Lead-cooled fast reactors impose harsh environments on the structural materials, including high damage doses, high temperatures and corrosive liquid lead. To withstand these environments, advanced steel concepts, such as a composite of 15-15Ti and FeCrAl, have been proposed as fuel cladding. Microstructural evolution of alloys is governed by fundamental properties, including the vacancy formation and migration energies, yet such data for novel alloy compositions is sparse. In this work, an extensive set of vacancy formation and migration energies in two alloys, 15-15Ti and FeCrAl, was calculated from first principles, employing density functional theory. Special quasirandom structures were generated for both alloys, and different magnetic states of the alloys were simulated. It was found that the vacancy formation energy is highly influenced by the chemical and magnetic environment in 15-15Ti, while in FeCrAl the size mismatch between Fe and the alloying elements dominates. The vacancy formation energy was calculated by two different density functional theory formulations, showing excellent agreement. The vacancy migration energy was found to be governed by changes in the magnetic and chemical environment as the atom migrates. Based on these findings, temperature-averaged behaviors of vacancies in the alloys are derived, which can be further used to define effective vacancy formation and migration energies at reactor-relevant temperatures. The effective vacancy formation and migration energies can be used to predict temperature-variable shifts needed to accommodate the higher dose rate when using ion irradiation to emulate neutron irradiation.

Thermal-desorption spectroscopy (TDS) is widely used to characterize hydrogen-isotope retention in plasma-facing tungsten, but a measured spectrum does not uniquely identify the underlying microscopic defect configurations: different kinetic parameters can produce similar curves, while distinct vacancy-hydrogen configurations may have nearly the same binding energy. To account for these ambiguities, we formulate a Bayesian inversion that determines the range of detrapping-energy spectra consistent with a measured curve and reports all defect configurations allowed by those energies. Applied to a published deuterium-TDS curve of damaged tungsten, the method successfully resolves two detrapping-energy peaks centered at 1.58 [1.49, 1.70] and 1.97 [1.87, 2.08] eV, where each bracket contains 90% of the inferred probability. Across the four predamage conditions, the changing spectra can be described by the same two energy components while the lower-energy component loses relative weight as predamage temperature rises; both features also recur in an independent experiment. Tests on curves with known inputs show that peak temperatures are better determined than the detrapping energies behind them, and that the inferred energies still correspond to many vacancy-hydrogen configurations. The spectral evolution thus points to changing relative contributions from recurring trapping-energy families, without identifying a unique microscopic defect population.

The filling of the large van der Waals gap in Transition Metal Dichalcogenides (TMDs) often leads to lattice and electronic instabilities, which prelude the onset of a rich phenomenology. Motivated by previous results from macroscopic measurements, we investigate the electronic structure of the TMDs ${\mathrm{ZrTe}}_2$ and Ni intercalated ${\mathrm{ZrTe}}_2$ $({\mathrm{Ni}}_x{\mathrm{ZrTe}}_2,$ $x\approx 0.05)$ employing angle-resolved photoemission spectroscopy (ARPES). We readily identify in ${\mathrm{Ni}}_x{\mathrm{ZrTe}}_2$ two flat bands, most likely associated with localized Ni-derived $3d$-states, at about $\approx -0.7\mathrm{eV}$ and $\approx -1.2\mathrm{eV}$ in binding energy. More significantly, at low $T$, we identify an electronic structure reconstruction in ${\mathrm{Ni}}_x{\mathrm{ZrTe}}_2$, which halves the electronic periodicity along the $k_z$ direction. This is reminiscent of a commensurate band folding with wave vector $q=(0,0,\pi )$. A mean-field model for a charge density wave (CDW) transition driven by interband hole-hole interactions is solved with inputs from the experimentally determined electronic band structure. Comparison between theory and experiments unveils a CDW transition in ${\mathrm{Ni}}_x{\mathrm{ZrTe}}_2$, for which the gap opens above the Fermi level. Our findings invite further investigation into the structural properties of intercalated ${\mathrm{ZrTe}}_2$.

We report the anomalous characteristics of magnetostructural phases in the vicinity of the orbital/charge-ordered state ($T_{\mathrm{OO}/\mathrm{CO}}\sim 220\mathrm{K}$) below the antiferromagnetic (AFM) Néel temperature ($T_{\mathrm{N}}\sim 130\mathrm{K}$) of the correlated electron system ${\mathrm{Ca}}_{0.75}{\mathrm{Sm}}_{0.25}{\mathrm{MnO}}_3$ by means of neutron diffraction, field-dependent heat-capacity, and magnetometry studies. Our neutron diffraction study reveals an apparent coexistence of two commensurate magnetic phases with the propagation vectors ${\mathit{k}}_{\mathit{C}}=(1/2,1/2,0)$ and ${\mathit{k}}_{\mathit{E}}=(1/2,\epsilon ,0)$ forming probably a $CE$ phase, with $\epsilon \sim 0.267\left(3\right)$ close to 1/4, indicating that the magnetic unit cell coincides with the enlarged superstructure of dimensions $a\times 4b\times c$. It was found that the moments of both magnetic phases are AFM-coupled along all directions forming an $A$- or a $G$-type ordering, where the magnetic moments of the $C$- and $E$-type phases are aligned within the $ab$ plane and along the $c$ axis, respectively. In the noncollinear magnetic structure, the $C$-type phase can be described with the irreducible representations of ${\mathrm{\Gamma }}_6(A_x,G_y)$ and ${\mathrm{\Gamma }}_8(G_x,A_y)$, where the Mn moments are oriented parallel to the directions [110] and $\left[1\overline{1}0\right]$. Moreover, phenomena such as field-induced metamagnetic transitions ($H_{\mathrm{T}}\sim 120\mathrm{kOe}$ at 3 K), critical behavior of specific heat ($C_P=A{|T-T_{\mathrm{N}}|}^{-\alpha }$), negative exchange bias effect ($H_{\mathrm{EB}}$), and a zero-crossover of magnetic entropy change ($\mathrm{\Delta }{S}_{\mathrm{M}}$) are newly observed in this unique composition.

The transition metal trichalcogenides (TMTs) are an interesting class of layered 2D materials that have strong anisotropic electrical and optical properties. We report on the polarization-dependent nonlinear optical response of exfoliated crystals at the third harmonic using nonresonant excitation with a 1560 nm femtosecond laser. All members of the TMT crystal family explored $({\mathrm{ZrS}}_3,$ ${\mathrm{HfS}}_3,$ ${\mathrm{TiS}}_3, \text{and} {\mathrm{NbS}}_3)$ display large anisotropy in their polarized third harmonic generation signal, with anisotropy ratios as large as ${\chi }_{11}/{\chi }_{22}\approx 6.5$. From the expected nonlinear dependence of these monoclinic and triclinic crystals, we extract the relative nonlinear susceptibility coefficients. We find that the anisotropy ratio is largest for ${\mathrm{ZrS}}_3$ and decreases across the family, a trend we associate with the proximity of the third harmonic energy to the strongly $b$-polarized absorption edge of each material. ${\mathrm{NbS}}_3$, the only triclinic crystal, displays a pronounced anisotropy in thick flakes that is strongly reduced in the thinnest flakes, which we attribute to a partial relaxation of the Peierls-type Nb–Nb dimerization that underlies the triclinic distortion. The large anisotropic nonlinear response in this crystal family sets it apart from other 2D materials and makes them particularly attractive for further investigation.

This study investigates the impact of a Pt underlayer on the antiferromagnetic properties of epitaxial NiO(001) films, focusing on the antiferromagnetic domain structure and interfacial exchange coupling. Two types of epitaxial NiO films were prepared: one directly deposited on an MgO(001) substrate and the other with a 10-nm-thick Pt layer inserted between the NiO film and the MgO substrate. Despite both films exhibiting epitaxial growth, detailed structural analyses reveal that the insertion of Pt underlayer leads to the strain relaxation and introduces the misfit dislocations at the Pt/NiO interface. Moreover, the exchange bias and coercive fields of the adjacent CoFeB layer are significantly enhanced in the sample with the Pt underlayer. X-ray magnetic linear dichroism photoemission electron microscopy (XMLD-PEEM) visualizes a drastic reduction in the antiferromagnetic domain size by the Pt insertion. The disappearance of micrometer-scale XMLD contrast and the emergence of an in-plane Néel vector orientation indicate that the strain relaxation and interfacial disorder introduced by the Pt underlayer strongly modify the antiferromagnetic domain configuration. These results demonstrate that the Pt underlayer serves as an effective structural and magnetic control parameter in epitaxial NiO, providing a pathway to tailor antiferromagnetic domain structures and interfacial exchange coupling for NiO-based spintronic devices.

We systematically investigate the microscopic origins of the intrinsic anomalous Hall effect (AHE) and spin Hall effect (SHE) in the rare-earth transition-metal (RE–TM) ferrimagnet ${\mathrm{GdCo}}_5$ using first-principles $\mathrm{DFT}+\mathrm{U}+\mathrm{J}$ calculations combined with Berry-curvature analysis. The Hall-active states near the Fermi energy in the ground-state antiparallel ferrimagnetic configuration are predominantly Co-derived. However, changes in the relative Gd–Co magnetic alignment substantially reconstruct these electronic states, modifying the relevant band dispersions and interband energy separations and thereby redistributing the Berry curvature and Hall response. Based on this mechanism, we elucidate the microscopic origin of the pronounced suppression of the anomalous Hall conductivity (AHC) during the field-induced spin-flop transition, showing that the dominant reduction occurs in the first stage of spin reorientation, despite the Gd–Co antiparallel alignment remaining largely preserved. At the Fermi energy, the AHC reaches its maximum magnitude of $885{\left(\mathrm{\Omega }\mathrm{cm}\right)}^{-1}$ in the antiparallel ground state. Furthermore, we show that ${\mathrm{GdCo}}_5$ exhibits a large intrinsic spin Hall conductivity (SHC), with the dominant tensor components reaching ${\sigma }_{zx}^y=1558\left(\hslash /\mathrm{e}\right){\left(\mathrm{\Omega }\mathrm{cm}\right)}^{-1}$ and ${\sigma }_{yx}^z=731\left(\hslash /\mathrm{e}\right){\left(\mathrm{\Omega }\mathrm{cm}\right)}^{-1}$ at the Fermi level, yielding a substantial spin Hall angle up to 0.13. In addition, selected SHC tensor components can be strongly modulated and even reversed in sign through magnetization rotation and changes in the relative Gd–Co alignment, reflecting the sensitivity of the spin Hall response to the magnetic Laue group symmetry and relative sublattice configuration. Our findings reveal a microscopic connection between magnetic configuration, electronic-structure reconstruction, and Berry-curvature-driven transport in ${\mathrm{GdCo}}_5,$ and highlight its potential for exploring magnetization-dependent intrinsic spin-current generation.

Laser ignition of energetic crystals involves coupled photophysical and chemical processes, beginning with photothermal conversion that transfers photoexcited-carrier energy to lattice vibrations and initiates local heating before decomposition. Here, first-principles calculations elucidate how intrinsic defects regulate this process in the quasi-two-dimensional molecular energetic crystal 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Atomic vacancies introduce in-gap states, with hydrogen vacancies efficiently trapping both electrons and holes and thereby promoting defect-assisted nonradiative recombination. Mode-resolved analysis shows that recombination at these defects preferentially couples to intramolecular vibrations associated with molecular deformation. By contrast, slower recombination in pristine TATB couples mainly to low-frequency interlayer collective modes, whose energy must be redistributed into higher-frequency intramolecular vibrations through phonon–phonon interactions. Thus, defects accelerate carrier-to-lattice energy transfer and directly channel the released energies into vibrations relevant to chemical-bond cleavage during the initial photothermal stage of laser ignition.

Charge carriers in organic semiconductors form polarons, which are self-localized states stabilized by interactions with their environment. Using a dielectric-stabilized tight-binding model parametrized from first-principles calculations, we compute ground and excited polaron states in poly(3-hexylthiophene) (P3HT). Our results quantitatively reproduce key midinfrared absorption features, notably the chain-length-dependent shift of the intrachain polaron excitation peak (peak B) and its variation between regioregular and regiorandom P3HT. Comparison to an alternative stabilization mechanism based on local ring distortions reveals that dielectric polarization dominates polaron formation, as ring distortions yield insufficient binding and excitation energies inconsistent with experiments. These findings clarify the microscopic origin of polarons in conjugated polymers and provide a predictive framework linking polaron energetics to spectroscopic observables, advancing the understanding of charge transport in organic semiconductors.

Cement paste serves as the universal binder in concrete, formed by mixing water with Ordinary Portland Cement (OPC). In its fresh state, cement paste behaves as a reactive suspension in which cement grains continuously dissolve, while colloidal calcium silica-hydrate (C-S-H) particles precipitate and progressively build a percolated load-bearing structure that densifies and hardens through hydration. Like many colloidal gels and concentrated suspensions, cement paste is sensitive to external stimuli such as mechanical vibrations and temperature variations. Here, we investigate the impact of power ultrasound (PUS) applied to OPC paste during the very early stages of hydration on the micromechanical properties of the hardened material. Fresh cement pastes are exposed to PUS at different amplitudes and durations before curing for 28 days. Microindentation testing reveals a progressive degradation of hardness, indentation modulus, and creep modulus with increasing PUS exposure. Remarkably, all mechanical properties collapse onto master curves controlled by the cumulative ultrasonic exposure. Microscratch testing further reveals enhanced acoustic-emission activity in sonicated samples, consistent with the development of additional mesoscale defects within the hardened material. In contrast, nanoindentation measurements show that the intrinsic mechanical properties of the individual phases composing the hardened paste—low-density and high-density C-S-H—remain largely unaffected. Together, these results indicate that PUS primarily alters the microstructure of hardened cement paste at scales larger than those of the hydration products themselves. These findings offer valuable experimental insights into novel pathways for modifying the mechanical properties of reactive colloidal gels.

Narrow-bandgap thermoelectric semiconductors typically suffer from excessively high intrinsic carrier density, which severely suppresses the Seebeck coefficient and compromises the power factor. Decoupling the entangled electronic parameters to resolve this intrinsic trade-off remains a central challenge in the pursuit of high-performance materials. Here, using $n$-type Te-free BiSe as a model system, we demonstrate a “staged dual-doping” strategy to decouple the regulation of carrier density and density of states (DOS) effective mass. We show that initial Sb alloying successfully mitigates the excessive carrier density, boosting the Seebeck coefficient and carrier mobility, yet inevitably reducing the DOS effective mass. Crucially, subsequent Ge incorporation recovers this compromised effective mass by modulating the band structure while simultaneously inducing hierarchical microstructural heterogeneities ranging from point defects to dislocations that strongly scatter phonons. As a result, the optimized ${\mathrm{Bi}}_{0.69}{\mathrm{Sb}}_{0.29}{\mathrm{Ge}}_{0.01}\mathrm{Se}$ achieves a peak $\mathit{ZT}$ of 0.54 at 473 K, a room-temperature $\mathit{ZT}$ of 0.33, and an average $\mathit{ZT}$ of 0.48 over 300–523 K. This work establishes a rational, scalable pathway for optimizing Te-free BiSe and offers a transferable blueprint for managing trade-offs in narrow-bandgap thermoelectrics.

Non-fullerene acceptors such as Y6 have enabled high-efficiency organic photovoltaic devices and motivated the development of single-component architectures; however, the microscopic mechanisms governing exciton transport and charge dissociation remain under active investigation. In particular, the interplay between Frenkel and charge-transfer excitations and their coupling to environmental fluctuations complicates the description of light absorption and subsequent exciton dynamics. Here, ultrafast transient absorption spectroscopy is used to probe exciton quenching dynamics in Y6 films interfaced with hole-transport layers. To interpret these measurements, we develop an analytical model based on hybrid Frenkel-charge-transfer states that enables direct extraction of intermolecular electronic couplings, charge-transfer character, and system-bath interaction strengths from experimental data. The analysis reveals a substantial charge-transfer admixture of 20–40 % in the exciton states and identifies delocalization-mediated transport on the short length and time scales probed by the measurements. Consistent with this interpretation, the corresponding quenching dynamics occur on a $\sim 1$ ps timescale within $\sim 4\mathrm{nm}$ of the interface, suggesting a short-range injection mechanism facilitated by exciton delocalization. In addition to providing physical parameters for Y6, these results establish a quantitative framework that connects spectroscopic observables to microscopic transport mechanisms and can be generalized to other non-fullerene acceptors.

Polar materials have recently attracted significant interest due to their rich multifunctional properties. The chalcogenide polar semiconductor ${\mathrm{Cu}}_{1-x}{\mathrm{Mn}}_{1+y}{\mathrm{SiTe}}_3$ (Cu-deficient, $0.04\le x\le 0.26$; $0.03\le y\le 0.15$) is an emerging multiferroic system in which electric polarization is coupled to magnetization. However, its macroscopic ferroelectric polarization is strongly suppressed due to the presence of a high density of stacking faults. In this work, we demonstrate that these crystal defects, likely originating from nonstoichiometry, can be substantially reduced by increasing the Cu content. Cu-enriched samples, ${\mathrm{Cu}}_{1+x}{\mathrm{Mn}}_{1-y}{\mathrm{SiTe}}_3$ ($0.04\le x\le 0.3;0.13\le y\le 0.31$), crystallize in a noncentrosymmetric monoclinic structure (space group $\mathit{Pm}$) as the Cu-deficient counterpart but show a nearly stacking-fault-free phase, which is attributed to the emergence of an interstitial site. Consequently, the Cu-enriched samples show a pronounced enhancement of the second-harmonic generation (SHG) response compared to Cu-deficient compositions. Magnetically, the Cu-enriched crystals retain long-range antiferromagnetic order with a Néel temperature of $T_{\mathrm{N}}\sim 33$ K without a glassy state but manifest a distinct metamagnetic transition along the polar $b$ axis that is absent in the Cu-deficient compositions. Furthermore, the electronic ground state evolves from insulating to doped semiconducting behavior upon Cu enrichment. Together, these results establish this material system as a unique and versatile platform for elucidating the interplay among composition, crystal defects, and multifunctional properties, offering a route to design magnetic polar systems with tunable quantum functionalities.

Heterointerfaces are ubiquitous in modern devices, found in technologies ranging from microelectronics to structural components for energy applications. Many of these emerging technologies are found in applications that are subject to harsh environments, such as satellites, batteries, and next-generation nuclear reactors. In some scenarios, multiple extreme conditions, such as irradiation and corrosion, act on the material simultaneously. Extending the lifetime of these technologies is dependent on a detailed understanding of how their component materials platforms and interfaces respond in extreme environments, where irradiation and corrosion may couple in unique ways, distinct from corrosion under ambient conditions. Oxides, which form readily over metal underlayers, can act as protective coatings; enhancing the robustness of oxide overlayers to protect underlying metal alloys is a potential avenue towards corrosion mitigation. Here, we study the impact of irradiation-induced nonequilibrium defects on charge segregation and electric fields at and near multi-phase oxide heterointerfaces. We perform a detailed study of irradiated ${\mathrm{Fe}}_2{\mathrm{O}}_3–{\mathrm{Cr}}_2{\mathrm{O}}_3$ thin film heterostructures using first-principles density functional theory (DFT) electronic structure modeling paired with four-dimensional-scanning transmission electron microscopy (4D-STEM) differential phase contrast (DPC) and electron energy loss spectroscopy (EELS) techniques to measure nanoscale changes in electric fields. Our results show clear evidence that irradiation drives substantial modulation of interfacial electric fields that can be tailored by controlling the atomistic chemical structure of the oxide interface. We show that irradiation can selectively induce built-in electric fields, thereby altering their direction; this suggests a pathway to engineering protective oxide heterostructure overlayers that can electrically control the spatial distribution of defects, with significant implications for the design of corrosion-resistant materials for extreme environments.

Accurate atomistic modeling of screw dislocations in body-centered cubic (BCC) metals remains challenging because their plasticity is governed by complex dislocation glide behavior due to their compact threefold symmetric core structure and a strongly temperature-dependent flow stress induced by the large Peierls barrier. In the context of group 5 (V, Nb, and Ta) and group 6 (Mo and W) refractory metals (RMs), both classical interatomic potentials and some machine-learning potentials consistently fail to reproduce density functional theory (DFT) Peierls barriers and the glide plane. Here, we developed an array of atomic cluster expansion (ACE) potentials for these RMs by extending an existing DFT database. The developed ACE potentials significantly improve the description of screw dislocation properties, showing good agreement with the DFT references for Mo and W and substantial improvement for V, Nb, and Ta. The results show that transferability to screw dislocation behavior depends sensitively on both database composition and element-specific energetics and that achieving a single-humped Peierls barrier alone is not a sufficient validation metric for accurate prediction of dislocation glide. For Nb, Mo, and W, the developed ACE models also enable reliable calculation of kink-pair activation enthalpies, which are well described by both Kocks' law and a line-tension model.

The nonlinear Hall effect (NLHE) provides a powerful probe into the quantum geometry and crystalline symmetry of time-reversal symmetric systems. However, the evolution of its underlying mechanisms across different transport regimes in semiconductors remains a subject of intense debate. In this work, we systematically investigate the NLHE in hydrothermally synthesized $p$-type 2D tellurium (Te) nanoflakes. By implementing oxygen plasma-assisted contact engineering, we achieve high-fidelity signal detection through the suppression of Schottky-barrier-induced artifacts. Our results reveal that the NLHE in Te is governed by extrinsic scattering, as evidenced by a precise quadratic scaling law at temperatures above 30 K. Notably, we identify a remarkable low-temperature scaling anomaly at $T_{\mathrm{R}}\approx 30\mathrm{K}$, where the scaling slope undergoes a dramatic sign reversal, a phenomenon that coincides with the low-temperature transport crossover. Furthermore, thickness-dependent studies show a 3.2-fold enhancement in nonlinear conductance as the flake thickness is reduced to 16 nm, identifying surface-induced symmetry breaking as the primary trigger for activating the nonlinear transport forbidden in the ideal bulk lattice. These findings not only elucidate the scattering-driven origins of NLHE in 2D Te but also establish the effect as a sensitive probe for scattering-mechanism competition and symmetry evolution in chiral semiconductors.

Surface diffusion is the key mass transport process and is commonly described as a Fickian random walk. Using STM and surface diffraction, we show that intercalated Pb under graphene on SiC moves by collective diffusion much faster than random-walk diffusion above a critical coverage ${\theta }_{\mathrm{c}}$ higher than the Pb(111) density. Massive deintercalation of the compressed intercalated layer is observed unexpectedly at room temperature (RT), well below the typical deintercalation temperature of $\sim 550{}^{\circ }\mathrm{C}$. The layer forms after several intercalation/deintercalation cycles, such that its coverage is high, as confirmed by the large drop in the intensity of the diffraction spots. Pb islands with uniform rings at their perimeters that grow at low temperatures are distinctive signatures of collective diffusion ideally studied with STM. LEEM videos of the Pb intercalation reported in the literature further support these nonclassical results.