Large Elastic Anisotropy Research Articles

Phase diagram and physical properties anisotropy of strontianite

The physical properties and anisotropy of carbonates at high pressure are fundamental to understanding the deep carbon cycle and storage. Here, we redraw the phase diagram of strontianite (SrCO3) by first-principles calculations combined with lattice dynamics and study its physical properties and anisotropy at high pressure. The results show that there are only Pnma and Pmmn phases in SrCO3 in the entire Earth's mantle, and there is no R3m phase. The SrCO3 polymorphs have a large elastic anisotropy. SrCO3 polymorphs are a kind of carbonate with high density, low wave velocity, and low wave velocity anisotropy. The linear thermal expansion coefficient of SrCO3-Pmmn was obtained for the first time by using the linear elastic compression coefficient combined with the volume thermal expansion coefficient. The results are of great significance for understanding the high-pressure behavior of Sr-carbonates.

Confinement twists achiral liquid crystals and causes chiral liquid crystals to twist in the opposite handedness: cases in and around sessile droplets.

We study the chiral symmetry breaking and metastability of confined nematic lyotropic chromonic liquid crystals (LCLCs) with and without chiral dopants. The isotropic-nematic coexistence phase of the LCLC renders two confining geometries: sessile isotropic (I) droplets surrounded by the nematic (N) phase and sessile nematic droplets immersed in the isotropic background. In the achiral system with no dopants, LCLC's elastic anisotropy and topological defects induce a spontaneous twist deformation to lower the energetic penalty of splay deformation, resulting in spiral optical textures under crossed polarizers both in the I-in-N and N-in-I systems. While the achiral system exhibits both handednesses with an equal probability, a small amount of the chiral dopant breaks the balance. Notably, in contrast to the homochiral configuration of a chirally doped LCLC in the bulk, the spiral texture of the disfavored handedness appears with a finite probability both in the I-in-N and N-in-I systems. We propose director field models explaining how chiral symmetry breaking arises by the energetics and the opposite-twist configurations exist as meta-stable structures in the energy landscape. These findings help us create and control chiral structures using confined LCs with large elastic anisotropy.

Stretchable and biodegradable chitosan-polyurethane-cellulose nanofiber composites as anisotropic materials

Chitosan is a naturally derived biodegradable polymer with abundancy, sustainability, and ease of chemical modification. Polyurethanes are a family of elastic biocompatible polymers, and composites of polyurethanes have versatile properties and applications. Chitosan-polyurethane composites were recently developed but had insufficient strength and limited stretchability. In the current study, cellulose nanofibers (CNFs) were integrated in chitosan-polyurethane composites to prepare stretchable and anisotropic materials. A biodegradable polyurethane was first synthesized, end-capped with aldehyde to become dialdehyde polyurethane (DP) nanoparticles, and added with CNFs to prepare the DP-CNF composite crosslinker (DPF). The waterborne DPF crosslinker was then blended with chitosan solution to make polyurethane-CNF-chitosan (DPFC) composites. After blending, DPFC may form hydrogel in ~33 min at room temperature, which confirmed crosslinking. Composite films cast and dried from the blends showed good elongation (~420.2 %) at 60 °C. Anisotropic films were then generated by tension annealing with pre-strain. The annealed films with 200 % pre-strain exhibited large elastic anisotropy with ~4.9 anisotropic ratio. In situ SAXS/WAXS analyses unveiled that rearrangement and alignment of the microstructure during tension annealing accounted for the anisotropy. The anisotropic composite films had the ability to orient the growth of neural stem cells and showed the potential for biomimetic and tissue engineering applications.

First-principles predictions of stable structure of AuAl2 under high pressure

Pressure-induced phase transformation of AuAl2 had been theoretically investigated by using crystal structure searching technique combined with first-principles calculations. The predicted orthorhombic Pbnm structure possesses a larger structural stability with pressure larger than 17 GPa, and transition pressure is consistent with experimental value. The simulated x-ray diffraction patterns of Pbnm structure are in satisfactory agreement with the experimental data. The specific density of states indicate that there are discontinuous changes of electrical resistance accompanying with phase transition, and these are in accordance with experimental observations. Moreover, phonon dispersions and elastic constants reveal that Pbnm structure has dynamical and mechanical stabilities. The directional dependence of Young's modulus was analyzed and Pbnm phase has a larger elastic anisotropy.

Deformation behavior of high-entropy oxide (Mg,Co,Ni,Cu,Zn)O under extreme compression

Following the discovery of high-entropy alloys, high-entropy oxides have gained considerable interest due to their unconventional structural characteristics and versatile functional properties for promising applications. Via synchrotron radial x-ray diffraction in a diamond anvil cell, the mechanical strength and deformation behavior of a typic high-entropy oxide (Mg,Co,Ni,Cu,Zn)O with a rock-salt structure under extreme compression has been investigated in situ. This compound in a polycrystalline state shows a large elastic anisotropy at the initial compression stage and then gradually becomes isotropic at around 21.4 GPa, similar with the behavior of MgO. Based on the lattice strain order conversion and texture evolution under compression, a dominant slip system transition from {100}<011> to {110}<1–10> is proposed in this high-entropy oxide. This work deepens our understanding on the role of chemical disorder in the mechanical properties of entropy-stabilized oxides, which would be indispensable to the design of advanced structural ceramics with optimal strength-to-ductility ratio.

Insight into elastic anisotropy, mechanical and dynamical stability, electronic properties, bonding and weak interactions analysis of LuAuSn Half-Heusler

Despite their great interest showing that LuAuSn half-Heusler is a topologically trivial semimetal, most of information about its physical behaviors seem rather remote from completion for the fact that several of its physical properties remain still unknown. Therefore, we try to outline, going into much specific details, a study on elastic anisotropy, mechanical and dynamical stability, electronic properties as well as the analysis of bonding and weak interactions. The lattice parameter value obtained by GGA-WC is very close to the experimental one, therefore, this functional has been chosen to carry out the rest of this work. The detailed study of the elastic behavior has revealed the mechanical stability of this compound, it results that its structure resists to slight strains. The obtained results also indicate a large elastic anisotropy of LuAuSn. Electronic results obtained by TB-mBJ(SOC) have confirmed its semimetallic behavior as well as being topologically trivial. This last property has been confirmed not only by the absence of band overlap but also by the absence of band inversion by the analysis of fat bands with and without SOC effect. The analysis of bonding and weak interactions has shown that the covalent character is predominant with the presence of weak repulsive interactions in cage regions and strong repulsive interactions between Lu and Sn. The vibrational study has revealed the dynamical stability of LuAuSn in the ground state, which indicates that this compound keeps its half-Heusler structure even at very low temperatures. Also, its zone center phonon modes have been determined and analyzed in detail by showing their frequencies and polarizations.

Twin Induced Reduction of Seismic Anisotropy in Lawsonite Blueschist

Lawsonite is an important mineral for understanding seismic anisotropy in subducting oceanic crust due to its large elastic anisotropy and prevalence in cold subduction zones. However, there is insufficient knowledge of how lawsonite twinning affects seismic anisotropy, despite previous studies demonstrating the presence of twins in lawsonite. This study investigated the effect of lawsonite twinning on the crystal preferred orientation (CPO), CPO strength, and seismic anisotropy using lawsonite blueschists from Alpine Corsica (France) and the Sivrihisar Massif (Turkey). The CPOs of the minerals are measured with an electron backscatter diffraction instrument attached to a scanning electron microscope. The electron backscatter diffraction analyses of lawsonite reveal that the {110} twin in lawsonite is developed, the [001] axes are strongly aligned subnormal to the foliation, and both the [100] and [010] axes are aligned subparallel to the foliation. It is concluded that the existence of twins in lawsonite could induce substantial seismic anisotropy reduction, particularly for the maximum S-wave anisotropy in lawsonite and whole rocks by up to 3.67% and 1.46%, respectively. Lawsonite twinning needs to be considered when determining seismic anisotropy in the subducting oceanic crust in cold subduction zones.

Seismic Anisotropy in Subduction Zones: Evaluating the Role of Chloritoid

Subduction zones are often characterized by the presence of strong trench-parallel seismic anisotropy and large delay times. Hydrous minerals, owing to their large elastic anisotropy and strong lattice preferred orientations (LPOs), are often invoked to explain these observations. However, the elasticity and the LPO of chloritoid, which is one of such hydrous phases relevant in subduction zone settings, are poorly understood. In this study, we measured the LPO of polycrystalline chloritoid in natural rock samples, obtained the LPO-induced seismic anisotropy, and evaluated the thermodynamic stability field of chloritoid in subduction zones. The LPO of chloritoid aggregates displayed a strong alignment of the [001] axes subnormal to the rock foliation, with a girdle distribution of the [100] axes and the (010) poles subparallel to the foliation. New elasticity data of single-crystal chloritoid showed a strong elastic anisotropy of chloritoid with 47% for S-waves (VS) and 22% for P-waves (VP), respectively. The combination of the LPO and the elastic anisotropy of the chloritoid aggregates produced a strong S-wave anisotropy with a maximum AVS of 18% and a P-wave anisotropy with an AVP of 10%. The role of chloritoid LPO in seismic anisotropy was evaluated in natural rock samples and a hypothetical blueschist. Our results indicate that the strong LPO of chloritoid along the subduction interface and in subducting slabs can influence the trench-parallel seismic anisotropy in subduction zones with “cold” geotherms.

Electronic and elastic properties of ternary fluoro-perovskite RbCaF3

We present the electronic and elastic properties of cubic perovskite type RbCaF3 computed using linear combination of atomic orbitals method within the framework of density functional theory (DFT). We have performed ab-initio calculations using the hybrid approach of Hartree-Fock and DFT namely, B3LYP (Becke’s 3 parameter functional combined with the nonlocal correlation functional of Lee-Yang-Parr) to determine the electronic response of Rb based cubic perovskite. In addition, we have computed elastic constants, bulk modulus, shear modulus, Young’s modulus and elastic anisotropes of RbCaF3. The results are found to be consistent with previously reported studies. The studied perovskite compound is mechanically stable, brittle in nature and show large elastic anisotropy. The band structure calculations reveal that RbCaF3 possesses indirect band gap with valence band maximum at R point and the conduction band minimum at the Γ point of the irreducible Brillouin zone.

Shear wave generation by mode conversion in picosecond ultrasonics: Impact of grain orientation and material properties

AbstractPicosecond ultrasonics has seen wide application in the investigation of interfaces in semiconductors and 3D imaging in biological systems. Shear ultrasonic waves are important for elastic constant and grain orientation measurement in ceramic materials. In this study, we investigate the impact of grain orientation and material's elastic properties on the generation efficiency of shear waves by mode conversion at a transducer thin film/substrate interface. The solution of acoustic wave equations suggests that crystal grain orientation has a strong impact on the generated shear wave amplitude. This dependence is found to be closely related to the magnitude of longitudinal component of wave displacements. The applicability of analytical model is validated by the experimental results from time‐domain Brillouin scattering. Moreover, material properties determine acoustic wave amplitudes based on the acoustic mismatch model and, particularly, large elastic anisotropy defined by Zener ratio favors strong shear waves. In the light of this analysis, several recommendations on suitable grain orientations and film materials are made to facilitate shear wave detection.

Surface-Dependent Stress-Corrosion Cracking in Ni-Rich Layered Oxide Cathodes

Structural degradation is the principal driving force for rapid voltage decay and capacity fading of Ni-rich layered oxide (NLO) cathode materials upon cycling, but its working mechanism is not yet fully elucidated. Here we apply multi-scale electron microscopy/spectroscopy techniques and theoretical calculations on both polycrystalline and single-crystal NLOs, and describe their structural evolution upon cycling. We discover that both the intergranular and intragranular cracks initiate along polar (001) basal plane due to its large elastic anisotropy upon cycling and surface structure evolution and transition metal dissolution occur on nonpolar (104) fresh surface. With this surface-dependent stress-corrosion coupling effect, severe intergranular cracking that accumulates within the polycrystalline NLO aggregates accounts mostly for the fast voltage decay and capacity fading, whereas minor intragranular cracking and less surface damage lead to substantial improvements on cyclability and reversible capacity of single-crystal NLOs. A universal understanding of the surface-dependent degradation in both polycrystalline and single-crystal NLOs provides clues on designing new cathode materials with high energy density and long cycle life through grain-boundary engineering.

Elastic constants of beta tungsten thin films studied by picosecond ultrasonics and density functional theory

Tungsten thin films are used for various applications and sometimes exhibit an A15 structure (β-W). They have some superior properties in comparison to the bcc structure (α-W), such as a higher superconducting transition temperature and larger spin Hall angle. However, elastic constants of β-W are unclear, which restricts mechanical applications and reliable density-functional-theory calculations. In this study, we synthesized α-W, β-W, and mixed-phase W films and determined their elastic constants by picosecond ultrasonics. We also calculated the elastic constants based on density functional theory and reveal that β-W has a larger elastic anisotropy and smaller shear modulus. Our calculation further indicates a stable stacking faulted β-W, which leads to a monoclinic structure.

Study of the ground-state magnetic ordering, magnetic and optoelectronic properties of (Lenaite) AgFeS2 in its chalcopyrite structure

Several previous works have shown that (Lenaite) AgFeS2 has a chalcopyrite structure with I-42d space group, but several information about its magnetic and optoelectronic behavior remain still unknown. The study of these properties is the main objective of our work, which is based on several theoretical approaches. The determination of the most stable magnetic ordering and the study of structural and elastic properties and that of most magnetic and optoelectronic properties have been carried out with FP-(L)APW + lo method, which is implemented in WIEN2k code. Our results have shown that AgFeS2-Chalcopyrite is an antiferromagnetic material with the same magnetic ordering as CuFeS2. The structural results are in good agreement with the previous results. The study of elasticity has shown that this compound is mechanically stable in its chalcopyrite structure and the analysis of the directional dependence of Young’s modulus has shown its large elastic anisotropy. The electronic properties have been studied taking into account the strong correlation between the electrons of 3d-Fe states and their spin-orbit coupling (SOC). The obtained results with these two corrections have shown that AgFeS2 is a semiconductor with an indirect band-gap. Néel temperature has been estimated by mean-field approximation (MFA), which is based on the estimation of the exchange coupling parameters (Jij). These latter were calculated by SPR-KKR method and TN found value is relatively very high in comparison with that of CuFeS2. Electronic transitions and optical absorption have also been studied respectively by the determination of the dielectric function and the study of the absorption coefficient variations as a function of energy.

Pressure effect on mechanical, magnetic and optoelectronic properties of SrCoO3-Perovskite: FP-(L)APW+lo investigation

The present work is a complementary and comparative study to the work already done on elastic, magnetic and optoelectronic behaviors of SrCoO3, from which we have studied the effect of hydrostatic pressure on these behaviors. FP-(L)APW+lo method was used with GGA-PBE and GGA-PBEsol as exchange-correlation functional. The structural results obtained by GGA-PBEsol at zero pressure are in perfect agreement with those found previously in comparison with those obtained by GGA-PBE. The obtained elastic constants under a pressure range between 0 GPa and 10 GPa have been calculated by the theoretical model implemented in IRelast package. Therefore, the generalized stability criteria are all positive under a pressure lower than 10 GPa which allows to say that SrCoO3 maintains its mechanical stability under this pressure range. Several related mechanical quantities have been determined and the obtained results are in agreement with those found previously. The obtained values of Zener's anisotropy factor and the universal elastic anisotropy index as well as the analysis of the directional dependence surface of Young's modulus indicate the large elastic anisotropy of SrCoO3, which decrease with increasing pressure. Despite the metallic behavior of SrCoO3, it is important to take into account the strong correlation between 3d-cobalt electrons from which GGA+U has been used for the study of magnetic and optoelectronic properties of this compound after estimating the effective on-site Coulomb interaction parameter “Ueff” by cLDA method. Despite Hubbard's correction, the electronic band structure has shown that SrCoO3 is a metal, which is in agreement with previous results. The qualitative and quantitative analysis of the bonds between the atoms that form SrCoO3 has shown that the ionic character is predominant. The optical properties under the effect of pressure, which are very important in practical applications, are extensively analyzed and interpreted by the determination of the dielectric function.

Complete determination of elastic stiffness coefficients and local symmetry breaking in the paraelectric barium titanate

The temperature dependence of all independent elastic stiffness coefficients of cubic BaTiO3 was determined over a wide temperature range from 400 °C to the Curie point (Tc ∼ 131 °C) by using Brillouin light scattering spectroscopy. Among the two elastic eigen-modes corresponding to the two measured transverse acoustic waves, (C11-C12)/2 showed a large softening in the paraelectric phase, while the change in C44 was very small. This result caused the elastic anisotropy A, defined as 2C44/(C11-C12), to increase from ∼2.1 to ∼2.7 upon cooling toward the phase transition temperature. The large elastic anisotropy was attributed to the tetragonal instability and the associated anisotropic polarization fluctuations of precursor polar clusters formed by the correlated Ti motions. The elastic anisotropy was fitted by using the Curie-Weiss law resulting in a significant deviation in a certain temperature range between Tc and ∼Tc + 50 °C, similar to the dielectric permittivity.

Self-organized layered growth phenomena of diffusion couples with spinodal decomposition in binary alloys

Abstract In order to investigate the formation mechanisms of the layered growth phenomena in diffusion couples with spinodal decomposition, a phase field model combined with elastic strain field was employed. Microstructure evolutions of diffusion couple with spinodal decomposition in binary alloys were numerically simulated by considering concentration fluctuation and elastic anisotropy. The simulation results indicate that the number of the periodical layers decreases with the increase of initial concentration fluctuation, even with large elastic anisotropy. The growth of layered microstructures can be attributed to the directional diffusion enhanced by initially discontinuous chemical potential at the interface.

Reducing mechanical hysteresis via tuning the microstructural orientations in Heusler-type Ni44.8Mn36.9In13.3Co5.0 elastocaloric alloys

Material coefficient of performance (COPmat), which is defined as the ratio of the latent heat extracted from a caloric material to the input work required, is fundamentally important in the material level for solid-sate cooling. For elastocaloric cooling, mechanical hysteresis affects the magnitude of hysteresis energy loss (reflecting the input work) in one mechanical cycle and even the fraction of reversible transformation phase (related to the output heat) during the successive mechanical cycles. Here, we achieved a narrow isothermal stress hysteresis (34 MPa) under a large compressive strain (6%) in a Ni–Mn–In–Co bulk polycrystalline alloy, by tuning the crystal orientation feature. Such a narrow-hysteresis alloy show dominant crystal orientations of [100]A and [331]A. Moreover，a variation in the COPmat can even vary by almost a factor of 2.6, due to the variation in the preferred orientation constitute. This optimization strategy, which enhances the COPmater by controlling the crystal orientations, provides a new clue in designing energy-efficient elastocaloric alloy systems with large elastic anisotropy.

Beta titanium single crystal with bone-like elastic modulus and large crystallographic elastic anisotropy

To develop single crystalline beta titanium implant as new hard tissue replacements for suppressing the stress shielding, we design a Ti-26.6Nb-6.7Al alloy (at. %) single crystal that exhibits large crystallographic elastic anisotropy and low Young's modulus. The anisotropy factor, A, reaches 3.42 that is the highest among all the reported values. The Young's modulus along <100> direction, E100, is only 36 GPa that is similar to the Young's modulus of cortical bone. These results prove our proposed design strategy and provide a new path to design beta titanium single crystal with bone-like elastic modulus for implant to minimize stress shielding.

Thermodynamic and Elastic Properties of Magnesite at Mantle Conditions: First‐Principles Calculations

AbstractMagnesite (MgCO3) is a likely main host of carbonates in the mantle and plays an important role in the transport and storage of carbon in the Earth's mantle. Its physical properties at high pressure and high temperature (PT) are crucial for understanding the deep carbon cycle. Here we investigated thermodynamic and elastic properties of magnesite under the mantle PT conditions using first‐principles calculations with local density approximation (LDA). Magnesite has the seismic velocities close to those of forsterite. The effect of the magnesite on seismic velocity of the carbonated peridotite and eclogite is subtle in the upper mantle. However, magnesite has much smaller seismic velocities and far larger elastic anisotropy than major minerals in the transition zone and lower mantle. The enrichment of magnesite in the transition zone and lower mantle will likely produce seismically detectable low‐velocity zone and velocity anisotropy.

Pressure effects on structural, electronic, elastic and lattice dynamical properties of XSi2(X = Cr, Mo, W) from first principles

First-principles calculations have been performed to study the structure, elastic and lattice dynamical properties of C40 XSi2(X=Cr, Mo, W) under hydrostatic pressure. The obtained structural parameters are in line with existing experimental and theoretical data. The evolutions of fundamental bandgap energies, elastic moduli, IR absorption spectra with pressure have been investigated in detail. Our results indicate that the energy gaps of XSi2(X=Cr, Mo, W) show different trends as the pressure increases. Larger BH/GHratio and Poisson’s ratio are achieved with pressure, suggesting an improved ductility for XSi2(X=Cr, Mo, W). Moreover, a large elastic anisotropy under pressure is exhibited in Young’s anisotropic factors. The infrared-active phonon frequencies exhibit substantial blueshifts under pressure.