Large Tensile Strain Research Articles

Oxygen Vacancy Ordering Modulation of Magnetic Anisotropy in Strained LaCoO3- x Thin Films.

Oxygen vacancy configurations and concentration are coupled with the magnetic, electronic, and transport properties of perovskite oxides, and manipulating the physical properties by tuning the vacancy structures of thin films is crucial for applications in many functional devices. In this study, we report a direct atomic resolution observation of the preferred orientation of vacancy ordering structure in the epitaxial LaCoO3- x (LCO) thin films under various strains from large compressive to large tensile strain utilizing scanning transmission electron microscopy (STEM). Under compressive strains, the oxygen vacancy ordering prefers to be along the planes parallel to the heterointerface. Changing the strains from compressive to tensile, the oxygen vacancy planes turn to be perpendicular to the heterointerface. Aberration-corrected STEM images, electron diffractions, and X-ray diffraction combined with X-ray photoelectron spectroscopy demonstrate that the vacancy concentration increases with increasing misfit strains and vacancy distribution is more ordered and homogeneous. The temperature-dependent magnetization curves show the Curie temperature increases, displaying a positive correlation with the misfit strains. With change in the strain from compressive to tensile, anisotropy fields vary and show large values under tensile strains. It is proposed that oxygen vacancy concentration and preferred ordering planes are responsible for the enhanced magnetic properties of LCO films. Our results have realized a controllable preparation of oxygen vacancy ordering structures via strains and thus provide an effective method to regulate and optimize the physical properties such as magnetic properties by strain engineering.

Impact of Strain-Induced Changes in Defect Chemistry on Catalytic Activity of Nd2NiO4+δ Electrodes.

It is well known that defect chemistry plays a vital role in determining the electronic structure, ionic conductivity, and catalytic activity of metal oxides, as demonstrated in perovskite-based oxides to achieve desired functionalities. In this work, we explored the possibility of tuning the defect chemistry and hydrogen oxidation reaction (HOR) activity of Nd2NiO4+δ model thin films by controlling the lattice strain. Highly textured Nd2NiO4+δ thin films with different strain states were prepared on (110)- and (100)-oriented single-crystal yttrium-stabilized zirconium (YSZ) substrates using pulsed laser deposition. Electrochemical impedance spectroscopy results indicated that the NNO(100) film on the YSZ(110) substrate with larger tensile strain in the a- b plane and compressive strain along the c axis exhibited higher HOR activity than the NNO(110) film on the YSZ(100) substrate at 500-600 °C. The enhancement in HOR activity is attributed to the strain-induced difference in the oxygen defect concentration, as confirmed by high-resolution X-ray diffraction analysis. We believe that the correlation among the strain state, defect chemistry, and catalytic properties is helpful for rational design of more efficient electrode materials.

Evolution of out‐of‐plane deformation and subsequent instability in rectangular RC walls under in‐plane cyclic loading: Experimental observation

SummaryIn this study, to understand the causes and consequences of out‐of‐plane instability in rectangular RC walls, the sequence of events observed during a rectangular wall experiment campaign where out‐of‐plane instability was the primary failure pattern is discussed in detail. Large tensile strains developed in the boundary zone longitudinal bars at large in‐plane curvature demands and caused subsequent yielding in compression during load reversal before crack closure could activate contribution of concrete to the load‐carrying capacity of the wall. The specimen deformed in the out‐of‐plane direction when this phenomenon progressed along a sufficient height and length of the wall and led to significant reduction of its stiffness in the out‐of‐plane direction. One of the major sources of inherent eccentricity that could potentially affect development of this failure pattern is identified to be the postyield response of the longitudinal bars across the wall thickness, generating different values of residual strains and consequently inducing their asynchronous yielding under compressive actions. Analytical models proposed in literature for prediction of out‐of‐plane instability failure as well as their relevant assumptions are compared with the test measurements. While the observations presented in past research on development of out‐of‐plane instability in concrete columns representing the boundary zones of rectangular walls are in line with the sequence of events observed in this study, the assumptions made in the analytical models regarding the height of the wall effectively involved in formation of out‐of‐plane deformations (effective buckling height) were found to be different.

Hyperelastic constitutive modelling for transversely isotropic composites and orthotropic biological tissues

This work presents an orthotropic hyperelastic strain energy function (SEF) and associated nonlinear constitutive theory that describes the response of transversely isotropic and orthotropic neo-Hookean materials under a range of physical deformations in which the strains are large. The proposed SEF is categorised as invariant-free and is presented as an expression involving quadruple contractions between fourth-order tensors. This form of the SEF retains directional information which can sometimes become lost in typical functions involving scalar invariants. To describe stress-strain relations, the well-known Hookean stiffness tensor for small deformations is decomposed into fourth-order Orthotropic Lamé material tensors separating coupled and non-coupled behaviours. By equating the material parameters in each direction, the model collapses to isotropic Lamé hyperelasticity. The proposed hyperelastic model remains consistent with the linear analysis of anisotropic bodies, when subject to infinitesimal deformations. The proposed SEF compares favourably to large tensile strain and simple shear experimental tests of both isotropic and transversely isotropic materials. Employing an Ogden-type formulation to include additional material terms, the proposed SEF is extended to model highly nonlinear responses such as material stiffening of biological tissues.

Stress Analysis of Pipeline Laying on Thrust Fault

It is taken one project of pipe installment in tunnel of China-Central Asia Line as one case. Set up one FEM contact element pairs, it simulates the relationship of pipe and thrust fault. With the thrust fault happening, the laying pipe occur large displacement, stress, and gap or pressure. Compare the maximum stress to 90% of allowable yield strength, it determines damage occurs or not about the pipe. Dislocation of ground face leads to pipe local shrinking, and then large tensile strain happens to local damage. To avoid that bad consequence, horizontal Compensators will be installed on tunnel both sides to coordinate deformation.

Boundary Elements of Special Reinforced Concrete Walls Tested under Different Loading Paths

Large inelastic tensile strains and wide horizontal cracks primarily caused by in-plane loading, may lead to local out-of-plane deformations of the end regions of reinforced concrete (RC) walls within a buckled zone that comprises the plastic hinge length. Critical parameters that influence the onset of this failure mode have been studied through past experimental tests on RC prisms subjected to axial loading, which simulates the response of end regions of RC walls under in-plane demands. Missing from those studies is the effect of bidirectional loading protocols and the effect of the longitudinal reinforcement ratio on the hysteretic response. Therefore, 12 RC prisms with 3 longitudinal steel ratios representative of prototype boundary elements of typical special RC walls and piers walls were tested. The experimental results showed that the longitudinal steel content and the in-plane loading demands mainly govern the onset of out-of-plane buckling instability of planar RC walls.

(Invited) Strain-Engineered Low-Threshold Group IV Lasers for Photonic-Integrated Circuits

Photonic-integrated circuits (PICs) are a key enabler for the ultimate miniaturization of next-generation optical computers that can fit in the palm of your hand. However, the realization of fully functional PICs is currently limited by the absence of an efficient light source on silicon (Si), thus making a practical Si-compatible light source the Holy Grail. Especially, it has been thus far considered close to impossible to create a practical on-chip laser using Si-compatible group IV semiconductor materials (e.g. germanium (Ge)) owing to their indirect bandgap nature. Strain-engineered Ge material has recently garnered much attention for the dramatic reduction of the lasing threshold of group IV lasers because large tensile strain fundamentally alters the Ge’s bandstructure. Here, we present our recent research works on highly strained group IV materials on a Si chip for the realization of low-threshold on-chip lasers. In the first part, we will introduce our innovative strain engineering platforms that can create direct bandgap Ge nanowires by inducing >5% elastic tensile strain. In the second part, we will present the first experimental observation of low-threshold optically pumped lasing in highly strained Ge nanowires. The strain engineering of direct bandgap germanium-tin will also be described for the ultimate reduction of the lasing threshold.

Epitaxial strain modulated electronic properties of interface controlled nickelate superlattices

Perovskite nickelate heterostructure consisting of single unit cell of EuNiO$_3$ and LaNiO$_3$ have been grown on a set of single crystalline substrates by pulsed laser interval deposition to investigate the effect of epitaxial strain on electronic and magnetic properties at the extreme interface limit. Despite the variation of substrate in-plane lattice constants and lattice symmetry, the structural response to heterostructuring is primarily controlled by the presence of EuNiO$_3$ layer. In sharp contrast to bulk LaNiO$_3$ or EuNiO$_3$, the superlattices grown under tensile strains exhibit metal to insulator transition (MIT) below room temperature. The onset of magnetic and electronic transitions associated with the MIT can be further separated by application of large tensile strain. Furthermore, these transitions can be entirely suppressed by very small compressive strain. X-ray resonant absorption spectroscopy measurements reveal that such strain-controlled MIT is directly linked to strain induced self-doping effect without any chemical doping.

Plastic Deformation Mechanism in Double-Roller Clamping Spinning of Flanged Thin-Walled Cylinder

Double-roller clamping spinning (DRCS) is a new process for forming a thin-walled cylinder with a complex surface flange. The process requires a small spinning force, and can visibly improve forming quality and production efficiency. However, the deformation mechanism of the process has not been completely understood. Therefore, both a finite element numerical simulation and experimental research on the DRCS process are carried out. The results show that both radial force and axial force dominate the forming process of DRCS. The deformation area elongates along the radial direction and bends along the axial direction under the action of the two forces. Both the outer edge and round corner of the flange show the tangential tensile stress and radial compressive stress. The middle region shows tensile tangential stress and radial stress, while the inner edge shows compressive tangential stress and radial stress. Tangential tensile strain causes a wall thickness reduction in the outer edge and middle regions of the flange. The large compressive thickness strain causes material accumulation and thus, an increase in the wall thickness of the round corner. Because of bending deformation, the round corner shows a large radial tensile strain in addition. The inner edge of the flange shows small radial compressive strain and tensile strain in thickness. Thus, the wall thickness on the inner edge of the flange continues to increase, although the increment is small. Furthermore, microstructure analysis and tensile test results show that the flanged thin-walled cylinder formed by DRCS has good mechanical properties. The results provide instructions for the application of the DRCS process.

Transport properties of FeSe epitaxial thin films under in-plane strain

We demonstrate successful fabrication of FeSe films with various magnitude of lattice strain, from tensile to compressive. The superconducting transition temperature, Tc, shows the systematic change by in-plane strain. It reaches 12 K for the films with compressive strain whereas the superconductivity disappears for the films with large tensile strain. The structural transition temperature, Ts, decreases slightly as the in-plane strain is more compressive. In other words, there is a negative correlation between Tc and Ts. It is also found that both the hole and the electron carrier densities evaluated by transport properties increase as the in-plane strain is more compressive. Therefore, there is a clear correlation between Tc and the carrier densities, which suggests that it is essential for the Tc enhancement of iron-based superconductors to increase carrier densities.

In situ Observation of Compression Damage in a Three-Dimensional Braided Carbon Fiber Reinforced Carbon and Silicon Carbide (C/C-SiC) Ceramic Composite.

Deformation and mechanical damage in a three-dimensional braided carbon fiber reinforced carbon and silicon carbide ceramic composite, subjected to compressive loading, has been studied in situ by laboratory X-ray computed tomography. Dimensional change was measured and damage visualized by digital volume correlation analysis of tomographs. Cracks nucleated from defects within the fiber bundles and tended to propagate along the fiber bundle/matrix interface. For longitudinal compression, parallel to the fiber bundles, the initial elastic modulus decreased with increasing compressive strain while significant transverse tensile strains developed due to distributed cracking. For transverse compression, perpendicular to the fiber bundles, the compressive elastic modulus was effectively constant; the tensile strains developed along the fiber direction were small, whereas macroscopic fracture between the fiber bundles caused very large bulk tensile strain perpendicular to the loading. The observations suggest that the mechanical strength might be improved through control of pre-existing defects and application of stitch fibers in the transverse direction.

Phase diagram and physical properties of (110) oriented KNbO3 film

Based on the phenomenological Landau-Devonshire theory, the phase diagram and physical properties of (110) oriented KNbO3 film are investigated. The “misfit strain-misfit strain” phase diagram at room temperature is constructed in the frame of eighth-order thermodynamic potential. Three tetragonal phases and two orthorhombic phases are stable in phase diagram due to the strain anisotropy. The large in-plane compressive or tensile misfit strains favor the tetragonal phases. Moreover, both the tensile misfit strain u1 (or u2) and compressive strain u2 (or u1) induce the orthorhombic phases. Large piezoelectric coefficient is obtained in orthorhombic phases which have the small in-plane tensile misfit strains. It makes (110) oriented KNbO3 film suitable for applications in electromechanical devices.

A novel stretchable supercapacitor electrode with high linear capacitance

Conventional flexible supercapacitors that can work under consecutive bending, folding and even twisting without performance degradation have been widely reported. Nevertheless, these devices can hardly be used under large tensile strain due to limited stretchability. In this regard, the application field of flexible supercapacitors can be remarkably broaden if they are designed as stretchable power supplies for wearable electronic devices. Herein, we report a stretchable supercapacitor electrode through in situ synthesis of hierarchical carbon tubular nanostructures (hCTNs) and conducting polyaniline (PANI) onto stainless steel spring (SSS) which features both excellent conductivity and high stretchability. The as-prepared helical electrode exhibits considerable specific capacitance of 277.8 F g−1 at 1 A g−1 and unprecedented linear capacitance of 402.8 mF cm−1 at the current density of 1 mA cm−1, which is much higher than most previously reported literatures. Besides, electrochemical performance of this electrode can be maintained under various mechanical loading such as compressing and bending. Additionally, 100% tensile strain of electrode is successfully demonstrated without sacrificing its electrochemical performance.

Superelastic wire-shaped supercapacitor sustaining 850% tensile strain based on carbon nanotube@graphene fiber

Stretchable and flexible supercapacitors are highly desired due to their many potential applications in wearable devices. However, it is challenging to fabricate supercapacitors that can withstand large tensile strain while maintaining high performance. Herein, we report an ultra-stretchable wire-shaped supercapacitor based on carbon nanotube@graphene@MnO2 fibers wound around a superelastic core fiber. The supercapacitor can sustain tensile strain up to 850%, which is the highest value reported for this type of device to date, while maintaining stable electrochemical performance. The energy density of the supercapacitor is 3.37 mWh·cm–3 at a power density of 54.0 mW·cm–3. The results show that 82% of the specific capacitance is retained after 1,000 stretch–release cycles with strains of 700%, demonstrating the superior durability of the elastic supercapacitor and showcasing its potential application in ultra-stretchable flexible electronics.

Strain relaxation via formation of cracks in compositionally modulated two-dimensional semiconductor alloys

Composition modulation of two-dimensional transition-metal dichalcogenides (TMDs) has introduced an enticing prospect for the synthesis of Van der Waals alloys and lateral heterostructures with tunable optoelectronic properties. Phenomenologically, the optoelectronic properties of alloys are entangled to a strain that is intrinsic to synthesis processes. Here, we report an unprecedented biaxial strain that stems from the composition modulation of monolayer TMD alloys (e.g., MoS2xSe2(1 - x)) and inflicts fracture on the crystals. We find that the starting crystal (MoSe2) fails to adjust its lattice constant as the atoms of the host crystal (selenium) are replaced by foreign atoms (sulfur) during the alloying process. Thus, the resulting alloy forms a stretched lattice and experiences a large biaxial tensile strain. Our experiments show that the biaxial strain relaxes via formation of cracks in interior crystal domains or through less constraint bounds at the edge of the monolayer alloys. Griffith’s criterion suggests that defects combined with a sulfur-rich environment have the potential to significantly reduce the critical strain at which cracking occurs. Our calculations demonstrate a substantial reduction in fracture-inducing critical strain from 11% (in standard TMD crystals) to a range below 4% in as-synthesized alloys.

Grain wall boundaries in centimeter-scale continuous monolayer WS2 film grown by chemical vapor deposition

Centimeter-scale continuous monolayer WS2 film with large tensile strain has been successfully grown on oxidized silicon substrate by chemical vapor deposition, in which monolayer grains can be more than 200 μm in size. Monolayer WS2 grains are observed to merge together via not only traditional grain boundaries but also non-traditional ones, which are named as grain walls (GWs) due to their nanometer-scale widths. The GWs are revealed to consist of two or three layers. Though not a monolayer, the GWs exhibit significantly enhanced fluorescence and photoluminescence. This enhancement may be attributed to abundant structural defects such as stacking faults and partial dislocations in the GWs, which are clearly observable in atomically resolved high resolution transmission electron microscopy and scanning transmission electron microscopy images. Moreover, GW-based phototransistor is found to deliver higher photocurrent than that based on monolayer film. These features of GWs provide a clue to microstructure engineering of monolayer WS2 for specific applications in (opto)electronics.

First-principles study of perpendicular magnetic anisotropy in ferrimagnetic D22-Mn3X (X = Ga, Ge) on MgO and SrTiO3

The magnetic anisotropy energy (MAE) of bulk D022-Mn3X (X = Ga, Ge), Mn3X/MgO, and Mn3X/STiO3(STO) heterostructures is calculated from first principles calculations. The main source of the large perpendicular magnetic anisotropy (PMA) of bulk Mn3X is identified as Mn atoms in the Mn-Mn layer. In the four heterostructures, the magnetic moment of interfacial Mn atoms was reversed when Mn3X was epitaxially grown on MgO and STO substrates. More importantly, a large in-plane tensile strain induced by lattice mismatch between Mn3X and MgO significantly changes the MAE, explaining the difficulty in experiments to obtain PMA in epitaxial Mn3X/MgO. Furthermore, interface and surface Mn atoms also help to enhance the PMA of Mn3X/STO (MgO) heterostructures due to dxy and dz2 states changing from occupied states in bulk Mn3X to unoccupied states in the interface (surface) Mn of the heterostructures. These results suggest that the PMA of manganese compound heterostructures can be produced by decreasing the lattice mismatch with substrates and will guide the search for ultrathin manganese compound films with high PMA epitaxially grown on substrates for the application of spintronic devices.

Graphene nanoribbon as an elastic damper

Heterostructures composed of dissimilar two-dimensional nanomaterials can have nontrivial physical and mechanical properties which are potentially useful in many applications. Interestingly, in some cases, it is possible to create heterostructures composed of weakly and strongly stretched domains with the same chemical composition, as has been demonstrated for some polymer chains, DNA, and intermetallic nanowires supporting this effect of two-phase stretching. These materials, at relatively strong tension forces, split into domains with smaller and larger tensile strains. Within this region, average strain increases at constant tensile force due to the growth of the domain with the larger strain, at the expense of the domain with smaller strain. Here, the two-phase stretching phenomenon is described for graphene nanoribbons with the help of molecular dynamics simulations. This unprecedented feature of graphene that is revealed in our study is related to the peculiarities of nucleation and the motion of the domain walls separating the domains of different elastic strain. It turns out that the loading–unloading curves exhibit a hysteresis-like behavior due to the energy dissipation during the domain wall nucleation and motion. Here, we put forward the idea of implementing graphene nanoribbons as elastic dampers, efficiently converting mechanical strain energy into heat during cyclic loading–unloading through elastic extension where domains with larger and smaller strains coexist. Furthermore, in the regime of two-phase stretching, graphene nanoribbon is a heterostructure for which the fraction of domains with larger and smaller strain, and consequently its physical and mechanical properties, can be tuned in a controllable manner by applying elastic strain and/or heat.

Polyurethane sponges decorated with reduced graphene oxide and silver nanowires for highly stretchable gas sensors

Unlike the stretchable physical sensors such as stretchable pressure sensors, strain sensors, and temperature sensors, few works have been reported on the stretchable gas sensors. This study presents that stretchable gas sensors can be fabricated by decorating reduced graphene oxide/silver nanowires (rGO/AgNWs) hybrids on the porous polyurethane (PU) sponges using a facile dip-coating method. The sensors show good room-temperature responses to NO2 gas under both a bending strain (r = 3 mm) and a large tensile strain up to 60%. The response of about −15% is measured at a 50 ppm of NO2 under a 60% strain. Furthermore, reducing gases like acetone and ethanol can also be detected under the large strains. The results of this study offer a new insight into realization of highly stretchable and easy-to-fabricate gas sensors.

Theoretical study of cubic-Li7La3Zr2O12(001)/LiCoO2(10-14) interface

Abstract