Superconductivity in the type-II Weyl semimetal candidate ${\mathrm{MoTe}}_2$ has attracted much attention due to the possible realization of topological superconductivity. Under applied pressure, the superconducting transition temperature is significantly enhanced, while the structural transition from the high-temperature $1T^{\prime }$ phase to the low-temperature $T_d$ phase is suppressed. Hence, applying pressure allows us to investigate the dimensionality of superconductivity in $1T^{\prime }-{\mathrm{MoTe}}_2$. We have performed a detailed study of the magnetotransport properties and upper critical field $H_{c2}$ of ${\mathrm{MoTe}}_2$ under pressure. The magnetoresistance (MR) and Hall coefficient of ${\mathrm{MoTe}}_2$ are found to decrease with increasing pressure. In addition, the Kohler's scalings for the MR data above $\sim 11\mathrm{kbar}$ show a change of exponent whereas the data at lower pressure can be well scaled with a single exponent. These results are suggestive of a Fermi-surface reconstruction when the structure changes from the $T_d$ to $1T^{\prime }$ phase. The $H_{c2}$-temperature phase diagram constructed at 15 kbar, with $H\parallel ab$ and $H\perp ab$, can be satisfactorily described by the Werthamer–Helfand–Hohenberg model with the Maki parameters $\alpha \sim 0.77$ and 0.45, respectively. The relatively large $\alpha$ may stem from a small Fermi surface and a large effective mass of semimetallic ${\mathrm{MoTe}}_2$. The angular dependence of $H_{c2}$ at 15 kbar can be well fit by the Tinkham model, suggesting the two-dimensional nature of superconductivity in the high-pressure $1T^{\prime }$ phase.

Phase separation of metallic and antiferromagnetic (AFM) insulating phases in alkaline iron selenides $\left({\mathrm{A}}_x\mathrm{F}{\mathrm{e}}_{2-y}\mathrm{S}{\mathrm{e}}_2\right)$ continues to attract intense interest because the relationship between two peculiar features probably is a key to clarifying the pairing mechanism of ${\mathrm{A}}_x\mathrm{F}{\mathrm{e}}_{2-y}\mathrm{S}{\mathrm{e}}_2$ superconductors. Here we report that the three-dimensional (3D) visualizations of nanoscale phase separation in ${\left(\mathrm{N}{\mathrm{a}}_{0.32}{\mathrm{K}}_{0.68}\right)}_{0.95}\mathrm{F}{\mathrm{e}}_{1.75}\mathrm{S}{\mathrm{e}}_2$ single crystals are revealed by hybrid focused-ion-beam scanning electron microscopy and the superconducting paths are fully percolative in 3D. Moreover, the phase-related ultrafast dynamics in ${\left(\mathrm{N}{\mathrm{a}}_{0.32}{\mathrm{K}}_{0.68}\right)}_{0.95}\mathrm{F}{\mathrm{e}}_{1.75}\mathrm{S}{\mathrm{e}}_2$ is studied by dual-color pump-probe spectroscopy. The anomalous changes in the electron and acoustic phonon components of transient reflectivity change $(\mathrm{\Delta }R/R)$ identify two characteristic temperatures $T^{*}\sim 100\mathrm{K}$ (the onset temperature of coupling between the nanometallic and AFM phases) and $T_{\mathrm{H}}\sim 230\mathrm{K}$ (the onset temperature of the metallic-interface phase). An energy-transfer channel between the nanometallic and AFM phases is inferred. This proposed channel provides insight into the pairing mechanism of alkaline iron selenide superconductors.

To shed light on the impact of doping on the conductivity of garnet-type electrolytes, we use molecular dynamics with an ab initio designed force-field to investigate the complex interplay between the carrier concentration and the kinetic and thermodynamic changes induced by the addition of hypervalent dopants. We focus in particular on the effect of the distribution of the doping agents, and we find that there is a need to perform a proper average over the frozen disorder introduced by the doping in order to achieved converged properties. We observe the competing effects induced by the decrease in concentration of the conducting ions (${\mathrm{Li}}^{+}$) and by the perturbation of the energy landscape resulting from the insertion of hypervalent dopants. These two phenomena give rise to an intricate balance between thermodynamic and kinetic properties, which make the interpretation of the experiments very challenging. In particular, while the increase in the dopant concentration stabilizes the conductive cubic phase of these garnet-type materials, the kinetic effects have two distinct components, one promoting and one hindering diffusion.

We have investigated temperature dependence of the elastic constants and higher-order EXAFS (extended x-ray-absorption fine structure) cumulant moments, both of which originate from vibrational anharmonicity. We focus our attention on how the third- or fourth-order anharmonicity contributes to these physical quantities. Although it may be believed that the fourth-order anharmonicity should dominantly contribute to the fourth-order EXAFS cumulant through the first-order quantum statistical perturbation theory, it is consequently found that the experimental fourth-order EXAFS cumulant observed in fcc Ni, Cu, and stainless steel 316 are described mainly by the third-order anharmonicity through the second-order perturbation. In case of the elastic constants, such a situation is more prominent, and the contribution of the fourth-order anharmonicity is negligibly small for the estimation of temperature dependence of the elastic constants. We have also observed significant lattice strains on Cr and Mo in stainless steel 316 through the Fe, Ni, Cr, and Mo K-edge EXAFS measurements: a compressive lattice strain on Cr associated with larger thermal fluctuations and a more significant compressive lattice strain on Mo without enhanced thermal fluctuation. Such a characteristic dissimilarity may be caused by the differences in the atomic weights and the cohesive energies between Cr and Mo. Moreover, we have performed path-integral effective classical potential and classical Monte-Carlo simulations to describe the bulk moduli of the Invar and Elinvar alloys that show noticeable anomalies due to the so-called Invar effect. Appropriate temperature dependence of the bulk moduli is successfully obtained for the Invar, Elinvar, and stainless steel 304 and 316 alloys as well as elemental fcc Cu and Ni metals.

This study aims to investigate the role of amorphous surface layers on the mechanical response of metallic nanoparticles under compression using molecular dynamics simulations. For this purpose, the transferability of three embedded-atom-method (EAM) potentials to model monoatomic Ni glass and amorphous-crystalline structures is examined. Particular attention is paid to the crystallisation rate of the amorphous shell surrounding the crystalline inner structure. Relying on the most appropriate model, the influence of the amorphous layer on the mechanical response of crystalline-amorphous Ni nanoparticles is further investigated. Regardless of its thickness, the amorphous surface layer significantly changes both the effective elastic modulus of the nanoparticle and the flow stress. Besides stress, dislocation nucleation processes as well as the final shape of the compressed particles are influenced by the presence of the amorphous shell. These results bring new insights on the influence of surface state on the mechanics of metallic nano-objects.

We report on the synthesis of a new material with a novel quasi-one-dimensional crystal structure consisting of chains of Cu and $M$ ions: ${\mathrm{Cu}}_{2}M{\mathrm{SiO}}_5$ with $M$ = Co, Ni. Large, centimeter-sized single crystals of ${\mathrm{Cu}}_2{\mathrm{CoSiO}}_5$ have been grown by the floating-zone technique and roughly hexagonally shaped single crystals of ${\mathrm{Cu}}_2{\mathrm{NiSiO}}_5$ have been grown by means of chemical vapor transport. ${\mathrm{Cu}}_2{\mathrm{CoSiO}}_5$ (${\mathrm{Cu}}_2{\mathrm{NiSiO}}_5$) orders antiferromagnetically below $T_N\sim$ 15 K (12.5 K). Polarized neutron scattering experiments on ${\mathrm{Cu}}_2{\mathrm{CoSiO}}_5$ reveal incommensurate magnetism below $T_N$ with propagation vectors ${\mathbf{k}}^{\pm }=\pm (\sim 0.200.3)$, and magnetic susceptibility measurements indicate a large unquenched orbital moment of about $1{\mu }_B$ per Co ion.

Controlling glass-glass interfaces in metallic nanoglasses is essential for tuning their mechanical properties and in particular, the ability to inhibit severe strain localization through distributed shear band formation. In this paper, molecular dynamics are employed to quantify the structural characteristics of interfaces in a scalable nanoglass model produced through hydrostatic compression of amorphous nanoparticles. Using a framework for distinguishing interfaces from amorphous grains based on the correlation between dilatation and atomic volume distributions, we show that the interfaces in our nanoglass model exhibit a volume fraction of 0.36, a width of approximately 2 nm, excess free volume of 1–2%, and full icosahedral (FI) fraction roughly 30% that of a bulk metallic glass counterpart. While these characteristics are quantitatively unique relative to other nanoglass models (e.g., planar interfaces and Poisson-Voronoi constructions), they are consistent with experimental results reported for nanoglasses consolidated from glassy nanoparticles produced through inert gas condensation. Increasing the consolidation temperature enhanced the FI fraction with a strong bias to the interfaces, thus demonstrating a route for tuning interfacial properties in nanoglasses.

Precise x-ray diffraction measurements using high-energy x rays of synchrotron radiation and systematic Raman scattering measurements were carried out for ${\mathrm{Ge}}_x{\mathrm{S}}_{100-x}$ $(10⩽x⩽40)$ network glasses. The structural models of the network glasses were proposed based on the results. In the stoichiometric composition ${\mathrm{Ge}}_{33}{\mathrm{S}}_{67}$, ${\mathrm{GeS}}_4$ tetrahedral units are connected forming either corner-sharing or edge-sharing structures. In the S-rich glasses, S atoms are inserted between two neighboring ${\mathrm{GeS}}_4$ tetrahedra, resulting in a flexible floppy network. In a much more S-rich region, some ${\mathrm{S}}_8$ ring molecules are isolated from the network, and assemble to form a crystal in nanoscopic scale. In this respect, ${\mathrm{Ge}}_{10}{\mathrm{S}}_{90}$ samples are regarded as crystallized glasses. In the Ge-rich region, the ${\mathrm{GeS}}_4$ tetrahedra are connected with bridging Ge atoms. The connection makes a new rigid network. The bridging Ge-S bond is weaker than the intratetrahedron bond, and this leads to drastic changes in the optical properties.

Zirconium alloys are the most widely used nuclear fuel cladding materials for light water power reactors where irradiation damage causes solute redistribution, leading to degradation of alloy properties such as corrosion resistance. Designing radiation-tolerant zirconium alloys requires a thorough understanding of the atomic-scale transport behavior of the alloying elements in Zr. We perform density function theory calculations to investigate the diffusion of Sn, Cr, Fe, Be, Al, and Ni in the hexagonal close-packed (HCP) Zr matrix. We develop a methodology to accurately model the metastable vacancy states along the basal migration path, known to occur in group IV metals. We compute the vacancy-mediated solute diffusion coefficients and drag ratios using the kinetic Monte Carlo method and an analytic Green's function method—the agreement between the two validates our methodology. The computed diffusion coefficients of Sn and Al show good agreement with the experimental data and we expect these solutes to diffuse via the vacancy-mediated mechanism. We use a Green's function approach, parameterized with data from density functional theory calculations, to compute the interstitial diffusion coefficients of Cr, Fe, Be, and Ni in the HCP Zr lattice. The computed diffusion coefficients of Cr, Ni, and Be agree with the experimental measurements within one order of magnitude, while those of Fe are within two orders of magnitude of the experimental measurements. The drag ratios for Cr, Fe, Be, and Ni are positive up to 1235 K, which suggests that nonequilibrium vacancy fluxes could drag these solutes toward sinks such as dislocation loops and grain boundaries. We also compute the transport coefficients without including the metastable states, and using the eight- and thirteen-frequency model. Our results show significant differences in drag ratio for the eight- and thirteen-frequency model predictions compared with the Green's function methodology, but smaller errors in the solute diffusivity. Combining interstitial and vacancy-mediated diffusivities, we predict the unusual result that increased vacancy concentration slows down solute diffusivity, while a sufficiently high vacancy concentration can change the dominant mechanism to an accelerated vacancy-mediated diffusion.

Crystals grow by gathering and bonding of atoms to form an ordered structure. Typically, the growth is equally probable in all crystalline directions, but sometimes it is not, as is the case of nanowire growth. Nanowire growth is explained, in most cases, by the presence of liquid metal droplets that mediate between an incoming flux of atoms and a substrate or an existing crystal nucleus, while defining the lateral dimension. Here, we report and explain a mode of nonisotropic crystal growth observed in two wurtzite semiconductors, InN and ZnO. Being of polar structure, wurtzite crystals possess a built-in internal electric field. Thermally excited charges screen the built-in electric field during growth in a nonuniform, yet symmetric, manner, causing the formation of symmetric domains of inverted polarity. These domains limit the lateral expansion of the crystal, inducing a fiber growth mode. The mechanism described here elucidates phenomena in the growth of group III nitrides on sapphire, emphasizing the need to consider the effects of built-in electric fields in the growth of polar semiconductors.

Phase separation and surface segregation are powerful levers that allow one to synthesize nanocomposites via self-assembly. In the present work, we combine these concepts with vertical epitaxial growth and study Co-Au-${\mathrm{SrTiO}}_3$ thin films as a model system. We demonstrate that ${\mathrm{SrTiO}}_3$, Co, and Au undergo phase separation during sequential pulsed laser deposition, giving rise to a dense array of ultrathin bilayered Co-Au nanowires (NWs) with highly anisotropic optical and magnetic properties. A detailed analysis of the structure of the embedded metallic NWs reveals stabilization of a Co fcc phase and pronounced coupling to the matrix, which leads to large magnetoelastic effects. We discuss possible growth mechanisms yielding bilayer phase separation in nanocolumnar composites and show how the present results can be used to estimate a lower bound for the Co-Au interface energy.

New-generation magnetostrictive applications in micromanipulation instruments, torque sensing, and transducers require materials that offer a combination of large magnetostriction and good structural properties. $\mathrm{F}{\mathrm{e}}_{100-x}\mathrm{G}{\mathrm{a}}_x\text{-based}\left(x=17–19\right)$ alloys are potential candidates. In this work, the solidification behavior of Tb-doped FeGa alloys is investigated by theoretical simulation and experimental observation; directional solidification parameters are optimized to obtain the largest solid solubility of Tb while keeping the $\langle 100\rangle$ preferred orientation. The multiscale evolution of the structure with Tb additions that enhances both magnetostriction and tensile properties is systematically studied in alloys prepared under optimal directional solidification conditions. Magnetostriction of 387 ppm is accompanied by a remarkable tensile fracture strain of 12.5% in 0.05 at.% Tb-doped ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$. The values represent an improvement of $\sim 29\%$ in magnetostriction and a sixfold enhancement in tensile fracture strain compared with undoped binary ${\mathrm{Fe}}_{81}{\mathrm{Ga}}_{19}$. The increase in magnetostriction is attributed to the higher density of tetragonally modified $\mathrm{D}{0}_3$ nanoinclusions induced by traces of Tb. The enhancement in ductility is explained by the dislocation concentration around the submicron-scale Tb-rich precipitates which can effectively hinder their motion. The FeGa alloys doped with traces of Tb can be easily processed to thin sheets or wires and are likely to be extensively applied because they contain only traces of rare earths.

${\mathrm{In}}_2{\mathrm{O}}_3$ is a prototype wide-band-gap semiconductor that exhibits metallic conductivity when highly doped with Sn whereas retaining a high degree of transparency to visible light. It is widely used as a transparent window/electrode in solar cells and light-emitting diodes. The functionality of ${\mathrm{In}}_2{\mathrm{O}}_3$ would be greatly extended if $p$-type conductivity could also be achieved. Using electronic structure calculations, we show that adding Bi to ${\mathrm{In}}_2{\mathrm{O}}_3$ in the form of dilute ${\left({\mathrm{In}}_{1-x}{\mathrm{Bi}}_x\right)}_2{\mathrm{O}}_3$ alloys leads to a new valence band that is sufficiently higher in energy than the original O $2p$ valence band to allow for $p$-type doping. Moreover, the raised valence band in the ${\left({\mathrm{In}}_{1-x}{\mathrm{Bi}}_x\right)}_2{\mathrm{O}}_3$ dilute alloys leads to strong optical absorption in the visible spectrum, opening up for new applications, such as a wide-band-gap absorber layer in tandem solar cells.

Vacancy-mediated diffusion along dislocations, often referred to as pipe diffusion, can contribute to creep deformation of metals in many engineering applications. This process is studied along an $\frac{a}{2}\langle 1\overline{1}0\rangle$ screw dislocation in fcc Ni using a density functional theory approach. An accurate geometrical configuration of the screw dislocation core, dissociated into Shockley partial dislocations and separated by a stacking fault, was previously derived using a lattice Green's function technique. Activation energies and jump frequencies are calculated for atom-vacancy exchanges that contribute to diffusion around and along one of the partial cores. This analysis reveals the significant role of the sites within the compressive component of the dislocation, the dominant contribution of the hops around the screw geometry rather than directly along the dislocation line, and the importance of including the stacking fault sites. Kinetic Monte Carlo simulations use these energies and frequencies to generate diffusion coefficients that account for correlation effects. Near 80% of the melting temperature $T_m$, these pipe diffusivities are an order of magnitude higher than those found in fcc regions, and they are eight orders higher at room temperature. Calculations are compared to experimental results and the differences are discussed. While pipe diffusion is unlikely to contribute to isotropic mass flux at low dislocation densities, it will accelerate dislocation mechanisms controlling creep and climb.

The last decade has seen intense research in materials with reduced dimensionality. The low dimensionality leads to interesting electronic behavior due to electronic confinement and reduced screening. The investigations have to a large extent focused on 2D materials both in their bulk form, as individual layers a few atoms thick, and through stacking of 2D layers into heterostructures. The identification of low-dimensional compounds is therefore of key interest. Here, we perform a geometric analysis of material structures, demonstrating a strong clustering of materials depending on their dimensionalities. Based on the geometric analysis, we propose a simple scoring parameter to identify materials of a particular dimension or of mixed dimensionality. The method identifies spatially connected components of the materials and gives a measure of the degree of “1D-ness,” “2D-ness,” etc., for each component. The scoring parameter is applied to the Inorganic Crystal Structure Database and the Crystallography Open Database, ranking the materials according to their degree of dimensionality. In the case of 2D materials the scoring parameter is seen to clearly separate 2D from non-2D materials and the parameter correlates well with the bonding strength in the layered materials. About 3000 materials are identified as one-dimensional, while more than 9000 are mixed-dimensionality materials containing a molecular (0D) component. The charge states of the components in selected highly ranked materials are investigated using density functional theory and Bader analysis showing that the spatially separated components have either zero charge, corresponding to weak interactions, or integer charge, indicating ionic bonding.

An investigation of bulk-terminated (001) surfaces of ${\mathrm{SrTiO}}_3$, a prototypical cubic perovskite, was made possible with a novel cleaving procedure. Controlled application of strain on a ${\mathrm{SrTiO}}_3$ single-crystal results in a flat cleavage with $\mu \text{m}$-size domains of SrO and ${\mathrm{TiO}}_2$. Distribution of these two terminations is dictated by ferroelectric domains induced by strain during the cleavage process. Atomically resolved scanning tunneling microscopy/atomic force microscopy measurements reveal the presence of point defects in a well-defined concentration of $(14\pm 2)\%$; Sr vacancies form at the SrO termination and complementary Sr adatoms appear at the ${\mathrm{TiO}}_2$ termination. These intrinsic defects stabilize the surface by balancing the interplay between ferroelectricity, surface polarity, and surface charge.