Rare-earth high-entropy oxides (RE-HEOs) have emerged as a promising class of functional ceramics for solid-state electrochemical applications due to their chemical complexity, structural tunability, and potential for fast oxygen-ion transport. In this work, we investigate oxygen diffusion in ceria-based RE-HEOs of the form Ce_x(YLaPrSm)_1-xO_2-δ using classical molecular dynamics simulations driven by the Crystal Hamiltonian Graph Neural Network (CHGNet) machine-learned interatomic potential. To improve predictive accuracy for lanthanide-containing systems, we benchmark three CHGNet variants, including a fine-tuned r^2SCAN-trained model, against targeted density functional theory (DFT) data that explicitly include f-valence electrons. Simulations across temperature, Ce content, oxygen vacancy concentration, and both fluorite and bixbyite structures reveal that oxygen transport in RE-HEOs is governed by the interplay of two factors: the concentration of mobile vacancies and the local cation environment through which they hop. At fixed composition, ionic conductivity exhibits a non-monotonic dependence on vacancy concentration, with optimal diffusion occurring at moderate vacancy levels and reduced mobility at higher concentrations. Increasing Ce content lowers migration activation energies and enhances diffusivity through low-barrier diffusion networks built from Ce-Ce and Ce-Y edges. Analysis of individual oxygen hopping events provides atomistic insight into how local chemical environments and short-range cation ordering govern transport in high-entropy oxides. Overall, this work demonstrates that machine-learned interatomic potentials can resolve composition-structure-transport relationships in chemically complex oxides, and identifies active pathways through which compositional tuning can enhance oxygen-ion conductivity in RE-HEO materials.

ABSTRACT We investigate the local atomic and electronic structure, thermodynamic stability, and defect chemistry of A 6 B 2 O 17 ( A = Zr/Hf, B = Nb/Ta) oxides using first‐principles density functional theory (DFT) calculations. We examine both ordered unit cells as well as fully disordered special quasirandom structures to clearly discern the effects of cation disorder. Structural predictions align closely with previous experimental results and follow established ionic radii trends. The electronic structure is strongly dependent on B ‐cation species: A 6 Ta 2 O 17 compositions have ~30% larger band gaps than their A 6 Nb 2 O 17 counterparts. Defect chemistry is similar for all compositions, with anion vacancies being more energetically favorable than corresponding cation defects. All explored A 6 B 2 O 17 compositions are enthalpically unstable with respect to their A O 2 and B 2 O 5 competing oxides and are therefore classified as entropy‐stabilized materials, supporting prior experimental results. The pronounced agreement between our disordered supercell predictions and experimental measurements indicates all explored A 6 B 2 O 17 compositions contain substantial cation disorder across all 6‐, 7‐, and 8‐coordinated sites. Our findings collectively provide a fundamental understanding of the A 6 B 2 O 17 material family through DFT calculations, establishing a framework for future compositional tuning to engineer targeted material properties.

ABSTRACT Focused ion beam (FIB)‐induced site‐specific implantation is a favorable patterning technology that enables the modification of optical and electrical properties of semiconductors by directly writing ions into the structure with controlled spatial coherence. Here, 30 kV Ga 1+ implantation is performed using a Ga‐sourced FIB into a 50 nm‐thick cadmium oxide (CdO) plasmonic thin film to achieve locally tunable mid‐infrared (MIR) plasmonic materials. A series of molecular dynamics (MD) simulations is first performed to analyze the Ga penetration depth into CdO as a function of the implantation offset angle. They show that offset angles greater than ∼5° result in dechanneling pathways. CdO films are Ga‐implanted over a similar angular range, and their transport properties are analyzed by Hall effect measurements. Following an activation anneal, all samples irradiated at 5° or more exhibit mobility values between 362 and 386 cm 2 V −1 s −1 . To understand this trend, microstructural evolution as a function of offset angle is studied using scanning transmission electron microscope (STEM) and atom probe tomography (APT) for normal and 5° incidence irradiation. It is revealed that interfacial cluster formation is the determining factor for carrier mobility, where lower volume fraction and density are observed for inclined implantation.

In applications such as atmospheric monitoring of greenhouse gases and pollutants, the detection and identification of trace concentrations of harmful gases is commonly achieved using nondispersive infrared (NDIR) sensors. These devices typically employ a broadband infrared emitter, thermopile detector, and spectrally selective bandpass filter tuned to the vibrational resonance of the target analyte. However, fabrication of these filters is costly and limited to a single frequency. This limitation introduces a fundamental trade-off, as broadening the optical passband width enhances sensitivity but compromises selectivity, whereas narrowing improves selectivity at the expense of sensitivity. In this work, we validate a filterless NDIR gas sensing approach utilizing a multipeak thermal emitter developed through an inverse design. This emitter enhances detection sensitivity by simultaneously targeting multiple absorption bands, demonstrated through the creation of a sensor designed for the C-H vibrational modes of propane (C3H8). Additionally, a second set of single-peak emitters was developed to showcase the capability of designing highly selective sensors operating within close spectral proximity. These emitters, targeting the stretching modes of carbon monoxide (CO) and carbon dioxide (CO2), exhibit quality factors (Q-factors) above 50 and minimal crosstalk, enabling accurate detection of the target gas without interference from gases with spectrally adjacent absorption bands. This is enabled by aperiodic distributed Bragg reflectors (a-DBRs), which achieve higher Q-factors with fewer layers than periodic Bragg reflectors. Experimental results demonstrate that this approach breaks the trade-off between sensitivity and selectivity.

Abstract High-entropy carbides (HECs) can be stabilized as single-phase solid-solution microstructures by kinetically trapping a “high-entropy state” under ambient conditions; however, such microstructures may represent metastable states rather than true thermodynamic equilibrium. Here, we investigate the thermodynamic stability of HECs using an integrated theoretical–experimental framework. Density functional theory calculations of carbon vacancy formation energies reveal two distinct energy landscapes, from which we hypothesize that rugged profiles correspond to reduced effective configurational entropy and promote multiphase microstructures, whereas smoother profiles are indicative of higher configurational entropy and stabilize single-phase microstructures. High-power impulse magnetron sputtering synthesis validates these predictions, showing single-phase HECs in the as-deposited state due to kinetic barriers, whereas postdeposition annealing induces phase segregation in compositions exhibiting rugged energy landscapes. Furthermore, machine-learning-derived descriptors enable systematic mapping of these energy landscapes, providing a predictive pathway to accelerate understanding of defect profile and its critical role in delineating phase stability in HECs.

Hyperbolic materials, which exhibit an extreme form of birefringence enabling the volume confinement and frequency-dependent propagation of deeply sub-diffractional optical modes, offer the opportunity for extreme confinement via the stimulation polaritonic modes, with substantially higher confinement obtained through the efficient excitation of of the higher-order (shorter wavelength) hyperbolic polaritonic modes, which they can support. However, while these higher-order hyperbolic polaritons (HO-HPhPs) form high-momentum ray-like propagation within the bulk, efficient excitation of these modes, especially in contrast to the long-wavelength lower-momentum surface polariton propagating modes, has remained a challenge. Critically, the large momentum mismatch between these modes and free-space light, alongside the spatial mismatch between the sub-diffractional scatterer and the distinct modal distribution of HO-HPhPs, lead to a suppressed launching efficiency of these higher-order modes, limiting their use in nanophotonic applications. Here, we report the experimental observation of a 10-fold enhancement in the excitation efficiency of HO-HPhPs through the use of subsurface scatterers over traditional surface scattering (e.g. a flake edge or gold launcher) within single-crystalline α-MoO3 slabs. We employ full-wave numerical simulations to investigate the role of the spatial overlap between HO-HPhP modal distributions and the scatterer placement upon excitation efficiency. Furthermore, we develop a generalized process using transfer matrix method to selectively design modal HO-HPhP excitation, which advances the capabilities of HPhP multiplexing for on-chip applications.

Optical second harmonic generation (SHG) exists as a popular tool for probing materials with broken inversion symmetry in the physical and biological sciences. SHG polarimetry can reveal material anisotropy with high sensitivity, including point group and phase transitions. Here, we probe ferroelectric wurtzite films with a nominal 6 mm symmetry under a normal reflection geometry using SHG microscopy and discover an unexpected symmetry breaking. Symmetry considerations would normally forbid the detection of the SHG signal when light propagates along the polar 6-fold rotation axis. Yet a uniquely anisotropic SHG response is observed in this geometry in Al1-xBxN, Al1-xScxN, Zn1-xMgxO, and AlN/Al1-xScxN heterostructures grown on silicon that can be modeled by an average monoclinic symmetry of point group m. A significant enhancement of the SHG signal corresponding to up to a 5.3 & times; increase in the SHG intensity (hence similar to 2.3 & times; in effective SHG tensor coefficient) is observed at antiparallel polar domain walls, suggesting local cooperative alignment of symmetry-breaking structural distortions. Namely, it is found that the monoclinic mirror plane is oriented predominantly perpendicular to the walls. Such increases in domain wall SHG thus reveal that subtle symmetry breaking can be a pathway to large property enhancements. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

ABSTRACT High‐entropy carbides are promising candidates for extreme‐temperature environments, but their grain‐boundary chemistry remains difficult to resolve because segregation involves both chemical disorder and finite‐temperature configurational sampling. Here, we quantify temperature‐dependent grain‐boundary segregation in high‐entropy carbides using a universal message‐passing atomic cluster expansion (MACE) machine learning interatomic potential combined with a hybrid Monte Carlo–molecular dynamics workflow. A 53.1 symmetric tilt grain boundary was sampled for six representative high‐entropy carbide compositions containing group IV, V, and VI transition metals at 300 and 2000 K. Element‐resolved metal‐sublattice composition profiles reveal composition‐dependent segregation modes. Several chemistries exhibit selective near‐boundary enrichment by one or two dominant metals, including Ti/Zr, Mo/Zr, W/Zr, and Cr/Zr motifs, whereas shows persistent multi‐element co‐segregation. Increasing temperature broadens the segregation profiles and expands the chemically perturbed interfacial region, with secondary metal species contributing more strongly to the near‐boundary composition at 2000 K. A Cr‐containing composition shows the most pronounced high‐temperature response, where Cr‐rich segregation is accompanied by boundary broadening, chemical heterogeneity, and structural disordering. These results show that grain‐boundary segregation in high‐entropy carbides does not follow a single universal trend, but instead depends strongly on carbide chemistry and temperature.

The orthorhombic van der Waals (vdW) layered crystal α-MoO3 is a promising material for infrared nanophotonics; in particular, it may host highly confined hyperbolic phonon polaritons (HPhPs) with wavelength-dependent in-plane anisotropy. However, large-area and uniform single crystals are challenging to grow on substrates, as current α-MoO3 growth methods struggle to manage adverse tendencies in size, texturing, and roughness. In this work, we establish an alkali salt-assisted chemical vapor deposition (SA-CVD) growth technique to produce smooth, high-quality, and millimeter-scale single-crystal α-MoO3 nanosheets directly on A-plane sapphire substrates. By cosublimating a NaCl source along with α-MoO3 during growth, we overcome the size and morphology challenges typical of alkali-free deposition, achieving ultrasmooth crystals with lateral dimensions reaching 6 mm and thicknesses ranging from <6 to 480 nm. We attribute the improved morphology to a molten Na2O-MoO3 intermediate, which forms on the substrate surface and induces a self-expanding vapor-liquid-solid (VLS) growth mode. The as-grown single-crystal nanosheets exhibit high crystal and optical quality without evident degradation by residual Na, enabling characteristically high HPhP quality (Q) factors (12-30) and long lifetimes (2.7-7.7 ps) as measured by scattering-type scanning near-field optical microscopy (s-SNOM). We relocate the large-area crystals onto arbitrary substrates using a water-assisted layer transfer technique, which effectively removes Na-containing residue and relieves residual strain. This work unlocks millimeter-scale, high-quality, uniform α-MoO3 single-crystal growth directly on substrates for large-area implementation in fields including mid-infrared nanophotonics and layered vdW heterostructures.

Alloying is an age-old strategy for synthesizing materials with enhanced properties. Recently, multicomponent systems such as high-entropy oxides have garnered widespread attention due to their tunable and often superior properties compared to their constituent oxides. Here, we study the local structural and chemical nuances of six-component (Mg0.167Co0.167Ni0.167Cu0.167Zn0.167Mn0.167)O and (Mg0.167Co0.167Ni0.167Cu0.167Zn0.167Cr0.167)O thin films. The Mn-alloyed thin film exhibits a higher exchange bias and greater magnetic frustration compared with the Cr-containing thin film. Scanning/transmission electron microscopy investigations reveal that the Mn-alloyed thin film exhibits the coexistence of rock salt and spinel-like regions, unlike the single-phase rock salt structure observed in the Cr-alloyed thin film. Electron energy loss spectroscopy indicates changes in Co and Mn valences within the Mn-containing thin film, suggesting the presence of mixed-valence states, which are further confirmed by X-ray absorption spectroscopy measurements. These observations are further validated by cation-site-preference energy calculations using density functional theory. Our results demonstrate how the chemistry, site occupations, and cation valences result in pronounced changes in the overall properties of high-entropy oxides.

We investigate the local atomic and electronic structure, thermodynamic stability, and defect chemistry of A(6)B(2)O(17) (A = Zr/Hf, B = Nb/Ta) oxides using first-principles density functional theory (DFT) calculations. We examine both ordered unit cells as well as fully disordered special quasirandom structures to clearly discern the effects of cation disorder. Structural predictions align closely with previous experimental results and follow established ionic radii trends. The electronic structure is strongly dependent on B-cation species: A(6)Ta(2)O(17) compositions have similar to 30% larger band gaps than their A(6)Nb(2)O(17) counterparts. Defect chemistry is similar for all compositions, with anion vacancies being more energetically favorable than corresponding cation defects. All explored A(6)B(2)O(17) compositions are enthalpically unstable with respect to their AO(2) and B2O5 competing oxides and are therefore classified as entropy-stabilized materials, supporting prior experimental results. The pronounced agreement between our disordered supercell predictions and experimental measurements indicates all explored A(6)B(2)O(17) compositions contain substantial cation disorder across all 6-, 7-, and 8-coordinated sites. Our findings collectively provide a fundamental understanding of the A(6)B(2)O(17) material family through DFT calculations, establishing a framework for future compositional tuning to engineer targeted material properties.

In this work, we develop a rapid reactive vapor transport technique to efficiently utilize limited isotopically pure precursors, particularly gaseous 18O2, and synthesize mm-scale, high-quality isotope-enriched crystals within few-minute growth durations. We unlock this capability by using metallic molybdenum precursors with high source temperatures (900 degrees C) and total pressures ('1 atm) to maximize precursor efficiency and yield. Subsequently, we grow alpha-MoO3 single crystals with high and uniform enrichment levels of 98Mo and 18O isotopes in several different permutations. As probed by Raman spectroscopy, modest and significant phonon energy redshifts occur following 98Mo and 18O enrichment, respectively. By demonstrating control over both molybdenum and oxygen isotopic enrichments, we establish a powerful tool to advance nanophotonics and thermal management goals using alpha-MoO3. This work is motivated by the possibility to enhance and engineer lattice vibrational mode phenomena including thermal conduction and hyperbolic phonon polariton dispersion- with particular interest in comparing the effects of light and heavy element enrichment.

High-entropy oxide (HEO) thin films uniquely superimpose exceptional chemical disorder with exceptional crystalline quality and coherence-an intersection we term anomalous crystallinity that arises from coupled structural, chemical, and valence degrees of freedom unique to the high-entropy and entropy-stabilized conditions. Here, we demonstrate unexpected and predictive control of this state using formulation, epitaxial constraints, and kinetic arrest of metastable macrostates. Specifically, aliovalent cation substitutions, tightly controlled substrate temperatures, and conditions favoring significant adatom kinetic energy, can program the out-of-plane lattice parameter of coherent rock salt HEOs while preserving in-plane epitaxial pinning to MgO. We highlight the exemplar (ScMgCoNiCuZn)O/(CrMgCoNiCuZn)O (JSc/JCr) system where Sc and Cr substitution into the rock salt structure produces pseudomorphic heterostructures between individual antiferromagnets, sustaining an exceptional 5.5% out-of-plane lattice parameter difference and enabling abrupt interfaces across which the Co valence switches from mostly 2+ to an even 2+/3+ mixture. The JSc/JCr valence interface heterostructure is accompanied by a 2 × exchange bias boost compared to single-layer constituents, that could be attributed to enhanced uncompensated spins in the layers themselves or around the buried JSc/JCr interface. These results establish pseudomorphic valence interfaces with anomalous crystallinity as a source of new magnetic macrostates that host emergent magnetic and spintronic functionality.

Polarization reversal in ferroelectrics arises from the coupled processes of domain nucleation and subsequent growth, yet the governing mechanisms differ fundamentally between classical perovskite oxides and emerging wurtzite ferroelectrics. While switching in perovskites is typically governed by mobile domain walls whose field-driven propagation dominates macroscopic kinetics, here we show that polarization reversal in wurtzite Zn1-xMgxO proceeds through a qualitatively different pathway. Using scanning oscillator microscopy, in combination with point pulse-imaging methods, we directly map local switching events and domain wall responses, revealing that domain walls in Zn1-xMgxO exhibit negligible lateral mobility (sub 10nm) and that polarization reversal proceeds predominantly through the nucleation of vertically extended columnar filaments with a lateral size on the order of the grains. This nucleation-controlled switching contrasts sharply with the growth-mediated dynamics characteristic of perovskite ferroelectrics and explains the abrupt, spatially localized switching behavior observed in wurtzite systems. These results establish nucleation-dominated filamentary reversal as a defining switching mechanism in Zn1-xMgxO and point towards the need for further studies to understand correlation lengths and nucleation processes across a range of grain sizes.

Metal oxides are used in a broad array of technological applications. However, only a small subset of oxide materials are semiconducting, which limits the range of chemical compositions available for engineering. Here we demonstrate a strategy for driving insulating metal oxides into a semiconducting state with ultra-low thermal conductivity (less than 1 W/m/K) by introducing configurational entropy. This change in electronic character is facilitated by cation mixing in a high-entropy phase, which activates several microscopic mechanisms in electronic and vibrational subsystems that combine to dominate the observed electronic and thermal response of the material. The electronic mechanisms include increased crystal field splitting and electronegativity differences, the preservation of split-off states from parent phases, in-gap states induced by charge transfer between mixed cations, and orbital degeneracy lifting due to lattice distortion. The ultra-low thermal conductivity is attributed to a combination of phonon-defect and crystal momentum non-conserving three-phonon scattering events, both of which arise from chemical disorder. We establish and quantify these effects through co-validated experimental and theoretical analyses of the high-entropy wolframite oxide A6WO4 (A = Mn, Fe, Co, Ni, Cu, Zn). Our analyses suggest that the proposed mechanisms are readily generalizable to a range of functional materials, and could be especially valuable in designing thermoelectric materials, which require simultaneous engineering of semiconducting and thermal properties. Transition metal oxides are interesting for advancing technology as they can combine ease of synthesis, resilience to defects, and high environmental stability, yet few exhibit semiconducting properties, limiting their engineering potential. Here, the authors transform insulating oxides into semiconductors with ultra-low thermal conductivity by introducing configurational entropy, offering a generalizable approach to designing advanced thermoelectric materials with tailored electronic and thermal properties.

Optimization of next-generation materials synthesis and manufacturing processes can be accelerated by effective use of digital datasets. However, a majority of existing custom research infrastructure, including that for thin film deposition, is primarily manually operated and not compatible with this new research paradigm. Here, a template is provided for upgrading existing manual deposition chambers to enable automated and autonomous experimentation. As an example, the upgrade of an existing magnetron sputtering chamber dedicated to synthesis of wurtzite ferroelectrics is presented. Focus is placed on automation of instrumentation; system and deposition control; and synchronized and automated data collection strategies. An example use case of the system for semi-autonomous determination of process-property relationships is presented, specifically minimization of coercive field in wurtzite Al_1-x-ySc_xB_yN thin films.

Cerium-based lanthanide high-entropy oxides (LN-HEOs) are promising candidates for solid-state electrolyte (mass transport) applications due to their ability to accommodate high concentrations of oxygen vacancies while retaining a fluorite-derived structure. However, synthesis often yields undesired ordered oxygen-deficient phases, such as bixbyite, depending on composition and processing conditions. We utilize first-principles density functional theory (DFT) calculations to systematically investigate phase stability in the model system , with the aim of elucidating the thermodynamic factors governing fluorite-bixbyite competition and identifying structure-property relationships to oxygen transport. By independently varying cerium concentration and oxygen vacancy content, we predict that the transition from disordered fluorite to ordered bixbyite is driven primarily by compositional and vacancy-ordering effects, rather than through changes in cation valence. Free-energy analysis reveals that at high vacancy concentrations, bixbyite is enthalpically favored due to ordered oxygen vacancies, while fluorite is stabilized at lower vacancy concentrations and higher cerium content through configurational entropy of the anion sublattice. These DFT results clarify the competing energetic contributions that control phase stability and structure-valence relationships in LN-HEOs and establishes a mechanistic framework for designing vacancy-tolerant oxide electrolytes with tunable phase behavior.

The implementation of polaritonic materials into nanoscale devices requires selective tuning of parameters to realize desired spectral or thermal responses. One robust material, α-MoO3, an orthorhombic crystal boasting three distinct phonon dispersions, provides three polaritonic dispersions of hyperbolic phonon polaritons (HPhPs) across the mid-infrared (MIR). Here, the tunability of both optical and thermal responses in isotopically enriched α-MoO3 (98MoO3, Mo18O3, and 98Mo18O3) is explored. A uniform ∼5% spectral redshift from 18O enrichment is observed in both Raman- and IR-active TO phonons. Both the in- and out-of-plane thermal conductivities for the isotopic variations are reported. Ab initio calculations both replicate experimental findings and analyze the select-mode three-phonon scattering contributions. The HPhPs from each isotopic variation are probed with s-SNOM, and we report an HPhP Q-factor maxima increase in 98Mo18O3 of ∼50% along the [100] in the RB2 and ∼100% along the [001] in the RB3 with respect to 98MoO3. Observations in both real and Fourier space of higher-order HPhP modes propagating in slabs of isotopically enriched α-MoO3 without the use of a subdiffractional surface scatterer are presented here. This work establishes the dual-element isotope enrichment of α-MoO3 as an intrinsic strategy to design optical, thermal, and polaritonic properties.

Real ferroelectric devices operate under mixed and distorted time-varying voltages, yet the standard nucleation-growth frameworks used to interpret ferroelectric switching, most notably the Kolmogorov-Avrami-Ishibashi (KAI) and nucleation-limited switching models (NLS), are derived under the critically limiting assumption of a constant electric field. Thus, the prevailing interpretation of ferroelectric switching dynamics fails under real operating conditions. Here we introduce a compact dynamic-field-driven nucleation and growth (DFNG) model that enables quantitative fits to switching transients across multiple ferroelectric materials to extract time-varying domain wall velocity and growth dimensionality, even under arbitrary voltage waveforms. This capability then motivates its use in device modeling under complex signals spanning disparate time and frequency scales. Coupling the compact model to application-related waveforms and a circuit-level simulation platform facilitates a predictive materials-circuit co-design framework by linking nucleation and growth parameters to memory window, disturb error, speed, and energy dissipation for next-generation ferroelectric technologies.

To explore and quantitatively map the cation-size mismatch solubility limits in high-entropy oxides (HEOs), we report on Ca^2+ substitution in prototypical MgCoNiCuZnO, because, while isovalent, Ca^2+ is 38