Honeycomb-layered oxides have attracted recent attention because of their rich crystal chemistry. However, the atomistic mechanisms of cationic transport in these structures remain vastly unexplored. Herein, we perform an extensive, systematic molecular dynamics study on ${\mathrm{Na}}_2{\mathrm{LiFeTeO}}_6$ using combined force-field and first-principles-based molecular dynamics simulations. We use a refined set of interatomic potential parameters of a previously reported potential model that represents various structural and transport properties of this recently reported promising material for all-solid-state battery applications. The present simulation study elucidates the roles of octahedral ordering and entropic contributions in ${\mathrm{Na}}^{+}$ ion distribution in the $ab$ plane. Our theoretical simulation also develops a ringlike atomistic diffusion mechanism and relevant atomistic energy barriers that help to understand the origin of fast ion conduction in honeycomb-layered oxides.

We present a thermodynamically self-consistent method to introduce dilation/density variation in continuum-scale phase-change models. Dilation incurs a pressure response via a hyperelastic contribution to the free energy that generalizes the lattice constraint. The dilation is represented entirely by species concentrations and permits composition, temperature, and phase-dependent specific volumes in a robust form. The impact of this approach is compared with the common assumption of the lattice constraint through demonstrative Stefan and phase-field models applied to the equilibrium of a Ni-Cu nanoparticle in equilibrium with its melt. Furthermore, the effect of phase and composition-dependent specific volume is explored in free dendritic growth behavior.

The development of quantitative models for understanding physical properties of alloys requires a proper treatment of magnetic interactions, which is of paramount importance for the microstructural stability, especially in steels and high-entropy alloys containing magnetic elements. These magnetic interactions also control the defects behavior which affects the mechanical properties and the response under irradiation. Current interatomic potentials for molecular dynamics (MD) simulations still lack an adequate formulation to include magnetism into the simulations. In this paper, the universal equation of states (UES) is revisited and generalized by including ferromagnetic (FM) and antiferromagnetic (AFM) configurations with the aim of proposing a new formulation to develop interatomic potentials with magnetic contribution. For the case of Fe, given a fixed magnetic configuration and magnitude of the magnetic moment, the energy of the system is calculated by means of three parameters, namely, the energy, volume, and corresponding scaling volume (directly related to the bulk modulus) at the local ground state of the corresponding lattice. These parameters depend on three terms: firstly, a distance-dependent function, which gathers the nonmagnetic influence of the surrounding atoms; secondly, a magnetically dependent function, contributing to the energy by means of the magnetic nature of the atom, irrespective of the magnetic moment magnitudes of its surrounding atoms; and finally, a term which is magnetically and distance dependent simultaneously, which describes the influence of the magnetic state of the surrounding atoms on the energy considering their interatomic distance. This latter term is built via two functions which cannot be disconnected: one dependent on the distance between two atoms (a decreasing function with the distance in absolute value) multiplied by another function which is dependent on the magnetic moment of these two atoms. In this way, the magnetic influence of a distant atom scales with its distance. The new formulation is tested for magnetic iron, where 18 240 spin polarized density functional theory (DFT) calculated energies for different lattices, volumes, and magnetic moments in FM and AFM configurations showed that the generalized UES (GUES) accurately describes the energy of the system. The root-mean-square error of the GUES is in the range of $5.9\times {10}^{-3}\mathrm{eV}$ over all DFT calculated energies, showing good accuracy and allowing us to propose a formulation for developing a magnetic interatomic potential (MIP) in Fe. The potential is developed for FM configuration in iron, aiming at studying the stability of the ferritic and austenitic phases but also defects and other configurations of special relevance as, for instance, in irradiation conditions for fusion or fission applications. The distance and magnetic functions of the GUES are tabulated to obtain a MIP, which describes the DFT calculated energies for different lattices, volumes, and magnetic moments in FM configuration. Further, the MIP has been validated in other crystal lattices (A15 and C15), elastic constants, stresses in the lattice, vacancies, interstitials, forces at different temperatures, transformation paths between body-centered cubic, face-centered cubic, hexagonal close-packed, and simple cubic structures as well as $\gamma$ surfaces. We conclude that the results in this paper pave the way to develop MIPs with accuracy and predictability beyond the state of the art in MD.

Recent classification efforts encompassing crystalline symmetries have revealed rich possibilities for solid-state systems to support a tapestry of exotic topological states. However, finding materials that realize such states remains a daunting challenge. Here, we show how the interplay of topology, symmetry, and magnetism combined with doping and external electric and magnetic field controls can be used to drive the ${\mathrm{SrIn}}_2{\mathrm{As}}_2$ materials family into a variety of topological phases. Our first-principles calculations and symmetry analysis reveal that ${\mathrm{SrIn}}_2{\mathrm{As}}_2$ is a dual topological insulator with $Z_2=(1;000)$ and mirror Chern number $C_M=-1$. Its isostructural and isovalent antiferromagnetic cousin ${\mathrm{EuIn}}_2{\mathrm{As}}_2$ is found to be an axion insulator with $Z_4=2$. The broken time-reversal symmetry via Eu doping in ${\mathrm{Sr}}_{1-x}{\mathrm{Eu}}_x{\mathrm{In}}_2{\mathrm{As}}_2$ results in a higher-order or topological crystalline insulator state depending on the orientation of the magnetic easy axis. We also find that antiferromagnetic ${\mathrm{EuIn}}_2{\mathrm{P}}_2$ is a trivial insulator with $Z_4=0$, and that it undergoes a magnetic-field-driven transition to an ideal Weyl fermion or nodal fermion state with $Z_4=1$ with applied magnetic field. Our study identifies ${\mathrm{Sr}}_{1-x}{\mathrm{Eu}}_x{\mathrm{In}}_2{(\text{As},\mathrm{P})}_2$ as a tunable materials platform for investigating the physics and applications of Weyl and nodal fermions in the scaffolding of crystalline and axion insulator states.

A wide band gap is a fundamental requirement for an ideal nonlinear optical material. A two-step investigation has been implemented to determine the relationship between the band-gap energy and the iodine-oxygen bond distance in optically nonlinear metal iodate materials. Firstly, we utilized high-pressure conditions on Mg and Zn iodates to correlate the pressure-induced changes in band-gap energy with changes in the iodine-oxygen bond distances. On both cases, the band-gap energy shows a nonlinear decrease under compression. The nonlinear behavior is a consequence of the interplay between the pressure-induced increase of the first-nearest neighbor iodine-oxygen bonds, which favors a narrowing of the band gap, and the decrease of the second-nearest neighbor iodine-oxygen bonds, which favors an opening of the band gap. The inverse correlation between the band-gap energy and the iodine-oxygen bond distance is confirmed in the second part of the investigation by collating and comparing the band-gap energies and corresponding average iodine-oxygen bond distances of the metal iodates reported in the literature. In the comparison, only nontransition and closed-shelled transition metals were included, without regard for their chemical formula, crystal structure, or stoichiometry.

Geometric effects in the infinite-layer nickelates $R{\mathrm{NiO}}_2$ associated with the relative size of the $R$-site atom are investigated via first-principles calculations. We consider, in particular, the prospective ${\mathrm{YNiO}}_2$ material to illustrate the impact of these effects. Compared to ${\mathrm{LaNiO}}_2$, we find that the $\text{La}\to \text{Y}$ substitution is equivalent to a pressure of 19 GPa and that the presence of topotactic hydrogen can be precluded. However, the electronic structure of ${\mathrm{YNiO}}_2$ departs from the cupratelike picture due to an increase in both self-doping effect and $e_g$ hybridization. Furthermore, we find that geometric effects introduce a quantum critical point in the $R{\mathrm{NiO}}_2$ series. This implies a $P4/mmm\leftrightarrow I4/mcm$ structural transformation associated to an $A_3^{+}$ normal mode, according to which the oxygen squares undergo an in-plane rotation around Ni that alternates along $c$. We find that such an $A_3^{+}$-mode instability has a generic character in the infinite-layer nickelates and can be tuned via either the effective $R$-site atom size or epitaxial strain.

Topological insulators (TIs) which exhibit spin-momentum locking constitute an interesting class of quantum materials. In this paper, we present a systematic method to prepare ${\mathrm{Bi}}_x{\mathrm{Te}}_y$ films having tunable Bi/Te composition by employing a direct current (DC) cosputtering technique. Films of three different Te compositions, namely, the Te-deficient (BiTe), Te-stoichiometric (${\mathrm{Bi}}_2{\mathrm{Te}}_3$), and Te-excessive (${\mathrm{BiTe}}_3$) phases, have been investigated in detail by performing the measurements of their temperature-dependent resistivity and in-plane and out-of-plane magnetoresistance responses. Clear evidence of the presence of a weak antilocalization effect and electron-electron interaction are observed in all three films having different phases of Bi-Te system. Using the Hikami-Larkin-Nagaoka and Al'tshuler-Aronov models, the topological characteristics have been evidently distinguished in these three different phases of ${\mathrm{Bi}}_x{\mathrm{Te}}_y$. The analysis of the fitting of the experimental magnetotransport data is performed to quantitatively determine the critical model parameters, viz., phase coherence length ($l_{\varphi }$), surface state penetration depth ($\lambda$), coherency factor ($\alpha$), and dephasing parameter ($p$) through which Berry phase and dimensionality of transport channels can be estimated. In this paper, we reveal a systematic correlation between the composition of the ${\mathrm{Bi}}_x{\mathrm{Te}}_y$ films and their topological properties. The parameter $\kappa$, slope of temperature dependence of conductivity correction, is studied at different magnetic fields, which suggested that the Te-stoichiometric sample shows better features of topological properties than the Te-deficient and Te-excessive samples. These experimental observations are supplemented by first-principles calculations. Additionally, we demonstrate that TIs can be grown by the sputtering technique as is desired for realizing industrial applications.

The recently developed angular-dependent potential for pure iron was advanced to the interatomic potential of the Fe-Cr-H ternary system. The new potential allows to simulate Fe-Cr alloys for a wide range of compositions and different concentrations of hydrogen. The angular-dependent format of the model and the development procedure based on the machine learning approach allow to achieve a favorable balance between the computation cost and the reliability of the created parametrization. As part of potential validation, we performed a large number of tests of both the binary metallic alloys and hydrogen interactions. The applicability of the potential is demonstrated by large-scale simulations of hydrogen diffusion in the vicinity of crystal defects.

When compressed, a metallic specimen will generally experience changes to its crystallographic texture due to plasticity-induced rotation. Ultrafast x-ray diffraction techniques make it possible to measure rotation of this kind in targets dynamically compressed over nanosecond timescales to the kind of pressures ordinarily encountered in planetary interiors. The axis and the extent of the local rotation can provide hints as to the combination of plasticity mechanisms activated by the rapid uniaxial compression, thus providing valuable information about the underlying dislocation kinetics operative during extreme loading conditions. We present large-scale molecular dynamics simulations of shock-induced lattice rotation in three model crystals whose behavior has previously been characterized in dynamic-compression experiments: tantalum shocked along its [101] direction, and copper shocked along either [001] or [111]. We find that, in all three cases, the texture changes predicted by the simulations are consistent with those measured experimentally using in situ x-ray diffraction. We show that while tantalum loaded along [101] and copper loaded along [001] both show pronounced rotation due to asymmetric multiple slip, the orientation of copper shocked along [111] is predicted to be stabilized by opposing rotations arising from competing, symmetrically equivalent slip systems.

We propose a new family of the $d^0$ orbital $XY$ ($X$ = K, Rb, Cs; $Y$ = N, P, As, Sb, Bi) monolayers with abundant and novel topology and valley properties. The KN, RbN, RbP, RbAs, CsP, CsAs, and CsSb monolayers possess remarkable quantum anomalous Hall effect (QAHE). The CsSb monolayer also exhibits extraordinary valley QAHE with giant splitting. Moreover, the topological properties of $XY$ monolayers can be efficiently tuned by the in-plane strain, owing to the strain-induced band inversion between the $p_{x,y}$ and $p_z$ orbitals. Our findings suggest that the $d^0$ orbital $XY$ monolayers can be good candidates for promising applications in the spintronics and multifunctional topological-based devices.

Pyrochlore oxides with the chemical formula $R_2{B}_2{\mathrm{O}}_7$ ($R=$ rare earth and $B=$ tetravalent metal) exhibit very low thermal conductivities (κ) and are considered as promising materials for thermal barrier coatings. To achieve better understanding of their intrinsic thermal properties, this study reports κ for single crystalline ${\mathrm{Gd}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$ and ${\mathrm{Dy}}_2{\mathrm{Ti}}_2{\mathrm{O}}_7$, and for a series of polycrystalline $R_2{\mathrm{Ti}}_2{\mathrm{O}}_7$, in the temperature range from 300 to 773 K. For the single crystals, κ values are evaluated in comparison to spinel ${\mathrm{MgAl}}_2{\mathrm{O}}_4$ and garnet ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ using the Slack equation. It is more difficult to obtain satisfactory analysis for the pyrochlores, and this is attributed to the strong involvement of low-lying optic phonons and very low energies of zone-boundary acoustic phonons. For polycrystalline $R_2{\mathrm{Ti}}_2{\mathrm{O}}_7$, κ values similar to single crystals are obtained. Comparison with published data shows a systematic trend of $\kappa \left(R_2{\mathrm{Sn}}_2{\mathrm{O}}_7\right)>\kappa \left(R_2{\mathrm{Ti}}_2{\mathrm{O}}_7\right)>\kappa \left(R_2{\mathrm{Zr}}_2{\mathrm{O}}_7\right)$ at 300 K, which reflects the increasing ionicity from ${\mathrm{Sn}}^{4+}$ to ${\mathrm{Ti}}^{4+}$ to ${\mathrm{Zr}}^{4+}$. For the three $R_2{B}_2{\mathrm{O}}_7$ systems, κ appears to decrease with either decreasing ionic radius or increasing cation mass of $R$.

Emerging as a new family of two-dimensional materials, transition-metal borides, namely MBenes, are expected to possess outstanding physical and chemical properties owing to their layered structures analogous to MXenes. Here, we explore the electrochemical properties of ScB and TiB monolayers as anode materials for lithium- and sodium-ion batteries by density-functional theory calculations. Our results reveal that Li/Na ions can be stably adsorbed on surfaces of both monolayers with moderate adsorption energy, rapid charge/discharge rate, higher storage capacity, and much lower diffusion energy barrier (0.108 eV for Li ion on ScB, 0.105 eV for Li ion on TiB, 0.072 eV for Na ion on ScB, and 0.063 eV for Na ion on TiB) as compared with other MBene monolayers currently reported. Meanwhile, the open-circuit voltages all fall in the range of 0–1 V for Li/Na ion on the monolayers, which may effectively suppress the formation of Li/Na dendrite on anodes during the charge/discharge process. Besides, at room temperature, Li adatoms could be adsorbed on the monolayers more stably than Na adatoms. Our work demonstrates that ScB and TiB monolayers should be promising two-dimensional anode materials for lithium-ion batteries and are less suitable for sodium-ion batteries. These results advance our understanding on the electrochemical performances of MBenes and provide important insights into the design and development of high-performance electrode materials for metal-ion batteries.

In metal printing processes such as laser-based additive manufacturing, typical solidification velocities yield a strongly out-of-equilibrium (SOE) growth regime that is intermediate between the slow solidification in conventional metal casting and rapid solidification regimes characterized by severe solute trapping. Using phase-field simulations supported by experimental observations, we provide evidence for an inherent growth mode of the SOE regime in slightly hypereutectic Al-Ni, leading to the destabilization of the planar eutectic coupled growth front and the development of a protruded state. We interpret this scenario theoretically in terms of a concomitant growth of different solidification modes, here the coupled eutectic together with $\alpha$ primary phase. As another example of concomitant growth under SOE conditions, we present simulation results for single-phase solidification of a Ni fcc-phase exhibiting dendrites and doublons.

Iron oxides are fundamental components of planet-forming materials. Understanding the Fe-O system's behavior and properties under high pressure can help us identify many new phases and states possible in exoplanetary interiors, especially terrestrial ones. Using the adaptive genetic algorithm, we investigate the structure of iron oxides for a wide range of stoichiometries $(0.25\le x_{\mathrm{O}}\le 0.8)$ at 1, 2, and 3 TPa. Five ground-state structures with ${\mathrm{Fe}}_2\mathrm{O}$, FeO, ${\mathrm{Fe}}_3{\mathrm{O}}_5$, ${\mathrm{FeO}}_2$, and ${\mathrm{FeO}}_4$ compositions are identified. Phonon calculations confirm their dynamical stability. The ab initio molecular dynamics simulations confirm the thermal stability of Fe-rich phases at high temperatures. The calculated density of states suggests that, except for ${\mathrm{FeO}}_4$, all phases are metallic, but their carrier densities decrease with increasing pressure and oxygen content. The cluster alignment analysis of stable and metastable phases shows that several motifs may coexist in a structure of iron oxides with low O content. In contrast, most iron oxides with high O content adopt a simple bcc motif at TPa pressures. Our results provide a crystal structure database of iron oxides for modeling and understanding the interiors of exoplanets.

Bulk metallic glasses (BMGs) naturally have excellent strength and elasticity while structural rejuvenation into higher energy glassy states is often required to improve ductility. However, our understanding of the detailed atomic ordering changes that occur during rejuvenation processes, such as plastic deformation, remains limited. This study utilizes nanobeam electron diffraction in a transmission electron microscope as an effective method to reveal the structural changes that occur after deformation in two Zr-based BMGs. Our findings indicate that heavy deformation from indentation or fracture causes an increase in the size of fcc-like medium-range order (MRO) clusters in a harder icosahedral dominated matrix, which corresponds to local softening of the BMGs. By examining the structure evolution at different points in the fracture process, we reveal that the mechanism of growth of MRO clusters is likely driven by enhanced diffusion from local temperature rise and/or free volume generation rather than deformation-induced nucleation and growth of new MRO sites.

State-of-the-art topological devices require the use of topologically protected surface states to drive electronic transport. In this paper, we examine a tunable topological system, $\mathrm{Ge}{\left({\mathrm{Bi}}_x{\mathrm{Sb}}_{1\text{−}x}\right)}_2{\mathrm{Te}}_4$, for a range of $x$ values from 0 to 1, using a combination of Fourier transform scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy. Our results show that the Dirac point shifts linearly with $x$, crossing the Fermi energy near $x=0.7$. This observation of a smoothly tunable, isolated Dirac point crossing through the topological transport regime and having strong linear dependence with substitution can be critical for future topological spintronics applications.