The recently identified multiprincipal-element alloy (MEA), known as GRX-810, exhibits a dramatic improvement in the creep resistance at elevated temperatures. Initial studies have identified segregation atmospheres around the oxide-dispersion particles, which likely contribute to this phenomenon. However, the many details remain elusive, especially the co-segregation effects. Such effects include both substitutional and interstitial type segregation, leading to a complex alloying environment. To investigate these segregation effects, Monte Carlo/ab initio based molecular dynamics (MC/AIMD) hybrid simulations were performed. Coupled with an algorithm to identify potential interstitial sites, evaluation of the joint interstitial and substitutional segregation events was made possible. The simulations have revealed critical elements of carbon segregation near the oxide-dispersoid particles, where carbon atoms are repelled from the oxygen-terminated metal-yttria interface but attracted to the yttrium-terminated interface. This discovery identifies critical distinctions between yttrium-based oxide dispersoids, which control critical solute atmospheres.

We introduce the Cyrrhus spin ice geometry, a variant of decimated square ice patterns that exhibits a form of magnetic frustration known as vertex frustration. Using synchrotron-based photoemission electron microscopy, we present a temperature-dependent study of magnetic moment fluctuations in this dipolar Cyrrhus lattice. The results confirm key signatures of vertex frustration marked by an elevated presence of energetically unfavorable moment configurations and a strong adherence to an emergent ice rule. Analyzing the observed dynamics within the framework of the Thirumalai-Mountain stress metric reveals near-zero values for the relaxation exponent, suggesting ergodicity-breaking dynamics.

The multiferroic $\mathrm{LuFe}{\mathrm{O}}_3$ unusually shows a magnetic order that causes ferroelectricity up to a rather high temperature of 610 K indicating very strong magnetoelectric coupling. We present the inelastic neutron-scattering (INS) measurements and ab initio density-functional theory-based simulation studies of $\mathrm{LuFe}{\mathrm{O}}_3$ to elucidate the lattice and spin dynamics. We have analyzed the phonon density of states and magnon density of states from INS measurements and compared them with the results of our simulations. We identified that specific iron- and oxygen-dominated optical phonon modes largely govern the spin-lattice coupling. Besides these, our simulations also reveal that the computed acoustic phonon branches are sensitive to the underlying magnetic structure, inferring strong magnetoelastic coupling. The signature of magnetoelastic coupling is also observed in the reported measurement of lattice parameters showing significant change across the magnetic transition $T_{\mathrm{N}}\sim 610$ K. We further investigated the pressure dependent high-spin to low-spin transition and its influence on lattice dynamics. We have identified the critical structural parameters governing the spin phase transition.

Metastable states of matter are of great interest as they offer the promise of novel functionality. They are often a natural consequence of exposure to nonequilibrium environments. In oxides, metastability can take the form of new polymorphs, chemical disorder, and even amorphization. While significant attention has been given to the impact those changes have on the atomic properties of the material, the corresponding changes in the electronic structure have received less attention. Here, using density functional theory, we consider how the electronic structure varies with potential metastable structures in two classes of lanthanide-bearing oxides—pyrochlores and interlanthanide sesquioxides. We find that the changes depend strongly on both the crystal structure and crystal chemistry of the compound with, for example, disordering and amorphization either increasing or decreasing the bandgap depending on the chemistry. For the $A_2{B}_2{\mathrm{O}}_7$ pyrochlores, we find different dependencies of the bandgap on the $A=Ln$ cations as the $B$ cation is changed, which we relate to the nature of the density of states at the conduction band minimum for different $B$ chemistries. Our calculations are validated by electron energy loss spectroscopy measurements for two pyrochlore compounds in which amorphization does reduce the bandgap, consistent with our calculations on these two compounds. Our results highlight the relationship between atomic and electronic structure and how radiation can be used to modify and potentially control the electronic properties of oxides.

${\mathrm{SrRuO}}_3$ is a complex oxide with a large absorption coefficient in the visible range. Recent studies have suggested that it might exhibit photostrictive properties, which could pave the way for the design of alternative optomechanical or multiferroic heterostructures. However, the physical mechanisms underlying the observed, light-induced deformations have remained unclear. In the present work, we combine temperature-dependent Raman spectroscopy and thermometry with atomic force microscopy and x-ray diffraction measurements under continuous-wave laser irradiation to reassess earlier findings. Our experimental data show that in epitaxial ${\mathrm{SrRuO}}_3/{\mathrm{SrTiO}}_3$ thin films, measurable deformations can be achieved via optical excitation. Nevertheless, our results—corroborated by finite element method simulations—also indicate that the observed Raman shifts and the strain generated in the samples can be traced back to a significant temperature increase, thereby questioning the existence of nonthermal photostriction in ${\mathrm{SrRuO}}_3$.

The modification of two-dimensional (2D) materials with metal atoms can lead to additional structures and properties; however, a systematic classification of metal-2D material interactions is still lacking. We propose a general framework for classifying these interactions based on two primary modes: metal atom adsorption on the surface and intercalation between layers. This framework, validated by first-principles calculations on representative van der Waals layered and nonlayered 2D materials interacting with transition metals (TMs) and alkali metals, provides a comprehensive explanation for experimental observations across various systems. Furthermore, the classification serves as a guide for designing stable and functional 2D materials. Our investigation of nonlayered borophene shows that interlayer-intercalated TM borides (TMBs) exhibit significantly higher stability than intralayer-doped TMBs. Physical property calculations further reveal that these sandwich-type TMBs possess superior mechanical stability and additional electronic properties, underscoring their potential for future applications.

Pulsed neutron diffraction measurements on a barium borosilicate glass and its supercooled liquid reveal clear, quantitative evidence for a tetrahedral to trigonal boron transition above the glass transition temperature, $T_{\mathrm{g}}$. In particular the tetrahedral boron fraction, $N_4$($T$), is about 50(1)% in a $28\mathrm{BaO}·48{\mathrm{B}}_2{\mathrm{O}}_3·24\mathrm{Si}{\mathrm{O}}_2$ (BBS352) glass, independent of temperature, but falls continuously above $T_{\mathrm{g}}=901$ K to 36(1)% at 1200 K. The data are interpreted in terms of simplified chemical equilibria, from which it is inferred that the boron coordination change contributes between 30% to 40% of the total calorimetric configurational heat capacity at $T_{\mathrm{g}}$, as well as to the entropy and liquid fragility. The thermal expansion coefficient of the B–O bond in BBS352 glass is measured to be ${\alpha }_{\mathrm{BO}}=6.5$(1.7) ppm ${\mathrm{K}}^{-1}$, slightly larger than for pure ${\mathrm{B}}_2{\mathrm{O}}_3$ glass and very similar to the known bulk expansion, implying a remarkably simple vibrational thermal expansion mechanism for the solid. Resolution of B–O and Si–O correlations in the real-space pair distribution function is demonstrated for $50\mathrm{BaO}·25{\mathrm{B}}_2{\mathrm{O}}_3·25\mathrm{Si}{\mathrm{O}}_2$ (BBS211) glass, and the factors governing if these features can be resolved are discussed.

Calcite, $\mathrm{CaC}{\mathrm{O}}_3$, is a widely available biomaterial with remarkable properties. Its twin walls (TWs), formed during growth or deformation, show intriguing properties including a strong polarization. While calcite has no macroscopic dipole moment (by symmetry) the TWs show a big shift in the distance between $\mathrm{C}{\mathrm{a}}^{2+}$ and ${\mathrm{CO}}_3{}^{2-}$ resulting in dipole moments (polarization) estimated at $0.22\mathrm{C}/{\mathrm{m}}^2$. Such strong dipole moments have a substantial influence on the diffusion of atoms inside twin boundaries. Furthermore, deformation will also generate simple kinks inside the TWs. These kinks lead to local clusters of amorphized $\mathrm{CaC}{\mathrm{O}}_3$. Stressed calcite, in devices or in the natural environment, will be riddled with such kinks, which explains the tendency to form locally amorphized materials. The structural particularities of calcite originate from a sequence of phase transitions, thermal or by growth, from a cubic phase to a rhombohedral phase with $R\overline{3}m$ symmetry to the $R\overline{3}c$ phase known at room temperature. Symmetry aspects of these transitions are discussed. The complexity of the TW structure arises from both the odd-even effect at the twin boundary in the rhombohedral structure and the coupling between two order parameters in the phase transitions of calcite. The coupling scheme is linear quadratic and is discussed in detail.

Group-IV monochalcogenides are a class of layered ferroelectric semiconductors that have demonstrated spontaneous intrinsic polarization above room temperature. Here, we use the multiatomic cluster expansion machine learning architecture to train and test a force field capable of modeling the structural properties and second-order ferroelectric-to-paraelectric phase transition in a group-IV monochalcogenide, GeSe. The model captures the double-well potential energy surface associated with the onset of macroscopic polarization in bulk GeSe within $12.5\mathrm{meV}/\mathrm{atom}$, as well as near-equilibrium properties like the phonon dispersion. The development of this quantitatively accurate force field enables long-time molecular dynamics simulations, which predict the critical temperature of the ferroelectric-to-paraelectric phase transition in bulk GeSe to be $T_c=600\mathrm{K}$. This study demonstrates the capabilities of equivariant force fields to accurately describe phenomena associated with structural symmetry breaking.

Two-dimensional (2D) silicon phosphide (SiP) has recently emerged as a promising semiconductor for electronic, optoelectronic, and thermoelectric applications due to its unique electronic and structural characteristics. One-dimensional (1D) nanoribbons (NRs) derived from 2D SiP offer a versatile and scalable platform for device miniaturization and performance enhancement in nanoelectronics. Motivated by their potential, we present a comprehensive first-principles investigation of the structural, electronic, dynamical, and electronic transport properties of SiP-NRs. Specifically, we focus on both bare and hydrogen-passivated armchair (A-NRs, HA-NRs) and zigzag (Z-NRs, HZ-NRs) configurations. Our results reveal that hydrogen passivation effectively suppresses edge reconstructions observed in bare SiP-NRs, thus dynamically stabilizing their structures. Analysis of electronic band structures demonstrates a clear width-dependent oscillatory behavior of the band gap in bare A-NRs, which diminishes significantly upon hydrogen termination. The width-scaled electronic conductance ($G_e^{\mathrm{ws}}$) of HA-NRs exhibits a decreasing trend with increasing ribbon width, featuring distinct even-odd oscillations for $n$-type transport due to subband splitting effects. In contrast, HZ-NRs display notable deviations in $p$-type conductance from their 2D SiP counterpart, particularly at low temperatures (around 100 K), arising from residual localized edge states. However, with increasing width and temperature, transport behavior converges toward that of 2D SiP monolayers, indicating diminishing edge effects. Unlike their $p$-type counterparts, the $n$-type $G_e$ values of the largest HA-NRs and HZ-NRs increase with the square root of temperature, similar to the $n$-type conductance trend observed in 2D SiP. This behavior is attributed to the evolution of the electronic transmission function ($\tau \left(E\right)$) from a steplike profile in narrow ribbons to an $E^{1/2}$ dependence in wider ribbons, analogous to the 2D counterpart. These findings highlight the significant influence of width and edge termination on the transport characteristics of SiP-NRs and underline their potential as fundamental building blocks for high-performance nanoelectronic and thermoelectric quasi-1D devices.

Barium titanate (BTO) is a representative perovskite oxide that undergoes three first-order ferroelectric phase transitions related to exceptional functional properties. In this work, we develop two atomic cluster expansion (ACE) models for BTO to reproduce fundamental properties of bulk and defective BTO phases. The two ACE models do not target full transferability but rather aim to examine the influence of implicit and explicit treatment of long-range Coulomb interactions. We demonstrate that both models describe equally well the temperature-induced phase transitions and field-induced polarization switching. Even though the parametrizations are based on a limited number of configurations that are mostly not far away from the equilibrium, the ACE models are also able to capture properties of important crystal defects, such as oxygen vacancies, stacking faults, and domain walls. The phase transitions and the fundamental properties of the investigated defects can be described with similar accuracy with or without explicit treatment of charges and Coulomb interactions, allowing for efficient short-range machine learning potentials.

Hydrogenated $a$-Si films grown by magnetron sputtering have greatly reduced subgap optical absorption, down to 122 ppm (9.0 ${\mathrm{cm}}^{-1}$) at 1064 nm, 6 ppm (0.4 ${\mathrm{cm}}^{-1}$) at 1550 nm, and 2 ppm (0.1 ${\mathrm{cm}}^{-1}$) at 2000 nm for quarter-wavelength-thick films, and they reduced room-temperature mechanical loss below $2\times {10}^{-5}$. The dangling bond density is reduced to ${10}^{17}{\mathrm{cm}}^{-3}$ and the refraction index remains above that of crystalline silicon for all wavelengths. The above wavelengths are well below the Urbach edge of $a$-Si, and thus absorption is associated with deep-trap states. Although reductions in absorption and dissipation increase with increasing hydrogen content in the working gas, the hydrogen concentration in the films remains low (below 1 at.%), and neither absorption nor mechanical loss correlate with dangling bond density. Raman-derived bond angle deviation measurements of $a$-Si show a reduction in structural disorder as the films are further processed by vacuum annealing and post-hydrogenation, while $a$-Si:H films show a lower disorder in the as-deposited state without further reductions after thermal processing. These results suggest that the presence of hydrogen during film growth, acting as a catalyst, facilitates local rearrangement of atoms and removes strained Si–Si bonds that are more responsible for sub-band-gap absorption and dissipative mechanisms than dangling bonds.

Tensile tests of 50-nm-thick single-crystalline $\left(001\right)$ gold thin films containing nanotwins are monitored in situ with x-ray diffraction (XRD) and transmission electron microscopy (TEM). It is argued that for uniaxial tensile tests along the $\left[110\right]$ direction, the induced average stress in the films during loading hardly depends on whether they are deposited onto a polymeric substrate (for XRD) or free-standing (for TEM). When straining along this direction, XRD experiments show an impressive $\approx 500\%$ increase in the twin volume for two favorably twin orientations at an applied strain of only $4.0\%$. Furthermore, the twin volume increase is accompanied by a twin rotation. Submicron scale TEM observations show that the increase in volume is correlated with the glide of partial dislocations, either along the coherent twin boundaries (TB) or at the incoherent TBs, or close to microstructure imperfections. In the last case, twins coalesce and acquire a micrometer size. An intense dislocation activity occurs in these large twins, still increasing the strain concentration and resulting in crack expansion. The multiplicity of plasticity mechanisms suggests that the twinning quantification may significantly depend on the initial defect type (twins, dislocations, nanometric holes) and density. The twin rotation is also observed postmortem in TEM. However, the XRD data analysis shows that twinning is not the only plasticity mechanism: first, the yield point of the film supported on a substrate is $\approx 0.5\%$, but the twinning starts only at $1.0\%$, and, second, at an applied strain of $4.0\%$, the plastic strain induced by the twin is less than $0.8\%$.

Antiferromagnetic ${\mathrm{NiPS}}_3$ has recently emerged as a quantum material of considerable interest, thanks to the discovery of multiple new couplings involving electrons, spins, orbitals, phonons, and magnons. However, controversies and open questions persist concerning the fundamental origins of these couplings. A critical piece of information required to advance the understanding is the precise electronic band structure of ${\mathrm{NiPS}}_3$. Angle-resolved photoemission spectroscopy (ARPES), combined with alkali metal dosing (AMD), can enable us to directly observe the subtle electronic states that appear around the Fermi surface, offering valuable insights into the intriguing quantum properties and interplays of the examined material. Here, we present a comprehensive characterization and analysis of the band structure of van der Waals layered antiferromagnet ${\mathrm{NiPS}}_3$, leveraging state-of-the-art $\mu$-ARPES measurements supported by density functional theory (DFT) calculations. Theoretical DFT results identify the orbital contributions to the observed bands, providing a precise understanding of the experimental ARPES data. Crucially, AMD enables the observation of conduction band and defect-related states above the valence band maximum in ${\mathrm{NiPS}}_3$. Furthermore, temperature dependent ARPES results across the Néel transition temperature of ${\mathrm{NiPS}}_3$ reveal that the paramagnetic and antiferromagnetic phases have nearly identical band structures, underlining the highly localized character of Ni $d$ states. These findings substantially deepen our understanding of the electronic properties of ${\mathrm{NiPS}}_3$ and lay a vital foundation for exploring the intriguing quantum phenomena it exhibits.

The discovery of altermagnets has led to the study of nonrelativistic spin splitting in materials with compensated magnetic moments. Despite the experimental validation of altermagnets in many bulk materials, two-dimensional altermagnets or compensated ferrimagnets are rare. Here, we show that nonrelativistic spin splittings can be robustly induced by constructing van der Waals heterostructures consisting of intraplane antiferromagnetic materials and suitable substrates. Using $\mathrm{MnP}{\mathrm{X}}_3$ ($\mathrm{X}=\mathrm{S}$ or Se) as an example, which has a Néel magnetic order, we demonstrate that altermagnetic spin splitting can arise in the AA-stacking $\mathrm{MnP}{\mathrm{X}}_3/\mathrm{MP}{\mathrm{X}}_3$ ($\mathrm{M}=\mathrm{Cd}$, Mg, or Zn) heterostructures. For the AB-stacking heterostructures, ferrimagnetic-type spin splitting emerges, and the fully compensated magnetization is guaranteed by the Luttinger theorem when the system has a band gap. By combining with a van der Waals ferroelectric substrate like $\mathrm{CuIn}{\mathrm{P}}_2{\mathrm{S}}_6, \mathrm{MnP}{\mathrm{X}}_3$-based heterostructures can show tunable spin splitting and spin-related properties that depend on the electronic band structures and ferroelectric polarization, which can be nonvolatilely reversed by applying an out-of-plane electric field. Our study provides a route to induce tunable nonrelativistic spin splitting in experimentally synthesizable two-dimensional magnets.

We report a neutron diffraction study using epithermal neutrons to probe the origin of negative magnetization (NM) and its correlation with exchange bias and electronic transport in $\mathrm{G}{\mathrm{d}}_2\mathrm{CoRu}{\mathrm{O}}_6$. This double perovskite crystallizes in the monoclinic $P{2}_1/\mathrm{n}$ space group and exhibits magnetic ordering at $T_{\mathrm{C}}\approx 51$ K. Magnetization measurements reveal NM below the compensation temperature ($T_{\mathrm{comp}}\approx 11$ K), which shifts to lower temperatures with increasing magnetic field and vanishes for $H$ ≥ 500 Oe. Low temperature (6 K) neutron diffraction study shows that $\mathrm{C}{\mathrm{o}}^{2+}$ and $\mathrm{R}{\mathrm{u}}^{4+}$ sublattices undergo a canted antiferromagnetic type ordering with antiferromagnetic spin alignment along the $c$ axis and a ferromagnetic component along the $b$ axis, while no ordered magnetic moment is detected for ${\mathrm{Gd}}^{3+}$ ions. Specific heat exhibits a sharp λ-anomaly at 3.5 K, confirming the long-range magnetic ordering of ${\mathrm{Gd}}^{3+}$ sublattice. The observed NM behavior in $M$($T$) curves is explained by polarization of ${\mathrm{Gd}}^{3+}$ moments induced by the internal field from the canted Co/Ru sublattice, consistent with Cooke's model. A detailed examination of field-cooled $M$ vs $H$ curves reveals the presence of exchange bias and its sign reversal around the $T_{\mathrm{comp}}$ in the sample. Interestingly, exchange-bias magnitude depends on the maximum field applied during the hysteresis measurements. Furthermore, the coercivity and remnant magnetization values, derived from the $M$($H$) curves, exhibit a minimum around $T_{\mathrm{comp}}$. Electrical resistivity follows a semiconducting variable-range hopping model below 100 K, with a sharp increase below 50 K coinciding with $T_{\mathrm{C}}$, indicating a strong coupling between structural distortions, magnetic interactions, and charge localization. These findings reveal an intricate coupling of structural, magnetic, and electronic degrees of freedom in $\mathrm{G}{\mathrm{d}}_2\mathrm{CoRu}{\mathrm{O}}_6$, highlighting its potential for spintronic and magnetic device applications where tunable compensation and exchange bias effects and their intertwined behavior are desirable.