When a material is heated, generally, it dilates. Here, we find a general trend that the average distance between a center atom and atoms in the first nearest-neighbor shell contracts for several metallic melts upon heating. Using synchrotron X-ray diffraction technique and molecular dynamics simulations, we elucidate that this anomaly is caused by the redistribution of polyhedral clusters affected by temperature. In metallic melts, the high-coordinated polyhedra are inclined to evolve into low-coordinated ones with increasing temperature. As the coordination number decreases, the average atomic distance between a center atom and atoms in the first shell of polyhedral clusters is reduced. This phenomenon is a ubiquitous feature for metallic melts consisting of various-sized polyhedra. This finding sheds light on the understanding of atomic structures and thermal behavior of disordered materials and will trigger more experimental and theoretical studies of liquids, amorphous alloys, glasses, and casting temperature effect on solidification process of crystalline materials.

We investigate Cu-Zr liquid alloys using molecular dynamics simulation and well-accepted embedded atom method potentials over a wide range of chemical composition and temperature as model metallic glass-forming (GF) liquids. As with other types of GF materials, the dynamics of these complex liquids are characterized by “dynamic heterogeneity” in the form of transient polymeric clusters of highly mobile atoms that are composed in turn of atomic clusters exhibiting string-like cooperative motion. In accordance with the string model of relaxation, an extension of the Adam-Gibbs (AG) model, changes in the activation free energy ΔG_a with temperature of both the Cu and Zr diffusion coefficients D, and the alpha structural relaxation time τ_α can be described to a good approximation by changes in the average string length, L. In particular, we confirm that the strings are a concrete realization of the abstract “cooperatively rearranging regions” of AG. We also find coexisting clusters of relatively “immobile” atoms that exhibit predominantly icosahedral local packing rather than the low symmetry packing of “mobile” atoms. These two distinct types of dynamic heterogeneity are then associated with different fluid structural states. Glass-forming liquids are thus analogous to polycrystalline materials where the icosahedrally packed regions correspond to crystal grains, and the strings reside in the relatively disordered grain boundary-like regions exterior to these locally well-ordered regions. A dynamic equilibrium between localized (“immobile”) and wandering (“mobile”) particles exists in the liquid so that the dynamic heterogeneity can be considered to be type of self-assembly process. We also characterize changes in the local atomic free volume in the course of string-like atomic motion to better understand the initiation and propagation of these fluid excitations.

The stability of high-entropy alloys (HEAs) is a key issue before their selection for industrial applications. In this study, in-situ high-pressure and high-temperature synchrotron radiation X-ray diffraction experiments have been performed on three typical HEAs Ni₂₀Co₂₀Fe₂₀Mn₂₀Cr₂₀, Hf₂₅Nb₂₅Zr₂₅Ti₂₅, and Re₂₅Ru₂₅Co₂₅Fe₂₅ (at. %), having face-centered cubic (fcc), body-centered cubic (bcc), and hexagonal close-packed (hcp) crystal structures, respectively, up to the pressure of ∼80 GPa and temperature of ∼1262 K. Under the extreme conditions of the pressure and temperature, all three studied HEAs remain stable up to the maximum pressure and temperatures achieved. For these three types of studied HEAs, the pressure-dependence of the volume can be well described with the third order Birch-Murnaghan equation of state. The bulk modulus and its pressure derivative are found to be 88.3 GPa and 4 for bcc-Hf₂₅Nb₂₅Zr₂₅Ti₂₅, 193.9 GPa and 5.9 for fcc-Ni₂₀Co₂₀Fe₂₀Mn₂₀Cr₂₀, and 304.6 GPa and 3.8 for hcp-Re₂₅Ru₂₅Co₂₅Fe₂₅ HEAs, respectively. The thermal expansion coefficient for the three studied HEAs is found to be in the order as follows: fcc-Ni₂₀Co₂₀Fe₂₀Mn₂₀Cr₂₀ > bcc-Hf₂₅Nb₂₅Zr₂₅Ti₂₅ ≈ hcp-Re₂₅Ru₂₅Co₂₅Fe₂₅.

A sheet-on-sheet reduced graphene oxide–β-In₂S₃ (RGO–In₂S₃) composite, was successfully synthesized via a one-step mild method. This fresh composite used as an anode material exhibits enhanced cyclability and specific capacity for lithium storage. These results are linked with the intrinsic layered structure of β-In₂S₃ sheets and the effective combination of β-In₂S₃ and RGO sheets. This results in a high specific surface area and good conductivity of RGO–In₂S₃ composites, with higher transport rates of electrolyte ions and electrons, and a more effective electrochemical reaction of the active material. This facile and rapid synthesis method is a promising route for a large-scale production of graphene-based metal sulfides, which could be used as electrode materials for Li-ion batteries.

Liquid-liquid crossover is promising and closely related to the atomic dynamics during heating and cooling processes. Here we reveal a reversible structural crossover in the liquid $\mathrm{G}{\mathrm{a}}_{85.8}\mathrm{I}{\mathrm{n}}_{14.2}$ eutectic alloys by using in situ synchrotron x-ray diffraction and ab initio molecular dynamics simulation. A kink always appears on the temperature dependent behaviors of density, ratio of the second peak position to the first in the pair correlation function, coordination number, heat capacity, free energy, and atomic diffusivity in the temperature range of about 400–550 K. It is likely ascribed to atomic rearrangements of Ga and In atoms from a relative random packing at high temperatures to a relative nonuniform packing at low temperatures, in which In atoms prefer to have more In neighbors. This observation will promote more understanding of the liquid structure of eutectic alloys.