Anisotropic Lattice Strain Research Articles

Contribution of Anisotropic Lattice‐Strain to Piezoelectricity and Electromechanical Power Generation of Flexible Inorganic Halide Thin Films

AbstractStrain engineering has recently emerged as a critical strategy in improving the optoelectronic properties of perovskite halide materials. However, the effects of lattice strain on piezoelectricity and related device performance have not been realized in perovskite halides. Herein, an in situ‐strain‐engineering method is proposed to induce a compressive or tensile strain of up to 0.75% for flexible inorganic–halide CsPbBr3 thin films, resulting in anisotropic lattice strain, e.g., a contraction in the ab‐plane and elongation along the c‐axis in the case of compressive strain. The optimal piezoelectric energy harvesting values of ≈22.6 V and ≈1.13 µA are achieved, which are nearly 3.8 and 7.1 times better than those of the unstrained reference, for the compressively 0.75%‐strained CsPbBr3 thin films further optimized with electric poling. These output values are the best so far compared to any previously reported values for perovskite‐halide‐based thin‐film harvesters. The structural origins of these superlative results are systematically revealed to be associated with the distortion of coupled PbBr6 octahedra and the atomic displacement within each octahedron.

Strain enhancement due to oxygen vacancies in perovskite oxide films

Misfit-induced crystallographic alignment of elastic dipoles of oxygen vacancies enhances anisotropic lattice strain beyond the misfit magnitude and raises inhomogeneous strain in epitaxial perovskite oxide films.

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Understanding the formation of antiphase boundaries in layered oxide cathode materials and their evolution upon electrochemical cycling

Well-dispersed single-crystalline nickel-rich cathode for long-life high-voltage all-solid-state batteries

Traditional heterogeneous polycrystalline layered oxides suffer from serious chemo-mechanical degradations, which is extremely true in nickel-rich cathodes under high-voltage operation. Although single-crystalline structure is proved to be able to withstand anisotropic lattice strain and prevent cracks formation, the long cycle stability at high-voltage in all-solid-state batteries (ASSBs) with nickel-rich layered oxides as the cathode are still far from commercial applications. Herein, we synthesize a micro-sized single-crystalline nickel-rich oxides LiNi0.83Co0.11Mn0.06O2 (SC–N83) to eliminate the chemo-mechanical failures. The well-dispersed SC-N83 in the ASSBs delivers an excellent cyclic stability under high-voltage (4.4 V vs Li/Li+) operation, which shows a capacity retention of 85.1% after 500 cycles at 0.5C. Even at high active areal loading of 22.6 cm−2 (corresponding to an initial areal capacity of 4.19 mAh cm−2) and high temperature of 50 °C, the SC-N83 cathodes can still maintain 75.5% discharge capacity after 200 cycles at 0.5C. The high cycling stability is further proved to be attributed to dramatically suppressed mechanical failure caused by the build-up of strain and stress. This proposed strategy with highly dispersed single-crystalline nickel-rich oxides paves the way to develop advanced high-capacity and high-voltage operating ASSBs.

Peering into Batteries: Electrochemical Insight Through In Situ and Operando Methods over Multiple Length Scales

Summary In order to overcome the limitations of static and destructive characterizations of Li-ion battery materials and components, comprehensive investigation peering into batteries over various length and time scales is essential. In this regard, emerging in situ and operando characterization methodologies focusing on multiple size domains become a powerful approach to resolve current challenges and navigate future directions. This perspective provides a series of illustrative examples of in situ and operando characterizations over atomic, crystallite/particle, electrode, and battery system length scales with a focus on two electrode material classes: insertion and conversion materials. The operating principles, features, analysis methods, and information gained from each characterization method are discussed. Herein, we present the necessity and opportunity for in situ and operando characterization of electrochemical energy storage materials and systems. Further, we suggest future directions to gain the insight needed to tackle currently intractable issues on Li-ion battery application, failure, and emerging design concepts.

In Situ Strain Evolution on Pt Nanoparticles during Hydrogen Peroxide Decomposition.

Fundamental understanding of structural changes during catalytic reactions is crucial to understanding the underlying mechanisms and optimizing efficiencies. Surface energy and related catalytic mechanisms are widely studied. However, the catalyst lattice deformation induced by catalytic processes is not well understood. Here, we study the strain in an individual platinum (Pt) nanoparticle (NP) using Bragg coherent diffraction imaging under in situ oxidation and reduction reactions. When Pt NPs are exposed to H2O2, a typical oxidizer and an intermediate during the oxygen reduction reaction process, alternating overall strain distribution near the surface and inside the NP is observed at the (111) Bragg reflection. In contrast, relatively insignificant changes appear in the (200) reflection. Density functional theory calculations are employed to rationalize the anisotropic lattice strain in terms of induced stress by H2O2 adsorption and decomposition on the Pt NP surface. Our study provides deeper insight into the activity-structure relationship in this system.

(Invited) Engineering Strain, Defects, and Electronic Properties of (110)-Oriented Strained Si

Strain engineering of group IV semiconductors has been extensively investigated with an aim to produce high mobility platform for high performance electronic devices. The lattice strain significantly affects the carrier mobility via modulation of the energy band structure and its effect on the crystalline defect formation. The lattice structure of the strained crystal is determined by the amount of the strain and the boundary condition. In this study, the morphological aspects and the electronic properties of the (110)-oriented strained Si/SiGe/Si heterostructures grown by molecular beam epitaxy (MBE) have been studied. Potential of this material system as a high hole mobility semiconductor platform is discussed. It has been found that highly anisotropic lattice strain and defect configuration can be realized in this heterostructure and that this anisotropic feature plays important roles in the enhancement of the hole mobility.

Effect of heat treatment on the tensile behavior of selective laser melted Ti-6Al-4V by in situ X-ray characterization

Selective Laser Melted Ti-6Al-4V (as-SLMed) exhibits decreased yield strength, increased work hardening, and increased ductility after heat treatment at 730 °C (HT-730) or 900 °C (HT-900) for 2 h. To understand the change of mechanical properties, in situ high energy X-ray diffraction (HEXRD) is used to examine the phase composition, load partitioning, slip system activity, and dislocation density evolution in all three specimens. The as-SLMed specimen is dominated by martensitic α΄. After heat treatment, α΄ partly or fully decomposes into α+β, reducing the yield strength. In HT-730, β precipitates with confined size show much higher lattice strain than the α΄/α matrix during deformation; in HT-900, the lattice strain difference is mostly eliminated. This is a key reason for the increased ductility in HT-900. From the anisotropic lattice strain development, basal slip is identified as the easiest slip system in α΄/α. Using an elasto-plastic self-consistent (EPSC) model, the critical resolved shear stress ratio between prismatic slip and basal slip (CRSSprism/CRSSbasal) is estimated to be 1.31 and 1.16 in the as-SLMed and the HT-900 specimens, respectively. The α phase in HT-900 is able to activate multiple slip systems and accumulate more dislocations during plastic deformation. This explains why HT-900 has better ductility and higher work hardening rate than the other two specimens.

Electric-field-induced structure and domain texture evolution in PbZrO3-based antiferroelectric by in-situ high-energy synchrotron X-ray diffraction

Antiferroelectrics (AFEs) have a great potential for modern electronic devices by virtue of the large strain during the antiferroelectric-to-ferroelectric (AFE-FE) phase transition under external electric fields. Although the fascinating macroscopic properties of AFE materials have been extensively studied, it is still unclear how the underlying structure evolution engenders their defining properties. Here we employ an electric biasing in-situ high-energy synchrotron X-ray diffraction technique to reveal the phase, domain texture, and lattice evolution in a high performance PbZrO3-based AFE material. During the reversible AFE-FE transition triggered by electric fields, the evolution of the superstructure for AFE pseudo-tetragonal and FE rhombohedral phase is found to display strong dependence on the angle with respect to the field direction. In contrast to previous prediction, it is found that there is no obvious domain reorientation in the AFE phase, when the system is far away from the AFE-FE transitions. The electric-field-induced FE rhombohedral phase exhibits an unusual microscopic behavior, distinguished from the normal one, presenting small changes in domain texture and lattice strain with electric field, and leading to a small piezoelectric response. The longitudinal, transverse, and volume strains estimated from the XRD peak profiles are well consistent with the macroscopic strain measurements. It is demonstrated that the large strain arises from the structural change associated with anisotropic lattice strain and highly preferential domain reorientation during the AFE-FE transitions. The AFE-FE switching sequence is constructed based on the present study, which provides a further understating of AFE materials.

Li[Ni0.9Co0.09W0.01]O2: A New Type of Layered Oxide Cathode with High Cycling Stability

AbstractSubstituting W for Al in the Ni‐rich cathode Li[Ni0.885Co0.10Al0.015]O2 (NCA89) produces Li[Ni0.9Co0.09W0.01]O2 (NCW90) with markedly reduced primary particle size. Particle size refinement considerably improves the cathode's cycling stability such that the NCW90 cathode retains 92% of its initial capacity after 1000 cycles (compared to 63% for NCA89), while the cathode produces a high initial discharge capacity of 231.2 mAh g−1 (at 0.1 C). Thus, the proposed NCW90 can deliver high energy density and a long battery lifetime simultaneously, unlike other Ni‐rich layered oxide cathodes. This unprecedented cycling stability is mainly attributed to a series of interparticular microfractures that absorb the anisotropic lattice strain caused by a deleterious phase transition near the charge end, thereby improving the cathode's resistance to fracture. Microcrack suppression preserves the mechanical integrity of the cathode particles during cycling and protects the particle interior from detrimental electrolyte attack. The proposed NCW90 cathode provides an improved material from which a new series of Ni‐rich layered cathode can be developed for next‐generation electric vehicles.

Anisotropic lattice strain induced by the enhanced electronic hybridization in SrTiO3

We introduce enhanced hybridization of Ti 3d-O 2p electronic states by applying an inhomogeneous electric field to a perovskite oxide, SrTiO3, which leads to lattice deformation through electrostriction and the converse flexoelectric effect. However, unlike most studies revealing lattice responses to dipolar polarization, the enhanced electronic hybridization introduced in SrTiO3 is not strong enough to compensate local repulsions and gives rise to the off-centered Ti displacement. This is consistent with the fact that SrTiO3 has a small vibronic coupling constant compared to other ferroelectric materials. In situ time-dependent X-ray diffraction studies reveal lattice relaxation. Band structures and electronic hybridization play important roles in lattice relaxation, which is different from the relaxation of metals where the carrier concentration may be dominant. Our results provide insight into the coupling behaviors between the lattice and electronic hybridization, considering both static and dynamic aspects.

A new diffraction line profile breadth analysis approach for evaluating plastic lattice strain anisotropy in cold-worked nickel under various strain paths

Plastic lattice strain anisotropy in polycrystalline aggregates involves complicated integration of single crystal elastic anisotropy, grain-grain interactions and orientation-dependent slip activations. It is essential to experimentally determine plastic lattice strain anisotropy for in-depth understanding elasto-plastic deformation mechanisms and rationalizing advanced models. Unlike the widely applied method for quantifying elastic lattice strain anisotropy utilizing diffraction peak shift, accurately evaluating plastic lattice strain anisotropy is still enormously challenging over the decades. In this work, we developed a new diffraction line profile breadth analysis approach to reliably assessing plastic lattice strain anisotropy based on the simple linear dependence in quasi elasto-plastic model. The approach is confirmed to be effective and adaptive in practical application by linearization of the experimental dependences for line profile broadening in nickel under various cold-working strain paths. Then the orientation-dependent plastic lattice strain values could be reliably estimated up to high strain levels, which were identical to the magnitude of published elastic lattice strain. The strain levels and strain paths dependent plastic anisotropy magnitude was also inferred and further compared with the results from classical elastic models, i.e., Reuss, Voigt, Reuss-Voigt average and Eshelby-Kröner models. Simultaneously, by further carrying out microstructural characterization and dislocation model based line profile analysis, correlative texture and dislocation (arrangement and edge/screw constituent) developments were found to be strongly depended on strain paths, as well as verified to be the primary contributions to strain anisotropy. In addition to the proposed explanations in two-phase composite model, the strain hardening was demonstrated to be impacted by strain anisotropy behaviors as well. The fundamental mechanisms and significance of above interrelated effects under various strain paths were also well discussed.

Strain engineering of monoclinic domains in KxNa1−xNbO3 epitaxial layers: a pathway to enhanced piezoelectric properties

A novel concept to obtain a ferroelectric material with enhanced piezoelectric properties is proposed. This approach is based on the combination of two pathways: (i) the evolution of a ferroelectric monoclinic phase and, (ii) the coexistence of different types of ferroelectric domains leading to polarization discontinuities at the domain walls. Each of these pathways enables polarization rotation in the material which is responsible for giant piezoelectricity. Targeted incorporation of anisotropic epitaxial lattice strain is used to implement this approach. The feasibility of our concept is demonstrated for K0.9Na0.1NbO3 epitaxial layers grown on NdScO3 substrates where the coexistence of (100)pc and (001)pc pseudocubic oriented monoclinic domains is experimentally verified. This coexistence results in a complex periodic domain pattern with alternating emergence of ferroelectric in-plane a1a2 and inclined MC monoclinic phases, which differ in the direction of the electrical polarization vector. Our approach opens the possibility to exploit ferroelectric properties in both vertical and lateral directions and to achieve enhanced piezoelectric properties in lead-free material caused by singularities at the domains walls.

Isostructural crystal hydrates of rare-earth metal oxalates at high pressure: from strain anisotropy to dehydration

Abstract The crystal structures of a series of isostructural rare-earth metal oxalates, (REE)2(C2O4)3·10H2O (REE=Sm, Y) and a 1:1 YSm(C2O4)3·10H2O solid solution, have been studied in situ by single-crystal X-ray diffraction and optical microscopy. The structures were followed from ambient pressure to 6 GPa in a DAC with paraffin as the hydrostatic fluid. Bulk compressibilities, anisotropic lattice strain on hydrostatic compression and the corresponding changes in the atomic coordinates were followed. Discontinuities/sharp changes in the slopes of the pressure dependences of volume and selected cell parameters have been observed for yttrium-containing salts at ~3.5 GPa. This may be related to the re-distribution of water molecules within the crystal structure. Y2(C2O4)3·10H2O undergoes a partial dehydration at 1 GPa, forming monoclinic Y2(C2O4)3·6H2O as single-crystalline inclusions in the original phase.

Anisotropic Lattice Strain and Mechanical Degradation of High- and Low-Nickel NCM Cathode Materials for Li-Ion Batteries

In the near future, the targets for lithium-ion batteries concerning specific energy and cost can advantageously be met by introducing layered LiNixCoyMnzO2 (NCM) cathode materials with a high Ni content (x ≥ 0.6). Increasing the Ni content allows for the utilization of more lithium at a given cell voltage, thereby improving the specific capacity but at the expense of cycle life. Here, the capacity-fading mechanisms of both typical low-Ni NCM (x = 0.33, NCM111) and high-Ni NCM (x = 0.8, NCM811) cathodes are investigated and compared from crystallographic and microstructural viewpoints. In situ X-ray diffraction reveals that the unit cells undergo different volumetric changes of around 1.2 and 5.1% for NCM111 and NCM811, respectively, when cycled between 3.0 and 4.3 V vs Li/Li+. Volume changes for NCM811 are largest for x(Li) < 0.5 because of the severe decrease in interlayer lattice parameter c from 14.467(1) to 14.030(1) A. In agreement, in situ light microscopy reveals that delithiation leads to differe...

Charge-lattice interplay in layered cobaltates RBaCo2O5+x

X-ray diffraction, electrical resistivity and thermal expansion measurements are used to study the interrelation between the structural, magnetic and electron-transport peculiarities in RBaCo2O5+x (R=Y, Gd) over a wide range of oxygen contents. We find that the anisotropic lattice strain caused by the oxygen chain ordering in these compounds favors the metallic state and is a necessary condition for the coupled insulator-to-metal and spin-state phase transitions to occur. The obtained data point to the key role of the crystal lattice in selecting the preferred spin and orbital states of cobalt ions.

Multiple charge density wave states at the surface of TbTe3

We studied TbTe$_{3}$ using scanning tunneling microscopy (STM) in the temperature range of 298 - 355 K. As seen in previous STM measurements on RTe$_{3}$ compounds, our measurements detect a unidirectional charge density wave state (CDW) in the surface Te-layer with a wavevector consistent with that of the bulk, q$_{cdw}$ = 0.30 $\pm$ 0.01c$^{*}$. However, unlike previous STM measurements, and differing from measurements probing the bulk, we detect two perpendicular orientations for the unidirectional CDWs with no directional preference for the in-plane crystal axes (a- or c-axis) and no noticeable difference in wavevector magnitude. In addition, we find regions in which the bidirectional CDW states coexist. We propose that observation of two CDW states indicates a decoupling of the surface Te-layer from the rare-earth block layer below, and that strain variations in the Te surface layer drive the local CDW direction to the specific unidirectional or, in rare occurrences, bidirectional CDW orders observed. This indicates that similar driving mechanisms for CDW formation in the bulk, where anisotropic lattice strain energy is important, are at play at the surface. In our bias-dependent measurements, we find no contrast inversion for the CDW state between occupied and empty states. This finding differs from other quasi 2-dimensional materials containing a hidden 1-dimensional character which leads to a favorable Fermi surface nesting scenario. Our temperature-dependent measurements provide evidence for localized CDW formation above the bulk transition temperature, T$_{cdw}$.

Synchrotron high energy X-ray diffraction study of microstructure evolution of severely cold drawn NiTi wire during annealing

Microstructure evolution of a cold-drawn NiTi shape memory alloy wire was investigated by means of in-situ synchrotron high-energy X-ray diffraction during continuous heating. The cold-drawn wire contained amorphous regions and nano-crystalline domains in its microstructure. Pair distribution function analysis revealed that the amorphous regions underwent structural relaxation via atomic rearrangement when heated above 100 °C. The nano-crystalline domains were found to exhibit a strong cold work induced lattice strain anisotropy along 〈111〉, which coincides with the crystallographic fiber orientation of the domains along the wire axial direction. The lattice strain anisotropy systematically decreased upon heating above 200 °C, implying a structural recovery. Crystallization of the amorphous phase led to a broadening of the angular distribution of 〈111〉 preferential orientations of grains along the axial direction as relative to the original 〈111〉 axial fiber texture of the nanocrystalline domains produced by the severe cold wire drawing deformation.

Monoclinic MA domains in anisotropically strained ferroelectric K0.75Na0.25NbO3 films on (110) TbScO3 grown by MOCVD

A highly regular one-dimensional domain pattern is formed in ferroelectric K0.75Na0.25NbO3 thin films grown on (110) TbScO3 substrates using metal–organic chemical vapour deposition (MOCVD). The domain pattern exhibits a lateral periodicity of about 50 nm and extends over several micrometres. The monoclinic symmetry of the domains is controlled by the elastic anisotropy of K0.75Na0.25NbO3 and the anisotropic lattice strain, which is highly compressive in one in-plane direction and weakly tensile in the corresponding orthogonal direction. Using piezoresponse force microscopy and X-ray diffraction, the monoclinic MA phase is identified, which is associated with both a strong vertical and a lateral electric polarization component. The lateral component of the polarization vector is collinear with the ±[{\overline 1}10]pc shear direction of the pseudocubic unit cell of the film and changes periodically by 180° in adjacent domains. A structural variant of a 90° rotated MA domain pattern, where the monoclinic distortion of the pseudocubic unit cells occurs along ±[110]pc, is also observed. However, this variant appears with significantly lower probability, in agreement with energy considerations based on linear elasticity theory. Thus, the incorporation of highly anisotropic lattice strain provides the opportunity to grow one-dimensional nanostructures with high ferroelectric properties.

Nucleobase-functionalized graphene nanoribbons for accurate high-speed DNA sequencing.

We propose a water-immersed nucleobase-functionalized suspended graphene nanoribbon as an intrinsically selective device for nucleotide detection. The proposed sensing method combines Watson-Crick selective base pairing with graphene's capacity for converting anisotropic lattice strain to changes in an electrical current at the nanoscale. Using detailed atomistic molecular dynamics (MD) simulations, we study sensor operation at ambient conditions. We combine simulated data with theoretical arguments to estimate the levels of measurable electrical signal variation in response to strains and determine that the proposed sensing mechanism shows significant promise for realistic DNA sensing devices without the need for advanced data processing, or highly restrictive operational conditions.