Strong Orientation Dependence Research Articles

The effects of crystal orientation and common coal impurities on electronic conductivity in copper–carbon composites

The electronic conduction properties of copper–graphene composite materials including common coal impurities are studied. Exploring the transport properties for three crystallographic orientations [(111), (110), and (100)] of copper in copper–graphene composites, a strong orientational dependence on electronic conductivity is shown. Graphene exhibits near-ideal registries for (111) and (110) orientations, forming a connected network between grains that enables efficient carrier transport. The influence of non-carbon elements: nitrogen (N), oxygen (O), and sulfur (S) in graphene, representing possible structures in coal-based graphene are investigated. N, O, and S in graphene negatively impact the composite’s electronic conductivity relative to pristine graphene. A new method is introduced for visualizing the spatial distribution of electrical conduction activity in materials using the square of the electronic charge density near the Fermi level, based on the work of Mott. We call this technique the N2 method.

Multiple magnetic orders discovered in the superconducting state of EuFe2(As1−xPx)2

Abstract The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe2As2-based iron pnictides could offer an interesting plateau to study their relationship that has attracted considerable attention. So far, two magnetic phase transitions were observed in EuFe2As2-based crystal, which were deemed to originate from the itinerant Fe moments ( 190 K) and the localized Eu2+ moments ( 19 K), respectively. Here, we systematically studied the heat capacity for the EuFe2(As1−xPx)2 crystals with x = 0.21 (optimally doped) and x = 0.29 (overdoped). We have found two new magnetic orders in the superconducting state (ranging from 0.4 to 1.2 K) in the optimally doped crystal. As more P was introduced into the As site, one of the magnetic orders becomes absent in the overdoped crystal. Additionally, we observed strong field and orientation dependence in heat capacity. The present findings in EuFe2(As1−xPx)2 have detected the new low-temperature magnetic orders, which may originate from the localized Eu2+ spins order or the spin reorientation.

Transverse size effect of relaxor ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 film for one- and two-dimensional integrated sensors by simulation

In this work, the transverse size effect of the new-generation relaxor ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIMNT) thin film was studied by finite element method, aiming to revealing the lateral size and shape dependence of the piezoelectric, dielectric, and pyroelectric behavior for guiding one- and two-dimensional integrated array sensor applications. The results indicated that as the aspect ratio (width to thickness ratio) decreased from 100 to 0.01, for both one-dimensional rectangular and two-dimensional square PIMNT array elements, a sharp increase in piezoelectric and dielectric constants could be observed for the PIMNT with <001> direction while a slight increase could be found for those along <111> orientation, exhibiting a strong orientation dependence. In comparison, the PIMNT with <110> direction exhibited strong shape dependence. The piezoelectric and dielectric constants of <110>-oriented square element increased more remarkably than those of the rectangular one. The pyroelectric coefficients of PIMNT exhibited weak shape dependence, decreasing from 8.5 × 10−4 C/(m2·K) to about 8.0 × 10−4 C/(m2·K) for both element shapes with transverse size decreasing. These findings give insight into the transverse size and shape effect on the new-generation PIMNT thin film and provide a guide for its design in one- and two-dimensional piezoelectric and pyroelectric array sensor applications.

Preparation, Deformation Behavior and Irradiation Damage of Refractory Metal Single Crystals for Nuclear Applications: A Review.

Refractory metal single crystals have been applied in key high-temperature structural components of advanced nuclear reactor power systems, due to their excellent high-temperature properties and outstanding compatibility with nuclear fuels. Although electron beam floating zone melting and plasma arc melting techniques can prepare large-size oriented refractory metals and their alloy single crystals, both have difficulty producing perfect defect-free single crystals because of the high-temperature gradient. The mechanical properties of refractory metal single crystals under different loads all exhibit strong temperature and crystal orientation dependence. Slip and twinning are the two basic deformation mechanisms of refractory metal single crystals, in which low temperatures or high strain rates are more likely to induce twinning. Recrystallization is always induced by the combined action of deformation and annealing, exhibiting a strong crystal orientation dependence. The irradiation hardening and neutron embrittlement appear after exposure to irradiation damage and degrade the material properties, attributed to vacancies, dislocation loops, precipitates, and other irradiation defects, hindering dislocation motion. This paper reviews the research progress of refractory metal single crystals from three aspects, preparation technology, deformation behavior, and irradiation damage, and highlights key directions for future research. Finally, future research directions are prospected to provide a reference for the design and development of refractory metal single crystals for nuclear applications.

Tunable in-plane anisotropy of quasiparticles in twisted MoS2/CrOCl heterostructures

Twisted isotropic-anisotropic van der Waals heterostructures provide a platform for controlling the electronic and phononic properties of 2D materials and inducing in-plane anisotropy in some isotropic materials. Herein, angle-resolved polarized Raman spectroscopy and photoluminescence spectroscopy are used to investigate the induced in-plane anisotropy of the quasiparticles in the twisted MoS2/CrOCl heterostructures. Both the phonons (Eg2 MoS2 and Ag1 MoS2 modes) and excitons (A and B excitons) in MoS2 represent a strong in-plane orientation dependence, and the maximum intensities are along the [100]CrOCl. The induced anisotropy ratios of phonons vary continuously in the range from 1.22 to 1.13 for the Eg2 MoS2 mode and 1.15 to 1.09 for the Ag1 MoS2 mode with changing twisted angles, which originate from the anisotropic carrier mobility induced by the localized charge distribution from the anisotropic CrOCl substrates, and are further tuned by the uniaxial local limit of charge carriers caused by 1D moiré pattern. Our findings provide a way to controllably regulate the induced in-plane optical anisotropy in heterostructures.

Resolving the Dependence of Aluminum Alloy Corrosion on Grain Orientation by Scanning Electrochemical Cell Microscopy

The study of grain-dependent corrosion behaviors of practical polycrystalline metals remains challenging due to the influences of other microstructural features, such as intermetallic particles and grain boundaries. In this work, we employed the oil-immersed scanning electrochemical cell microscopy (SECCM) to investigate the effect of grain orientations of a practical aluminum alloy AA7075-T73 on the surface electrochemical behaviors. Thousands of spatially resolved microscopic potentiodynamic polarization (PDP) measurements were performed, allowing the extraction of information only from grain interior areas excluding intermetallic particles and grain boundaries. The differences in the corrosion behaviors between grains were revealed. Cathodic currents exhibited a strong grain orientation dependence with a decreasing order of {101} > {001} > {111}, agreeing with the prediction from the order of atomic planar density. By contrast, the dependence of anodic currents on grain orientation was weak, and pitting was independent of grain orientation, which could be due to the limited mass transport of ions within the surface oxide film. This work highlights the capability of oil-immersed scanning electrochemical cell microscopy in resolving small electrochemical differences, which will greatly promote the study of grain-dependent behaviors of practical polycrystalline samples.

RETRACTED: Influence of At%Ce on the electronic structure and mechanical properties of Al–Ce compounds from first-principles calculations

Ce as an additive in aluminum alloys can significantly improve the microstructure and properties of aluminum alloys. However, the structure and the associated overall properties of the Ce-Al binary system are not known. Here, we applied a first-principles approach to investigate the effects of At%Ce on the electronic structure, mechanical and thermodynamic properties of the Ce-Al compounds. The results show that CeAl2 exhibits the best stability at T = 0 K. The electronic structure analysis shows that they are both metallic. The ionic bonding of the Ce-Al compounds gradually weakened with increasing At%Ce. In addition, the Poisson's ratio of the Ce-Al compounds varies in the range of 0.2 and 0.32, and most of the Ce-Al compounds are brittle. The anisotropy results show that all the Ce-Al compounds exhibit more or less elastic anisotropy, where Young's modulus of the Ce-Al compounds has a strong orientation dependence. The obtained Debye temperatures indicate that Ce3Al11 has the strongest covalent bonds and good thermal conductivity.

Orientation dependence of the effect of short-range ordering on the plastic deformation of a medium entropy alloy

Multi-principal-element alloys (also known as medium and high entropy alloys) offer a much larger and richer design space than conventional alloys, providing opportunities for discovering new functionalities and their governing physics. Some of these alloys exhibit an outstanding combination of high strength and ductility, linked to the activation of various deformation modes triggered by low-energy stacking faults. However, a pressing question remains: Is the plasticity of medium- and high-entropy alloys governed only by stacking fault energy, or does atomic short-range order (SRO) play a role? To answer this, we investigated how SRO affects the deformation in single-crystalline NiCoCr, with previous contradictory findings. First, we established unique experimental evidence for SRO formation in bulk single crystals using high-energy synchrotron transmission X-Ray Diffraction. By tuning the degree of SRO by aging at high temperatures, twinning density and strain-induced martensitic phase transformation can be significantly increased in the [110] and [111] orientations under tension, increasing the tensile ductility; yet, no increase was observed along the [001] orientation due to lack of TWinning-Induced Plasticity (TWIP) or TRansformation-Induced Plasticity (TRIP), indicating a strong crystallographic orientation dependence. Our first-principles thermodynamic calculations unequivocally show SRO exists and governs the observed microstructural evolution and deformation hardening behavior. Here we find direct proof that SRO triggers a simultaneous TWIP and TRIP in NiCoCr, a rare microstructural evolution path. Our findings establish that the interplay of SRO and plasticity could be exploited to alter deformation modes and yield unprecedented mechanical response in medium- and high-entropy alloys.

Crystal orientation-dependent tensile mechanical behavior and deformation mechanisms of zinc-blende ZnSe nanowires

Crystal deformation mechanisms and mechanical behaviors in semiconductor nanowires (NWs), in particular ZnSe NWs, exhibit a strong orientation dependence. However, very little is known about tensile deformation mechanisms for different crystal orientations. Here, the dependence of crystal orientations on mechanical properties and deformation mechanisms of zinc-blende ZnSe NWs are explored using molecular dynamics simulations. We find that the fracture strength of [111]-oriented ZnSe NWs shows a higher value than that of [110] and [100]-oriented ZnSe NWs. Square shape ZnSe NWs show greater value in terms of fracture strength and elastic modulus compared to a hexagonal shape at all considered diameters. With increasing temperature, the fracture stress and elastic modulus exhibit a sharp decrease. It is observed that the {111} planes are the deformation planes at lower temperatures for the [100] orientation; conversely, when the temperature is increased, the {100} plane is activated and contributes as the second principal cleavage plane. Most importantly, the [110]-directed ZnSe NWs show the highest strain rate sensitivity compared to the other orientations due to the formation of many different cleavage planes with increasing strain rates. The calculated radial distribution function and potential energy per atom further validates the obtained results. This study is very important for the future development of efficient and reliable ZnSe NWs-based nanodevices and nanomechanical systems.

High-Throughput Investigation of Multiscale Deformation Mechanism in Additively Manufactured Ni Superalloy

In this paper, Inconel 718 (IN718) superalloy was processed by laser powder-bed fusion additive manufacturing (L-PBFAM), followed by heat treatment. High-resolution nanoindentation was used to investigate the complex deformation mechanisms that occurred at various length scales in both conditions. The nanoindentation elastoplastic maps show a strong crystal orientation dependency of modulus and hardness, which is attributed to the high mechanical anisotropy of IN718. The hardness map effectively resolves complex microscale strength variation imparted due to the hierarchical heat distribution associated with the thermal cycles of L-PBFAM. The disproportionately high hardening effect of Nb, Mo-rich chemical segregations and Laves phases in dendritic structures is also observed. The heat treatment resulted in a 67% increase in yield strength (from 731 MPa in the L-PBFAM condition to 1217 MPa in the heat-treated condition) due to the activation of multiple precipitation-strengthening mechanisms. The nanoindentation mapping of a heat-treated sample delineates the orientation-dependent hardness distribution, which apart from high mechanical anisotropy of the alloy, is also contributed to by a high degree of coherency strengthening of the D022 γ″-precipitates oriented parallel to the &lt;001&gt; crystal plane of the γ-matrix. The mean hardness of the sample increased from 13.3 GPa to 14.8 GPa after heat treatment. Evidence of extensive deformation of twin networks and dislocation cells was revealed by transmission electron microscopy of the deformed region under the nanoindentation tip.

Orthogonal single-mode helical Bragg gratings created in fiber cladding for vector bending measurement.

We demonstrate a novel, to the best of our knowledge, two-dimensional vector bending sensor based on orthogonal helical Bragg gratings inscribed in the cladding of a conventional single-mode fiber (SMF). The helical cladding fiber Bragg gratings (HCFBGs) are created by using a femtosecond laser direct writing technology and a quarter-pitch graded index fiber (GIF) is used in front of the HCFBGs to diverge the core mode into fiber cladding. In contrast to the multimode resonance observed in conventional cladding Bragg gratings inscribed by using a femtosecond laser point-by-point (PbP) or line-by-line (LbL) technology, the proposed HCFBGs exhibit stable narrowband single-mode Bragg resonance. An HCFBG with a low peak reflectivity of -50.77 dB and a narrow bandwidth of 0.66 nm was successfully fabricated by using a lateral offset of 45 µm between the HCFBG and the fiber core axis. Moreover, two orthogonal HCFBGs were fabricated in the SMF cladding and used for vector bending sensing. Strong orientation dependence could be seen in omnidirectional bending measurement, exhibiting a maximum bending sensitivity of up to 50.0 pm/m-1, which is comparable to that in a multicore FBG. In addition, both the orientation and amplitude of bending vector could be reconstructed by using the measured Bragg wavelength shifts in two orthogonal HCFBGs. As such, the proposed HCFBGs could be used in many applications, such as structural health monitoring, robotic arms, and medical instruments.

Effect of martensite ageing on the orientation dependence of the B2-phase yield stress and the shape memory effect in Ti-40Ni-10Cu alloy single crystals

For the [001]- and [123]-oriented single crystals of the Ti-40Ni-10Cu alloy, it was shown for the first time that martensite ageing at 250 MPa leads to a strong orientation dependence of the B2-phase yield stress under tension, which is weakly manifested in the initial crystals. The maximum increase in the B2-phase yield stress by 350 MPa compared with the initial state was found in the [001]-oriented crystals. At external tensile stresses of 100 MPa, the shape memory effect in [001]-oriented crystals was 4.0± 0.2% in the initial state and increased to 5.0± 0.2% after martensite ageing, while in [123] orientation, on the contrary, it decreased from 8.7± 0.2% to 5.4± 0.2%. Keywords: Single crystals, Martensite ageing, B2-phase, Shape memory effect, Tension.

Влияние старения в мартенсите на ориентационную зависимость предела текучести B2-фазы и эффект памяти формы в монокристаллах сплава Ti-40Ni-10Cu

For the [001]-and [-123] -oriented single crystals of the Ti–40Ni–10Cu alloy, it was shown for the first time that martensite ageing at 250 MPa leads to a strong orientation dependence of the B2-phase yield stress under tension, which is weakly manifested in the initial crystals. The maximum increase in the B2-phase yield stress by 350 MPa compared with the initial state was found in the [001]-oriented crystals. At external tensile stresses of 100 MPa, the shape memory effect in [001]-oriented crystals was 4±0.2% in the initial state and increased to 5±0.2% after martensite ageing, while in [-123] orientation, on the contrary, it decreased from 8.7±0.2% to 5.4±0.2%.

Оптическая анизотропия пленок из поливилового спирта с металлическими наностержнями при одноосном растяжении

The possibility of obtaining macroscale anisotropic thin films from polyvinyl alcohol with included metal nanorods under uniaxial tension under conditions that do not lead to a change in the morphology of metal nanoparticles is shown. Silver and gold nanorods were obtained by directed growth from nuclei and then embedded in a polymer matrix based on polyvinyl alcohol. Initially isotropic films with absorption independent of the polarization of the probing light became anisotropic after stretching, which manifested itself in the dependence of the extinction spectra on the polarization of the probing radiation. The weakening of the longitudinal dipole plasmon resonance mode with the simultaneous enhancement of the transverse dipole plasmon resonance when the light polarization is rotated from 0 to 90 degree indicates the orientation of the nanorods in the film along the direction of its stretching. In addition to the change in absorption in the bands of dipole modes, a strong orientational dependence of absorption in the band of the quadrupole mode of the plasmon resonance of metal nanorods was found.

Characterization of dislocation microstructures in near-[formula omitted] single crystal copper using high-voltage scanning transmission electron microscopy

Metallic structures are prone to failure caused primarily by fatigue-related damage to the structural material. Fatigue behavior is strongly correlated with dislocation structures in metals. Therefore, investigating the formation of dislocation structures is essential for understanding the fatigue process. The dislocation structure in face-centered cubic crystals has a strong orientation dependence. However, the detailed characteristics and evolution process of dislocation structures of fatigued [1‾11] single crystal copper are still insufficient. This study investigated dislocation structures in near-[1‾11] single crystal copper cyclically deformed at room temperature under different constant plastic shear strain amplitude (γpl) to analyze the formation mechanism of dislocation structures and their relationship with fatigue behavior. Characteristic dislocation structures were characterized by adopting multiple planes using a high-voltage scanning transmission electron microscope. With increasing shear strain amplitude, a vein-like structure along the (1‾11) plane gradually developed into a wall structure. When γpl ≥ 1 × 10−3, deformation bands and cell bands were formed to accommodate the higher plastic strain. The state of cell-band development significantly affected the cyclic softening of the single crystal copper. A positive linear relationship existed between the shear stress amplitude and the reciprocal of the cell width.

Density functional theory demonstrates orientation effects in the Raman spectra of hydroxy‐ and carbonated apatite

AbstractRaman spectroscopy is widely used to examine the carbonate content within bone apatite, but Raman spectra are also sensitive to orientation effects between the polarisation of the incoming laser light and the sample orientation. This may lead to discrepancies when using Raman spectroscopy to evaluate the carbonate content as the extent of crystal organisation can change depending on the type of bone, age, and presence of mineralisation disorders in the organism. It is experimentally very challenging to evaluate the effect of orientation using individual bone crystals. Therefore, we have used density functional theory to examine the effect of orientation in apatitic materials. We examined hydroxyapatite and three different types of carbonated apatite: A‐type where the carbonate ion substitutes the two OH groups in the unit cell, B‐type where co‐substitution occurs between carbonate in a phosphate position and Na+ for Ca2+ to maintain charge balance, and AB‐type where carbonate sits in both A‐site and B‐site. Our simulations show that the OH group in hydroxyapatite has a strong orientation dependence, consistent with previous literature. In addition, the phosphate and carbonate bands of the apatitic structures are predicted to be orientation dependent, where the maximum scattering efficiency occurs in configurations in which the laser polarisation is parallel to the crystallographic axes of the material. The intensity changes of the phosphate and carbonate bands are not consistent upon changing orientations and thus may lead to an underestimation of carbonate contents if insufficient sampling points are used during bone analysis.

Influence of loading orientation on deformation localization of irradiated tungsten

The plasticity of tungsten in low or medium temperature regimes is dominated by the screw dislocation mobility, which is well known to exhibit a strong non-Schmid effect and loading orientation dependence. As a typical plasma-facing material, many questions regarding the role of these plasticity features on the irradiation degradation performance of tungsten remain unanswered. Considering that deformation localization is a continuing critical problem in the nuclear application, in the current work, a systematic set of crystal plasticity calculations is designed to quantify the degree of deformation localization in irradiated tungsten, which is found to be sensitive to the loading orientation. The underlying physical mechanisms are carefully analyzed, highlighting the important role of the number of active slip systems, the non-Schmid effect controlled by the evolution of local stress state, and the high resistance stress induced by irradiation defects. Based on the micro-scale physical mechanisms, two physical indicators are proposed to provide guidance for predicting the orientation-dependent deformation localization in irradiated tungsten, which agrees well with the simulation results.

Correlating Corrosion to Surface Grain Orientations of Polycrystalline Aluminum Alloy by Scanning Electrochemical Cell Microscopy.

The study of grain-dependent corrosion behaviors of practical polycrystalline metals remains challenging due to the difficulty in eliminating the influences of other microstructural features, such as intermetallic particles and grain boundaries. In this work, we performed thousands of microscopic potentiodynamic polarization measurements on a polycrystalline aluminum alloy AA7075-T73 using the spatially resolved oil-immersed scanning electrochemical cell microscopy measurement. Data were extracted only from grain interior areas excluding intermetallic particles and grain boundaries. Based on the multiple potentiodynamic polarization measurements, the differences between grains can be revealed. Cathodic currents exhibited a strong grain orientation dependence with a decreasing order of {101} > {001} > {111}, agreeing with the prediction from the order of atomic planar density. By contrast, the dependence of anodic currents on grain orientation was weak, and pitting was independent of grain orientation, which could be due to the limited mass transport of ions within the surface oxide film. This work highlights the capability of oil-immersed scanning electrochemical cell microscopy in resolving small electrochemical differences, which will greatly promote the study of grain-dependent behaviors of practical polycrystalline samples.

Creep anisotropy characteristics and microstructural crystallography of marine engineering titanium alloy Ti6321 plate at room temperature

The anisotropy of the mechanical properties of high-performance titanium-alloy plates has always been a key challenge in the fabrication of alloy plates and the application of components in service. In this work, the room-temperature creep behavior and microstructural crystallography of Ti6321 alloy plates along the rolling direction (RD), 45°, and transverse direction (TD) have been thoroughly investigated and discussed. The study demonstrates that the plates exhibit significantly different room-temperature creep characteristics along the three sampling directions. Among them, the creep strain along the 45° direction was the largest, whereas the creep strain along the TD was the smallest. Such anisotropic deformation was associated with the global Schmid factor variation caused by the T-type microtexture. Both the basal and prismatic slips occur easily along 45°, whereas it was hard to activate along the TD. In addition, the basal and prismatic slips were the main contributors to creep deformation, which also showed strong crystallographic orientation dependence. Among them, the basal slip was found to be more easily activated than prismatic slip, especially in the high Schmid factor range. The study also discusses the potential influence of elastic anisotropy on the activation of basal slip.

Atomistic insights into early stage corrosion of bcc Fe surfaces in oxygen dissolved liquid lead-bismuth eutectic (LBE-O)

Classical molecular dynamics simulations with global neural network machine learning potential are used to study early stage oxidation and dissolution behaviors of bcc Fe surfaces contacting with stagnant oxygen dissolved liquid lead-bismuth eutectic (LBE-O). Both static and dynamic simulation results indicate that the early stage oxidation and dissolution behaviors of bcc Fe show strong orientation dependence under the liquid LBE environments, which may explain the experimental observations of uneven interface between iron-based materials and liquid LBE. Our investigations show that it is the delicate balance between the oxide growth and metal dissolution that leads to the observed corrosion anisotropy for bcc Fe contacting with liquid LBE-O.