Boehmite, an aluminum oxide hydroxide $\gamma$-AlO(OH), is broadly used in the form of particulate dispersions in industrial applications, e.g., for the fabrication of ceramics and catalyst supports or as a binder for extrusion processes. Under acidic conditions, colloidal boehmite dispersions at rest form gels, i.e., space-spanning percolated networks that behave as soft solids at rest, and yet yield and flow like liquids under large enough deformations. Like many other colloidal gels, the solid-like properties of boehmite gels at rest are very sensitive to their previous mechanical history. Our recent work [J. Rheol. 66, 91 (2022); Phys. Rev. Mater. 6, L042601 (2022)] has revealed such memory effects, where the shear experienced prior to flow cessation drives the elasticity of boehmite gels: while gels formed following application of a shear rate ${\dot{\gamma }}_{\mathrm{p}}$ larger than a critical value ${\dot{\gamma }}_{\mathrm{c}}$ are insensitive to shear history, gels formed after application of ${\dot{\gamma }}_{\mathrm{p}}<{\dot{\gamma }}_{\mathrm{c}}$ display reinforced viscoelastic properties and non-negligible residual stresses. Here, we provide a microstructural scenario for these striking observations by coupling rheometry and small-angle X-ray scattering. Time-resolved measurements for ${\dot{\gamma }}_{\mathrm{p}}<{\dot{\gamma }}_{\mathrm{c}}$ show that scattering patterns develop an anisotropic shape that persists upon flow cessation, whereas gels exposed to ${\dot{\gamma }}_{\mathrm{p}}>{\dot{\gamma }}_{\mathrm{c}}$ display isotropic scattering patterns upon flow cessation. Moreover, as the shear rate applied prior to flow cessation is decreased below ${\dot{\gamma }}_{\mathrm{c}}$, the level of anisotropy frozen in the sample microstructure grows similarly to the viscoelastic properties, thus providing a direct link between mechanical stiffening and flow-induced microstructural anisotropy.

High-entropy materials have emerged as a promising platform for exploring unique electronic and structural properties. In this study we investigated the orbital control of the metal-to-insulator transition in thin films of high-entropy nickelates, which are composed of five rare-earth elements in equiatomic concentrations. By manipulating the levels of misfit strain through substrate choice and film thickness, we modulated the electronic properties and examined the intricate interplay between strain, orbital interactions, and the metal-to-insulator transition. Compared to other nickelate thin films such as $\mathrm{NdNi}{\mathrm{O}}_3$ and $\mathrm{SmNi}{\mathrm{O}}_3$, thin films of high-entropy nickelates exhibited remarkable resilience in maintaining control over their transport properties and orbital polarization, even in the presence of considerable A-site disorder. This finding suggests that the electronic properties of A-site disordered high-entropy nickelates are still governed by the electronic bandwidth, primarily influenced by the Ni-O bonding geometry. This study provides valuable insights into the complex interplay among composition, structure, and electronic properties in perovskite oxides. These insights have the potential to guide the development of perovskite oxide materials with tailored electronic properties for a wide range of applications.

Endowing room-temperature ductility in refractory high-entropy alloys (RHEAs) is a challenge to their uses in nuclear energy systems, biomedical, and high-temperature applications. Recently, transformation-induced plasticity (TRIP) has been recognized as an effective strategy to simultaneously improve ductility and tensile strength of RHEAs. Hitherto, the design for a TRIP mechanism in RHEAs through material-dependent parameters typically follows empirical approaches. Here, we investigate the alloying effect of several body-centered cubic (bcc) transition metal elements (TM=V, Nb, Cr, Mo, and W) on the phase stability and the micromechanical properties of the TiZrHf alloy using a first-principles method. We show that the addition of the considered TM elements increases the stability of the bcc phase relative to the hexagonal close-packed (hcp) phase and the relative stability between these two phases can be tuned and inverted. We investigate the composition-dependent single-crystal elastic constants for the (${\mathrm{TiZrHf})}_{1-x}{\mathrm{Nb}}_x$ and (${\mathrm{TiZrHf})}_{1-x}{\mathrm{Mo}}_x$ alloys and analyze mechanical stability, elastic anisotropy, and polycrystalline moduli. Our results show that the anisotropy of Young's modulus is more pronounced the closer the alloy composition is to the composition where the bcc phase or hcp phase becomes mechanically unstable. We find that the hcp phase has higher shear and Young's moduli than the bcc phase below a critical composition for the Nb or Mo addition, while the bcc phase has larger moduli above the critical composition. Furthermore, our results imply that the $d$-band filling has a dominant influence on the phase stability and mechanical properties of the alloys.

We use ab initio calculations and theoretical analysis to investigate the influence of uniaxial tensile strain on valley drifts and Berry curvatures in the monolayer ${\mathrm{MoSi}}_2{\mathrm{N}}_4$, a prototypical septuple atomic layered two-dimensional material. The low energy electron and hole valleys drift far off the $\mathrm{K}/{\mathrm{K}}^{\prime }$ point under uniaxial strains. The direction and strength of valley drift strongly depend on the nature of the charge carrier and uniaxial strain with a more substantial response along the zigzag path. Our findings exhibit the pivotal role of microscopic orbital contribution and symmetry lowering. The changing geometric properties of Bloch states affect the Berry curvatures and circular dichroism. Specifically, Berry curvature dipole is significantly enhanced under the tensile strain along armchair and zigzag directions. Meanwhile, the particle-hole asymmetry arising from nonequivalent electron and hole valley drifts relaxes the selection rules, thus reducing the degree of circular polarization up to $\sim 0.98$. Therefore, strain engineering of valley physics in the monolayer ${\mathrm{MoSi}}_2{\mathrm{N}}_4$ is of prime importance for valleytronics.

We investigated the thermal transport properties of two $\alpha \text{−}{\mathrm{RuCl}}_3$ crystals with different degrees of stacking disorder to understand the origin of the previously reported oscillatory feature in the field dependence of thermal conductivity. Crystal I shows only one magnetic order around 13 K, which is near the highest $T_N$ for $\alpha \text{−}{\mathrm{RuCl}}_3$ with stacking faults. Crystal II has less stacking disorder, with a dominant heat capacity at 7.6 K along with weak anomalies at 10 and 13 K. In the temperature and field dependence of thermal conductivity, no obvious anomaly was observed to be associated with the magnetic order around 13 K for either crystal or around 10 K for crystal II. Crystal II showed clear oscillations in the field dependence of thermal conductivity, while crystal I did not. For crystal I, an L-shaped region in the temperature-field space was observed where thermal Hall conductivity ${\kappa }_{xy}$/T is within $\pm 20\%$ of the half quantized thermal Hall conductivity ${\kappa }_{HQ}$/T, while for crystal II, ${\kappa }_{xy}$/T reaches ${\kappa }_{HQ}$/T only in the high field and high temperature regime with no indication of a plateau at ${\kappa }_{HQ}$/T. Our thermal conductivity data suggest the oscillatory features are inherent to the zigzag ordered phase with $T_N$ near 7 K. Our planar thermal Hall effect measurements suggest the sensitivity of this phenomena to stacking disorder. Overall, our results highlight the importance of understanding and controlling crystallographic disorder for obtaining and interpreting intrinsic thermal transport properties in $\alpha \text{−}{\mathrm{RuCl}}_3$.

Lilithium cobalt dioxide (${\mathrm{LiCoO}}_2$) is a promising cathode material for rechargeable lithium-ion batteries (LIBs). To improve the electrochemical performance of LIBs, we theoretically investigated the structural changes in a ${\mathrm{LiCoO}}_2$ electrode through the thermodynamic convex hull analysis. To construct the convex hull, we combined cluster expansion and Bayesian optimization (BO) with high-throughput density functional theory (DFT) calculations. To improve the BO efficiency, we used hull distance as the target variable of BO, which considerably reduced the number of DFT calculations. At 300 K, the ${\mathrm{O}}_2$ gas release by the convex hull was confirmed. The defective stoichiometry of ${\mathrm{CoO}}_{2-y}$ deteriorated the layered structure of ${\mathrm{CoO}}_2$ and prevented the ${\mathrm{Li}}^{+}$ ion migration. Therefore, we considered that the formation of ${\mathrm{CoO}}_{2-y}$ contributed to the cathode degradation. Our findings will provide useful insights into the prevention of LIB degradation.

The interplay between solvent diffusion and swelling of the absorbing solid leads to a variety of possible behaviors. In the case of polymer matrices, sharp penetration and swelling fronts are commonly found, with their dynamics depending on the specific features of the polymer-solvent system. Here, at the continuum mechanical level, we introduce a model to predict both concentration profile and swelling for whatever motion of the penetration front, in the one-dimensional case. A distinctive feature of our approach is that a constitutive equation for the thermodynamics of the dry side is not required. The model is validated against paradigmatic experiments available in literature, as well as through our own data (including optical microscopy) on a water–polyvinyl alcohol system. In spite of using only a small number of parameters, the model succeeds in predicting all the tested observables of the diffusion/swelling process in those polymeric systems.

Short-range order (SRO) in alloys refers to deviations from a perfectly random distribution of atoms in lattice sites within a short distance. Conventionally, the degree of the deviations has been quantified using an average SRO parameter, but such a coarse-grained description does not reflect how the deviations occur at a finer level. Here we show the distribution of the local atomic SRO parameter, which describes the occurring frequency of a local structural motif, carries the crucial information for both structures and properties in Si-Ge-Sn alloy system. This is demonstrated through the fact that distinct SRO structures can exhibit the same average SRO parameter but very different distributions and disparate electronic structures. By deliberately creating special structures that explicitly match the structural information at different levels, we show the distribution of local atomic SRO parameters contain critical structural features that are missing in the average SRO parameter but can substantially contribute to material's properties. Our finding thus calls for the need for considering the finer structural details to effectively describe alloys' structures and properties.

Satisfactory theoretical treatment of double twin growth has thus far not been achieved. Phenomenological theories of double twinning are based on the assumption that a double twin embryo grows on an invariant plane of the double twin transformation by means of a simple shear mechanism. We demonstrate the equivalence of A. G. Crocker's approach, which aims to identify the double twin invariant planes, and of later models of nonclassical twinning, which entail the use of correspondence matrices. These treatments, however, do not account for features of double twin growth observed in experiment, namely that this is a two-step process, where a primary twin forms fully before secondary twinning occurs internally. To resolve this conundrum, we introduce topological models of double twinning, which focus on the motion of twinning disconnections as the actors of twin growth. We first treat the case of secondary twinning disconnections interacting with a primary twin interface and calculate the magnitude of the resulting rotation of the habit plane; secondly, we model the interaction of secondary twinning disconnections with an array of primary twinning disconnections in the primary twin interface. We show that the latter model produces similar predictions for the double twin habit plane as those of the phenomenological theories, and we discuss validation of the topological models by experiment.

An electronic structure and magnetic properties analysis of the recently proposed Cu-doped lead apatite is performed. We show that electronic structures of differently Cu-substituted structures are characterized by localized molecular Cu-O bands at or near the Fermi level. The Cu substitutions can happen at both Pb1 and Pb2 sites, leading to metallic and semiconducting systems differently. The electronic systems in these bands are highly unstable magnetically and form clusters of rigidly ferromagnetically coupled magnetic moments on Cu and neighboring oxygen atoms with a total moment of about ${1\mu }_{\mathrm{B}}$. The ground state of uniformly Cu-doped lead apatite appears to be magnetic and semiconducting. The nonuniform distribution of two Cu atoms at the nearest Pb2 sites leads to an antiferromagnetic semiconducting state with formation energy close to uniformly distributed Cu configurations. The inclusion of quantum spin fluctuations confirms the stability of magnetic Cu-O clusters. Our calculations revealed the absence of the long-range magnetic order between uniformly distributed Cu-O clusters, creating the spin glass type of system.

By utilizing a combination of first-principles calculations and machine-learning-interatomic-potential-based molecular dynamics simulations, we show that (contrary to the conventional understanding of electron-driven thermal transport in metals) the dominant carriers of heat in tungsten are phonons at high pressures. More specifically, we show that the contribution of phonons to the total thermal conductivity increases monotonically from $\sim 30\%$ at ambient pressure to $\sim 70\%$ at 100 GPa. This is attributed to considerable phonon hardening leading to enhanced phonon lifetimes and group velocities in pressurized tungsten. In contrast to the phonon-driven thermal conductivity, calculations of the electronic thermal conductivity based on density functional perturbation theory calculations of the full electron-phonon coupling matrix show that there is negligible change in the electron-driven thermal conductivity throughout the entire pressure range (up to 100 GPa) studied in this paper. Spectrally resolved electron-phonon coupling at elevated pressures reveals that while phonons are hardened, the peaks of the spectral function are unchanged, thus resulting in negligible variation of the mass enhancement parameter that describes the strength of the overall electron-phonon coupling with increasing pressures. In contrast, the characteristically reduced phonon-phonon scattering, a signature of the isotropic and highly degenerate phonon branches, leads to the phonon-dominated heat conduction in pressurized tungsten. Taken together, our results show that the pressure-driven changes in thermal transport can result in large deviations of the Lorenz number from the traditionally accepted Sommerfeld value in tungsten. Our work reveals an efficient way to separately manipulate the phononic thermal transport from the electronic heat conduction through the application of external pressure in tungsten, and as such can be highly beneficial for applications such as in integrated circuits where tungsten could replace the widely used copper interconnects.

${\mathrm{TiO}}_2$ has wide applications in catalysis and photocatalysis and is an attractive alternative to Pt or Pt-based catalysts due to its abundance, low cost, and nontoxicity. However, it does not display any worthwhile catalytic activity as far as the oxygen reduction reaction (ORR) is concerned. Attempts have been made to improve the activity of ${\mathrm{TiO}}_2$ by doping and creating defects on the surface. Nb-doped ${\mathrm{TiO}}_2$ is experimentally found to have good conductivity and electrochemical activity for low-Nb concentrations. This paper presents a systematic modeling study of how Nb doping influences the ORR activity of anatase ${\mathrm{TiO}}_2$ using plane-wave density-functional theory method. We elucidate the probable dopant sites, the effect of Nb doping on the oxygen binding capability at active sites, the favored reaction pathway, and the transition state. We find a remarkable enhancement in the capability of ${\mathrm{TiO}}_2$ to catalyze ORR upon doping with Nb. We have also modeled the effect of solvation on the binding of oxygen and other reaction intermediates, using a model where water molecules are added as a monolayer over Nb-doped ${\mathrm{TiO}}_2$. Solvation introduces additional hydrogen bonding, which improves the binding of intermediates to the active site and lowers activation barriers. Our model for ORR in Nb-doped ${\mathrm{TiO}}_2$ agrees with recent experimental results on the same.

Cubic yttria-stabilized zirconia has long been a ceramic material of interest for its many uses in thermal-based applications. Its very low and weakly temperature-dependent thermal conductivity has been ascribed to the large oxygen vacancies content, which introduces disorder and strongly scatters phonons. Still, despite many experimental works in the literature, phonon dynamics has not been fully understood yet, with several points to be clarified, such as the apparent absence of optic modes throughout the Brillouin zone. In this paper, we present findings on the phonon dispersions of this material, showing experimental evidence of low-lying optical branches throughout the Brillouin zone, which reduce the pure acoustic regime for some branches. Furthermore, the observed energy dependence of the intrinsic acoustic phonon linewidths clearly suggests the existence of competing Mie and Rayleigh scattering mechanisms. Our findings allow to uncover a different phonon dynamics scenario in this material and point to a deeper understanding of heat transport in yttria-stabilized zirconia, based on two different, concomitant mechanisms, generated by the large vacancy content.

Terrestrial exoplanets are of great interest for being simultaneously similar to and different from Earth. Their compositions are likely comparable to those of solar-terrestrial objects, but their internal pressures and temperatures can vary significantly with their masses/sizes. The most abundant nonvolatile elements are O, Mg, Si, Fe, Al, and Ca, and there has been much recent progress in understanding the nature of magnesium silicates up to and beyond $\approx 3$ TPa. However, a critical element, Fe, has yet to be systematically included in materials discovery studies of potential terrestrial planet-forming phases at ultrahigh pressures. Here, using the adaptive genetic algorithm crystal structure prediction method, we predict several unreported stable crystalline phases in the binary Fe-Mg and ternary Fe-Mg-O systems up to pressures of 3 TPa. The analysis of the local packing motifs of the low-enthalpy Fe-Mg-O phases reveals that the Fe-Mg-O compound favors a bcc motif under ultrahigh pressures. In addition, oxygen enrichment is conducive to lowering the enthalpies of the Fe-Mg-O phases. Our results extend the current knowledge of structural information of the Fe-Mg-O system to exoplanet pressures.

We present a first-principles study of the effect of $3d$ transition metal intercalation on the magnetic properties of the $2H\text{−}{\mathrm{NbS}}_2$ system, using spin-resolved density functional theory calculations to investigate the electronic structure of $N_{1/3}{\mathrm{NbS}}_2$ ($N=\text{Ti}$, V, Cr, Mn, Fe, Co, Ni). We are able to accurately determine the magnetic moments and crystal-field splitting, and find that the magnetic properties of the materials are determined by a mechanism based on filling rigid bands with electrons from the intercalant. We predict the dominant magnetic interaction of these materials by considering Fermi-surface topology, finding agreement with experiment where data are available.

In contrast to the cuprates, where the proximity of antiferromagnetism (AFM) and superconductivity is well established, first indications for AFM interactions in superconducting infinite-layer nickelates were only recently obtained. Here, we explore, based on first-principles simulations, the nature of the magnetic coupling in ${\mathrm{NdNiO}}_2$ as a function of the on-site Coulomb and exchange interaction, varying the explicit hole doping and the treatment of the Nd $4f$ electrons. The $U\text{−}J$ phase diagrams for undoped nickelates and cuprates indicate $G$-type ordering, yet show opposite $U$ dependency. By either Sr hole doping or explicit treatment of the Nd $4f$ electrons, we find a transition to a Ni $C$-type AFM ground state. We trace back the effect of Sr doping to a distinct accommodation of the holes by the Ni versus Cu $e_g$ orbitals. The interaction between Nd $4f$ and Ni $3d$ states stabilizes $C$-type AFM order on both sublattices. Though spin-orbit interactions induce a band splitting near the Fermi energy, the bad-metal state is retained even under epitaxial strain. These results establish the distinct role of the magnetic interactions in the nickelates versus the cuprates and suggest the former as a unique platform to investigate the relation to unconventional superconductivity.

The tensile toughness $\mathcal{T}$ of a brittle polymeric solid can be enhanced by blending a ductile polymer. While this common wisdom is generally valid, a generic picture is lacking that connects the microscopic details to the macroscopic nonlinear mechanics. Using all-atom and complementary generic simulations, we show how a delicate correlation between the side group contact density of the brittle polymers ${\rho }_{\mathrm{c}}$ and its dilution upon adding a second component controls $\mathcal{T}$. A set of chemically distinct systems follows a generic trend in $\mathcal{T}$ with $d{\rho }_{\mathrm{c}}/d\varepsilon$, where $\varepsilon$ is the tensile strain. The observed trend is explained using a simple mechanical model based on the parallel spring analogy.

Heterogeneity in the deformation field, especially in the form of shear bands, is a universal feature in disordered solids. The current paradigm presents the deformation heterogeneity as the result of structural inhomogeneity which is controlled by the concentration of atomic ordering clusters or flow defects. Here, we show that, in contrast to the population of atomic clusters, their topology, i.e., spatial distribution, is the root cause of the strain localization. This conclusion is reached via a decoupling tactic which completely eliminates the effect of concentration. Under loading stimuli, model glasses with identical concentration but various topological connectivity of atomic ordering clusters show remarkably distinct mechanical behaviors. Deformation heterogeneity and shear banding emergence are linked to glasses with strong topological connectivity. Topological connectivity can be not only characterized as the structural origin of strain localization, but is also transferable to detect the dynamical heterogeneity. These results are instrumental to rationalize the emergence of shear bands in disordered solids in terms of the pure structural information.

The recent experimental fabrication of monolayer and few-layer ${\mathrm{C}}_{60}$ polymers paves the way for synthesizing two-dimensional (2D) cluster-assembled materials. Compared to individual atoms, clusters as superatoms (e.g., ${\mathrm{C}}_{60}$) have an additional rotational degree of freedom, greatly enriching the phase spaces of superatom-assembled materials. Using first-principles calculations, we investigate a series of quasitetragonal and quasihexagonal polymeric ${\mathrm{C}}_{60}$ monolayers which are related by cluster rotation. The energy barriers of cluster rotation in quasitetragonal monolayer ${\mathrm{C}}_{60}$ structures are rather low (about 10 meV/atom). The small rotational energy barrier leads to a series of tetragonal ${\mathrm{C}}_{60}$ polymorphs with energies that are close to the experimental quasitetragonal phase. Similarly, several dynamically stable quasihexagonal monolayer ${\mathrm{C}}_{60}$ structures are found to have energies within 7 meV/atom higher than the experimental quasihexagonal phase. Our calculations demonstrate photoexcited electron-hole pairs and electrostatic doping of electrons can effectively modulate the relative energies of quasitetragonal ${\mathrm{C}}_{60}$ polymorphs, while the relative energies of different quasihexagonal polymorphs are insensitive to electrostatic doping of electrons. The experimental quasitetragonal phase, which is not dynamically stable in its monolayer form, can be stabilized when it is electrostatically doped with electrons.

The ${\mathrm{Mn}}_{3}XY$ ($X$ = Co, Rh, Ir and $Y$ = Si, Ge) family of materials adopts an ordered form of the chiral $\beta$-Mn structure lacking inversion symmetry. Polycrystalline samples of ${\mathrm{Mn}}_3\mathrm{IrSi}$ and a new member in this family, ${\mathrm{Mn}}_3\mathrm{RhGe}$, have been synthesized and investigated with heat capacity, magnetic susceptibility, and neutron powder diffraction measurements. ${\mathrm{Mn}}_3\mathrm{RhGe}$ and ${\mathrm{Mn}}_3\mathrm{IrSi}$ exhibit long-range magnetic order below 225(2) and 230(2) K, respectively. The neutron diffraction data reveal a high-temperature incommensurate magnetic structure in ${\mathrm{Mn}}_3\mathrm{RhGe}$, which transitions into a noncollinear commensurate antiferromagnetic ground state upon cooling via a phase coexistence in a wide temperature range. The presence of the incommensurate magnetic order reveals a significant role of exchange interactions beyond nearest and next-nearest neighbors. ${\mathrm{Mn}}_3\mathrm{IrSi}$ shares the noncollinear commensurate magnetic structure for all temperatures and shows no evidence of incommensurate magnetism.