In this paper, we explore the chemical-property phase diagram of the $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ family through $A$-site alloying. We demonstrate full miscibility of the alkali site, highlighting that the three parent compounds are the terminal ends of a single solid solution. Using both polycrystalline and single crystal methods, we map the dependence of the two primary electronic instabilities: (1) the onset of charge-density wave (CDW) order ($T_{\mathrm{CDW}}$) and (2) the onset of superconductivity ($T_{\mathrm{c}}$) with alkali-site composition. We show continuous trends in both $T_{\mathrm{CDW}}$ and $T_{\mathrm{c}}$, including a region of enhanced CDW stability in ${\mathrm{K}}_{1-x}{\mathrm{Cs}}_x{\mathrm{V}}_3{\mathrm{Sb}}_5$ alloys. Together, our results open new routes for chemical perturbation and exploration of the chemical-property relationships in the class of $A{\mathrm{V}}_3{\mathrm{Sb}}_5$ kagome superconductors.

Atomic structure determines physical properties, but for glassy materials, the nature of structure-property relationships remains ambiguous. Since glass properties are governed by both chemistry and structure, it is difficult to dissociate these two effects. Here, the sole effect of the structure on property is isolated by treating an industrial aluminosilicate glass with either thermal-annealing or pressure-quenching processes to produce glasses with varying densities and hardnesses (at constant composition). To explore the underlying structural origin of property changes, neutron total-scattering patterns of these glasses were measured. These results confirm the applicability of rigid-unit mode theory since the short-range tetrahedra were found to remain unaffected. In contrast, close correlations are derived between properties and medium-range structure (as encoded in various features of the first sharp diffraction peak). Overall, it reveals that the increase in the medium-range order is the structural origin of the extra extent of hardness increase beyond the densification effects.

It has been widely accepted that the plastic events of amorphous solids after mechanical yield belong to a highly correlated avalanche state. However, whether the plastic events before yield are correlated or not is still unsettled, leaving their interactions largely unexplored. In this paper, by means of atomistic simulations, typical ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ metallic glasses, as the model system, are sheared under athermal quasistatic limit to study these plastic events. The statistical analysis of both stress drops and waiting times reveals that plastic events before yield are in the correlated avalanche state and the interactions among them are mediated by the robust elasticity. The temporal correlation analysis of the nonaffine displacement fields further reveals that the elastic interactions are short-lived strong but long-standing weak, which results in the fractal morphology of potential energy landscape. By introducing vibrational modes to explore plastic events, we clearly exhibit the way how the elastic interactions organize the Eshelby-type shear transformations into avalanched plastic events. The correlation matrix, with its component being the dot product of the vibrational modes at different configurations, is defined to trace the evolution of vibrational modes during elastic deformation and across plastic events. Three reasons accounting for the robust elasticity are identified: (i) the limited destruction of plastic events on global elasticity, (ii) the persistent hard spots embedded in elastic matrix, and (iii) the self-recovery of elastic matrix during elastic deformation. Our results clarify the atomic-scale nature of both elastic deformation and plastic instabilities before yield in amorphous solids, providing fundamental information for the development of elastoplastic constitutive models.

Kelvin probe force microscopy (KPFM) is a powerful tool for studying contact electrification (CE) at the nanoscale, but converting KPFM voltage maps to charge density maps is nontrivial due to long-range forces and complex system geometry. Here we present a strategy using finite-element method (FEM) simulations to determine the Green's function of the KPFM probe/insulator/ground system, which allows us to quantitatively extract surface charge. Testing our approach with synthetic data, we find that accounting for the atomic force microscope (AFM) tip, cone, and cantilever is necessary to recover a known input and that existing methods lead to gross miscalculation or even the incorrect sign of the underlying charge. Applying it to experimental data, we demonstrate its capacity to extract realistic surface charge densities and fine details from contact-charged surfaces. Our method gives a straightforward recipe to convert qualitative KPFM voltage data into quantitative charge data over a range of experimental conditions, enabling quantitative CE at the nanoscale.

Ternary transition metal carbides and nitrides in the so-called MAX phases constitute a rich family of compounds that host interesting electronic and magnetic properties, and thus, these materials have been drawing increasing levels of attention. Similar ternary boride compounds, the MAB phases, have been studied much less despite being equally if not more promising. In this paper, we investigate ${\mathrm{Fe}}_{2}A{\text{B}}_2$ and ${\mathrm{Mn}}_{2}A{\text{B}}_2 (A=\mathrm{Al},\mathrm{Si},\mathrm{Ga},\text{and}\mathrm{In})$ ternary layered transition metal borides with orthorhombic, hexagonal, and tetragonal crystal structures using first-principles density functional theory (DFT). We assess the reliability of different exchange-correlation functionals for the accurate prediction of the material properties of MAB phases. In addition to the electronic and crystal structures of ${\mathrm{Fe}}_{2}A{\text{B}}_2$ and ${\mathrm{Mn}}_{2}A{\text{B}}_2$ ($A$ = Ga, In, and Si), we predict the dynamical and thermodynamic stabilities against the competing phases. We conducted bonding analysis to comprehend the bonding characteristic between different atoms, which provides a fundamental understanding whether the exfoliation of these compounds into so-called two-dimensional MBene structures is likely or not. In addition to spin-polarized $\mathrm{DFT}+U$ calculations, which predict ordered magnetic moments, our $\mathrm{DFT}+$embedded dynamical mean field theory calculations predict a significant degree of electronic correlations in the paramagnetic phase of these compounds. These calculations also predict the formation of fluctuating magnetic moments before the onset of a magnetic order in the MAB compounds like an earlier report on the MAX compound ${\mathrm{Mn}}_2\mathrm{GaC}$.

Ferroic switching of 90 ° domains in ${\mathrm{BaTiO}}_3$ can be simultaneously ferroelectric and ferroelastic. Although the general features of their respective ferroelectric and ferroelastic hysteresis loops are similar, the dynamic properties are not. Switching proceeds via avalanches, where changes of the domain structure trigger further nanostructural changes until the avalanches expire and the sample remains in a metastable state. Avalanches are characterized by energy singularities (energy “jerks”), which are power law distributed with an energy exponent ε. Using acoustic emission spectroscopy, we find that the energy exponent in ceramics during ferroelectric switching is near the mean field value $\varepsilon \sim 1.3$, whereas stress driven ferroelastic switching is characterized by $\varepsilon \sim 1.8$. This value is much larger than the field integrated mean field value $\varepsilon \sim 1.66$, which was found for ferroelectric switching of single crystals. Thus, ${\mathrm{BaTiO}}_3$ displays three separate dynamical processes for microstructural changes under electric and mechanical stress fields.

Structural transformations of unpoled $(1-x)\mathrm{Pb}\left({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}\right){\mathrm{O}}_{3-x}\mathrm{PbTi}{\mathrm{O}}_3\left(\mathrm{PMN}\text{−}\mathrm{PT}\right)$ single crystals ($x=0.28$ and $x=0.32$) were analyzed by calorimetry and acoustic spectroscopy. The compositions are close to the morphotropic boundary (MPB). We find extended two-phase regions where cubic and rhombohedral ($x=0.28$), cubic and tetragonal, tetragonal and monoclinic phases ($x=0.32$) coexist during cooling and heating. The observed structural transitions in PMN-PT are first order, despite their proximity to the MPB. The predicted tricritical points, if they exist, are possibly located extremely close to the MPB.

Unlike covalent two-dimensional (2D) materials like graphene, 2D metals have nonlayered structures due to their nondirectional, metallic bonding. While experiments on 2D metals are still scarce and challenging, density-functional theory (DFT) provides an ideal approach to predict their basic properties and assist in their design. However, DFT methods have rarely been benchmarked against metallic bonding at low dimensions. Therefore, to identify optimal DFT attributes for a desired accuracy, we systematically benchmark exchange-correlation functionals from LDA to hybrids and basis sets from plane waves to local basis with different pseudopotentials. With 1D chain, 2D honeycomb, 2D square, 2D hexagonal, and 3D bulk metallic systems, we compare the DFT attributes using bond lengths, cohesive energies, elastic constants, densities of states, and computational costs. Although today most DFT studies on 2D metals use plane waves, our comparisons reveal that local basis with often-used Perdew-Burke-Ernzerhof exchange correlation is quite sufficient for most purposes, while plane waves and hybrid functionals bring limited improvement compared to the greatly increased computational cost. These results ease the demands for generating DFT data for better interaction with experiments and for data-driven discoveries of 2D metals incorporating machine learning algorithms.

Systematic research was performed to investigate magnetic properties of the Tsai-type $\mathrm{Ga}\text{−}\mathrm{Pd}\text{−}RE$ ($RE=\mathrm{Gd}$, Tb, Dy, and Ho) systems, where both 1/1 and 2/1 quasicrystal approximants (ACs) are attainable at the same compositions as thermodynamical stable phases. Most of the samples exhibited spin-glass (SG)-like freezing behavior at low temperatures except Ga-Pd-Tb 2/1 AC and Ga-Pd-Ho 1/1 AC. The former showcased antiferromagnetic order at 5.78 K while the latter did not show any anomaly down to 1.8 K. Furthermore, 2/1 ACs were noticed to be less frustrated than their corresponding 1/1 ACs (based on the empirical rule of $|{\theta }_{\mathrm{w}}/T_{\mathrm{f}}|$ ) presumably due to the disorder-free environment in the nearest neighbor of the rare-earth sites that form a network of distorted octahedron in the 2/1 ACs. The spin dynamic in SG samples was also characterized by means of ac magnetic susceptibility measurements. The results evidenced a weak response of the freezing temperatures to the measurement frequency in the Heisenberg systems, i.e., Gd-contained ACs, in contrast to the non-Heisenberg systems, i.e., Tb-, Dy-, and Ho-contained ACs, where significant dependency is noticed for the latter. The spin-glass samples were further examined by fitting their freezing temperatures to the Vogel-Fulcher law.

The initial stages of hydrogen adsorption on GaAs(110) surfaces at room temperature are investigated by atomically resolved scanning tunneling microscopy and spectroscopy. Two effects are found to occur simultaneously: On the one hand a surface phase separation occurs, creating $1\times 1$ reconstructed fully hydrogen-covered areas while leaving the surface in between completely hydrogen free. In the fully hydrogen-covered areas, hydrogen bonds equally to As- and Ga-derived dangling bonds, unbuckling and passivating the surface. On the other hand, hydrogen-induced point defects are formed with increasing density. The dominating defects consist of As vacancy–hydrogen defect complexes, formed by preferential hydrogen etching of As. Using a defect-molecule model the Ga-H bridge bonds and double-occupied Ga dangling bonds are suggested to be at the origin of the observed surface Fermi level pinning 0.25 to 0.3 eV above the valence band edge, identical within error margins for $p$- and $n$-doped GaAs(110).

Using the creation relaxation algorithm developed for the atomistic modeling of the high-dose irradiation limit of crystalline systems, we explore the limits of the structural rejuvenation of a highly excited model binary glass. This high-energy athermal amorphous structure exhibits a direct transition to homogeneous plastic flow and a microstructure that is largely insensitive to this flow, being characterized by a porous system-spanning network of minimally frustrated structural motifs. The observed homogeneous plasticity is mediated by the same string-like structural excitations, which mediate structural relaxation and microplasticity at finite temperature in more relaxed structures. This highly rejuvenated structural asymptote is not far from the structural state of regions, which have experienced athermal shear localization in more relaxed samples, suggesting an optimally rejuvenated glassy structure will always be limited by that produced by shear localization.

Polymer networks that are crosslinked jointly by covalent bonds and reversible physical bindings usually offer superior mechanical strength and toughness compared to their permanently crosslinked counterparts. By introducing short oligomers as stickers that bind physically to different polymer chains, the resulting polymer networks show a unique feature of dissipating stretching-induced energy, which is absent in permanent networks. We show that large sized clusters of physical crosslinks in a transient network break into smaller pieces when the transient network is stretched at strain rates sufficiently high that the transiently crosslinked structure is not given enough time to relax. After deducting the part of the stress that is generated solely by a thermal motion-driven structural readjustment of the transient network, the stress enhancement arising from a stretching-enforced breakup of physical crosslinks is quantitatively verified, demonstrating the sacrificial role played by these physical crosslinks in safeguarding the unrelaxed structure.

II–IV nitrides and their alloys represent an earth-abundant and potentially cost-efficient alternative to the well-developed AlN-GaN-InN system. A major drawback with the II–IV nitrides is that $\mathrm{Zn}\mathrm{Sn}{\mathrm{N}}_2$, the lowest band gap material, exhibits unfavorably high carrier concentrations for as-grown, stoichiometric material, limiting the material systems potential use in applications such as solar cells and light-emitting diodes. Lithium (Li) has been suggested as a shallow acceptor defect in $\mathrm{Zn}\mathrm{Sn}{\mathrm{N}}_2$ if substituting for Zn, and hence doping with Li has been identified as a possible way to improve the electronic properties. Herein, theoretical calculations by hybrid functional density functional theory have been employed and extended to include defect complexes as well, which to this point remained unexplored. The calculations reveal that even though Li on the Zn site (the ${\mathrm{Li}}_{\text{Zn}}$) is an acceptor, the defect may easily complex with the ${\mathrm{Li}}_i$ donor, rendering the complex neutral. Our theoretical findings are supported by a Li-doping series of $\mathrm{Zn}\mathrm{Sn}{\mathrm{N}}_2$, where a doping concentration ranging from $2.10\times {10}^{19}{\mathrm{cm}}^{-3}$ to $1.85\times {10}^{20}{\mathrm{cm}}^{-3}$ was obtained. The $\mathit{n}$-type carrier concentration was found to be unaffected by the doping concentration, and no systematic change in the absorption onset, probably affected by a Burstein-Moss shift, was observed. Possible group-III dopants, as have been found to yield interesting results for $\mathrm{Zn}\mathrm{Ge}{\mathrm{N}}_2$, such as In, Ga, Al, and B, have also been investigated as an alternative dopant in $\mathrm{Zn}\mathrm{Sn}{\mathrm{N}}_2$.

The structure of the magnesium aluminosilicate glasses ${\left(\mathrm{MgO}\right)}_x{\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)}_y{\left({\mathrm{SiO}}_2\right)}_{1-x-y}$, where $0\le x<1$, $0\le y<1$ and $x+y<1$, was explored by neutron and x-ray diffraction, aided by the results from ${}^{27}\mathrm{Al}$ magic angle spinning nuclear magnetic resonance spectroscopy. A wide composition range was investigated, using aerodynamic levitation with laser heating to extend the glass-forming region well into the peraluminous regime where $R=x/y<1$. The results were interpreted with the aid of an analytical model for the composition-dependent structure where magnesium ions do not contribute towards the glass network. The model delivers Al-O bond distances typical of fourfold and fivefold coordinated aluminum atoms. It also delivers Mg-O coordination numbers of 4.46(9) and 5.39(10) for magnesium in a predominantly network-modifying versus charge-compensating role, corresponding to Mg-O bond distances of 2.024(10) and 2.120(20) Å, respectively. The more compact coordination environment of the network modifier is related to an enhanced probability of magnesium finding nonbridging oxygen (NBO) atoms as the nearest neighbors. Structural change is observed along the tectosilicate tie line in the transformation from a “normal” to “anomalous” glass, where the mechanism of deformation under sharp-contact loading changes from shear flow to densification. A minimum in the composition dependence of the glass hardness is related to a minimum in the Al-O coordination number and to a competition between the availability of NBO atoms, which break the connectivity of the tetrahedral network, versus high cation field-strength ${\mathrm{Mg}}^{2+}$ and fivefold and sixfold coordinated ${\mathrm{Al}}^{3+}$ ions, which cross-link the pieces of the network thus fragmented.

The resistivity scaling of metals is a crucial limiting factor for further downscaling of interconnects in nanoelectronic devices that affects signal delay, heat production, and energy consumption. Here, we generalize a commonly considered figure of merit for selecting promising candidate metals with highly anisotropic Fermi surfaces in terms of their electronic transport properties at the nanoscale. For this, we introduce a finite-temperature transport tensor, based on band structures obtained from first principles. This transport tensor allows for a straightforward comparison between highly anisotropic metals in nanostructures with different lattice orientations and arbitrary transport directions. By evaluating the temperature dependence of the tensor components, we also assess the validity of a Fermi surface-based evaluation of the transport properties at zero temperature, rather than considering standard operating temperature conditions.

${\mathrm{WTe}}_2$, a type-II Weyl semimetal, exhibits extremely large magnetoresistance (XMR) that is attributed to perfect electron-hole compensation. Here, we studied the evolution of the electronic properties of ${\mathrm{WTe}}_2$ with Ni substitution at W sites. Transport measurements exhibit a metal-to-insulator transition at low temperatures with the application of magnetic field; the field-induced effect is significantly reduced in the doped sample. The XMR of about ${10}^6$% at 2 K in ${\mathrm{WTe}}_2$ is reduced to ${10}^4$% in the 10% Ni-doped sample. The magnetoresistance shows an $H^2$ dependence and follows the temperature dependence of classical carrier mobility. We observe a deviation from Kohler's rule in both cases, indicating the presence of multiple types of charge carriers. Quantum oscillation data exhibit a signature of four Fermi pockets (two electron and two hole pockets) in both cases, and the nontrivial nature of the electron and hole bands. Interestingly, the electron-hole compensation is nearly perfect even in the doped compound, although the size of the Fermi pockets and the charge-carrier interaction parameters are slightly changed with doping. These results reveal intriguing insight into the XMR behavior of this class of materials and the possibilities of tuning the properties of charge carriers within the XMR regime.

We investigate the effects of diamagnetic doping in the solid-solution series ${\mathrm{Tb}}_{1\text{−}x}{\mathrm{Y}}_x{\left(\mathrm{HC}{\mathrm{O}}_2\right)}_3$, in which the parent $\mathrm{Tb}{\left({\mathrm{HCO}}_2\right)}_3$ phase has previously been shown to host a combination of frustrated and quasi-one-dimensional (quasi-1D) physics, giving rise to a triangular Ising antiferromagnetic ground state that lacks long range 3D order. Heat capacity measurements show three key features: (i) a low temperature Schottky anomaly is observed, which is constant as a function of $x$; (ii) the transition temperature and associated entropy change are both surprisingly robust to diamagnetic doping; and (iii) an additional contribution at $T<0.4\mathrm{K}$ appears with increasing $x$. The origin of this unusual behavior is rationalized in terms of the fragmentation of quasi-1D spin chains by the diamagnetic ${\mathrm{Y}}^{3+}$ dopant. Magnetocaloric measurements show a nonlinear dependence on $x$. The mass-weighted magnetocaloric entropy decreases across the series from the promising values in $\mathrm{Tb}{\left({\mathrm{HCO}}_2\right)}_3$; however, the magnetocaloric entropy per magnetic ${\mathrm{Tb}}^{3+}$ ion first decreases then increases with increasing $x$. Our results establish ${\mathrm{Tb}}_{1\text{−}x}{\mathrm{Y}}_x{\left(\mathrm{HC}{\mathrm{O}}_2\right)}_3$ as a model system in which to explore the functional ramifications of dilution in a low-dimensional magnet.

Using the Landau-Ginzburg-Devonshire approach, we study screening-induced phase transitions in core-shell ferroic nanoparticles for three different shapes: an oblate disk, a sphere, and a prolate needle. The nanoparticle is made of a ferroic ${\mathrm{CuInP}}_2{\mathrm{S}}_6$ core and covered by a tunable screening shell made of a phase-change material with a conductivity that varies as the material changes between semiconductor and metallic phases. We reveal a critical influence of the shell screening length on the phase transitions and spontaneous polarization of the nanoparticle core. Since the tunable screening shell allows the control of the polar state and phase diagrams of core-shell ferroic nanoparticles, the obtained results can be of particular interest for applications in nonvolatile memory cells.

Machine learning techniques can greatly accelerate material discovery while high-dimensional representation often causes overfitting problems and leads to poor model performance. Building a structure-property relationship with low-dimensional representation is always an open challenge, especially for diverse structures within small datasets. To address this issue, a low-dimensional representation named the transformed atom vector (TAV) is proposed, which is a crystal-graph-based descriptor. As an example, we apply it in two-dimensional materials and predict the band gap at the Heyd-Scuseria-Ernzerhof level with only 500 samples at acceptable accuracy. Moreover, TAV representation retains interpretability, based on which a property-oriented search method through element substitution is developed. This work provides a universal low-dimensional representation containing rich material information, as well as an intuitive interpretation approach for material design, which improves the feasibility and interpretability of machine learning models for small datasets and helps realize accurate yet meaningful property prediction at a lower cost.