Anisotropic Strain Research Articles

Highly Sensitive, Stretchable, and Transparent Multidirectional Wearable Strain Sensors Based on Patterned Vertical Graphene Array

Abstract Since traditional uniaxial strain sensors constructed from isotropic materials mainly focus on identifying strain amplitude without the information of strain direction, multidimensional strain sensors are critical for capturing complex movements, such as human motions. Here, we propose a highly sensitive, stretchable, and transparent multidirectional strain sensor based on patterned vertical graphene array (PVGA) synthesized by plasma-enhanced chemical vapor deposition (PECVD) followed by selective etching and transferring. The obtained PVGA/Polydimethylsiloxane (PDMS) strain sensor exhibits outstanding anisotropic strain sensing performance, including high gauge factor (GF=85.8 at 10% strain), excellent linearity (R2 = 0.99), and outstanding selectivity (|▽|=4.17). Cross-plied PVGA /PDMS strain sensors are also fabricated to demonstrate the application of detecting joint movements of the human body, as well as monitoring wrist motion for controlling a fruit-slicer game in the virtual environment. The sensor’s remarkable multi-dimensional sensing performance confirms their significant potential for diverse applications, notably in wearable electronics, such as personal health sensing, artificial intelligence, human-computer interaction, and soft robotics.

Micro-corrugated chiral nematic cellulose nanocrystal films integrated with ionic conductive hydrogels leads to flexible materials for multidirectional strain sensing applications.

Multidirectional strain sensors are of technological importance for wearable devices and soft robots. Here, we report that flexible materials capable of multidirectional anisotropic strain sensing can be constructed leveraging diffusion-induced infiltration of monomers and in situ polymerization of metal ion-containing double network hydrogels in and on the surface of micro-corrugated chiral nematic cellulose nanocrystal/glucose films. Integrating the micro-corrugated cellulose nanocrystal/glucose chiral nematic films with ionic conductive hydrogels of PAA-co-AAm/sodium alginate/Al3+ endows the materials with multidirectional mechanoelectrical resistivity and mechanochromism anisotropy. The anisotropic responses to multidirectional stress, which are sensitive, swift and reversible, are owing to the synergistic effects of micro-corrugation, helicoidal arrangement, one-dimensional photonic bandgap, mobility of Al3+ ions, and water-rich architecture. These flexible materials hold promises as multidirectional and multimodal anisotropic strain sensors in wearable electronics and soft robotic applications.

Microscopic electrochemical–mechanical coupling in layered cathodes under high-voltage and fast-charging conditions

This review examines electrochemical-mechanical coupling in layered oxide cathodes, linking delithiation-induced electrochemical degradation to anisotropic mechanical strain, while summarizing recent advances in cathode material modifications.

Pre-straining effect on ferrite/pearlite anisotropic transformation strain in steels

The effect of pre-straining on ferrite/pearlite phase transformation in high strength steels is investigated. Two steels differing mainly in their Nb content (0.03C 0.68Si 1.82Mn 0.00 or 0.04Nb in mass%) are either pre-tensioned or pre-compressed and the same-directional transformation strain is measured. A crystal plasticity fast Fourier transform numerical model with back stress effect is used for further investigation and the results are compared. Experimentally, it was found that 30% pre-tension reduces the transformation strain in the same direction by 0.09% (0.00Nb) and 0.13% (0.04Nb), while 30% pre-compression increases it by 0.16% (0.00Nb) and 0.02% (0.04Nb). The numerical simulation estimates the experimentally observed anisotropic transformation strain. In the numerical simulation, even though the anisotropy in transformation plasticity has been qualitatively reproduced, a larger anisotropy effect was observed. The quantitative discrepancies found in between experimental results and numerical results are due to the annihilation of dislocations during the interval between the pre-straining and the onset of phase transformation. The anisotropy in transformation strain found in the experiments is large enough to cause an unacceptable dimensional change in e.g. heat treated steel sheet products.

Negative creep of single-crystals nickel-based superalloys

The negative creep of single crystals of nickel-based superalloys SR99 and CMSX-4 has been investigated. This phenomenon was observed for both superalloys at temperatures of 980–1000 °C and low or zero loading stresses. It is assumed that the main reason for the negative creep is the formation of a short-range order of atoms in a strongly alloyed crystal lattice of the g-matrix. Additional factors affecting the magnitude and anisotropy of the negative creep strain may be the relaxation of residual stresses: at the microscopic level, misfit stresses between the g-matrix and strengthening g′-precipitates, and at the mesoscopic level, dendritic stresses between the dendrite axes and interdendritic regions.

Fluorination from Surface to Bulk Stabilizing High Nickel Cathode Materials with Outstanding Electrochemical Performance.

High nickel layered oxides provide high energy densities as cathodes for next-generation batteries. However, critical issues such as capacity fading and voltage decay, which derive from labile surface reactivity and phase transition, especially under high-rate high-voltage conditions, prevent their commercialization. Here we propose a fluorination strategy to simultaneously introduce F atoms into oxygen layer and create a F aggregated interface. Substitution F for O stabilizes the layered ionic framework as the F ions can anchor the internal transition metal ions through strong TM-F bonding interaction, alleviating anisotropic lattice strain accumulation and release during the cycle, and promoting the Li+ dynamics diffusion. Meanwhile, the fluorinated interface induces the formation of a thin and stable CEI, ameliorating the detrimental issues like oxygen vacancy formation, the HF attacks and metal dissolution. The resultant fluorinated cathode delivers a high reversible capacity of 192.9 mAh g-1 at 10 C within the voltage range of 2.7-4.5 V. This fluorination strategy approach provides design concepts for the advanced cathodes that can meet the demands of high-rate and high-voltage applications in next-generation batteries.

Anisotropic Strain Evolution of Layered LiNi0.5Co0.2Mn0.3O2 Cathode in Formation Cycle.

The formation process plays a key role in developing long life and high energy density materials, during which the phase transition, strain evolution, and structural self-adaption interact rationally with each other to produce a qualified electrode for Li-ion batteries (LIBs). Taking the layered LiNi0.5Co0.2Mn0.3O2 cathode as an example, the substantial structural changes, both in the bulk and at the surface are thoroughly documented during the formation cycle. Upon initial charging, different phases emerge continuously, resulting in lattice mismatches, inhomogeneous strain, and microstructural distortions. The irreversible loss of lattice oxygen, combined with the spontaneous cation mixing and the formation of rock-salt phase at the surface, contributes to the initial capacity loss. As a self-adjustment process, this initial capacity loss facilitates the development of a robust LixNi0.5Co0.2Mn0.3O2 electrode by relieving internal strain and stabilizing the rippled layered structure, thereby ensuring highly reversible electrochemical behavior in subsequent cycles. These findings lay a solid foundation for the design and optimization of layered cathodes for rechargeable batteries.

Mechanical Degradation by Anion Redox in LiNiO2 Countered via Pillaring

AbstractA promising next‐generation high‐energy cathode material, LiNiO2 (LNO) has failed to realize commercialization due to severe capacity degradation during cycling. The dual mechanisms of surface oxygen evolution due to anion redox and anisotropic volume change upon delithiation synergistically pulverize and degrade the material. Detailed Density Functional Theory (DFT) modeling and analysis of the anisotropic structural changes associated with crack formation in LiNiO2 (LNO) reveals the link of mechanical behavior to charge transfer and oxygen redox activity upon deep charge cycling (>4.2 V vs Li/Li+). In the two‐phase region and H2–H3 transition from 66% to 100% delithiation, oxygen of [NiO6] octahedra is discovered to undergo redox in growing the Li‐deficient regions, causing c‐lattice mechanical weakening and collapse as the Li‐slab becomes depleted. Li‐site dopants are investigated to locally compensate against anion redox, resulting in enhanced coulombic repulsion and supporting the interslab layer thickness even at 100% depth of charge. Ionic size and oxidation state of M in Lix‐yMyNiO2 are found to fundamentally impact stabilization capability, moderating the anisotropic strain and volume expansion asynchronously. Optimization of mixed doping composition may then enable “zero strain” high‐Ni Li(Ni,Co,Mn)O2 (NCM) or LNO.

Restraining Planar Gliding in Single-Crystalline LiNi0.9Co0.05Mn0.05O2 Cathodes by Combining Bulk and Surface Modification Strategies.

The delamination cracking from planar gliding along the (003) facets and anisotropic lattice strain perpendicular to the (003) facets inevitable lead to degradation of Ni-rich single-crystal cathode materials, adversely affecting their cyclability. Herein, we rationally design a single-crystal LiNi0.9Co0.05Mn0.05O2 (SC90) cathode with robust chemo-mechanical properties, in which coherently grown MgO6 octahedra and BO4 tetrahedra are incorporated into the lattice, and a stabilizing Mg3(BO3)2 layer is concurrently formed on the particle surface. Multiscale in/ex situ characterizations and theoretical calculations indicate that introducing the MgO6 and BO4 units leads to a "pinning effect" within the layered structure. This in turn strongly mitigates mechanical degradation by reducing planar gliding and delamination cracking over extended cycling. Moreover, the Mg3(BO3)2 coating maintains fast lithium diffusion by suppressing parasitic reactions at the cathode|electrolyte interface. The tailored SC90 cathode exhibits a capacity retention of ~88 % after 300 cycles at 5 C rate, significantly outperforming the pristine counterpart (~60 %). Additionally, a pouch-type full cell with a graphite anode sustains a specific discharge capacity of 177 mAh g-1 after 500 cycles, with 90 % capacity retention. This work highlights the "pining effect" in preventing unfavorable slab sliding and structural deterioration, offering new insights for designing advanced ultrahigh Ni single-crystal cathodes.

LiNiO2 Mechanical and Phase Stability Improvements at Deep Charge Predicted by Pillaring

Increasing energy density of Li-ion layered cathode materials will require access to deep charge states of high-nickel NCM/NCA and LiNiO2, predicated by overcoming numerous issues. In liquid electrolyte systems, the strain following anisotropic volumetric strain at the deep charge state induces separation of secondary particles and crack formation in primary particles, revealing greater surface area and exacerbating interfacial instabilities and pulverizing the cathode active material.[1] This anisotropic strain must also be arrested to mitigate delamination of solid-solid interfaces with solid-state electrolytes, thus enabling next-generation battery technology via “zero-strain” cathodes.[2] Density functional theory calculations evaluated the structural evolution throughout delithiation of Li1-xNiO2 (x = 0 → 1), highlighting the monoclinic structure and H2-H3 phases at deep charge.[3] The Li-interlayer contribution to the lattice collapse and mechanical stiffness is found to be highly correlated, and so interlayer cation concentration strongly influences mechanical property and phase stability. Detailed analysis of the local electronic environment for LixNiO2 contrasted the impact of delithiation, cation mixing, and dopants — both pillaring and transition metal substitutive. Modeling of select Li-interlayer pillaring dopants show improvements across the full range of delithiation with lessened volumetric change and more consistent mechanical stiffness trends by compensating anion electron density in the interlayer.[1] H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater 2018, 30, 1155[2] R. Zhang, C. Whang, P. Zou, R. Lin, L. Ma, L. Yin, T. Li, W. Xu, H. Jia, Q. Li, S. Sainio, K. Kisslinger, S. E. Trask, S. N. Ehrlich, Y. Yang, A. M. Kiss, M. Ge, B. J. Polzin, S. J. Lee, W. Xu, Y. Ren, H. L. Xin, Nature 2022, 610, 67-73[3] M. Mock, M. Bianchini, F. Fauth, K. Able, S. Sicolo, J. Mater. Chem. A 2021, 9, 14928

Surface Phase Engineering stabilizes cycling of zero-cobalt single-crystalline layered cathodes

The imperative of addressing cobalt scarcity and the pursuit of heightened energy density propels the exploration of cobalt-free, single-crystalline layered oxide cathodes for lithium-ion batteries (LIBs). Notwithstanding, such cathodes are confronted with rapid capacity degradation due to mechanical instability especially for pronounced crack propagation under high voltage. Herein, we present surface molybdenum-doped single-crystalline LiNi0.8Mn0.2O2 (Mo-NM82) cathode with excellent cycling stability. Our work reveals that the incorporation of Mo engenders surface reconstruction featuring antisite defects. This Mo enrichment layer not only significantly alleviates anisotropic strain during cycling thus substantially diminishing crack formation, but also serves as a protective layer that suppresses the dissolution of transition metal ions into the electrolyte. We found that the short-range disorder induced by surface Mo doping significantly enhances the structural stability of NM82 during the lithiation and delithiation processes. Consequently, the Mo-NM82 cathode exhibits an impressive 92.9 % capacity retention after 300 cycles at 2.8–4.5 V, demonstrating great potential for practical application. This investigation unveils surface modification as a critical determinant of the mechanical stability of cobalt-free single-crystalline cathodes, offering a promising avenue in the structural design of high-performance, cost-effective cathodes.

Strain mediated transition between skyrmion and antiskyrmion in ferromagnetic thin films

Magnetic topological structures have attracted great attention due to their potential applications in memory and logic devices. Achieving the controllable transition between different magnetic topological structures is crucial for their application. Here, we develop a phase field model with strain-modulated Dzyaloshinskii-Moriya interaction (DMI) and predict the controllable transitions between skyrmion and antiskyrmion states in a ferromagnetic thin film through the application of different strains. It is found that the anisotropic DMI induced by anisotropic strains in the thin film plays an important role in the transitions between various magnetic structures, including skyrmion, antiskyrmion, single domain, and helical domain. Anisotropic DMI also has a significant impact on the chirality and deformation of magnetic topological structures, among which anisotropic DMI can cause anisotropic deformation of skyrmions and antiskyrmions. Furthermore, the formation mechanism of antiskyrmions is elucidated by decomposing the magnetization vectors into Bloch and Néel-type components based on the Lifshitz invariant. This work not only provides an insight into the dynamic behaviors of topological structures but also suggests a new method for controlling magnetic configurations through strain engineering.

Anisotropic Ferroelectricity in Polar Vortices.

The exotic polarization configurations of topologically protected dipolar textures have opened new avenues for realizing novel phenomena absent in traditional ferroelectric systems. While multiple recent studies have revealed a diverse array of emergent properties in such polar topologies, the details of their atomic and mesoscale structures remain incomplete. Through atomic- and meso-scale imaging techniques, the emergence of a macroscopic ferroelectric polarization along both principal axes of the vortex lattice while performing phase-field modeling to probe the atomic scale origins of these distinct polarization components is demonstrated. Additionally, due to the anisotropic epitaxial strain, the polarization switching behavior perpendicular and parallel to the vortices is highly anisotropic, with switching along the vortex axes occurring over numerous decades in field-pulse width. This slow switching process allows for the deterministic control of the polarization state, enabling a non-volatile, multi-state memory with excellent distinguishability and long retentiontimes.

Effects of Thickness and Anisotropic Strain on Polarization Switching Properties of Sub-10nm Epitaxial Hf0.5Zr0.5O2 Thin Films

Abstract Doped HfO2-based ferroelectric (FE) films are emerging as leading contenders for next-generation FE non-volatile memories due to their excellent compatibility with complementary metal oxide semiconductor processes and robust ferroelectricity at nanoscale dimensions. Despite the considerable attention paid to the FE properties of HfO2-based films in recent years, enhancing their polarization switching speed remains a critical research challenge. We demonstrate the strong ferroelectricity of sub-10 nm Hf0.5Zr0.5O2 (HZO) thin films and show that the polarization switching speed of these thin films can be significantly affected by HZO thickness and anisotropically strained La0.67Sr0.33MO3-buffered layer. Our observations indicate that the HZO thin film thickness and anisotropically strained La0.67Sr0.33MO3 layer influence the nucleation of reverse domains by altering the phase composition of the HZO thin film, thereby reducing the polarization switching time. Although the increase in HZO thickness and anisotropic compressive strain hinder the formation of the FE phase, they can enable faster switching. Our findings suggest that FE HZO ultrathin films with polar orthorhombic structures have broad application prospects in microelectronic devices. These insights into novel methods for increasing polarization switching speed are poised to advance the development of high-performance FE devices.

Linear strain gradient-regulated bifurcation of circular bilayer plates

Bilayer structures with controllable self-folding capability have found applications in a variety of cutting-edge fields such as flexible electrics, wearable devices and soft robotics. The folding of bilayer structures occurs when the mismatch strain between the two layers exceeds the bifurcation threshold, resulting in a deformation transition from an axisymmetric to a folded state. Previous efforts have predominantly focused on bilayer structures with uniform and/or anisotropic strain distributions. However, the role of non-uniform in-plane strain distributions in regulating the bifurcation of bilayer structures has not been fully understood. In this study, the effects of linear in-plane strain gradients on the bifurcation of circular bilayer plates, both with and without geometric mismatch, are systematically investigated by combining theoretical analysis, finite element simulations and experiments. Our results reveal that both the mismatch strain gradient and the geometric mismatch between the two layers play crucial roles in regulating bifurcation. Notably, linear mismatch strain gradients with larger strain at the center delay bifurcation, while those with larger strain along the edge promote bifurcation. This work offers new insights into the design of controllable self-folding bilayer structures, which is of great significance for advanced applications.

Toward Superior Stiffness in Carbon: The Interplay between Bond Strength and Anisotropic Response.

Carbon's ability to form diverse structures with varying hybridizations motivates the search for novel materials surpassing diamond's exceptional mechanical rigidity. We analyze previously predicted superhard phases and find that some exhibit average bond stiffness and density higher than those of diamond, hinting at potentially superior stiffness. However, these structures show a lower bulk modulus. We delve into this contradiction and demonstrate that it stems from the structures' anisotropic response to isotropic deformation. The concept of strain anisotropy is introduced to quantify this phenomenon. Our findings reveal a key connection between bond stiffness and bulk modulus in carbon materials, highlighting the importance of considering anisotropic behavior for a comprehensive understanding of the mechanical properties.

Impact of halogen⋯halogen interaction on the mechanical motion of a 3D Pb(II) coordination polymer of elusive topology.

Herein, we report the synthesis of a Pb(II) based three-dimensional coordination polymer (3D CP), [Pb(DCTP)]n (1) [H2DCTP = 2,5-dichloroterephthalic acid] with an unprecedented topology, which exhibits a photomechanical effect wherein crystals show jumping upon UV irradiation. The Pb(II) CP forms a type II Cl⋯Cl interaction, which weakens further upon UV irradiation to resolve the anisotropic mechanical strain. The work presented here could be a beacon to the nascent field of photoactuating smart materials.

Cryogenic Digital Image Correlation as a Probe of Strain in Iron-Based Superconductors

Abstract Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors. However, accurately characterizing anisotropic strain can be challenging and complex. Here, we utilize a cryogenic optical system equipped with a high-spatial-resolution microscope to characterize surface strains in iron-based superconductors using the digital image correlation method. Compared with other methods such as high-resolution X-ray diffraction, strain gauge, and capacitive sensor, digital image correlation offers a non-contact, full-field measurement approach, acting as an optical virtual strain gauge that provides high spatial resolution. The results measured on detwinned BaFe2As2 are quantitatively consistent with the distortion measured by X-ray diffraction and neutron Larmor diffraction. These findings highlight the potential of cryogenic digital image correlation as an effective and accessible tool for probing the isotropic and anisotropic strains, facilitating the application of uniaxial strain tuning in the study of quantum materials.

Hypoplastic constitutive model of inherently anisotropic sand

The modeling of anisotropic sand has always been a challenging and prominent issue in geotechnical constitutive research. This paper presents a hypoplastic constitutive model for inherently anisotropic sand. An anisotropic state variable A, which is defined by the joint invariants of the stress and fabric tensor, is introduced to account for the fabric anisotropy. This form of A can be referred to as a re-arrangement that allows for easier calibration. And this modification leads to the anisotropic contraction of the failure surface. The softening parameter in the critical state line is revised from a fixed to a state-dependent type, for achieving unified simulations of monotonic sand mechanical behaviour under different drainage conditions and within a wide range of stress levels and densities. Simulations of various monotonic element tests show that the salient features of inherently anisotropic sand, including barotropy, pyknotropy, strain softening, and dilatancy, can be well captured. Particularly, we make the first attempt to simulate pure stress-controlled true triaxial tests using hypoplastic constitutive under both drained and undrained conditions. Moreover, we provide a method to further optimize the flow direction by introducing an exponential formula.

Polar Metallicity Controlled by Epitaxial Strain Engineering.

The discovery of polar metal opens the door to incorporating electric polarization into electronics with the potential to invigorate next-generation multifunctional electronic devices. Especially, electric polarization can be induced by geometric design in non-polar perovskite oxides. Here, the epitaxial strain exerted on the deposited single-crystalline NdNiO3 thin films is systematically varied in both sign and amplitude by choosing substrates with different lattice mismatch. The pseudocubic NdNiO3(111) film, which is non-polar in its bulk state, is induced to be polar under both compressive and tensile strain. The fine-tuning of epitaxial strain is realized by continuously varying the film thickness using the "thickness-wedge" growth technique, and from the elucidated thickness dependence, the electric polarization and metallicity can be further optimized. Moreover, transitioning from isotropic to anisotropic epitaxial strain gives rise to an ideal polar metal state in the pseudocubic NdNiO3(102) film on an orthorhombic substrate, achieving a remarkably low resistivity of 173 µΩcm at room temperature. The metal-insulator transition in NdNiO3 is completely suppressed and the polar metal state becomes the ground state at all temperatures. These results demonstrate alluring possibilities of induction and manipulation of both electric polarization and electric transport properties in functional perovskite oxides by epitaxial strain engineering.