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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Saturday 10 January

Materials Science

Influence of CaO and SiO2 additives on the sintering behavior of Cr,Ca:YAG ceramics prepared by solid-state reaction sintering

.A. Chaika, G. Mancardi and O.M. Vovk

Optical ceramics of yttrium aluminum garnet (Y3-xCaxAl4.95Cr0.05O12) doped with 0.1 at.% of chromium ions and 0.5, 0.8, and 1.2 at.% of calcium ions were prepared by reactive sintering in vacuum at 1750 degrees C. The influence of SiO2 and CaO sintering aids on the optical properties and microstructure of Cr,Ca:YAG ceramics was investigated. A decrease in CaO concentration led to a reduction of Cr,Ca:YAG transparency from 81 to 0 percent at 1064 nm; moreover, ceramics with lower CaO content exhibited abnormal grains and high porosity. These features were attributed to interactions between silica and calcium oxide during vacuum sintering. Two mechanisms are proposed to explain the effect of CaO and SiO2 on the formation of Ca,Cr:YAG ceramics. The first involves the formation of a liquid phase due to the CaO-SiO2 interaction during the heating stage, resulting in abnormal grain growth. The second mechanism is the mutual consumption of Si4+ and Ca2+ ions during the isothermal stage of sintering, which leads to a decrease in Cr4+ concentration. Both mechanisms negatively affect the optical and laser properties of the ceramics.
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Materials Science

Synthesis of epitaxial TaO$_2$ thin films on Al$_2$O$_3$ by suboxide molecular-beam epitaxy and thermal laser epitaxy

Yorick A. Birkhölzer, Anna S. Park, Noah Schnitzer et al. (+28 more)

Tantalum dioxide (TaO2) is a metastable tantalum compound. Here, we report the epitaxial stabilization of TaO2 on Al2O3 (1-102) (r-plane sapphire) substrates using suboxide molecular-beam epitaxy (MBE) and thermal laser epitaxy (TLE), demonstrating single-oriented, monodomain growth of anisotropically strained thin films. Microstructural investigation is performed using synchrotron X-ray diffraction and scanning transmission electron microscopy. The tetravalent oxidation state of tantalum is confirmed using X-ray absorption and photoemission spectroscopy as well as electron energy-loss spectroscopy. Optical properties are investigated via spectroscopic ellipsometry and reveal a 0.3 eV Mott gap of the tantalum 5d electrons. Density-functional theory and group theoretical arguments are used to evaluate the limited stability of the rutile phase and reveal the potential to unlock a hidden metal-insulator transition concomitant with a structural phase transition to a distorted rutile phase, akin to NbO2. Our work expands the understanding of tantalum oxides and paves the way for their integration into next-generation electronic and photonic devices.
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All authors Yorick A. Birkhölzer, Anna S. Park, Noah Schnitzer, Jeffrey Z. Kaaret, Benjamin Z. Gregory, Tomas A. Kraay, Tobias Schwaigert, Matthew R. Barone, Brendan D. Faeth, Felix V.E. Hensling, Iris C.G. van den Bosch, Ellen M. Kiens, Christoph Baeumer, Enrico Bergamasco, Markus Grüninger, Alexander Bordovalos, Suresh Chaulagain, Nikolas J. Podraza, Waldemar Tokarz, Wojciech Tabis, Matthew J. Wahila, Suchismita Sarker, Christopher J. Pollock, Shun-Li Shang, Zi-Kui Liu, Nongnuch Artrith, Frank M.F. de Groot, Nicole A. Benedek, Andrej Singer, David A. Muller, Darrell G. Schlom

Materials Science

Higher order magnetoelasticity energy corrections in bcc and fcc systems

Jakub Šebesta, Ondřej Faiman and Dominik Legut

Magnetoelastic properties play a vital role in industrial applications. Despite being hidden behind either purely magnetic or elastic behavior, magnetoelasticity takes place in a wide range of devices as transducers, acoustic actuators, or fast response sensors. In this work, we inspect the impact of higher-order terms on the anisotropic magnetostriction behavior. Regarding ab-initio calculations, the anisotropic magnetostriction can be related to the strain dependence of the magnetocrystaline energy. Commonly, the description is restricted to a linear strain dependence in the magnetoelastic energy. Here, we derive higher-order terms in strain for bcc and fcc crystal structures. Using a simple parametrization, we show that the influence of the higher-order strain terms is negligible for the studied cubic systems.
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Materials Science

A phase field model of the effects of dislocation microstructure on grain boundary motion during recrystallization

Yufan Zhang and Michael Zaiser

The internal energy associated with the defect microstructure of strongly deformed crystals provides an important driving force for grain boundary motion during recrystallization. Typical dislocation microstructures are strongly heterogeneous and this heterogeneity affects the motion of recrystallization boundaries. In this study, a phase field model for microstructure evolution encompassing the evolution of both dislocation densities and grain order parameters is formulated. The model is employed to generate typical dislocation microstructures exhibiting multiscale features such as incidental and geometrically necessary dislocation walls. It is then used to study the motion of recrystallization boundaries in the associated complex defect energy 'landscape'. Results are compared to experimental observations.
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Materials Science

Detecting the Onset and Progression of Spinodal Decomposition using Transient Grating Spectroscopy

Maxwell Rae, Merrill Chiang, Mahmudul Islam et al. (+9 more)

Spinodal decomposition can degrade corrosion resistance and embrittle materials. The ability to quickly, conclusively, and non-destructively detect the onset of spinodal decomposition before catastrophic materials degradation would represent a significant advance in materials testing. We demonstrate that spinodal decomposition can be detected in binary Fe-Cr alloys via modulus stiffening using in situ and ex situ transient grating spectroscopy (TGS). The key mechanistic insight is the non-linearity in elastic moduli as function of Cr content renders a spinodally decomposed Fe-Cr alloy stiffer than an equivalent solid solution for a certain range of initial chromium compositions. We confirm the presence of spinodal decomposition in the 36 at.% chromium alloy using differential scanning calorimetry (DSC), linked to known spinodal decomposition energetics, and show via atomistic simulations that elastic modulus stiffening is expected after spinodal decomposition in the 36 at.% chromium alloy. The results of this study suggest the potential use of TGS as a practical tool for non-destructive evaluation of key materials susceptible to such degradation.
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All authors Maxwell Rae, Merrill Chiang, Mahmudul Islam, Angus P. C. Wylie, Avery Nguyen, Myles Stapelberg, Saleem A. Al Dajani, Kristýna Repček, Tomáš Grabec, Abby Kaplan, Rodrigo Freitas, Michael P. Short

Materials Science

Deterministic domain selection of antiferromagnets via magnetic fields

Sophie F. Weber and Veronika Sunko

Antiferromagnets (AFMs) hold promise for applications in digital logic. However, switching AFM domains is challenging, as magnetic fields do not couple to the bulk antiferromagnetic order parameter. Here we show that magnetic-field-driven switching of AFM domains can in many cases be enabled by a generic reduction of magnetic exchange at surfaces. We use statistical mechanics and Monte Carlo simulations to demonstrate that an inequivalence in magnetic exchange between top and bottom surface moments, combined with the enhanced magnetic susceptibility of surface spins, can enable deterministic selection of antiferromagnetic domains depending on the magnetic-field ramping direction. We further show that this mechanism provides a natural interpretation for experimental observations of hysteresis in magneto-optical response of the van der Waals AFM $\mathrm{MnBi_2Te_4}$. Our findings highlight the critical role of surface spins in responses of antiferromagnets to magnetic fields. Furthermore, our results suggest that antiferromagnetic domain selection via purely magnetic means may be a more common and experimentally accessible phenomenon than previously assumed.
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Materials Science

Influence of Surface Functionalization on the Colloidal Stability and Magnetic Properties of Ferrite Nanoparticles

Arif Iqbal Sheikh and Radha Srinivasan

Magnetite ferrite (Fe3O4) nanoparticles have attracted considerable interest due to their tunable physico-chemical properties and relevance in functional materials. In this work, uncoated Fe3O4 nanoparticles and surface-modified Fe3O4 nanoparticles coated with polyethylene glycol (PEG-6000) and citric acid (CA) were synthesized via a chemical co-precipitation method. The effect of surface functionalization on the structural, spectroscopic, magnetic, and colloidal properties of the nanoparticles was systematically investigated. X-ray diffraction analysis confirmed the formation of phase-pure Fe3O4 with an inverse spinel structure for all the samples. Fourier transform infrared and Raman spectroscopy verified successful surface modification while preserving the Fe-O framework of the magnetite core. Dynamic light scattering and zeta potential measurements indicated improved dispersion and colloidal stability for the surface-modified nanoparticles. Magnetization studies performed at room temperature revealed superparamagnetic behaviour for all samples, accompanied by a coating-dependent reduction in saturation magnetization. Overall, the results emphasize the critical role of surface chemistry in tailoring the physicochemical, magnetic, and colloidal behaviour of Fe3O4 nanoparticles. Keywords: Fe3O4 nanoparticles, PEG, Citric acid, Co-precipitation, Surface functionalization, Zeta potential, Colloidal stability, Magnetic properties
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Materials Science

A Rechargeable Chromium Battery

Apurva Anjan, Adwitiya Rao, Rohit M. Manoj et al. (+6 more)

Multivalent ions exchange multiple electrons during redox reactions, leading to the possibility of improved energy storage performance. A variety of multivalent ions, including zinc (Zn$^{2+}$), magnesium (Mg$^{2+}$), calcium (Ca$^{2+}$), aluminum (Al$^{3+}$), and indium (In$^{3+}$), have been deployed in rechargeable batteries with varying degrees of success \cite{1-9}. While chromium (Cr$^{3+}$) offers a superior volumetric capacity (approximately $11117\ \mathrm{mAh\ cm^{-3}}$) compared to the aforementioned cations, there is no report of a rechargeable chromium battery. This is because chromium metal spontaneously oxidizes to form a passivating oxide layer \cite{10} that blocks Cr$^{3+}$ ingress and egress. Here, we show that this fundamental limitation can be overcome by developing a chromium-rich high-entropy alloy. The alloy consists of five elements (Cr, bismuth (Bi), copper (Cu), tin (Sn), and nickel (Ni)), producing a multi-element native oxide rich in heterointerfaces. Some of these interfaces (such as Cr$_2$O$_3$/Bi$_2$O$_3$) exhibit a very low barrier for Cr$^{3+}$ diffusion, offering multiple pathways for efficient Cr$^{3+}$ insertion and extraction, while others (such as Cr$_2$O$_3$/CuO) block oxygen transport, thereby suppressing further oxidation. In a symmetric cell configuration, the chromium alloy supports approximately $10000$ hours (about $5000$ cycles) of reversible chromium insertion and extraction at an overpotential of only $20$ mV. The chromium-rich alloy anode was also successfully paired with a sulfur cathode to cycle reversibly in a full-cell configuration. These findings could stimulate fundamental studies on chromium-ion batteries and high-entropy alloy electrodes, opening new pathways for multivalent energy storage.
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All authors Apurva Anjan, Adwitiya Rao, Rohit M. Manoj, Vrindha Pongalat, Varad Mahajani, Sohail Shah, Mukesh Bacchav, Chandra Veer Singh, Nikhil Koratkar

Materials Science

Beyond Predicted ZT: Machine Learning Strategies for the Experimental Discovery of Thermoelectric Materials

Shoeb Athar and Philippe Jund

The discovery of high-performance thermoelectric (TE) materials for advancing green energy harvesting from waste heat is an urgent need in the context of looming energy crisis and climate change. The rapid advancement of machine learning (ML) has accelerated the design of thermoelectric (TE) materials, yet a persistent "gap" remains between high-accuracy computational predictions and their successful experimental validation. While ML models frequently report impressive test scores (R^2 values of 0.90-0.98) for complex TE properties (zT, power factor, and electrical/thermal conductivity), only a handful of these predictions have culminated in the experimental discovery of new high-zT materials. In this review, we identify and discuss that the primary obstacles are poor model generalizability-stemming from the "small-data" problem, sampling biases in cross-validation, and inadequate structural representation-alongside the critical challenge of thermodynamic phase stability. Moreover, we argue that standard randomized validation often overestimates model performance by ignoring "hidden hierarchies" and clustering within chemical families. Finally, to bridge this gap between ML-predictions and experimental realization, we advocate for advanced validation strategies like PCA-based sampling and a synergetic active learning loop that integrates ML "fast filters" for stability (e.g., GNoME) with high-throughput combinatorial thin-film synthesis to rapidly map stable, high-zT compositional spaces.
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Materials Science

On unconstrained solidification of spherical metallic drops

Priti Ranjan Panda, Harish Singh Dhami and Koushik Viswanathan

The solidification of metallic droplets into powder particles involves a complex interplay between heat diffusion, surface tension, and geometric constraints. In confined, curved systems – such as those encountered in atomisation, abrasion, and micrometeorite formation – positive curvature and finite boundaries significantly modify classical solidification dynamics. In this study, we systematically investigate the solidification of metallic spheres, focusing on how curvature and confinement influence nucleation pathways, growth kinetics, and interfacial stability. Two competing growth modes – radial outward and circumferential – are analysed using Stefan-type models under a quasi-steady approximation. A generalisation of Mullins–Sekerka stability theory is developed to account for finite spherical domains, revealing that particle size and curvature introduce new destabilising parameters that govern microstructural length scales. Experimental observations of dendritic and cellular morphologies are interpreted through this framework, demonstrating that the interaction between growth fronts, undercooling, and curvature collectively determines the final particle structure. These findings underscore the need to re-evaluate classical solidification theories in the context of curved geometries, with implications for both engineered and naturally occurring metal powders.
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Materials Science

Effect of substrate mismatch, orientation, and flexibility on heterogeneous ice nucleation

Miguel Camarillo, Javier Oller-Iscar, María M. Conde et al. (+2 more)

Heterogeneous nucleation is the main path to ice formation on Earth. The ice nucleating ability of a certain substrate is mainly determined by both molecular interactions and the structural mismatch between the ice and the substrate lattices. We focus on the latter factor using molecular simulations of the mW model. Quantifying the effect of structural mismatch alone is challenging due to its coupling with molecular interactions. To disentangle both factors, we use a substrate composed of water molecules in such a way that any variation on the nucleation temperature can be exclusively ascribed to the structural mismatch. We find that a one per cent increase of structural mismatch leads to a decrease of approximately 4 K in the nucleation temperature. We also analyse the effect of the orientation of the substrate with respect to the liquid. The three main ice orientations (basal, primary prism and secondary prism) have a similar ice nucleating ability. We finally asses the effect of lattice flexibility by comparing substrates where molecules are immobile with others where a certain freedom to fluctuate around the lattice positions is allowed. Interestingly, we find that the latter type of substrate is more efficient in nucleating ice because it can adapt its structure to that of ice.
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All authors Miguel Camarillo, Javier Oller-Iscar, María M. Conde, Jorge Ramírez, Eduardo Sanz

Materials Science

ZnO/ZnS heterostructures as hole reservoir to boost Ni foam energy storage performance

Alessia Fischetti, Giacometta Mineo, Daniela Russo et al. (+8 more)

Low-cost and environmentally friendly electrochemical energy storage systems are crucial to address the increasing global energy demand. Nanomaterials can play a pivotal role in catalysing charge storage and/or exchange, still the underlying mechanism often remains poorly investigated, as for ZnO/ZnS nanostructures onto Ni foam. In this work, we investigate hydrothermally grown ZnO/ZnS nanostructures decorating Ni foam for energy storage application. Morphology, structure and composition are evaluated via electron microscopy-based methodologies. The electrochemical energy storage performance is evaluated by cyclic voltammetry (CV) measurements with the aim to highlight the energy storage mechanism. When nickel foam (NF) is used as substrate, the system shows a predominant pseudocapacitive behaviour. By contrast, a modest and capacitive performance is measured on graphene paper (GP). Mott-Schottky (M-S) and open circuit potential (OCP) measurements suggests a key role of hole reservoir in ZnS decoration which boosts NF performances.
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All authors Alessia Fischetti, Giacometta Mineo, Daniela Russo, Francesco Salutari, Claudio Lentini Campallegio, Elena Bruno, Jordi Arbiol, Giorgia Franzò, Salvatore Mirabella, Vincenzina Strano, M. Chiara Spadaro

Materials Science · Cross-listed from cond-mat.supr-con

Superconductivity in epitaxial PtSb(0001) thin films

C. Müller, S. P. Bommanaboyena, A. Badura et al. (+12 more)

We report superconductivity in epitaxial PtSb(0001) thin films grown on SrF2(111). Electrical transport measurements reveal a superconducting transition at $T_{\mathrm c}=1.72$ K. The field-induced broadening of the transition and the presence of finite upper critical fields are consistent with type-II superconductivity. We determine the resistively defined upper critical fields for magnetic fields applied perpendicular and parallel to the film plane and parameterize their temperature dependence using an anisotropic Ginzburg-Landau approach. For the thickest film ($d=50$ nm), this yields coherence lengths of $\xi_{ab}\approx 55$ nm and $\xi_c\approx 14$ nm. Current-voltage characteristics show sizeable critical currents, with a critical current density reaching $J_{\mathrm c}\approx 6e4$ A/cm$^2$ at 0.5 K. These results establish epitaxial PtSb as a superconducting thin-film platform compatible with lattice-matched heterostructures in the NiAs-type materials family.
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All authors C. Müller, S. P. Bommanaboyena, A. Badura, T. Uchimura, F. Husstedt, B. V. Schwarze, S. Banerjee, M. Ledinský, J. Michalicka, M. Míšek, M. Šindler, T. Helm, S. Fukami, F. Krizek, D. Kriegner

Materials Science · Cross-listed from cs.LG

Physics-Informed Tree Search for High-Dimensional Computational Design

Suvo Banik, Troy D. Loeffler, Henry Chan et al. (+4 more)

High-dimensional design spaces underpin a wide range of physics-based modeling and computational design tasks in science and engineering. These problems are commonly formulated as constrained black-box searches over rugged objective landscapes, where function evaluations are expensive, and gradients are unavailable or unreliable. Conventional global search engines and optimizers struggle in such settings due to the exponential scaling of design spaces, the presence of multiple local basins, and the absence of physical guidance in sampling. We present a physics-informed Monte Carlo Tree Search (MCTS) framework that extends policy-driven tree-based reinforcement concepts to continuous, high-dimensional scientific optimization. Our method integrates population-level decision trees with surrogate-guided directional sampling, reward shaping, and hierarchical switching between global exploration and local exploitation. These ingredients allow efficient traversal of non-convex, multimodal landscapes where physically meaningful optima are sparse. We benchmark our approach against standard global optimization baselines on a suite of canonical test functions, demonstrating superior or comparable performance in terms of convergence, robustness, and generalization. Beyond synthetic tests, we demonstrate physics-consistent applicability to (i) crystal structure optimization from clusters to bulk, (ii) fitting of classical interatomic potentials, and (iii) constrained engineering design problems. Across all cases, the method converges with high fidelity and evaluation efficiency while preserving physical constraints. Overall, our work establishes physics-informed tree search as a scalable and interpretable paradigm for computational design and high-dimensional scientific optimization, bridging discrete decision-making frameworks with continuous search in scientific design workflows.
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All authors Suvo Banik, Troy D. Loeffler, Henry Chan, Sukriti Manna, Orcun Yildiz, Tom Peterka, Subramanian Sankaranarayanan

Materials Science

Weakly spin-dependent band structures of antiferromagnetic perovskite LaMO$_3$ (M = Cr, Mn, Fe)

Takuya Okugawa, Kaoru Ohno, Yusuke Noda et al. (+1 more)

We investigate spin-dependent electronic states of antiferromagnetic (AFM) lanthanum chromite (LaCrO$_3$), lanthanum manganite (LaMnO$_3$), and lanthanum ferrite (LaFeO$_3$) using spin-polarized first-principles density functional theory (DFT) with Hubbard U correction. The band structures are calculated for 15 types of their different AFM structures. It is verified for these structures that there is a very simple rule to identify which wave number k exhibits spin splitting or degeneracy in the band structure. This rule uses the symmetry operations that map the up-spin atoms onto the down-spin atoms. The resulting spin splitting is very small for the most stable spin configuration of the most stable experimental structure. We discuss a plausible benefit of this characteristic, i.e., the direction-independence of the spin current, in electrode applications.
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All authors Takuya Okugawa, Kaoru Ohno, Yusuke Noda, Shinichiro Nakamura

Materials Science

Reaction-Diffusion Driven Patterns in Immiscible Alloy Thin Films

Vivek C. Peddiraju, Shourya Dutta-Gupta and Subhradeep Chatterjee

Controlling the microstructure of thin films is of critical importance for various applications. We demonstrate a methodology for tuning the local microstructure through film-substrate interactions using Ag-Cu as a model system. Metastable single-phase Ag-Cu thin films are deposited on Si substrates pre-patterned by FIB milling. During post-deposition annealing, localized film-substrate reaction around the milled patterns produces a distinct microstructure termed as the 'halo'. It consists of copper silicide and almost pure Ag, while the far-field film forms a random mixture of Cu and Ag-rich domains through phase separation. We show that the extent of the halo can be controlled by varying the temperature and duration of annealing. We present a semi-analytical kinetic model of product and halo growth that incorporates species balance, diffusional transport and a modified Stefan condition. Predictions from the model reveal two distinct growth regimes of the product with power law indices of 1/2 and 2/7 and experimental data fall into the latter regime. These regimes originate from the dimensionality of growth (2d or 3d) compared to that of solute transport (2d), which in turn depend on film thickness and species diffusivity. Using an inverse optimization procedure, we also estimate the diffusivity, which suggests grain boundary diffusion to be the dominant transport mechanism. This study provides an avenue and framework for microstructural engineering of alloy thin films through interfacial reaction.
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Materials Science

Mechanisms of alkali ionic transport in amorphous oxyhalides solid state conductors

Luca Binci, KyuJung Jun, Bowen Deng et al. (+1 more)

Amorphous oxyhalides have attracted significant attention due to their relatively high ionic conductivity ($>$1 mS cm$^{-1}$), excellent chemical stability, mechanical softness, and facile synthesis routes via standard solid-state reactions. These materials exhibit an ionic conductivity that is almost independent of the underlying chemistry, in stark contrast to what occurs in crystalline conductors. In this work, we employ an accurately fine-tuned machine learning interatomic potential to construct large-scale molecular dynamics trajectories encompassing hundreds of nanoseconds to obtain statistically converged transport properties. We find that the amorphous state consists of chain fragments of metal-anion tetrahedra of various lenght. By analyzing the residence time of alkali cations migrating around tetrahedrally-coordinated trivalent metal ions, we find that oxygen anions on the metal-anion tetrahedra limit alkali diffusion. By computing the full Einstein expression of the ionic conductivity, we demonstrate that the alkali transference number of these materials is strongly influenced by distinct-particles correlations, while at the same time they are characterized by an alkali Haven ratio close to one, implying that ionic transport is largely dictated by uncorrelated self-diffusion. Finally, by extending this analysis to chemical compositions $AMX_{2.5}\textsf{O}_{0.75}$, spanning different alkaline ($A$ = Li, Na, K), metallic ($M$ = Al, Ga, In), and halogen ($X$ = Cl, Br, I) species, we clarify why the diffusion properties of these materials remain largely insensitive to variations in atomic chemistry.
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All authors Luca Binci, KyuJung Jun, Bowen Deng, Gerbrand Ceder

Materials Science

Dynamic nanoscale spatial heterogeneity in a perovskite to brownmillerite topotactic phase transformation

Nicolò D'Anna, Erik S. Lamb, Robin Glefke et al. (+5 more)

Phase transitions are omnipresent in modern condensed matter physics and its applications. In solids, first-order phase transformations typically occur by nucleation and growth under non-equilibrium conditions. Under constant external conditions, $\textit{e.g.}$, constant annealing temperature and pressure, the nucleation and growth dynamics are often thought of as spatially and temporally independent. Here, $\textit{in-situ}$ Bragg X-ray photon correlation spectroscopy (XPCS) reveals nanoscale spatial and dynamical heterogeneity in the perovskite-to-brownmillerite topotactic phase transformation in La$_{0.7}$Sr$_{0.3}$CoO$_3$ thin films annealed under constant reducing conditions over a time span of multiple hours. Specifically, a timescale associated with domain growth remains stable, with a corresponding domain wall speed of $v_d = 6 \pm 0.5 \times10^{-4}$~nm/s ($2 \pm 0.2$~nm/h), while a slower timescale, associated with temperature-driven de-pinning of domains, leads to accelerating dynamics with timescales following an aging power law with exponent -2.2$\pm$0.5. This experiment demonstrates that Bragg XPCS is a powerful tool to study nanoscale dynamics in structural phase transformations, with the ability to extract quantitative average values related to nano-domain motion $\textit{in-situ}$. The results are relevant for phase engineering of phase-change devices, as they show that nanoscale dynamics, linked to domain and domain-wall motion, can continuously evolve and speed up with time, even hours after the initiation of the phase transformation, with potential repercussions on electrical performance.
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All authors Nicolò D'Anna, Erik S. Lamb, Robin Glefke, Daseul Ham, Ishmam Nihal, Su Yong Lee, Yayoi Takamura, Oleg Shpyrko

Friday 9 January

Materials Science

Sizes of Ferroelectricity Appearance and Disappearence in Nanosized Hafnia-Zirconia:Landau-type Theory

Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin et al. (+1 more)

Nanosized hafnia-zirconia HfxZr1-xO2 in the form of thin films, multilayers and heterostructures are indispensable silicon-compatible ferroelectric materials for advanced electronic memories and logic devices. The distinctive feature of nanoscale hafnia-zirconia are the critical sizes of ferroelectricity appearance, whereas the critical sizes of ferroelectricity disappearance exist in other ferroelectrics. Using the Landau-Ginzburg-Devonshire free energy functional with higher powers, trilinear and biquadratic couplings of polar, nonpolar and antipolar order parameters, we calculated analytically the strain-dependent critical sizes of the ferroelectricity appearance and disappearance, analyzed how the size effect and mismatch strains influence the phase diagrams and polarization switching barrier in epitaxial HfO2 thin films and nano-islands with the out-of-plane spontaneous polarization. We have shown that the critical thickness/height of out-of-plane spontaneous polarization disappearance is determined by the size dependence of the depolarization field and correlation effects. The critical thickness/height of the ferroelectricity appearance is determined by the size dependence of the effective mismatch strain considering possible appearance of misfit dislocations and lateral relaxion of strains. Derived analytical expressions can be generalized for HfxZr1-xO2 solid solutions, providing that corresponding parameters of the free energy are known from the first principles calculations.
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All authors Anna N. Morozovska, Eugene A. Eliseev, Sergei V. Kalinin, Maksym V. Strikha

Materials Science

An assessment of mechanism-based plasticity models for polycrystalline magnesium alloys

R. Vigneshwaran, Showren Datta, A. A. Benzerga et al. (+1 more)

The objective of this work is to assess computationally efficient coarse-grained plasticity models against high-fidelity crystal plasticity simulations for magnesium polycrystals over a wide range of textures and grain sizes. A basic requirement is that such models are able to capture evolving plastic anisotropy and tension-compression asymmetry. To this end, two-surface and three-surface plasticity models are considered. The two-surface constitutive formulation separately accounts for slip and twinning, while the three-surface model further apportions the contributions of basal and nonbasal slip. Model identification is based on stress-strain responses for loading along six orientations under both tension and compression. The evolution of overall plastic anisotropy, as well as microscale relative activities of slip and twin systems, is analyzed in detail. The prospects of using coarse-grained plasticity models in guiding the development of physically sound damage models for magnesium alloys are discussed.
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All authors R. Vigneshwaran, Showren Datta, A. A. Benzerga, Shailendra P. Joshi

Materials Science · Cross-listed from cond-mat.mes-hall

Evolution of the Berry curvature dipole in uniaxially strained bilayer graphene

Karel Cuypers, Robin Smeyers, Bert Jorissen et al. (+1 more)

While in pristine bilayer graphene the Berry curvature dipole (BCD), a necessary ingredient for the nonlinear anomalous Hall effect, is zero, uniaxial strain can give rise to finite BCD. We investigate this by using a tight-binding (TB) approach build on the Slater-Koster parameterization to capture lattice deformation effects often missed by continuum models. We demonstrate that the BCD's evolution with strain and doping is highly sensitive to the choice in parameterization, particularly when including the longer range interlayer skew hoppings. Additionally, out-of-plane compression enhances the response by broadening the Dirac cones. These findings benchmark low-energy continuum models and highlight the necessity of realistic tight-binding models for accurately predicting strain-engineered Hall effects in bilayer graphene.
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All authors Karel Cuypers, Robin Smeyers, Bert Jorissen, Lucian Covaci

Materials Science

Thermally Configurable Multi-Order Polar Skyrmions in Multiferroic Oxide Superlattices

Kefan Liu, Yuhui Huang, Xiangwei Guo et al. (+3 more)

Polar topological textures in low-dimensional ferroelectrics have emerged as a versatile platform for high-density information storage and neuromorphic computing. While low-order topological states, such as vortices and skyrmions, have been extensively studied, high-order polar topological families remain largely unexplored due to their higher energy requirements and limited stabilization methods. Here, using a BiFeO3 (BFO)-based multiferroic superlattice as a model system, we demonstrate a thermal-modulation strategy that stabilizes multi-order polar skyrmions and enables reversible tuning of their topological order through phase-field simulations. It was found that temperature modulation drives the system from polar solitons through 1{\pi}-, 2{\pi}-, 3{\pi}-, and 4{\pi}-skyrmion states, with closed heating-cooling path analyses revealing the widest thermal stability window for 2{\pi}-skyrmions (up to 600 K). Leveraging this robustness, 2% Sm doping in BFO lowers the transition temperatures, enabling room-temperature stabilization of 2{\pi}-skyrmions. These findings enrich the fundamental understanding of multi-order polar topologies and establish a tunable strategy for realizing variable-order topological configurations in practical memory devices.
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All authors Kefan Liu, Yuhui Huang, Xiangwei Guo, Yongjun Wu, Juan Li, Zijian Hong

Materials Science

A Critical Examination of Active Learning Workflows in Materials Science

Akhil S. Nair and Lucas Foppa

Active learning (AL) plays a critical role in materials science, enabling applications such as the construction of machine-learning interatomic potentials for atomistic simulations and the operation of self-driving laboratories. Despite its widespread use, the reliability and effectiveness of AL workflows depend on implicit design assumptions that are rarely examined systematically. Here, we critically assess AL workflows deployed in materials science and investigate how key design choices, such as surrogate models, sampling strategies, uncertainty quantification and evaluation metrics, relate to their performance. By identifying common pitfalls and discussing practical mitigation strategies, we provide guidance to practitioners for the efficient design, assessment, and interpretation of AL workflows in materials science.
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Materials Science · Cross-listed from physics.atom-ph

Electron Energy Loss Spectroscopy of oriented targets and magnetic transitions

Ioannis Iatrakis and Valerii Brudanin

Electron beam energies in Transmission Electron Microscopes (TEMs) reach the relativistic realm constituting Quantum Electrodynamics (QED) the appropriate framework for the study of electron matter interaction in TEMs. We focus on the inelastic scattering of relativistic electrons from a generic oriented target. The inelastic differential cross section factorizes to the fast electron part which is calculated analytically, and the dynamic form factor of the target, which encodes the response of the medium to the interaction with the beam. The properties of the dynamic form factor of oriented targets are analyzed. We then derive the scattering cross section of electrons by magnetic targets where spin-flip transitions are induced. We comment on the kinematic regimes where the coefficient of the transverse magnetic interaction is amplified compared to the coulomb matrix element.
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Materials Science

First-principles study of hydrogen diffusion in polycrystalline Nickel

Bhanuj Jain, Alaa Olleak, Junyan He et al. (+2 more)

Hydrogen embrittlement in metals is strongly governed by hydrogen diffusion and trapping, yet predicting these effects in polycrystalline systems remains challenging. This work introduces a multiscale modeling framework that links atomistic energetics to continuum-scale transport. Migration barriers for bulk and grain-boundary environments, obtained from first-principles calculations, are used in kinetic Monte Carlo simulations to compute anisotropic effective diffusivities. These diffusivities are then incorporated into finite element models of polycrystalline microstructures, explicitly accounting for grain-boundary character and connectivity. The approach captures both fast-path and trapping effects without relying on empirical parameters and reproduces experimental trends for nickel, including the dependence of effective diffusivity on grain size and boundary type. This methodology provides a physically grounded route for predicting hydrogen transport in engineering alloys and can be extended to other materials and defect types.
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All authors Bhanuj Jain, Alaa Olleak, Junyan He, Adarsh Chaurasia, Davide Di Stefano

Materials Science

On the Feasibility of Extreme Heating Rates in SEM using MEMS Heater Platforms

C. Koenig, P. Mayr, J.R. Jinschek et al. (+1 more)

Understanding microstructural evolution under extreme thermal conditions is essential for advancing metal additive manufacturing (AM). This work demonstrates the feasibility of employing micro-electro-mechanical system (MEMS) heating platforms for in-situ scanning electron microscopy (SEM) characterization of bulk-like samples during rapid thermal cycling. Using electron backscatter diffraction (EBSD), we tracked the ferrite-to-austenite phase transformation in a pure iron specimen and confirmed that the sample surface temperature closely follows the MEMS temperature setpoint within device accuracy. Under vacuum conditions, stable heating and cooling rates of up to 1000 C/s were achieved with minimal power input and without compromising EBSD pattern quality. These findings establish MEMS-based heating as a robust approach for in-situ microstructural characterization of AM-relevant thermal processes in the SEM, enabling quantitative studies of thermally activated phenomena such as diffusion, phase transformations, and microstructural evolution under far-from-equilibrium conditions.
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All authors C. Koenig, P. Mayr, J.R. Jinschek, A. Bastos Fanta

Materials Science · Cross-listed from cond-mat.str-el

Cooperative concurrence of 4f and 3d flat bands in kagome heavy-fermion metal YbCr6Ge6

Wenxin Lv, Pengcheng Ma, Tianqi Wang et al. (+6 more)

Flat-band (FB) systems originating from special lattice geometry like in kagome metals as well as localized orbitals in the materials such as heavy-fermion (HF) compounds have induced intensive interest due to their band topology and strong electron correlation effects, leading to emergent quantum states of matter. However, the question of how these two distinct FBs coexist and interact remains unsettled. Here, we report that YbCr6Ge6 hosting both Cr-kagome lattice and Yb-4f electrons exhibits HF behaviors and a robust antiferromagnetic ground state with transition temperature TN = 3 K, significantly higher than other similar kagome metals with Yb ions. Angle-resolved photoemission spectroscopy measurements reveal the coexistence of FBs originating from both Cr-kagome lattice and localized Yb-4f electrons near Fermi energy level EF. More importantly, the clear spectroscopic signatures of a hybridization of Yb-4f FB with kagome-lattice-derived conduction bands and the high density of states of Cr-kagome FB near EF provide the underlying microscopic mechanisms of HF behaviors and enhanced antiferromagnetism in YbCr6Ge6. Our findings demonstrate that the novel kagome HF metals can not only host the cooperative coexistence of two different types of FBs, but also provide a paradigm material platform to explore the exotic correlated topological quantum phenomena.
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All authors Wenxin Lv, Pengcheng Ma, Tianqi Wang, Shangjie Tian, Ying Ma, Shouguo Wang, Xiao Zhang, Zhonghao Liu, Hechang Lei

Materials Science · Cross-listed from cond-mat.soft

Early bloodmaterial interfacial events and capillary transport on nanoparticle modified nanofibers

Romain Scarabelli, Mehdi Abbasi, Magali Gary-Bobo et al. (+3 more)

Electrospun poly(\epsilon-caprolactone) (PCL)nanofibrous mats are widely considered for blood-contacting wound dressings and small-diameter vascular applications; however, their intrinsic hydrophobicity limits rapid wetting and controlled interaction with blood. In this work, we modulate the interfacial response of PCL nanofibers by incorporating oxide-shelled silicon nanoparticles (SiNPs) synthesized by pulsed laser ablation in liquid, a ligand-free approach that avoids organic stabilizers and preserves surface reactivity. Two composite architectures were designed: SiNPs embedded within the fiber bulk (PAC1,4,16) and SiNPs preferentially exposed at the fiber surface (SPAC1,4,16), with systematically increasing nanoparticle loadings. Structural characterization confirmed the retention of a homogeneous fibrous morphology and the targeted nanoparticle distribution. The dynamic interaction with whole blood was quantified using time-resolved contact-angle measurements, complemented by top-view optical microscopy and three-dimensional profilometry of dried droplets. Pristine PCL remained strongly hydrophobic whereas a hydrophilic PCL functionalized with APTES showed rapid spreading. Incorporation of SiNPs within the fiber volume led to only a moderate enhancement of wettability, and dried droplets retained compact morphologies with limited spreading. In contrast, surface-decorated mats displayed a sharp, concentration-dependent transition toward highly wettable behavior: for SPAC16, the contact angle fell below 20, droplet profiles became markedly flattened, and microscopy revealed extended plasma-rich regions surrounding a red-cell-rich core, indicative of pronounced phase separation within the nanofibrous network.
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All authors Romain Scarabelli, Mehdi Abbasi, Magali Gary-Bobo, Christophe Drouet, Marc Leonetti, Ahmed Al-Kattan

Materials Science

Noncollinear spin structure in Dy-doped classical ferrimagnet

Anupam K. Singh, Katayoon Mohseni, Verena Ney et al. (+13 more)

Noncollinear spin structures have attracted tremendous attention because they offer a versatile platform for spin control and manipulation, essential in spintronics. Realizing noncollinearity in ferrimagnetic insulators is of particular interest as they can be potentially utilized in low-damping spintronics with tunable magnetic order. Within the spinel-ferrite family, Zn and Al-substituted nickel ferrite (NiZAF) has emerged as an excellent choice for low-damping spintronics. However, realizing noncollinearity in such systems remains challenging. Here, we present evidence of noncollinear spin structure in the NiZAF thin films induced by the rare earth Dy-doping, utilizing the soft x-ray spectroscopy methods such as magnetic circular dichroism and x-ray resonant magnetic reflectivity (XRMR). In particular, XRMR reveals a spiral-type spin structure, which is attributed to the Dzyaloshinskii-Moriya interaction, arising due to broken inversion symmetry by the Dy-induced local strain field as confirmed by our theoretical calculations. The realization of noncollinearity in the spinel-ferrite opens pathway to explore the possibility of chiral magnetic domains and topological spin textures exhibiting promise for oxide-based spintronics
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All authors Anupam K. Singh, Katayoon Mohseni, Verena Ney, Andreas Ney, Yicheng Guan, Ilya Kostanovski, Malleshwararao Tangi, Mostafa I. S. Marzouk, Manuel Valvidares, Pierluigi Gargiani, Jean-Marc Tonnerre, P. F. Perndorfer, P. A. Buczek, Arthur Ernst, Holger L. Meyerheim, Stuart S. P. Parkin

Materials Science

Heterogeneous ice nucleation on model substrates

Miguel Camarillo, Javier Oller-Iscar, María M. Conde et al. (+2 more)

Ice nucleation is greatly important in areas as diverse as climate change, cryobiology, geology or food industry. Predicting the ability of a substrate to induce the nucleation of ice from supercooled water is a difficult problem. Here, we use molecular simulations to analyse how the ice nucleating ability is affected by the substrate lattice structure and orientation. We focus on different model lattices: simple cubic, body centred cubic and face centred cubic, and assess their ability to induce ice nucleation by calculating nucleation rates. Several orientations are studied for the case of the face centred cubic lattice. Curiously, a hexagonal symmetry does not guarantee a better ice nucleating ability. By comparing the body centred cubic and the cubic lattices we determined that there is a significant role of the underlying crystal plane(s) on ice nucleation. The structure of the liquid layer adjacent to the substrate reveals that more efficient nucleants induce a more structured liquid. The most efficient substrates present a strong sensitivity of their ice nucleating ability to the lattice parameters. Introducing a novel methodological approach, we use Classical Nucleation Theory to estimate the contact angle of the ice nucleus on the studied substrates from the calculated nucleation rates. The method also provides the nucleation free energy barrier height, the kinetic pre-factor and the critical cluster size. The latter is in agreement with the nucleus size obtained through a microscopic analysis of the nucleation trajectories, which supports the validity of Classical Nucleation Theory down to small critical clusters.
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All authors Miguel Camarillo, Javier Oller-Iscar, María M. Conde, Jorge Ramírez, Eduardo Sanz