Lattice distortions, i.e. small atomic displacements away from the average lattice, are linked to a number of functional and mechanical properties of concentrated metallic alloys, particularly their yield strength. Here we develop an elastic model of lattice distortions where every atom is modeled as an Eshelby inclusion in a homogeneous elastic matrix. Local environment effects are included by considering fluctuating anisotropic eigenstrain tensors associated to the inclusions. The model is tested on several concentrated alloys, face-centered cubic (FCC) AlMg and FeNiCr alloys, as well as a fictitious body-centered cubic (BCC) binary alloy to study systematically and independently the effects of a size and an elastic modulus mismatch between the constituents. The elastic model predicts lattice distortions well when the size and elastic modulus mismatches are typically less than 5% and 25%, respectively. Interestingly, we find that when the size mismatch is small, as in FeNiCr alloys, the lattice distortion is dominated by the fluctuations of the dilatational eigenstrains rather than their average value as often assumed in elastic models of concentrated alloys. Moreover, models usually assume homogeneous elastic constants, while the limit obtained here of 25% is often exceeded in concentrated alloys, particularly with a BCC structure.

Defects in nanomaterials have been widely used to introduce new properties of pristine materials for electrochemical energy storage. However, most of the research has focused on the effect of single defect while ignoring the synergy of multifold defects on enhancing electrochemical performance. Herein, we have modeled bulk phase oxygen substitution and surface oxygen vacancy on ZnCo2O4 nanowires grown on nickel foam for the first time (F-ZnCo2O4-x), revealing the role of double defects and providing new insights into the effects of electrochemical properties. The enhanced oxygen vacancy concentration and increased active sites enable rapid and sufficient redox reaction of the active components. Therefore, the representative F-ZnCo2O4-x electrode achieves a high specific capacity of 664 mAh·g−1 at 1 A·g−1. Moreover, high energy density (EHSC, 60 Wh·kg−1) and good cycle stability (90.44% capacity retention after 10000 cycles) could be provided as a battery-type electrode of hybrid supercapacitor. The electrodes also have high energy density (Ecell, 692 Wh·kg−1) and good durability (capacity retention of 98.8% after 2000 cycles) when used as zinc ion batteries. This work supplies a new avenue on the universality of defect engineering to design bimetallic oxide with high electrochemical performance.

We present comparisons of kinetic Monte Carlo (kMC) simulations of isothermal short-range ordering (SRO) and clustering (SRC) kinetics in binary FCC alloys with a mean-field concentration wave (CW) model. We find that the CW model is able to give order-of-magnitude agreement with kMC simulations for ordering/clustering relaxation times over a wide range of temperatures and compositions. The advantage of the CW model is that it does not require parameterization of vacancy hopping energy barriers, which, for a concentrated alloy, becomes prohibitive. We assess limits in the accuracy of the model, and discuss the effect of cooling rates as well as the extension to multi-component systems. Ultimately, the simplicity and performance of the CW model compared to kMC simulations suggests that it is a useful tool to connect with models of properties dependent on SRO/SRC as well as for designing thermal treatments to control formation of SRO/SRC.

Pyrochlore sublattice is an integral structural component of numerous families of electronic and magnetic materials, including pyrochlores, spinels, and Laves phases C15, which exhibit plethora of magnetic behavior and multiple functionalities. The geometrical frustration inherent in the pyrochlore lattice leads to the formation of a broad diversity of unconventional magnetic states with unique physical properties. This article focuses on the symmetry-based concept of the Landau order parameter (OP) for uniform description of the most common types of long-range ordered magnetic structures (aristotypes) and related multi-ordered states derived from the pyrochlore lattice. Based on the combination of group-theoretical and crystallographic approaches the symmetry hierarchy of the magnetic structures and the corresponding OPs are established. The symmetry analysis reveals the role of the secondary OPs in the magnetic structure formation and emergent phenomena such as spin-driven ferroelasticity, ferroelectricity and orbital ordering. Within the framework of Landau thermodynamics, possible phase diagrams including multicritical points are determined. This study shows the significant potential of applying OP concept in a wide range of tasks, from the construction of microscopic theories to the search for new advanced magnetic and electronic materials.

Micro-nano ultraviolet light sources have recently attracted great attention due to their promising applications in future quantum display, photoelectric detection sensors, biomedical devices, and so on. Design of ultraviolet light sources with smaller size, stronger emission intensity, and higher integration, are the key aspects for the development of high-performance micro-nano ultraviolet devices. Here, we demonstrate that unidirectional threading dislocation arrays in an AlN thin film can emit ultraviolet light with wavelength of ∼ 317 nm. The density of AlN dislocations is ∼ 4 × 1010 cm−2, and the light emission intensity of AlN dislocations is comparable to the intrinsic emission of the AlN thin film. By combining aberration-corrected transmission electron microscopy, atomic-resolution valence electron energy-loss spectroscopy, and first-principles calculations, the atomic and electronic structures and the band gaps of the AlN threading dislocations are determined. It is found that the AlN threading dislocations are comprised of edge, screw, and mixed dislocations. All the AlN dislocations exhibit smaller band gaps compared to the AlN bulk due to the increase of the Al-N bond length at the dislocation cores. The dangling bonds of Al and N at the edge dislocations, Al-Al and NN bonds at the screw dislocations cause the defect states in the band gaps. This study not only has clarified the atomic origin of dislocation nano-optics, but also will encourage the development of microelectronics and optoelectronic devices based on dislocation ultraviolet light emission.

Stacking-fault tetrahedron (SFT) is one kind of typical three-dimensional vacancy defect in quenched, deformed or irradiated face-centered cubic (FCC) metals, which can seriously degrade the mechanical properties of materials. It's generally believed that high stacking fault energy (SFE) is unfavorable for the formation of SFTs. Here, we report the first in-situ investigation of irradiation-induced formation of novel Frank loop-SFT complexes in Pd with extremely high SFE. Our findings reveal a new mechanism that vacancy clusters rearrange directionally to form SFTs due to the ambient stress deviations and compressive stress fields induced by interstitial Frank loops. Continuous hydrogen implantation will lead to a synergistic growth of the complex, while direct interaction between the Frank loop and SFT under thermal effect can cause the complex to disappear. These results uncover a unique formation mechanism for SFT and provide a new perspective for understanding nano-defects in high SFE metals.

AuNi is a classic long-studied fcc alloy combining a very “large” atom (Au) and a very “small” atom (Ni), and the large atomic size misfits suggest very high strengthening. Here, AuNi is used as a model alloy for the testing of new strengthening theories in random alloys that include the effects of both size misfits and solute-solute interactions. Experimentally, AuNi samples are fabricated, characterized, and tested, and show no segregation after annealing at 900 °C and a very high yield strength of 769 MPa. Theoretically, the main inputs to the theory (alloy lattice and elastic constants, solute misfit volumes, energy fluctuations associated with slip in the presence of solute-solute interactions) are extracted from experiments or computed using first-principles DFT. The parameter-free prediction of the yield strength is 809 MPa, in very good agreement with experiments. Solute-solute interactions enhance the strength only moderately (13%), demonstrating that the strengthening is dominated by the solute misfit contribution. Various aspects of the full theory are discussed, the general methodology is presented in an easy-to-apply analytic framework, and a new analysis for strengthening in alloys with zero misfits but non-zero solute-solute interactions is presented. These results provide support for the theories and point toward applications to many fcc complex concentrated alloys.

Transformation-induced plasticity (TRIP)-assisted steels exhibit an excellent combination of strength and ductility due to enhanced strain hardening rate associated with deformation-induced martensitic transformation (DIMT). Quantitative evaluation on the role of DIMT in strain hardening behavior of TRIP-assisted steels and alloys can provide guidance for designing advanced materials with strength and ductility synergy, which is, however, difficult since the phase composition keeps changing and both stress and plastic strain are dynamically partitioned among constituent phases during deformation. In the present study, tensile deformation with in situ neutron diffraction measurement was performed on an Fe-24Ni-0.3C (wt.%) TRIP-assisted austenitic steel. The analysis method based on stress partitioning and phase fractions measured by neutron diffraction was proposed, by which the tensile flow stress and the strain hardening rate of the specimen were resolved into factors associated with each phase, i.e., the austenite matrix, deformation-induced martensite, and the transformation rate of DIMT after differentiation, and then the role of each factor in the global strain hardening behavior was discussed. In addition, the plastic strain partitioning between austenite and martensite was indirectly estimated using the dislocation density measured by diffraction profile analysis, which constructed the full picture of stress and strain partitioning between austenite and martensite in the material. The results suggested that both the transformation rate and the phase stress borne by the deformation-induced martensite played important roles in the global tensile properties of the material. The proposed decomposition analysis method could be widely applied to investigating mechanical behavior of multi-phase alloys exhibiting the TRIP phenomenon.

Amorphous Ge2Sb2Te5 phase change material is considered as a prototype material for non-volatile memories due to the reversibility of the amorphous-to-crystalline transition on a nanosecond timescale. In this context, the kinetics of atomic self-diffusion has important bearings for the crystallization process and the switching behavior of phase change materials. It is thus important for applications as well as for the general understanding of the rapid and reversible switching behavior to understand atomic self-diffusion, especially in the amorphous phase. However, up to now, reliable data on the kinetics of atomic self-diffusion in amorphous phase change materials is almost non-existent. For this reason, Te tracer diffusion was measured using secondary ion mass spectroscopy and applying the highly enriched natural 122Te isotope. For the first time, Te self-diffusion coefficients in amorphous Ge2Sb2Te5 are experimentally measured and the activation energy of Te self-diffusion was determined as (1.43±0.08) eV.

Heterogeneous microstructural design has been proven to be an effective strategy in breaking the strength–ductility dilemma in nanostructured metals. However, the precise control of heterogeneous microstructures to achieve strength–ductility synergy remains challenging. Here, we demonstrate a novel powder metallurgy approach for creating three-dimensional (3D) core–shell nanostructures with highly tunable shell thickness and grain size distributions. These 3D nanostructures enable superior strength–ductility synergy in pure copper, pushing the boundary of the Ashby map to unchartered territory. A combination of microstructural characterization, atomistic simulations and crystal plasticity modeling reveals that the generation and accumulation of geometrically necessary dislocations near the core–shell interface play a pivotal role in accommodating the strain gradient and sustaining a high strain-hardening rate during plastic deformation. Our work provides a viable approach for designing bulk nanostructured materials with 3D heterogeneous ingredients and demonstrates a promising pathway for the development of strong and ductile materials.

Length scale dependent microstructural heterogeneities serve as effective pathways in engineering materials for providing simultaneous strength-ductility enhancement. In this regard, hexagonal close-packed (hcp) materials that exhibit a combination of slip and multiple twinning modes potentially act as ideal candidates that generate heterogeneous microstructures. However, such an inhomogeneous distribution of crystallographic defects also results in build-up of spatially heterogeneous local stress gradients that can be distinct from globally applied stress state. In particular, stress fields arising at the vicinity of deformation twins and due to their interaction with grain interfaces often act as precursors to damage nucleation in most hcp metals and alloys. Hence, assessment of such local stresses and their overall impact on plasticity becomes necessary in order to understand the relationship between twinning and fracture in hcp materials. The current work utilizes commercially pure titanium (cp-Ti) as a model material to investigate the impact of twinning induced stress gradients on the local mechanical response. By means of correlative multiscale structural characterization and local stress gradient measurements, we establish a definitive relationship between applied stress vis-à-vis local stress on the local plasticity behavior ahead of a {112¯2} compression twin-grain boundary intersection in cp-Ti. Additionally, the role of twin interfacial structure for tension and compression twinning modes are experimentally determined and their corresponding impact on the local stress fields and associated twin migration mechanisms is assessed.

Interfacial segregation of selected elements can be exploited to manipulate the potency of solid substrates for heterogeneous nucleation, thus controlling the solidification process. As the native inclusions in Mg alloys, MgO acts as the nucleating substrate, but it has rarely been studied in terms of its interactions with alloying elements. In this work, investigations of yttrium (Y) segregation at interfaces between native MgO particles and Mg in an Mg-0.5Y alloy were carried out by state-of-the-art aberration-corrected scanning transmission electron microscopy (STEM) and associated spectroscopy. Experimental results show that native MgO particles in Mg-0.5Y possess two typical morphologies: truncated octahedron primarily faceted by {111}MgO and minorly by {100}MgO, and cubic shape with unique {100}MgO facets. Y atoms are found to segregate at both Mg/{111}MgO and Mg/{100}MgO interfaces, leading to the formation of two different 2-dimensional compounds (2DCs). The 2DC at the Mg/{111}MgO interface is identified as two atomic layers of a face-centered cubic Y2O3 phase in terms of crystal structure and chemistry, whilst it is an Mg(Y)-O monolayer at the Mg/{100}MgO interface, coherently matching with the terminating {100}MgO plane. Discussion is focused on the mechanisms underlying the formation of the 2DCs, their effects on the nucleation potency of MgO particles, and grain refinement. This work sheds light on how heterogeneous nucleation can be manipulated by altering the nucleation potency of a substrate through deliberately promoting elemental segregation of carefully chosen element(s).

High-entropy perovskite oxides (HEPOs) suffer from inferior stability in high-power battery-supercapacitor hybrid (BSH) devices. Therefore, revealing their energy storage mechanism is extremely important for optimizing appliance stability. Herein, La0.7Bi0.3Mn0.4Fe0.3Cu0.3O3 nano-HEPO exhibits the dual-ion energy storage mechanism in aqueous alkaline BSH devices. The rapid deintercalation of oxygen anions from the (sub)surface facilitates the intercalation of hydrogen cations into the bulk during charging; however, the deintercalation of hydrogen cations upon the discharge process is hindered because of the surface filling with oxygen vacancies, resulting in an irreversible phase transition and volumetric expansion. Meanwhile, the evolution of surface oxygen species leads to the weak binding between the surface metal-oxygen polyhedron and the bulk, causing severe capacity deterioration due to the active cation leaching and surface inactive La(OH)3 aggregation. Finally, optimal strategies are presented based on the dual-ion intercalation chemistry of HEPOs for application in high-performance BSH devices with long service life.

This study introduces new alloys, which combine the age-hardening capability of Al-Mg-Si alloys with the microstructure-controlling effect on processing of primary Fe-rich intermetallic phases used in foil stock. In detail, the processing and microstructure–property relations in new crossover aluminum alloys derived from 6xxx and 8xxx foil stock alloys, is shown. A highly Fe-rich intermetallic phase content was deployed to conceptually mimic high scrap content. Fast and slow solidification rates were applied to represent thin strip and direct chill casting, respectively. The effects of adding Fe and Mn to alloy 6016 were examined, while the Si consumed in primary phases was partly adjusted to maintain age-hardening potential. It was shown that upon thermomechanical processing, primary intermetallic phases in the new alloys are finely fragmented and well dispersed, resulting in strong grain refinement and a uniform texture. Attractive combinations of strength and ductility were revealed, also in material processed under direct chill casting conditions. The new alloys’ high elongation values of up to 30%, and their age-hardening response, were similar to those seen in commercial alloy 6016, while their strain hardening capacity was significantly greater. This can be attributed mainly to the formation of geometrically necessary dislocations near primary Fe-rich intermetallic phases. The study discusses microstructure refinement on the basis of particle stimulated nucleation. It uses a simple model to describe the individual contributions to yield strength, including the effect of primary phases. It also models the effect of these particles on increased strain hardening and ductility.

We propose a quantum-mechanical dimensionless metric, the local-lattice distortion (LLD), as a reliable predictor of ductility in refractory multi-principal-element alloys (RMPEAs). The LLD metric is based on electronegativity differences in localized chemical environments and combines atomic-scale displacements due to local lattice distortions with a weighted average of valence-electron count. To evaluate the effectiveness of this metric, we examined body-centered cubic (bcc) refractory alloys that exhibit ductile-to-brittle behavior. Our findings demonstrate that local-charge behavior can be tuned via composition to enhance ductility in RMPEAs. With finite-sized cell effects eliminated, the LLD metric accurately predicted the ductility of arbitrary alloys, which compares well with existing tensile-elongation experiments. To validate further, we qualitatively evaluated the ductility of two refractory RMPEAs, i.e., NbTaMoW and Mo72W13Ta10Ti2.5Zr2.5, through the observation of crack formation under indentation, again showing excellent agreement with LLD predictions. A comparative study of three refractory alloys provides further insights into the electronic-structure origin of ductility in refractory RMPEAs. This proposed metric enables rapid and accurate assessment of ductility behavior in the vast RMPEA composition space.

Nanostructured metals and alloys often exhibit high strengths but at the expense of hallmark ductility. Through harnessing the far-from-equilibrium processing conditions of laser powder-bed fusion (L-PBF) additive manufacturing, we develop a dual-phase nanolamellar structure comprised of FCC/L12 and BCC/B2 phases in a Ni40Co20Fe10Cr10Al18W2 eutectic high-entropy alloy (EHEA), which exhibits a combination of ultrahigh yield strength (>1.4 GPa) and large tensile ductility (∼17%). The deformation mechanisms of the additively manufactured EHEA are studied via in-situ synchrotron X-ray diffraction and high-resolution transmission electron microscopy. The high yield strength mainly results from effective blockage of dislocation motion by the high density of lamellar interfaces. The refined nanolamellar structures and low stacking fault energy (SFE) promote stacking fault (SF)-mediated deformation in FCC/L12 nanolamellae. The accumulation of abundant dislocations and SFs at lamellar interfaces can effectively elevate local stresses to promote dislocation multiplication and martensitic transformation in BCC/B2 nanolamellae. The cooperative deformation of the dual phases, assisted by the semi-coherent lamellar interfaces, gives rise to the large ductility of the as-printed EHEA. In addition, we also demonstrate that post-printing heat treatment allows us to tune the non-equilibrium microstructures and deformation mechanisms. After annealing, the significantly reduced SFE and thicknesses of the FCC nanolamellae further facilitate the formation of massive SFs. The dissolution of nano-precipitates in the BCC/B2 nanolamellae reduces spatial confinement and further promotes martensitic transformation to enhance work hardening. Our work provides fundamental insights into the rich variety of deformation mechanisms underlying the exceptional mechanical properties of the additively manufactured dual-phase nanolamellar EHEAs.

The crystal structure of the interfacial areas of a δ-FCC water-quenched nano-hydride was characterized by electron energy-loss spectroscopy (EELS) and electron diffraction. EELS revealed ribbons with plasmon energy (PE) values of 17.4±0.01 eV and 18.3±0.01 eV (nominally characteristic of the ζ- and γ-hydride phases, respectively) in the interfacial area between the δ-core and α-Zr matrix. Electron diffraction patterns (DPs) obtained from the axes of the interface contained reflections that could be indexed as {0001} reflections of the ζ-phase. Such ζ-type reflections, however, disappeared after tilting the interface away from the -axes; implying that they originated from sources other than a hypothetical ζ-phase. Moreover, electron DPs obtained from multiple zone axes of the interface, did not show characteristic {110}/{112} superlattice reflections of the γ-phase. These results ruled out the existence of ζ- and γ-phases in the interface (down to the spatial resolution of the utilized techniques) despite the measured plasmon energy values.Subsequently, dielectric theory was utilized to clarify the origin of interfacial ribbons with PE values characteristic of the ζ- and γ-phases. Dielectric functions of the α-Zr and δ-core were extracted from the energy-loss spectra of the two phases, to simulate the energy-loss functions across the interface. Simulations suggested that the observed interfacial ribbons in EELS maps (with PE values of 17.4±0.01 eV and 18.3±0.01 eV) could have stemmed from the delocalized nature of plasmon vibration and the effect of interface on shifting the plasmon vibration frequency, but not necessarily from the existence of the ζ- and γ-phases.

Oxide glasses with a network structure are omnipresent in daily life. Often, they are regarded as isotropic materials; however, structural anisotropy can be induced through processing in mechanical fields and leads to unique materials properties. Unfortunately, due to the lack of local, atomic-scale analysis methods, the microscopic mechanisms leading to anisotropy remained elusive. Using novel analysis methods on glasses generated by molecular dynamics simulations, this paper provides a microscopic understanding of topological anisotropy in silica (SiO2) glass under mechanical loads. The anisotropy observed in silica glass originates from a preferred orientation of SiO4 tetrahedra at both short- and medium-range levels that can be controlled via the mode of mechanical loading. The findings elucidate the relation between the deformation protocol and the resulting anisotropic structure of the silica network (involving both persistent and transient effects), and thus provide important insight for the design of oxide glasses with tailored materials properties.

In the present study, the formation mechanism of tearing topography surface (TTS), which is observed after slow strain-rate tensile tests of H-charged pearlitic specimens, was investigated in detail. The TTS always appeared at the subsurface of failed H-charged specimens, where H atoms were concentrated after room-temperature electrochemical H-charging. The TTS consisted of stepped flat surfaces and dimpled surfaces. The flat surface was caused by the coalescence of sharp micro-shear cracks, not micro-voids, of H-enriched cementite (θ) platelets in a pearlite colony, namely brittle transcolonial fracture. The regions surrounding the flat surface were H-depleted due to the migration of H atoms into neighboring micro-shear cracks during tensile deformation. As a result, the H-depleted regions were fractured by the typical coalescence of micro-voids, namely relatively ductile shear cracking, resulting in dimpled surfaces after tensile fracture. These results mean that the TTS region, strictly speaking, the flat surface region, which is generated by transcolonial fracture inside the TTS region, is an initial site of H-induced cracking of pearlitic steel. The ab-initio calculations of the energy value of H desorption from a C vacancy in θ supported the recent report that H atoms are concentrated inside the θ platelets after H charging.

The calorimetric and dynamical glass transitions are uncoupled in high entropy metallic glasses (HEMGs). That is, the thermal glass-transition or vitrification temperature (Tg) and α-relaxation temperature (Tα) are uncorrelated as a function of alloy stoichiometry. The underlying mechanism that gives rise to this is not understood, nor is the connection to atomic structure. Here, molecular dynamic (MD) simulations of different HEMG model systems are performed to investigate the glass transition behavior. In addition to the high configurational entropy of mixing (for an ideal solution), we show that the effect of mismatch entropy plays a critical role in decoupling vitrification kinetics/α-relaxation in HEMGs. Microscopically, the atomic size difference contributes significantly to the sluggishness of long-range diffusion and decreased dynamic heterogeneities. This gives rise to a depressed structural α-relaxation. More importantly, we find that HEMGs with the decoupling vitrification kinetics/α-relaxation can show unique mechanical performance, such as better radiation tolerance and higher resistance to shear banding. Our results provide insights into the high entropy effect of glassy metallic materials, and suggest a means for tuning properties of HEMGs.