Anisotropic Strain Research Articles

Cracking and associated volumetric expansion of NMC811 secondary particles

Secondary particles comprising a large number of nickel-rich single crystal primary particles are extensively used as storage particles in cathodes of lithium-ion batteries. It is well-established that crack formation in secondary particles is an important degradation mode that contributes to decline in battery performance. Recent X-ray tomographic observations suggest that, at very low C-rates, concentration gradients of lithium within an NMC811 secondary particle are negligible yet cracking still occurs. Additionally, during delithiation the primary particles shrink yet a volumetric expansion of the secondary particle occurs. These observations are explained by a numerical model of distributed cracking due to the extreme anisotropy of lithiation strain of primary particles. The incompatible deformation from grain to grain induces large self-stresses even in the absence of spatial gradients in the lithium concentration. The stress state is sufficient to drive a dynamic catastrophic fracture event, and the associated kinetic energy acquired by the primary particles moves them apart (akin to an explosive event) with the carbon and binder domain surrounding each secondary particle restricting the outward motion of the primary particles. It is predicted that a volume expansion of the secondary particles on the order of 20 % accompanies cracking, in agreement with recently reported observations.

Tensile properties of transversely isotropic closed-cell PVC foam under quasi-static and dynamic loadings

The uniaxial tensile mechanical properties of PVC foam considering the effects of strain rate ([Formula: see text]) and anisotropy ([Formula: see text]) have been investigated by quasi-static and dynamic (Split Hopkinson Tensile Bar, SHTB) tests. Combined high-speed camera system and Digital Image Correlation (DIC) technique, the real-time surface strain field of the specimen during the whole tensile process was obtained. On this basis, the macroscopic response and failure mode of PVC foam were investigated. The failure mechanism of PVC foam under tensile loading was revealed through Scanning Electron Microscope (SEM) images on fracture cross-section of loaded specimen. Finally, based on experimental data, a prediction equation on tensile strength of PVC foam considering the effects of strain rate and loading angle (anisotropy) is proposed. Furthermore, a nonlinear constitutive model is developed to describe the uniaxial tensile mechanical properties of PVC foam.

Regulating Phase Transition and Oxygen Redox to Achieve Stable High‐Voltage O3‐Type Cathode Materials for Sodium‐Ion Batteries

AbstractO3‐type layered oxides are promising cathode materials for sodium‐ion batteries. However, unsatisfying cyclic stability hinders its practical application, mainly resulting from harmful phase transition and irreversible oxygen redox, especially in high‐voltage regions. Herein, a co‐doped strategy by incorporating Li+, Mg2+, Ca2+, and Sb5+ into the O3‐Na0.8Ni0.4Fe0.2Mn0.4O2 cathode materials is proposed. Both suppressing the undesired phase transition over 4.1 V (vs Na/Na+) and reducing the anisotropic strain are achieved with the novel Na0.8Ni0.3Fe0.2Mn0.3Li0.1Mg0.02Ca0.05Sb0.03O2 (LMCS NFM). Moreover, restricted but highly reversible oxygen redox is observed due to strong attraction from Sb5+ and special “Li–O‐vacancy” and “Mg–O‐vacancy” configurations. The strategy brings about excellent high‐voltage cyclic stability with a reversible capacity of 130 mAh g−1 and a capacity retention of 85% after 250 cycles at 4.2 V, and less thermal runaway risk and moisture sensitivity, increasing the probability of O3‐type oxide cathode practical applications.

Helical model of compression and thermal expansion

A negative linear temperature expansion and a negative linear compressibility were observed for imidazolium benzoate salt. Its strongly anisotropic strain induced by the temperature and pressure changes has been explained by the mechanism of H-bonded helices deformed in the structure. X-ray diffraction and vibrational spectroscopy were used to analyze interactions in the crystal. The Quantum Theory of Atoms in Molecules (QTAiM) approach was applied to analyze the hydrogen bonds and other interactions. In the salt under study, the interactions within the helix are substantially higher in energy than between helices. With decreasing temperature and increasing pressure, the value of the helix pitch increases while the value of the semi-major axis decreases, which results in the negative linear expansion and negative linear compression, respectively.

Comparison of anisotropic yield functions and calibrations for accurate thickness prediction in hole expansion test

The hole expansion test is an appropriate evaluation method for assessing the formability of automotive parts, where fracture prediction using simulated localized thickness is crucial. However, the accurate thickness prediction in the hole expansion test remains challenging. In this study, the selection of yield functions and calibration strategies were investigated to accurately predict the thickness of advanced high-strength steel subjected to the hole expansion test. An accurate description of the material anisotropy is important for thickness prediction because of the generation of various multiaxial stress states. To describe plastic anisotropy, a series of uniaxial tension, bulge, and in-plane biaxial tension tests were conducted on DP980 steel. Because conventional biaxial tension tests for DP980 steel showed a small strain range owing to its low ductility, a new laser-welding-reinforced biaxial tension test was developed to investigate the anisotropy of the plane strain at large strains. Differences in the ratio of the plastic strain rates were observed between the conventional and new tests. Finally, a hole expansion test and corresponding finite element simulations were conducted with different yield functions and calibrations for the Yld2000-2d yield function. The thickness strain profiles along the hole circumference and 3 mm inward were measured and predicted using simulations. In conclusion, both the yield stress and the ratio of plastic strain rates in the plane strain state were equally important for accurate thickness prediction during the DP980 hole expansion test. Furthermore, the crack location was inconsistent with the thinnest region in the experiment, which might be because of the shear fracture anisotropy encountered in DP980 steel.

Anisotropic In-Plane strain engineering Ni(OH)2 to activate alkaline hydrogen evolution reaction

Anisotropic In-Plane strain engineering Ni(OH)2 to activate alkaline hydrogen evolution reaction

Evaluation of Anisotropic Biaxial Stress in Extremely-Thin Body (100) Silicon-Germanium-on-Insulator p-Type Metal-Oxide-Semiconductor Field-Effect-Transistor by Oil-Immersion Raman Spectroscopy

We evaluated the anisotropic biaxial strain in the channel region of extremely-thin body silicon-germanium-on-insulator p-MOSFETs by oil-immersion Raman spectroscopy. Oil-immersion Raman spectroscopy can measure the transverse optical (TO) phonon mode which cannot be detected by conventional Raman spectroscopy under the backscattering configuration for (001) substrate. Therefore, we can calculate the anisotropic biaxial stress in the SiGe channel region and investigate the channel width dependence of stress. From the Raman spectra obtained in the polarization configurations of longitudinal optical (LO)-active and TO-active, we confirmed that compressive stress is induced in the SiGe channel region. In addition, we observed that the strain state of the SiGe channel region becomes quasi-uniaxial strain by narrowing the channel width.

Anisotropic Tunability of Vibrational Modes in Black Phosphorus Under Uniaxial Compressive/Tensile Strain

AbstractStrain engineering is a powerful strategy for tuning the optical, electrical, vibrational properties of 2D nanomaterials. In this work, a four‐point bending apparatus is constructed to apply both compressive and tensile strain on 2D anisotropic black phosphorus flake. Further polarized Raman spectroscopy is used to study the vibrational modes of black phosphorus flakes under uniaxial strain applied along various crystalline orientations. Here, a strong anisotropic blue/redshift of A1g, B2g, and A2g modes is found under compressive/tensile strain, respectively. Interestingly, mode A1g exhibits the maximum/minimum shift while mode B2g and mode A2g present the minimum/maximum shift when the strain is applied along armchair/zigzag direction. Density functional theory calculations are carried out to investigate the anisotropic strain response mechanism, finding that the strain‐induced regulation of the P─P bond angle, bond length, and especially interlayer interaction has a giant influence on the Raman shift.

In Situ Constructing Ultrastable Mechanical Integrity of Single-Crystalline LiNi0.9 Co0.05 Mn0.05 O2 Cathode by Interior and Exterior Decoration Strategy.

Planar gliding along with anisotropic lattice strain of single-crystalline nickel-rich cathodes (SCNRC) at highly delithiated states will induce severe delamination cracking that seriously deteriorates LIBs' cyclability. To address these issues, a novel lattice-matched MgTiO3 (MTO) layer, which exhibits same lattice structure as Ni-rich cathodes, is rationally constructed on single-crystalline LiNi0.9 Co0.05 Mn0.05 O2 (SC90) for ultrastable mechanical integrity. Intensive in/ex situ characterizations combined with theoretical calculations and finite element analysis suggest that the uniform MTO coating layer prevents direct contact between SC90 and organic electrolytes and enables rapid Li-ion diffusion with depressed Li-deficiency, thereby stabilizing the interfacial structure and accommodating the mechanical stress of SC90. More importantly, a superstructure is simultaneously formed in SC90, which can effectively alleviate the anisotropic lattice changes and decrease cation mobility during successive high-voltage de/intercalation processes. Therefore, the as-acquired MTO-modified SC90 cathode displays desirable capacity retention and high-voltage stability. When paired with commercial graphite anodes, the pouch-type cells with the MTO-modified SC90 can deliver a high capacity of 175.2 mAh g-1 with 89.8% capacity retention after 500 cycles. This lattice-matching coating strategy demonstrate a highly effective pathway to maintain the structural and interfacial stability in electrode materials, which can be a pioneering breakthrough in commercialization of Ni-rich cathodes.

Aluminum and Indium Co‐Modified Ni‐Rich Layered Cathode with Enhanced Microstructure and Surface Stability for Lithium‐Ion Batteries

AbstractNi‐rich layered oxides are considered as promising cathodes for next‐generation lithium‐ion batteries. However, they still suffer microstructure and surface instability particularly under high operating voltage, leading to rapid capacity fading and battery failure. In this context, Ni‐rich layered cathodes (LiNixCoyMn1−x−yO2; LNCM) with aluminum and indium co‐modified crystal and surface structures are developed by a simple one‐pot calcination approach. Battery tests show that the Al and In co‐modified LNCM electrodes demonstrate remarkably enhanced rate capability and cycling stability compared with the pristine LNCM, Al‐doped LNCM, and In‐modified LNCM counterparts. Further characterizations reveal a simultaneous suppression of cracking and resistive film growth. The improved microstructural and surface stability originate from the synergistic functions of Al and In co‐modification. The incorporation of Al3+ into transition metal slab significantly reduces the Li+/Ni2+ antisite, which noticeably mitigates the undesired layer to rock‐salt phase transformation. The In3+ dopant dispersed in Li interslab can dissipate the anisotropic lattice strain, enabling greatly improved reversibility of H2↔H3 phase transition occurred in delithiation‐lithiation processes. Meanwhile, the synchronously formed LiInO2 adherent coatings deplete lithium residues, facilitate lithium‐ion transfer, and resist electrolyte corrosion. Microstructure and surface engineering through Al and In co‐modification offer a promising design strategy for Ni‐rich layered cathodes.

Onset of Multiferroicity in Prototypical Single-Spin Cycloid BiFeO3 Thin Films.

In the room-temperature magnetoelectric multiferroic BiFeO3, the noncollinear antiferromagnetic state is coupled to the ferroelectric order, opening applications for low-power electric-field-controlled magnetic devices. While several strategies have been explored to simplify the ferroelectric landscape, here we directly stabilize a single-domain ferroelectric and spin cycloid state in epitaxial BiFeO3 (111) thin films grown on orthorhombic DyScO3 (011). Comparing them with films grown on SrTiO3 (111), we identify anisotropic in-plane strain as a powerful handle for tailoring the single antiferromagnetic state. In this single-domain multiferroic state, we establish the thickness limit of the coexisting electric and magnetic orders and directly visualize the suppression of the spin cycloid induced by the magnetoelectric interaction below the ultrathin limit of 1.4 nm. This as-grown single-domain multiferroic configuration in BiFeO3 thin films opens an avenue both for fundamental investigations and for electrically controlled noncollinear antiferromagnetic spintronics.

The Cold Angular Rolling Process of Copper Sheets: Unraveling Plastic Deformation Behavior and Unveiling Microstructural Transformations

The cold angular rolling process (CARP) is being developed as a continuous severe plastic deformation technique, which can process metal sheets without any length limitations at room temperature. CARP contains cold rolling and equal‐channel angular process components. The sheet thickness is kept consistent before and after CARP, allowing multiple passes of the sheet. The desired microstructure and mechanical properties can be achieved in the processed metallic sheets. The current study is aimed to evaluate the capability of CARP by processing copper sheets with different sheet widths for repetitive passes. The CARP‐treated sheets are examined by lab‐scale X‐ray and high‐energy synchrotron X‐ray diffraction to investigate the evolution in dislocation density, texture, and strain anisotropy, and by tensile testing to identify the bulk mechanical properties. The digital image correlation method is applied to tensile testing so that strain localization within the sample gauge is visualized and deformation behavior is evaluated after yielding till postnecking by estimating the hardening exponent and strain hardening rate of the CARP‐treated sheet. Comparing the reported continuous and multiple‐step processes on Cu and its alloys, the present study confirms that the CARP is potentially a useful sheet process for strengthening ductile metals.

Anisotropic Pressure Sensors Fabricated by 3D Printing‐Aligned Carbon Nanotube Composites

The flexibility and controllability of 3D printing technologies have made them popular for creating integrated wearable sensors. However, producing sensors with 3D anisotropic response is still difficult with current printing materials and techniques. To address this challenge, digital light process (DLP) printing technology with blading function to fabricate 3D anisotropic pressure and strain sensors is used. By applying blading‐induced shearing force, nanoalignment of carbon nanotubes (CNTs) in each layer is achieved, while the continuous liquid interface production of the DLP printing process facilitates good electrical communication between adjacent microlayers. The constructed 3D sensor displays high tensile and pressure responses up to 40 MPa and the ability to detect pressure changes in all directions. Additionally, the resistance anisotropy ratio range is adjustable. Finite‐element method (FEM) simulation shows that the relative change in resistance has an anisotropic distribution that aligns well with experimental results. The work would offer a new way to create 3D anisotropic pressure/strain sensors for advanced flexible and stretchable sensing applications.

Anisotropic strain-modulated monoclinic phases with giant piezoelectricity in high-index-oriented PbTiO3 films

By combining phase-field simulations and first-principles calculations, we proposed to modulate the monoclinic phases of high-index-oriented PbTiO3 films through epitaxial anisotropic strain to obtain superior piezoelectric performance. It was found that the piezoelectric coefficients e22 were remarkably enhanced (up to 2400%) in both (111)- and (110)-oriented PbTiO3 films. The excellent piezoelectric property is mainly attributed to the polarization rotation due to the flatter energy landscapes in the monoclinic phases, while the variation of polarization magnitude contributes little to piezoelectricity. Our research suggests modulating material properties through anisotropic strain, which might bring some insight to other functional materials.

Computational Study for Insight into LixNiO2 Interlayer Collapse and Pillar Dopant to Counter Oxygen Charge-Transfer at High Depth of Charge (x < 0.25)

As demand for high power and energy capacity has continued to rise, increasing nickel content in Li[Ni1-y-zCoyMnz]O2 (NCM) or Li[Ni1-y-zCoyAlz]O2 (NCA) cathode materials has been the subject of extensive study to improve the specific capacity of Li-ion batteries. Commercialized (Ni composition ~60%) NCM/NCA can deliver specific capacity near 170 mAh/g while LixNiO2 (LNO) has been shown to offer over 200 mAh/g, but coincidently suffers from instability, and anisotropic volume strain due to Ni(III)-O6 Jahn-Teller (JT) distorted shearing and especially lattice collapse during charging. The resulting crack formation in primary particles and pulverization of secondary particles increases surface area exposed to the liquid electrolyte and accelerates phase decomposition due to oxygen evolution and side reactions, with capacity fading increasingly well studied and characterized, including the known chemical instability of Ni—O system yields oxygen redox and evolution at LNO surfaces near 4.2 V. In potential solid-state battery applications, the mechanical nature of large anisotropic strain will incur broken contact with solid electrolyte and shorten lifespan. As the most critical lattice collapse occurs in charging beyond 75% de-lithiation (x < 0.25), mitigation by implementing cutoff voltage near 4.2 V (vs Li anode) has commonly been implemented, consequently restricting practical energy density. Detailed analysis of electronic charge and charge density distribution via first-principles calculations reveals oxygen-nickel charge transfer during charge/discharge is well correlated to oxygen-cation coordination. While charging, each Ni layer shrinks monotonically throughout de-lithiation, from 2.17 Å to 1.9 Å, and the Li interslab thickness first increases, from 2.55 Å to 2.82 Å at 75% de-lithiation, then decreases to 2.48 Å. The former is consistent with the perspective of Ni(III) [3d7: t2g 6 eg 1] oxidation to smaller Ni(IV) [3d6: t2g 6 eg 0], collaborated by respective magnetic moments, a / b lattice constant decrease, and Ni-O bond length changes associated with the loss of JT distortion. The interslab behavior, however, requires recognition of Ni-O bonding character of eg states, where modeling the interslab expansion and collapse in finer detail confirms approximately linear behavior in each regime, notably collapsing even with low but finite Li (e.g. 20-8%) in each interlayer (no empty layers or stacking order transitions). By Bader charge analysis, it is found that Ni exhibits less redox activity directly; rather oxygen charge is more significantly depleted due to charge transfer as eg bonding states are de-occupied by electrons during charge, indicated in projected density of states. Smaller and substantially charge-depleted oxygens appear around 25% Li content and were all identified as oxygens lacking any Li nearest neighbors. Intuitively, as concentrations progress below 25% (> 4.2 V), the number of such oxygen rapidly increases with a corresponding dwindling of higher charge state oxygens local to the few remaining Li. The interslab (Li-layer) thickness decrease follows from these smaller oxygen ins and significantly lessened repulsion across the Li layer in local close-packed, O3 stacking sequence. To mitigate the collapse, high valent cations as dopants at Li-site are investigated in similar detail with this mechanism in mind. Potential cations were chosen on a basis of compatibility with Li-site octahedra, with radii similar to Li+, and less comparable to Ni(II), Ni(III), or Ni(IV). Models of LNO doped as Lix-yMyNiO2 are found to donate charge to all six neighboring oxygen and the respective NiO6 octahedra throughout de-lithiation (decreasing x, 1 > x > y). The charge-compensated oxygens retain stronger local coulomb interaction near the cation dopant and provide a pillaring effect to reduce lattice collapse even to 100% depth of discharge. Select dopants indicate low anisotropy and volumetric strain, e.g. ∆V/V ~ 2% over the range of 0-90% capacity. The presented role of cation dopants reinforces the promise of “zero-strain” LNO cathode material, with simultaneous improvement to thermal and mechanical stability, encouragingly reported by experimental works, and both greater capacity and power by unlocking deeper charging.

(Best Paper Award, Invited) Manufacturing of Nanosheets and Multilayer Nanogaps in Silicon

Nanogap technology is the basic concept for many promising devices such as localized SOI, multichannel FETs, and resonant tunneling diodes.It will be shown that intrinsic bulk strain in single crystalline silicon can be used to create homogeneous nanogaps with a few nanometer gap distance. The strain has been created by epitaxial growth of Si1-xGex/Si multi-layer stacks on 200 mm (100) silicon wafers. The stacks were patterned by RIE to reveal the side walls for subsequent lateral etching with gaseous hydrochloric acid. In accordance with former investigations [1] we found that a selectivity up to 1000:1 for Si1-xGex/Si can be achieved for Ge-concentrations >30% and growth temperatures T<650°C. XRD measurements, SEM pictures and wagon wheel test structures prove that for the anisotropic lateral etching behavior intrinsic strain is the dominant factor. Furthermore, the crystal orientation plays a dominant role (Fig. 1). Based on this behavior multilayer nanogaps with spacings <10 nm had been fabricated.In a subsequent process nanogaps down to 5 nm have been successfully filled completely with dielectrics and/or metals by low temperature (T<450°C) plasma oxidation, LPCVD as well as ALD (Fig. 2). The resulting nanosheets can be used for device applications.Vertical diodes and lateral MOS transistors with nanogaps and nanosheets have been fabricated. Diodes with a SiO2 gap filling show perfect Fowler-Nordheim tunneling, which proves the high quality of the gap filling process. The electrical properties of nanogap-MOSFETs and various nanogap-diodes will be presented.[1] Destefanis et al., Semiconductor Sci. Technol. 23, 1 (2008) Fig. 1: Wagon wheel structure showing the etch anisotropy of 8 nm SiGe layer in Si Fig. 2: SEM cross section of a multistack of 6 SiGe layers selectively etched and completely filled with LPCVD oxide

Surface plasmon resonances in anisotropic strained graphene

Straintronics of two-dimensional (2D) materials is a new research area in condensed matter physics for studying 2D materials under strain. Anisotropic strained graphene does not seem to preserve the polarization of the incident light. This suggests intriguing possibilities for developing surface plasmon resonances (SPRs) in graphene-based optoelectronics. In this work, we investigate the SPR properties of a graphene–prism coupling structure under a relatively small anisotropic strain. We demonstrate that, for an incident linearly polarized light in the strained graphene–prism coupling structure, anisotropic SPRs would emerge along with specific strain directions.

Wireless-Powering Deep Brain Stimulation Platform Based on 1D-Structured Magnetoelectric Nanochains Applied in Antiepilepsy Treatment.

Electrical deep brain stimulation (DBS) is a top priority for pharmacoresistant epilepsy treatment, while less-invasive wireless DBS is an urgent priority but challenging. Herein, we developed a conceptual wireless DBS platform to realize local electric stimulation via 1D-structured magnetoelectric Fe3O4@BaTiO3 nanochains (FBC). The FBC was facilely synthesized via magnetic-assisted interface coassembly, possessing a higher electrical output by inducing larger local strain from the anisotropic structure and strain coherence. Subsequently, wireless magnetoelectric neuromodulation in vitro was synergistically achieved by voltage-gated ion channels and to a lesser extent, the mechanosensitive ion channels. Furthermore, FBC less-invasively injected into the anterior nucleus of the thalamus (ANT) obviously inhibited acute and continuous seizures under magnetic loading, exhibiting excellent therapeutic effects in suppressing both high voltage electroencephalogram signals propagation and behavioral seizure stage and neuroprotection of the hippocampus mediated via the Papez circuit similar to conventional wired-in DBS. This work establishes an advanced antiepilepsy strategy and provides a perspective for other neurological disorder treatment.

Anisotropic strain of anthracite induced by different phase CO2 injection and its effect on permeability

To study the swelling/shrinkage strain effects of different phases of CO2 when injected into anthracite and the influence that has on the dynamic evolution of coal permeability, an experimental study of coal anisotropic adsorption of CO2 was carried out by using a triaxial compression test device, and the relationship between the swelling/shrinkage strain and permeability of the coal was discussed. The results show that the adsorption strain and time of gas exposure throughout different phase states of the CO2 injected show three stages of evolutionary behavior. The adsorption swelling of the coal sample increases with rising gas pressure. The adsorption strain of coals under the action of supercritical CO2 increased by 16.28% and 17.36% against the action of subcritical CO2, respectively. The coal portrayed anisotropic characteristics during the process of adsorption-caused swelling deformation and desorption-caused contraction, and the deformation in the vertical layer direction was greater than that in the parallel layer direction, and the anisotropy gradually weakened with increasing pressure. The permeability of the coal and the temperature is a quadratic function relationship under different effective stress conditions, and there is a zone where the changes occur. The study provides a theoretical basis CO2- Enhanced coalbed methane recovery.

Strain effects on stability of topological ferroelectric polar configurations in (PbTiO3)n/(SrTiO3)n superlattices

The (PbTiO3)n/(SrTiO3)n (PTO/STO) superlattice system has been shown to exhibit interesting topological phases (e.g., vortices and skyrmions) in addition to normal ferroelectric domain states. Existing studies are mostly focused on the dependence of topological polar distributions and properties of PTO/STO superlattice on its periodicity. Here, we study the strain effect on the topological phase transitions and ferroelectric domain structures employing phase-field simulations. We summarized in an isotropic strain (in-plane misfit strain along the x direction is equal to that along the y direction) periodicity phase diagram displaying the stability regions of different polar topological states, including normal ferroelectric twins, vortices, skyrmions, and mixtures of vortices and twins. We also analyzed the polarization configurations under anisotropic in-plane strains (in-plane misfit strain along the x direction is not equal to that along the y direction) and demonstrated that the strain anisotropy can be used to tune the directions of vortex arrays along either the [100] pc or [010] pc directions or labyrinth vortex arrays. This work offers guidance to manipulating polar structures in the PTO/STO superlattices via strain engineering.