The efficiency of supported catalysts depends on the porous microstructure of their solid support, which regulates mass transfer, exposure to the active phase, and mechanical strength. Here, we focus on the manufacturing of a specific type of catalytic support, $\gamma$-alumina extrudates, by a kneading-extrusion process. In this process, a paste is initially formed by blending and subsequently kneading a boehmite powder, an aluminum oxide hydroxide precursor of $\gamma$-alumina, with various liquids before undergoing extrusion. The crucial step in this process is the kneading step, which allows control over the textural and mechanical properties of the extrudate. The present experimental study aims to measure the impact of the kneading step on boehmite pastes prepared using a pilot kneader. The pastes are obtained by mixing boehmite powder subsequently with an acid and a basic solution in a two-step process known as peptization and neutralization. In this study, kneading is conducted at various mixing speeds and durations while monitoring the torque exerted by the boehmite paste on the kneader blades. Moreover, samples are extracted from the pilot kneader at various stages of the kneading process, and their textural properties are determined by both nitrogen sorption and mercury intrusion porosimetry. Our findings show that, at fixed composition, the textural properties of boehmite pastes are controlled by the overall deformation accumulated during kneading. Conversely, for a fixed accumulated deformation, the pH sets the textural properties. Finally, we identify an empirical control parameter that captures the combined effects of pH and accumulated deformation on the key textural attributes of boehmite pastes. These results set the stage for a systematic design approach of boehmite-based catalyst supports.

The low valley polarization of monolayer transition-metal dichalcogenides at room temperature poses a significant obstacle to the development of valleytronic devices, and a mechanistic insight into the valley depolarization in such systems is still lacking. In this study, we demonstrate that substitutional doping leading to alloyed monolayers offer an effective strategy for enhancing valley polarization at room temperature. The degree of valley polarization, as determined by helicity-resolved transient absorption spectroscopy, is 15% for Se-doped and 30% for Se- and V-doped monolayer layer $\mathrm{Mo}{\mathrm{S}}_2$ (referred to as MoSSe and VMoSSe, respectively). The valley polarization persists for longer durations in MoSSe (∼15 ps) and VMoSSe (>500 ps) compared to pristine $\mathrm{Mo}{\mathrm{S}}_2$ (∼1 ps). The prolonged valley depolarization in MoSSe is attributed to a reduction in long-range electron-hole exchange interactions due to thermal mixing of bright and dark excitons. However, the valley depolarization in VMoSSe takes place via intervalley scattering of carriers between hybridized and defect excitons. Our study elucidates that altering the exciton ground state through the inclusion of additional levels near the conduction-band or valence band edges via alloying can enhance and prolong valley polarization in $\mathrm{Mo}{\mathrm{S}}_2$. These findings are pivotal in realizing valleytronics devices at room temperature.

We report negative thermal quenching of photoluminescence (PL) in few-layered $\mathrm{M}{\mathrm{o}}_{0.6}{\mathrm{W}}_{0.4}\mathrm{S}{\mathrm{e}}_2$ flakes. A comparative study of temperature-dependent PL from two groups of $\mathrm{M}{\mathrm{o}}_{0.6}{\mathrm{W}}_{0.4}\mathrm{S}{\mathrm{e}}_2$ flakes, one with defects and the other with negligible defects, shows that this anomalous enhancement in the PL with increasing temperature is due to the dissociation of defect-bound excitons at higher temperatures. The relaxation dynamics of the carriers localized at these defect states were studied using the ultrafast pump-probe technique, which shows that the photogenerated carriers are trapped at these defects on a timescale of $\approx 3$ ps.

We explore the emergence of phonon-mediated superconductivity in bilayer borophenes by controlled intercalation with elements from the groups of alkali, alkaline-earth, and transition metals, using systematic first-principles and Eliashberg calculations. We show that the superconducting properties are primarily governed by the interplay between the out-of-plane ($p_z$) boron states and the partially occupied in-plane ($s+p_{x,y}$) bonding states at the Fermi level. Our Eliashberg calculations indicate that intercalation with alkaline-earth-metal elements leads to the highest superconducting critical temperatures ($T_c$). Specifically, Be in ${\delta }_4$, Mg in ${\chi }_3$, and Ca in the kagome bilayer borophene demonstrate superior performance with $T_c$ reaching up to 58 K. Our study therefore reveals that intercalated bilayer borophene phases are not only more resilient to chemical deterioration, but also harbor enhanced $T_c$ values compared to their monolayer counterparts, underscoring their substantial potential for the development of boron-based two-dimensional superconductors.

Grain boundaries can dissociate into facets if that reduces their excess energy. This, however, introduces line defects at the facet junctions, which present a driving force to grow the facets in order to reduce the total number of junctions and thus the system's energy. Often, micrometer-sized facet lengths are observed and facet growth only arrests for kinetic reasons. So far, energetically stable, finite-sized facets have not been observed, even though theoretical stability conditions have already been proposed. Here, we show a case where nanometer-sized facets are indeed stable compared to longer facets in $\left[11\overline{1}\right]$ tilt grain boundaries in Cu by atomistic simulation and transmission electron microscopy. The facet junctions lack a Burgers vector component, which is unusual, but which removes the main energy cost of facet junctions. Only attractive interactions via line forces remain, which result from a discontinuity of grain boundary excess stress at the junction. Atomistic simulations predict that the same phenomenon also occurs in at least Al and Ag.

Dislocation-twin boundary interactions in Cu are systematically studied using molecular dynamics simulations. Specifically, interactions between screw dislocations and 60° mixed dislocations with both coherent and incoherent twin boundaries are examined. Importantly, the study considers both metastable and minimum-energy configurations of these twin boundaries to explore the impact of local atomic arrangements on dislocation-twin boundary interactions. The results indeed reveal two distinct mechanisms for dislocation transmission through twin boundaries: partial dislocation reaction versus full dislocation absorption followed by emission in the adjacent grain. The observed interaction mechanisms are found to be similar in the case of other symmetric tilt GBs with similar local structural units. Therefore, the interplay between dislocation type and grain boundary (GB) structure can strongly influence the transmission of dislocations across GBs. Even a subtle change of approximately 1.5% in the nearest-neighbor distance of the coherent twin boundary (metastable vs minimum-energy structure) alters the outcome of the dislocation-twin boundary interaction (transmission vs absorption). Specifically, the screw dislocation can transmit through metastable but not the minimum-energy coherent twin boundary. This further highlights the important role of GB structure, especially those metastable structures, in material strength modeling.

High temperature ($>100{}^{\circ }\mathrm{C}$) shape memory alloys (HTSMAs) are needed for devices in aerospace, automotive, manufacturing, and other sectors of industry, but the available binary HTSMAs are few, posing a limitation to these devices' operating temperatures. One promising approach is to alloy a binary with other elements to tune its martensitic transition temperature (MTT). There exist numerous combinations of metals to form ternaries, quaternaries, etc., and the martensitic phase transitions in these multicomponent SMAs are more complicated than those in binaries. In this work, we studied the martensitic phase transitions in ${\mathrm{Pd}}_x{\mathrm{Ni}}_{0.5-x}{\mathrm{Ti}}_{0.5}$ ternaries using ab initio methods. Based on energy calculations we find that the behavior of energy vs monoclinic angle of ${\mathrm{Pd}}_x{\mathrm{Ni}}_{0.5-x}{\mathrm{Ti}}_{0.5}$ is substantially different from those of binary end members, except for very small $x$. The energetic analysis suggests that the martensite phase is monoclinic for $x\lesssim 0.1$ and orthorhombic for $x\gtrsim 0.1$. Using the ab initio molecular dynamics simulations and thermodynamic integration, we calculated MTT and latent heat vs Pd content $x$ and our theoretical results are in good agreement with measured data. Since relatively small supercells were used in our dynamic simulations, the present first-principles approach is both efficient and accurate and we expect it to become a useful tool in the search for multicomponent HTSMAs with desirable properties.

Using first-principles density-functional theory calculations and free energy analysis, we demonstrate that for ${\mathrm{RbV}}_3{\mathrm{Sb}}_5$, the long-range $2\times 2\times 2$ charge density wave (CDW) is condensed from the disordered $2\times 2$ charge orders at $T_{\mathrm{CDW}}$, indicating an order-disorder nature of CDW phase transition. It is revealed that the dynamic fluctuations of four degenerate $2\times 2$ charge orders exist above $T_{\mathrm{CDW}}$, giving rise to a configurational entropy. Our free energy analysis predicts the first-order transition with a release of entropy at $T_{\mathrm{CDW}}\approx$ 95 K, consistent with the measured specific heat data showing the presence of a sharp peak across the phase transition. Furthermore, we identify that the CDW fluctuations above $T_{\mathrm{CDW}}$ occur through a thermal reaction with the concerted V-V bond breakages and formations of V trimers and hexamers, corroborated by the experimental evidence of strong CDW fluctuations extending to higher than $\sim 1.7\times T_{\mathrm{CDW}}$. The present results not only shed light on the nature of the first-order, order-disorder CDW phase transition in ${\mathrm{AV}}_3{\mathrm{Sb}}_5$ but also have broader implications for understanding the disorder-induced collapse of long-range CDW order in other kagome metals such as ${\mathrm{ScV}}_6{\mathrm{Sn}}_6$ and FeGe.

A theoretical framework for analyzing the mechanical exfoliation of 2D materials at finite temperature is introduced. As an example, this framework, based on transition-state theory and calculation of the reaction pathway, is applied to the mechanical exfoliation of multilayer ${\mathrm{MoS}}_2$. The theory predicts that altering the bonding of the top layer to the bulk through straining or twisting and slowly exfoliating at low temperatures will enhance the yield of the monolayer material.

Alloying the topological semimetal ${\mathrm{Cd}}_3{\mathrm{As}}_2$ with ${\mathrm{Zn}}_3{\mathrm{As}}_2$ provides a potential route for controlling the electronic properties. We predict the alloy phase diagram from first-principles calculations, considering that both end members have a crystal structure derived from the antifluorite lattice, but with different arrangements of the unoccupied cation sites. To overcome the limitations of the regular solution approximation and to include short-range order effects, we perform Monte Carlo simulations, parameterize the temperature dependence of the mixing enthalpy $\mathrm{\Delta }{H}_{\mathrm{m}}$, and perform thermodynamic integration of the free energy. The resulting phase diagram exhibits features that are unique to heterostructural alloy systems and provides computational predictions of solubility limits and composition ranges that are stable against spinodal decomposition.

Electrical manipulation of exchange bias by spin-orbit torque (SOT) is promising for the design of spintronic devices, such as multilevel memory and neuromorphic computing. However, an external magnetic field is required to assist manipulation of exchange bias, which poses a challenge for applications. In this work, we propose a promising approach to the field-free manipulation of exchange bias through an in-plane ferromagnetic layer deposited on the current line of the Hall bar device, which can generate an internal effective in-plane field to realize field-free SOT switching. Furthermore, our devices present memristive behaviors in the absence of an external field, offering the practical potential for the construction of artificial synapses based on exchange-biased systems. Meanwhile, this method can ensure the high SOT efficiency and a thermal stability factor ($\mathrm{\Delta }$) of around 56, indicating over 10 years of data retention. The approach to field-free manipulation of exchange bias by SOT is promising for applications and the development of spintronic devices.

Multipoles in a material, which describe the degrees of freedom of electrons, have recently attracted much attention from the perspective of a unified understanding of diverse physical phenomena. Therefore, demand has been increasing for probes that can detect various types of multipoles. Here, we report the detection of multiple multipoles in collinear antiferromagnet ${\mathrm{MnTiO}}_3$ using optical second harmonic generation (SHG). Utilizing SHG selection rules and an imaging technique, we detect ferroaxial and antiferromagnetic orders and visualize their domains, and show that SHG is a powerful tool for the simultaneous observation of underlying multipoles with different symmetries.

We detail the magnetic properties of monolayer $\mathrm{Cr}{X}_2$ and its Janus counterparts $\mathrm{Cr}XY$ ($X,Y=\mathrm{S},\mathrm{Se},\mathrm{Te}$, with $X\ne Y$) using ab initio methods and Landau-Lifshitz-Gilbert magnetization dynamics, and uncover the pronouncedly strong interplay between their structure symmetry and the magnetic order. The relaxation of nonmagnetic chalcogen atoms, that carry large spin-orbit coupling, changes the energetically preferential magnetic order between in-plane antiferromagnetic and tilted ferromagnetic one. The considered Janus monolayers exhibit sizable Dzyaloshinskii-Moriya interaction, in some cases above 20% of the isotropic exchange, and critical temperature of the long-range magnetic order in the vicinity or even significantly above the room temperature.

Crystallization of amorphous layers has been demonstrated under various radically different laser-exposure conditions, including continuous wave (cw) and pulsed lasers. Here, we investigate the specific role of ionization in the crystallization of dielectric ${\mathrm{SiO}}_2/{\mathrm{SiN}}_x$ multilayers. This choice is motivated by the technological relevance of the interaction between lasers and a multilayer thin films system in distributed Bragg reflectors. Specimens were exposed to both femtosecond laser pulses, triggering bulk ionization thanks to nonlinear absorption processes, and a cw infrared laser, whose photon energy is lower than the dielectrics band gap, resulting in a purely linear absorption mechanism rather than ionization. While femtosecond laser exposure leads to the formation of Si nanocrystals homogeneously confined within the focal volume and extending to adjacent ${\mathrm{SiN}}_x$ layers, cw laser exposure leads to the formation of polymorphic crystalline phases of ${\mathrm{Si}}_3{\mathrm{N}}_4$ in the ${\mathrm{SiN}}_x$ layers, along with a Si phase within the ${\mathrm{SiO}}_2$ layers, which otherwise remain amorphous.

The vast amount of computational studies on electrical conduction in solid-state electrolytes is not mirrored by comparable efforts addressing thermal conduction, which has been scarcely investigated despite its relevance to thermal management and (over)heating of batteries. The reason for this lies in the complexity of the calculations: on one hand, the diffusion of ionic charge carriers makes lattice methods formally unsuitable, due to the lack of equilibrium atomic positions needed for normal-mode expansion. On the other hand, the prohibitive cost of large-scale molecular dynamics (MD) simulations of heat transport in large systems at ab initio levels has hindered the use of MD-based methods. In this paper, we leverage recently developed machine-learning potentials targeting different ab initio functionals (PBEsol, ${\mathrm{r}}^2\text{SCAN}$, PBE0) and a state-of-the-art formulation of the Green-Kubo theory of heat transport in multicomponent systems to compute the thermal conductivity of a promising solid-state electrolyte, ${\mathrm{Li}}_3{\mathrm{PS}}_4$, in all its polymorphs ($\alpha , \beta$, and $\gamma$). By comparing MD estimates with lattice methods on the low-temperature, nondiffusive $\gamma -{\mathrm{Li}}_3{\mathrm{PS}}_4$, we highlight strong anharmonicities and negligible nuclear quantum effects, hence further justifying MD-based methods even for nondiffusive phases. Finally, for the ion-conducting $\alpha$ and $\beta$ phases, where the multicomponent Green-Kubo MD approach is mandatory, our simulations indicate a weak temperature dependence of the thermal conductivity, a glass-like behavior due to the effective local disorder characterizing these Li-diffusing phases.

The discovery of superconductivity in infinite-layer nickelates has drawn considerable attention and boosted numerous theoretical and experimental studies. Here, combining density functional theory and Wannier function calculations, we study the electronic structure of nickelate $\mathrm{NdNi}{\mathrm{O}}_2{\mathrm{H}}_x$ ($x=0$, 0.25, 0.5) (NNOH) under five different in-plane strains. We unveil that, with H introduced, the orbital occupation of Ni $3d_{x^2\text{−}{y}^2}$ increases, accompanied by the shift of band structure toward lower energy under constant strain. Meanwhile, the H $1s$ orbital hybridizes and forms a bonding-antibonding state with the Ni $3d_{z^2}$ orbital, reducing the occupation of the Ni $3d_{z^2}$ orbital, which results in the decreased filling of Ni $3d$ orbital. By contrast, the strain has negligible influences on the filling of Ni $3d$ and Ni $e_g$ orbital polarization. As the H concentration increases, the contribution of the itinerant interstitial $s$ (IIS) orbital to the band structure near the Fermi level gradually decreases and disappears at $x=0.5$ due to the doped H obliterating the IIS band. In addition, with compressive strain applied, the bandwidth of the Ni $3d_{x^2\text{−}{y}^2}$ orbital increases, consistent with the calculated stronger effective Ni $3d_{x^2\text{−}{y}^2}$ nearest-neighboring hopping. In addition, we find that the impact of H concentration and strain on the projected orbitals and calculated density of states is slight. Also, the influences of the Sr concentration (0–20%) and Hubbard $U$ parameter on the electronic properties of NNO without strain are explored and found not to change the main conclusions.

The migration of grain boundaries leads to grain growth in polycrystals and is one mechanism of grain-boundary-mediated plasticity, especially in nanocrystalline metals. This migration is due to the movement of dislocationlike defects, called disconnections, which couple to externally applied shear stresses. While this has been studied in detail in recent years, the active disconnection mode was typically associated with specific macroscopic grain boundary parameters. We know, however, that varying microscopic degrees of freedom can lead to different atomic structures without changing the macroscopic parameters. These structures can transition into each other and are called complexions. Here, we investigate $\left[11\overline{1}\right]$ symmetric tilt boundaries in fcc metals, where two complexions—dubbed domino and pearl—were observed before. We compare these two complexions for two different misorientations: In $\mathrm{\Sigma }19\mathrm{b}\left[11\overline{1}\right]\left(178\right)$ boundaries, both complexions exhibit the same disconnection mode. The critical stress for nucleation and propagation of disconnections is nevertheless different for domino and pearl. At low temperatures, the Peierls-like barrier for disconnection propagation dominates, while at higher temperatures the nucleation is the limiting factor. For $\mathrm{\Sigma }7\left[11\overline{1}\right]\left(145\right)$ boundaries, we observed a larger difference. The domino and pearl complexions migrate in different directions under the same boundary conditions. While both migration directions are possible crystallographically, an analysis of the complexions' structural motifs and the disconnection core structures reveals that the choice of disconnection mode and therefore migration direction is directly due to the atomic structure of the grain boundary.

Under ambient conditions, Zn is a hexagonal metal with a large $c/a$ ratio of 1.856. Plastic deformation is predominantly accommodated by basal $\langle a\rangle$ slip and compression twins on the $\left\{10\overline{1}2\right\}$ planes. Increasing hydrostatic pressure drastically reduces the $c/a$ ratio of Zn and, when a critical threshold of $c/a=\sqrt{3}$ at about 10 GPa is crossed, the $\left\{10\overline{1}2\right\}$ twins are predicted to change from compressive to tensile in nature. What happens at the transition point, when $c/a=\sqrt{3}$, remains unknown. Here, we strain-cycle a textured polycrystalline sample of pure Zn at uniform hydrostatic pressures ranging between 2 and 17 GPa, over which the $c/a$ ratio crosses the $c/a=\sqrt{3}$ compressive-tensile transition for $\left\{10\overline{1}2\right\}$ twins. During deformation, the state of the sample is monitored in situ through x-ray diffraction to extract texture and internal strain evolution. By comparing the experimental results with the predictions of an elastoviscoplastic polycrystal simulation, we confirm the androgynous nature of $\left\{10\overline{1}2\right\}$ twin response at low and high pressures. When $c/a=\sqrt{3}$, polycrystalline Zn does not display any evidence of twinning and its plastic behavior is controlled by mostly basal and pyramidal $\langle c+a\rangle$ slip activity, with a very small contribution of prismatic $\langle a\rangle$ slip. Evidence for the activity of other $\left\{10\overline{1}n\right\}$ twinning modes, which have been suggested for Zn under high pressure, are not observed.

Targeted material design is at the center of research efforts on epitaxial, complex oxide heterostructures. Due to the strong electron-lattice coupling, small structural modifications are often decisive for the resulting macroscopic, physical properties of artificially layered materials. Here we report on a detailed structural analysis of a set of differently stacked ${\mathrm{LaNiO}}_3\text{−}{\mathrm{LaGaO}}_3$ superlattices by transmission electron microscopy. We find that the relative thickness ratio of the two superlattice sublayers affects the structural network, resulting in different Ni–O bond lengths and Ni–O–Ni angles under the same epitaxial strain conditions. Whereas the bond length values depend mainly on the ${\mathrm{LaNiO}}_3$ layer thickness, bond angles are mainly influenced by the ${\mathrm{LaGaO}}_3$ layer thickness. The orbital polarization determined from x-ray absorption spectroscopy measurements shows that the superlattice with the smallest deviation of both values compared to bulk shows the highest orbital polarization. Therefore, the thickness ratio of the two superlattice components can be regarded as an additional effective tool to tune the functional properties of nickelates.