors

Microstructure engineering serves as a potent approach to counteract the mechanical deterioration of Ni-rich layered cathodes, stemming from anisotropic strain during Li+ (de)intercalation. However, a pressing challenge persists in devising a direct method for fabricating radially aligned cathodes utilizing oriented hydroxide precursors. In this study, we synthesized LiNi0.92Co0.04Mn0.04O2 oxides boasting superior radially aligned, size-refined primary particles through a combination of strategic precipitation regulation and lithiation tuning. Elongated primary particles, achieved by stepwise control of ammonia concentration and pH during particle growth, facilitate the formation of radially aligned hydroxide precursor particles. Leveraging the size-refined and radially aligned primary particles, our prepared LiNi0.92Co0.04Mn0.04O2 cathode exhibits a high discharge capacity of 229 mAh g−1 at 0.05 C, alongside excellent cycle stability, retaining 93.3% capacity after 200 cycles at 0.5 C (30 °C) in a half cell, and 86.4% capacity after 1000 cycles at 1 C (30 °C) in a full cell. Revisiting the regulation from precursor to oxide underscores the significance of controlling primary particles to maximize size perpendicular to [001] and attain suitable size along [001] during precursor precipitation and high-temperature calcination, offering valuable insights for synthesizing high-performance Ni-rich cathodes.

Formulation and numerical realization of anisotropic permeability coefficient for fluid-solid coupling in underground engineering

Underground engineering soil functions as a typical porous medium wherein groundwater flow and alterations in pore water pressure can influence the medium’s porosity, thereby affecting soil permeability. Moreover, changes in porosity (volumetric strain) result in anisotropy in the permeability coefficient, complicating the accurate depiction of the entire fluid-solid coupling process using a uniform permeability coefficient. Fluid–solid coupling is achieved by establishing a connection between soil and fluid parameters in response to changes in the permeability coefficient during soil deformation. Considering the limitations of the deformation mode described by volumetric strain, this paper proposes different influencing factors of anisotropic principal strains (εx, εy , and εz ) on the anisotropic permeability coefficient k i, based on the Kozeny–Carman semi-empirical equation for the permeability of porous media. Additionally, a numerical simulation method for the fluid-solid interaction effect in underground engineering is implemented by incorporating variations in the permeability coefficient with strain, using a fish-parameterized programming language within the FLAC 3D software. The coupling effect of the seepage field with the strain-dependent permeability coefficient on the mechanical field is validated using a specific calculation example. This methodology presents a novel approach for expressing fluid-solid coupling processes.

Study on the anisotropic small strain stiffness of marine clay in China using bender elements

Small strain stiffness anisotropy of marine soils plays an important role in determining the natural frequency of offshore wind turbine structures. The small strain stiffness anisotropy is contingent on stress anisotropy and fabric anisotropy, with the latter being assessable via stiffness anisotropy under isotropic stress conditions. In this study, the small strain stiffness of marine clay obtained from the site of an offshore wind farm on the southeast coast of China was measured using a bender element. The effects of void ratio, effective mean pressure, and overconsolidation ratio on small strain stiffness were investigated and the related empirical equations were proposed for predicting the small strain stiffness of the marine clay. Furthermore, the small strain stiffness anisotropy of the marine clay under isotropic consolidation was also investigated. The findings revealed remarkable anisotropy in the small strain stiffness of the tested marine clay.

Constitutive modeling of anisotropic small-strain stiffness behavior of Shanghai soft clay

Small strain stiffness plays an important role in determining the deformation of geotechnical engineering in soft soils. To model the anisotropic small strain stiffness behavior of soft clay, an enhancement to the bounding surface plasticity model is proposed. This enhancement involves incorporating the anisotropy in soil stiffness at very small strains and its non-linear degradation. Small strains are considered via cross-anisotropy elasticity, while the concept of intergranular strain is used to reflect the non-linear degradation of stiffness with strains and the effect of recent stress history. Using the proposed model, the triaxial test results on K0 consolidated Shanghai clay specimens are simulated to investigate the model’s performance. In the simulation, three typical shear stress paths are adopted. The comparison of the model simulations against experimental evidence is discussed, where the effects of anisotropy in initial soil stiffness and stress-induced anisotropy on the variation of small-strain stiffness, pore pressure, and shear-volume coupling response are highlighted.

An anisotropic hyperelastic strain energy function based on 21 icosahedron fiber distributions

The microscopic Cauchy strain energy for linear elasticity based on the sum of quadratic strain energies due to pair potentials has only 15 material rari-constants. It is shown that the six vectors connecting opposing vertices of a regular icosahedron can be used to develop a strain energy function for general linear elastic anisotropic response with 21 material constants. Specifically, the six strains of material fibers characterized by these vectors are enhanced by 15 fiber distribution strains due to all combinations of distinct pairs of these vectors. These two-vector fiber distributions introduce coupling that is essential to obtaining general anisotropy. The model is generalized for large deformations by replacing the strains with stretches and by using a Fung-type exponential strain energy which couples the responses of the 21 stretches. The resulting nonlinear hyperelastic strain energy function can be used to model the anisotropic hyperelastic response of fibrous tissues.

Anisotropic Breakage Mechanics for cemented granular materials

The anisotropy of granular geomaterials is sensitive to their fabric, which exhibits anisotropic mechanical properties as a function of deposition history, microscopic fabric, and loading paths. Here, a new fabric-enriched continuum breakage model is proposed to examine the relation between elastic and inelastic anisotropy in granular materials and cemented granular materials. A microstructure model is first implemented in the framework of fabric-enriched continuum breakage mechanics (F-CBM), where the anisotropic behaviour prior to yielding is introduced through a symmetric second-order fabric tensor embedded in the expression of the elastic energy potential. The anisotropic strain energy storage prior to grain crushing leads to the rotation and distortion of the yield surface of cemented granular materials. Parametric analyses are performed to assess the overall capability of the model to characterize the anisotropic inelastic processes in cemented granular. It is shown that the proposed model can accurately predict the strong correlation between anisotropic elasticity and breakage-damage processes in cemented granular materials. When damage involving the skeleton is the dominant inelastic process, the size of the elastic domain contracts and the material exhibits augmented brittleness with the disintegration of cement. While breakage processes are predicted to dominate the response of lightly cemented granular materials resulting in hardening behaviour. This work can be further extended to dynamically capture the anisotropic response of cemented granular materials with water-sensitive mineral constituents by accounting for the evolution of microstructural anisotropy.

True stress-strain identification accounting for anisotropy of sheet metals

Sheet metals for the automotive industry are subjected to continuous research efforts aiming at ever increasing mechanical performance. A remarkable feature of modern high strength sheet metals is their anisotropy, intrinsic in the technologic process of their production. When the effect of anisotropy on the mechanical response of a material cannot be neglected, specimens along different directions are usually tested, possibly under different stress states, to assess the flow curves and the deforming ratios for each direction and each loading mode. Such data are then used to calibrate many possible plastic anisotropy models available in the literature. In this work, the experimental procedures for determining the stress-strain curve and the anisotropic straining ratio are studied in detail, referring to representative tensile tests along the rolling direction of two anisotropic sheet metals, respectively PHS-1800 steel and 6181 aluminium alloy. Both alloys are ductile and exhibit remarkably long post-necking phases in tension, revealing that, in such cases, the standard procedures for the experimental derivation of the hardening curves and of the anisotropic strain ratios are limited to the very early phases of the material life and miss to cover the major part of the strain range up to failure. Different alternative procedures for the derivation of experimental data and for their postprocessing are considered and compared to each other, identifying a set of guidelines for achieving a good engineering accuracy up to failure in deriving both the stress-strain curves and the anisotropic strains ratios. The above analyses are made on the results of tensile tests at static, intermediate and high strain rate, confirming the generality of the identified procedure.