Suboxides and subselenides: intermediate reaction products to form GaO, GaSe, InO, InSe, SnO, and SnSe during molecular-beam epitaxy.

The molecular-beam epitaxial (MBE) growth of III-O and IV-O materials (, GaO, InO, and SnO) is known to be reaction-limited by complex 2-step kinetics and the desorption of volatile suboxides (, GaO, InO, SnO). We find that the different surface reactivities of suboxides and respective elements (, Ga, In, Sn) with active oxygen define the film-growth-windows (FGWs) and suboxide-formation-windows (SFWs) of III-O and IV-O materials, respectively. To generalize, we provide elementary reaction pathways and respective Gibbs energies to form binary III-O, III-Se, IV-O, and IV-Se ground-states as well as their subcompounds during their MBE growth.

Electronic-grade epitaxial (111) KTaO heterostructures.

KTaO heterostructures have recently attracted attention as model systems to study the interplay of quantum paraelectricity, spin-orbit coupling, and superconductivity. However, the high and low vapor pressures of potassium and tantalum present processing challenges to creating heterostructure interfaces clean enough to reveal the intrinsic quantum properties. Here, we report superconducting heterostructures based on high-quality epitaxial (111) KTaO thin films using an adsorption-controlled hybrid PLD to overcome the vapor pressure mismatch.

Salt-Assisted Selective Growth of H-phase Monolayer VSe with Apparent Hole Transport Behavior.

Vanadium diselenide (VSe) exhibits versatile electronic and magnetic properties in the trigonal prismatic (H-) and octahedral (T-) phases. Compared to the metallic T-phase, the H-phase with a tunable semiconductor property is predicted to be a ferrovalley material with spontaneous valley polarization. Herein we report an epitaxial growth of the monolayer 2D VSe on a mica substrate via the chemical vapor deposition (CVD) method by introducing salt in the precursor.

Enhancing Moisture Stability of Sulfide Solid-State Electrolytes by Reversible Amphipathic Molecular Coating.

The all-solid-state battery (ASSB) is a promising next-generation energy storage technology for both consumer electronics and electric vehicles because of its high energy density and improved safety. Sulfide solid-state electrolytes (SSEs) have merits of low density, high ionic conductivity, and favorable mechanical properties compared to oxide ceramic and polymer materials. However, mass production and processing of sulfide SSEs remain a grand challenge because of their poor moisture stability.

Atomic control of active-site ensembles in ordered alloys to enhance hydrogenation selectivity.

Intermetallic compounds offer unique opportunities for atom-by-atom manipulation of catalytic ensembles through precise stoichiometric control. The (Pd, M, Zn) γ-brass phase enables the controlled synthesis of Pd-M-Pd catalytic sites (M = Zn, Pd, Cu, Ag and Au) isolated in an inert Zn matrix. These multi-atom heteronuclear active sites are catalytically distinct from Pd single atoms and fully coordinated Pd.

Forming mechanism of equilibrium and non-equilibrium metallurgical phases in dissimilar aluminum/steel (Al-Fe) joints.

Forming metallurgical phases has a critical impact on the performance of dissimilar materials joints. Here, we shed light on the forming mechanism of equilibrium and non-equilibrium intermetallic compounds (IMCs) in dissimilar aluminum/steel joints with respect to processing history (e.g.

Correlation analysis of materials properties by machine learning: illustrated with stacking fault energy from first-principles calculations in dilute fcc-based alloys.

Advances in machine learning (ML), especially in the cooperation between ML predictions, density functional theory (DFT) based first-principles calculations, and experimental verification are emerging as a key part of a new paradigm to understand fundamentals, verify, analyze, and predict data, and design and discover materials. Taking stacking fault energy () as an example, we perform a correlation analysis ofin dilute Al-, Ni-, and Pt-based alloys by descriptors and ML algorithms. Thesevalues were predicted by DFT-based alias shear deformation approach, and up to 49 elemental descriptors and 21 regression algorithms were examined.

Realization of Epitaxial Thin Films of the Topological Crystalline Insulator Sr SnO.

Topological materials are derived from the interplay between symmetry and topology. Advances in topological band theories have led to the prediction that the antiperovskite oxide Sr SnO is a topological crystalline insulator, a new electronic phase of matter where the conductivity in its (001) crystallographic planes is protected by crystallographic point group symmetries. Realization of this material, however, is challenging.

Data set for diffusion coefficients and relative creep rate ratios of 26 dilute Ni-X alloy systems from first-principles calculations.

The development of future generations of Ni-base superalloys will depend on a systematic understanding of how each alloying element affects the fundamental properties of Ni-base superalloys, particularly with respect to their creep behavior. First, this article presents the temperature-dependent data of all factors entering into dilute impurity diffusion for 26 Ni-X alloy systems, including atomic jump frequencies, thermodynamic parameters, and diffusivity plots. Second, this article presents the data used to calculate the relative creep rate ratios showing the effect of each of the 26 alloying elements, X, on the dilute Ni-X alloy.

Fundamentals of Thermal Expansion and Thermal Contraction.

Thermal expansion is an important property of substances. Its theoretical prediction has been challenging, particularly in cases the volume decreases with temperature, i.e.

Origin of Outstanding Phase and Moisture Stability in a NaPAsS Superionic Conductor.

Sodium ion (Na) solid-state electrolytes (SSEs) are critical to address notorious safety issues associated with liquid electrolytes used in the current Na ion batteries. Fulfilling multiple innovations is a grand challenge but is imperative for advanced Na ion SSEs, such as a combination of high ionic conductivity and excellent chemical stability. Here, our first-principles and phonon calculations reveal that NaPAsS (0 ≤ x ≤ 1) is a solid-state superionic conductor stabilized at 0 K by zero-point vibrational energy and at finite temperatures by vibrational and configurational entropies.

Exceptionally High Ionic Conductivity in Na P As S with Improved Moisture Stability for Solid-State Sodium-Ion Batteries.

A Na-ion solid-state electrolyte, Na P As S , is developed with an exceptionally high conductivity of 1.46 mS cm at 25 °C and enhanced moisture stability. Dual effects of alloying element As (lattice expansion and a weaker AsS bond strength) are responsible for the superior conductivity.

Lateral Versus Vertical Growth of Two-Dimensional Layered Transition-Metal Dichalcogenides: Thermodynamic Insight into MoS2.

Unprecedented interest has been spurred recently in two-dimensional (2D) layered transition metal dichalcogenides (TMDs) that possess tunable electronic and optical properties. However, synthesis of a wafer-scale TMD thin film with controlled layers and homogeneity remains highly challenging due mainly to the lack of thermodynamic and diffusion knowledge, which can be used to understand and design process conditions, but falls far behind the rapidly growing TMD field. Here, an integrated density functional theory (DFT) and calculation of phase diagram (CALPHAD) modeling approach is employed to provide thermodynamic insight into lateral versus vertical growth of the prototypical 2D material MoS2.

Data set for diffusion coefficients of alloying elements in dilute Mg alloys from first-principles.

Diffusion coefficients of alloying elements in Mg are critical for the development of new Mg alloys for lightweight applications. Here we present the data set of the temperature-dependent dilute tracer diffusion coefficients for 47 substitutional alloying elements in hexagonal closed packed (hcp) Mg calculated from first-principles calculations based on density functional theory (DFT) by combining transition state theory and an 8-frequency model. Benchmark for the DFT calculations and systematic comparison with experimental diffusion data are also presented.

Thermal expansion anomaly regulated by entropy.

Thermal expansion, defined as the temperature dependence of volume under constant pressure, is a common phenomenon in nature and originates from anharmonic lattice dynamics. However, it has been poorly understood how thermal expansion can show anomalies such as colossal positive, zero, or negative thermal expansion (CPTE, ZTE, or NTE), especially in quantitative terms. Here we show that changes in configurational entropy due to metastable micro(scopic)states can lead to quantitative prediction of these anomalies.

First-principles study of lattice dynamics and thermodynamics of TiO2 polymorphs.

The structural, phonon, and thermodynamic properties of six TiO(2) polymorphs, i.e., rutile, anatase, columbite, baddeleyite, orthorhombic I, and cotunnite, have been systematically investigated by density functional theory.

Temperature-dependent elastic stiffness constants of α- and θ-Al2O3 from first-principles calculations.

Temperature-dependent elastic stiffness constants (c(ij)s), including both the isothermal and isoentropic ones, have been predicted for rhombohedral α-Al(2)O(3) and monoclinic θ-Al(2)O(3) in terms of a quasistatic approach, i.e., a combination of volume-dependent c(ij)s determined by a first-principles strain versus stress method and direction-dependent thermal expansions obtained by first-principles phonon calculations.

First-principles study of structural and elastic properties of monoclinic and orthorhombic BiMnO3.

The structural and elastic properties of BiMnO(3) with monoclinic (C 2/c) and orthorhombic (Pnma) ferromagnetic (FM) structures have been studied by first-principles calculations within LDA + U and GGA + U approaches. The equilibrium volumes and bulk moduli of BiMnO(3) phases are evaluated by equation of state (EOS) fittings, and the bulk properties predicted by LDA + U calculations are in better agreement with experiment. The orthorhombic phase is found to be more stable than the monoclinic phase at ambient pressure.

Magnetic phase transformations of face-centered cubic and hexagonal close-packed Co at zero Kelvin.

The 0 K pressure-induced magnetic phase transformations of face-centered cubic (FCC) and hexagonal close packed (HCP) Co have been examined using first-principles calculations. Issues of fitting an equation of state to the first-principles energy versus volume data points containing a magnetic transformation and comparing to experimental phase equilibria are discussed. It is found that a fitting scheme employing only data where the magnetic moment decreases linearly with volume offers a physically meaningful behavior for the equation of state at metastable volumes.

Thermodynamic properties of Co3O4 and Sr6Co5O15 from first-principles.

The Gibbs energy function of Sr(6)Co(5)O(15) is calculated by first-principles for use in CALPHAD thermodynamic modeling. An efficient method is employed, using the Debye-Grüneisen model to predict the temperature dependence of the heat capacity and entropy. The equation of state from first-principles and the Debye temperature from harmonic phonon calculations by the supercell approach are taken as input.