Solid solution strengthening (SSS) significantly influences the mechanical properties of alloy materials, which strongly depends on the solute type and concentration and various alloy structures. However, it still presents a significant challenge to identify a universal structure-property relationship of SSS. Here, we propose an intrinsic descriptor to quantify the electronic effect of SSS for both dilute and concentrated alloys from the point of bond breaking and forming, which allows to evaluate the SSS effect across various alloys, such as binary, medium-entropy, and high-entropy alloys, regardless of the solute type and concentration and alloy structures. Our descriptor reflects the key parameter—solute/dislocation interactions, indicates that the center and upper edge of d-bands control the SSS effects, and identifies that the d-d/d-s coupling dominates the size effects of SSS for dilute alloys and the d-d coupling for concentrated alloys. This simple element-determined recipe provides a deep understanding of the SSS mechanism and a physical guidance for designing high-performance alloys.

A tetragonally distorted FeCo alloy is a ferromagnetic material exhibiting perpendicular magnetic anisotropy (PMA) with a large saturation magnetization. Theoretical investigations have proposed that PMA in FeCo is caused by the hybridization of the certain orbitals near the Fermi energy ($E_{\mathrm{F}}$) in the minority-spin channel, but experimental verification of the electronic structure has yet to be performed. Here, using spin- and angle-resolved photoemission spectroscopy (SARPES) combined with first-principles calculations, we investigated the spin- and orbital-dependent electronic structure of tetragonally distorted FeCo films on a Rh(001) substrate. Our SARPES results show clear out-of-plane spin polarization at room temperature. Furthermore, by considering the matrix element effect and experimental geometry, we revealed that the spin-polarized bands around $E_{\mathrm{F}}$ of FeCo films possessing PMA are mainly composed of minority-spin $d_{xy}$ and $d_{x^2-y^2}$ orbitals. Our findings provide deep insight into the emergence of PMA in rare-element-free magnetic materials.

Amorphous alumina thin films (TFs) have attracted great attention in the last decade due to their unconventional properties that are distinct from other oxide glasses. The ion migration mechanism was systematically investigated for surface amorphous alumina TFs on aluminum in comparison with bulk amorphous/crystalline alumina by using reactive molecular dynamics simulations combined with free-energy calculations. The results reveal that the ion migration mechanism within the surface alumina TFs on Al is different from that of bulk alumina due to the incorporation of Al at the interface. We show that incorporating Al into surface alumina TF remarkably decreases the ion migration barriers to around 1 eV by increasing the ion site volume along the migration paths. The calculated ion diffusivity in surface alumina above the Al melting point significantly increases to ${10}^{-8}\sim {10}^{-6}\mathrm{c}{\mathrm{m}}^2/\mathrm{s}$, lowering the temperature threshold for massive ion migration by $\sim 1000$ K. We finally discussed the temperature and structural anisotropy dependence for activating the ion migration in the surface oxide TF. The results reveal the atomistic origin of the enhanced ion migration within surface alumina TF and provide insights into thermal oxidation mechanism of metal/alloy-based energetic materials.

Planar π-conjugated borides not only attract fundamental interests in bonding chemistry, but also offers wide-ranging applications in catalysis, bioimaging, and biosensing. To stabilize π-conjugated ${\mathrm{B}}_6$ rings without out-of-plane bonding, we propose a design strategy that involves inserting low-compressible $\mathrm{C}{\mathrm{N}}_3$ triangles into tessellation of ${\mathrm{B}}_6$ rings to create planar borides. Based on this concept, we designed the planar hypercoordinate boride $\mathrm{ScC}{\mathrm{N}}_3{\mathrm{B}}_6$, which features the planar structure and represents a theoretically predicted π-conjugated ${\mathrm{B}}_6$ ring. The molecular dynamics simulations suggested that ${\mathrm{B}}_6$ rings in $\mathrm{ScC}{\mathrm{N}}_3{\mathrm{B}}_6$ remain intact at a high temperature of 1500 K. The metal adsorption energy of ${\mathrm{B}}_6$ rings in $\mathrm{ScC}{\mathrm{N}}_3{\mathrm{B}}_6$ is comparable to borophene, and superior to that of graphene and two-dimensional hexagonal boron nitride. As a result, the designed $\mathrm{ScC}{\mathrm{N}}_3{\mathrm{B}}_6$ demonstrates both high stability and chemical activity attributed to $\mathrm{C}{\mathrm{N}}_3$ triangles and ${\mathrm{B}}_6$ rings, respectively. Consequently, the designed $\mathrm{ScC}{\mathrm{N}}_3{\mathrm{B}}_6$ could serve as a potential sensor for biomolecules. Moreover, the planar ninefold hypercoordinate Sc weakly bonds to the ${\mathrm{N}}_3{\mathrm{B}}_6$ wheel, drives a flat band of the $d{\mathrm{z}}^2$ orbital, suggesting that flat band can be generated by splitting of $\mathrm{d}{z}^2$ orbital in planar hypercoordinate crystal field.

The rich and fascinating physics of topological spin textures in van der Waals (vdW) two-dimensional magnets has motivated recent growing interests, though a comprehensive understanding remains elusive. Here, in atomistic simulations on monolayer CrSBr, we find two magnetic phases emerging under nonequilibrium conditions at distinct temperatures: a standard ferromagnetic transition $T_c$ and a lower temperature $T^{*}$. Moreover, the real-space analysis of the spin texture reveals the emergence of metastable topological bimeron defects below $T^{*}$, showing an algebraic-like decaying spin-spin correlation function. The Dzyaloshinskii-Moriya interaction, induced by the local site asymmetry in the centrosymmetric CrSBr monolayer, is proved to be the origin of the bimeron's formation. Furthermore, the increasing bimeron density upon increasing the cooling rate follows a Kibble-Zurek behavior, suggesting a handle to drive and control topological bimerons below $T^{*}$. Our results put forward CrSBr as an important candidate for the investigation of the nonequilibrium behavior of bimerons in vdW magnets.

We report a systematic study of the magnetic, electrical, specific heat, and electrocatalytic properties of the quasi-one-dimensional hexagonal perovskite oxide ${\mathrm{Sr}}_6{\left({\mathrm{Co}}_{0.955}{\mathrm{Fe}}_{0.045}\right)}_5{\mathrm{O}}_{15}$ high-quality single crystal. Magnetic susceptibility exhibits an antiferromagnetic ground state perpendicular to the spin-chain direction (the $c$ axis) and a ferromagnetic state along the $c$ axis. Notably, the broad peak near 90 K possibly originates from short-range spin correlations rather than a typical spin-glass or cluster-glass state, and the estimated frustration factor indicates the presence of spin frustration, reflecting competing magnetic interactions. The specific heat data show that the average sound velocity in Fe-substituted ${\mathrm{Sr}}_6{\mathrm{Co}}_5{\mathrm{O}}_{15}$ is lower than that of parent ${\mathrm{Sr}}_6{\mathrm{Co}}_5{\mathrm{O}}_{15}$, attributing to the significant scattering of conduction phonons by magnetic impurities. Intriguingly, in the ${\mathrm{Sr}}_6{\left({\mathrm{Co}}_{1-x}{\mathrm{Fe}}_x\right)}_5{\mathrm{O}}_{15}$ single-crystal system, the Fe content significantly influences the electrocatalytic performance for hydrogen evolution reaction (HER). Furthermore, each single crystal displays pronounced electrocatalytic anisotropy, offering insights into their intrinsic physical properties while highlighting their potential for future applications.

A heterophase containing both the optically active $\alpha \text{−}{\mathrm{CsPbI}}_3$ and nonactive $\delta \text{−}{\mathrm{CsPbI}}_3$ has been demonstrated as an efficient white light emitter. This has challenged the conventional perspective that nonactive phases of perovskites are undesirable in any metal halide perovskite-based optoelectronic devices. To understand the role that yellow phase $\delta \text{−}{\mathrm{CsPbI}}_3$ plays in the light-emission process, we performed a systematic computational study on its electronic and optical properties, which are relatively unexplored in the literature. Using the Fröhlich model we showed that both the electron and hole exhibit moderate coupling to longitudinal optical phonons. Explicit density functional theory calculations show that small hole polarons exist with a formation energy of $-96\mathrm{meV}$, corresponding to the contraction of the Pb-I bonds within a $\left[{\mathrm{PbI}}_6\right]$ octahedron. Nudged elastic bands calculations show that the hole polaron can hop into neighboring $\left[{\mathrm{PbI}}_6\right]$ octahedral sites with a small activation barrier of $2.1\mathrm{meV}$. Molecular dynamics simulations also show that the hole polaron exhibit periodic localization and delocalization behavior similar to carrier hopping with a characteristic lifetime of $0.3\mathrm{ps}$. Our results have elucidated the role that $\delta \text{−}{\mathrm{CsPbI}}_3$ plays in the self-trapped emission in perovskite-based white light emitting diodes by supporting the presence of the localized small hole polaron.

Dislocations, both screw and nonscrew, in fcc metals are crucial in forming dislocation substructures, significantly influencing deformation mechanisms such as deformation twinning and martensite transformation. In this work, the effects of dislocation types on the deformation behaviors of fcc Al, Cu, and Fe are investigated using the semidiscrete variational Peierls-Nabarro (PN) model. The three-dimensional (3D) misfit potentials are determined from first-principles calculations. The deformation mechanisms and mechanical behaviors are analyzed in terms of variations in the dislocation core structures, along with the PN stress ${\tau }_{\mathrm{p}}$ and Peierls potential $E_{\mathrm{p}}$. It is found that the decomposition behaviors of dislocations in fcc metals, as characterized by the stacking fault width, are influenced by the dislocation line angle θ. The interplanar distance $\mathrm{\Delta }x$ perpendicular to the dislocation line, as a function of θ in fcc metals, dominates the magnitude of PN stress ${\tau }_{\mathrm{p}}$ and Peierls potential $E_{\mathrm{p}}$. For instance, with $\mathrm{\Delta }x$ decreasing from $\sqrt{3}/2$ to $1/2$, the ${\tau }_{\mathrm{p}}$, e.g., for fcc Cu, reduces from 3.20 MPa (screw dislocation) to 0.002 MPa (edge dislocation). The increase of θ is unfavorable to dislocation cross-slip but promotes the occurrence of dislocation climb, deformation twinning, and ε-martensite transformation. Consequently, the strain hardening rate can be enhanced in terms of such variations in the deformation behaviors for fcc Al, Cu, and Fe. Our investigations offer an insightful guidance for qualitatively assessing the likelihood and degree of deformation twinning and ε-martensite transformation in fcc metals via examining the dislocation core structures.

Bulk single-crystal ${\mathrm{ZnGa}}_2{\mathrm{O}}_4$ samples with varying free-carrier concentrations are investigated using spectroscopic ellipsometry and Raman spectroscopy to explore their vibrational and excitonic properties. The fundamental band gap of inverse spinel ${\mathrm{ZnGa}}_2{\mathrm{O}}_4$ is determined to be $4.4\pm 0.05\mathrm{eV}$, while the normal spinel phase exhibits a band gap of $5.4\pm 0.02\mathrm{eV}$. For comparison, analysis of an insulating ${\mathrm{MgGa}}_2{\mathrm{O}}_4$ sample in the ultraviolet region yields a band gap of $5.64\pm 0.03\mathrm{eV}$. The high-frequency dielectric constant is measured as ${\varepsilon }_{\infty }=3.67\pm 0.04$ for ${\mathrm{ZnGa}}_2{\mathrm{O}}_4$ and ${\varepsilon }_{\infty }=3.46\pm 0.08$ for ${\mathrm{MgGa}}_2{\mathrm{O}}_4$. The analysis of the infrared plasma frequency provides an effective electron mass of $m^{*}=\left(0.20\pm 0.02\right)m_{\mathrm{e}}$ for low carrier concentration. An increase in the effective mass to $m^{*}=\left(0.30\pm 0.03\right)m_{\mathrm{e}}$ at $n=2.3\times {10}^{19}{\mathrm{cm}}^{-3}$ is observed, reflecting the nonparabolicity of the conduction band. Optical mobility values are found to be consistent with Hall-effect measurements. Infrared phonon observations are in agreement with previous reports, while Raman spectra confirm five Raman-active phonon modes in their expected polarization symmetries. An additional Raman mode at higher frequencies suggests inversion of the spinel structure in all samples. Furthermore, Raman-inactive modes with Fano line shapes are observed at infrared-active frequencies and are attributed to off-stoichiometry in the samples.

We carried out an investigation of the electrical properties of the Co-intercalated $\mathrm{Zr}{\mathrm{Te}}_2$ compound ${\mathrm{Co}}_{0.08}\mathrm{Zr}{\mathrm{Te}}_2$. This compound exhibits metallic behavior at ambient temperature with the electrical resistivity (ρ) dropping linearly upon cooling from 300 to 60 K. The electrical resistivity shows a minimum near $T_{\min }\approx 18$ K upon further cooling, and the low temperature upturn is interrupted by the onset of superconductivity at $T_c\approx 3.8$ K, with the zero-resistivity state being reached at $T\approx 2.0$ K. The minimum in electrical resistivity is consistent with the Kondo scattering and the behavior of ρ($T$) near $T_{\min }$ is analyzed in the context of the Hamman model, yielding excellent fits considering the presence of ${\mathrm{Co}}^{2+}$ ions in octahedral sites within the van der Waals gaps of $\mathrm{Zr}{\mathrm{Te}}_2$. Electrical resistivity measurements under pressures up to 23.6 kbar show the suppression of the superconductivity and an increase in the Kondo temperature $T_{\mathrm{K}}$ at intermediate pressures, with strong reduction at higher pressures. This behavior is accompanied by a suppression of Ruderman-Kittel-Kasuya-Yosida correlations at intermediate pressures, followed by a resurgence at higher pressures, reflecting the oscillatory nature of the exchange coupling energy with respect to the distance between impurity ions.

Sodium (Na), silicon (Si), and oxygen (O) are main abundant elements to form the minerals inside the Earth's interior. Here, combining first-principles calculations and crystal structural prediction methods, we propose the formation of a distinct stoichiometry, ${\mathrm{Na}}_6{\mathrm{SiO}}_5$, and two high-pressure phases of ${\mathrm{Na}}_4{\mathrm{SiO}}_4$ ($Cmca$) and ${\mathrm{Na}}_2{\mathrm{Si}}_3{\mathrm{O}}_7$ ($C2/m$), all exhibiting thermodynamic and dynamical stability at extreme conditions relevant to the Earth's mantle. ${\mathrm{Na}}_6{\mathrm{SiO}}_5$ is stable over a broad pressure range (66–150 GPa) and high temperatures (up to 4000 K), with unique polyhedral configurations, and strong ionic and covalent bonding. ${\mathrm{Na}}_6{\mathrm{SiO}}_5$ and $Cmca\text{−}{\mathrm{Na}}_4{\mathrm{SiO}}_4$ retain their solid-state character at temperatures up to 4,000 K, whereas the $P\overline{1}$ and $Cc$ phases of ${\mathrm{Na}}_4{\mathrm{SiO}}_4$ undergo phase transitions to superionic or liquid states as temperature increases. $P\text{waves}$ ($V_P$) and $V$ waves ($V_S$) of ${\mathrm{Na}}_6{\mathrm{SiO}}_5$ and ${\mathrm{Na}}_4{\mathrm{SiO}}_4$ match trends observed in the Preliminary Reference Earth Model, suggesting that these compounds may contribute to the seismic anomalies observed in the core-mantle boundary (CMB). These findings provide theoretical insights into the potential role of Na-rich silicates in the Earth's deep interior and their influence on the dynamics of ultra-lowvelocity zones and large low-shear-velocity provinces.

Molecular dynamics (MD) employing machine-learned interatomic potentials (MLIPs) serve as an efficient, urgently needed complement to ab initio molecular dynamics. By training these potentials on data generated from ab initio methods, their averaged predictions can exhibit comparable performance to ab initio methods at a fraction of the cost. However, insufficient training sets might lead to an improper description of the dynamics in strongly anharmonic materials because critical effects might be overlooked in relevant cases or only incorrectly captured or hallucinated by the MLIP, i.e., falsely predicted when they are not actually present. In this work, we show that an active learning scheme that combines MD with MLIPs (MLIP-MD) and uncertainty estimates can avoid such problematic predictions. In short, efficient MLIP-MD is used to explore configurational space quickly, whereby an acquisition function based on uncertainty estimates and energetic viability is employed to maximize the value of the newly generated data and to focus on the most unfamiliar but reasonably accessible regions of phase space. To verify our methodology, we screen over 112 materials and identify 10 examples experiencing the aforementioned problems. Using CuI and ${\mathrm{AgGaSe}}_2$ as archetypes for these problematic materials, we discuss the physical implications for strongly anharmonic effects and demonstrate how the developed active learning scheme can address these issues.

Altermagnets are a special class of magnetic materials that exhibit an unusual combination of features from both ferromagnets and antiferromagnets. That is, they have zero net magnetization (i.e., antiferromagnetic properties) with electronic bands that are not Kramers spin degenerate (i.e., ferromagnetic behavior). This offers the possibility of generating spin-polarized currents without the stray magnetic fields associated with ferromagnets, making them ideal candidates for potential applications in quantum computing and energy-efficient spintronic devices. In this work, we investigate altermagnets of the form ${{\mathrm{A}}_2\mathrm{X}}^i{\mathrm{X}}^{ii}$ based on $\alpha \text{−}{\mathrm{Mn}}_2{\mathrm{Te}}_2$, a well-known altermagnet, using high-throughput density functional theory calculations. Promising candidates are determined by analyzing their preferred magnetic ordering and spin degeneracy. The magnetic ground states of the altermagnet candidates are then confirmed using spin-spiral calculations. Based on the presence of Kramers degeneracy in the band structure, which is linked to crystal symmetry, we classify the candidate structures as $d$-wave and $g$-wave altermagnets, as well as fully compensated ferrimagnets.

The formation of the intermetallic $\sigma$ phase (space group $P{4}_2/mnm$) has a detrimental effect on the ductility of transition-metal alloys. This theoretical study uses first-principles calculations to investigate the stability and thermodynamic properties of the WRe and WOs $\sigma$ phases. Our study indicates that the $\sigma$ phase becomes thermodynamically stable at its ideal composition for temperatures above 1050 K and 130 K for the WRe and WOs phases, respectively. We find that models that neglect the phonon contribution to the free energy may underestimate the amount of disorder in the $\sigma$ phase at elevated temperatures. Furthermore, the $\sigma$ phase becomes dynamically unstable for Re concentrations above 73 at.% Re and 53 at.% Os. For the WOs phase, the dynamic stability is sensitive to the lattice site occupation, and vibrations of the Os atoms are linked to the transformation into a dynamically stable orthorhombic phase.

The $Ln\mathrm{SbTe}$ ($Ln$ = Lanthanides) family, like isostructural ZrSiS-type compounds, has emerged as a fertile playground for exploring the interaction of electronic correlations and magnetic ordering with the nodal line band topology. Here, we report on a detailed electronic band structure investigation of TbSbTe, corroborated by electrical transport, thermodynamic, and magnetic studies. Temperature-dependent magnetic susceptibility and thermodynamic transport studies indicate the onset of antiferromagnetic ordering below $T_N\sim 5.8\mathrm{K}$. The electronic band structure study, carried out with high-resolution angle-resolved photoemission spectroscopy measurements aided with density functional theory–based first-principles calculations reveal presence of a nonsymmorphic symmetry-protected Dirac crossing in the $\mathrm{\Gamma }$-X high-symmetry (HS) direction, which is part of a nodal line along the X-R HS direction. Another Dirac crossing occurs along the $\mathrm{\Gamma }$-X direction at a relatively higher binding energy, which occurs from ${\tilde{\mathcal{C}}}_{2\nu }\mathcal{P}$ symmetry which is gapped in the theoretical calculations with the effect of spin-orbit coupling considered. Parallel to this direction, our theoretical calculations and experimental results exhibit strongly momentum-dependent surface bands. In this paper, we open an avenue to further uncover the intricate interplay among symmetry-protected topological band structure, spin-orbit coupling, and magnetism in this material and the $Ln\mathrm{SbTe}$ family, in general.

Two-dimensional polymeric ${\mathrm{C}}_{60}$ monolayers possess distinctive properties, yet their stability and physical characteristics related to various bonding motifs and topologies are not well understood. Here, we use first-principles calculations to examine five different ${\mathrm{C}}_{60}$ phases with distinct covalent network patterns: triclinic phase (TP) and trigonal phase (TP2), quasitetragonal phase (qTP), quasihexagonal phase (qHP), and rhombic phase (RP) ${\mathrm{C}}_{60}$. Our findings indicate that all these ${\mathrm{C}}_{60}$ monolayers are both dynamically and mechanically stable. The mechanical properties of these monolayers vary significantly, primarily due to their bonding patterns. qTP ${\mathrm{C}}_{60}$, with its nearly uniform $\left[2+2\right]$ bonding, exhibits weak, nearly isotropic mechanical behavior. In contrast, TP ${\mathrm{C}}_{60}$, with its varied bond alignments, and qHP ${\mathrm{C}}_{60}$, with additional C-C single bonds, display considerable mechanical anisotropy. RP and TP2 ${\mathrm{C}}_{60}$, having symmetric bonding, demonstrate isotropic properties. Notably, TP2 ${\mathrm{C}}_{60}$ features a unique negative Poisson's ratio, attributed to the deformation of its chairlike conformation under tensile strain. Electrically, all the ${\mathrm{C}}_{60}$ phases exhibit semiconductor characteristics with band gaps ranging from 0.85 to 1.55 eV. Optically, RP and TP2 ${\mathrm{C}}_{60}$ demonstrate isotropic properties, while the others are anisotropic. This work offers valuable insights for designing ${\mathrm{C}}_{60}$-derived materials with tailored functionalities.

The intrinsic anomalous Hall effect (AHE) has been reported in numerous ferromagnetic Weyl semimetals. However, the AHE in the antiferromagnetic (AFM) or paramagnetic (PM) state of Weyl semimetals has rarely been observed experimentally. Different mechanisms have been proposed to account for the emergence of the AHE from different types of magnetic order. In this Letter, we propose a new model that explains the observed AHE in both the AFM and PM states of the noncentrosymmetric Weyl semimetal SmAlSi. The newly proposed mechanism is based on magnetic-field-induced Weyl node evolution, which qualitatively explains the temperature dependence of the anomalous Hall conductivity, which displays unconventional power-law behavior in both the AFM and PM states of SmAlSi.