Structure and density of silicon carbide to 1.5 TPa and implications for extrasolar planets

MXenes vs. clays: emerging and traditional 2D layered nanoarchitectonics

Although MXene materials are considered an emerging research topic, they are receiving considerable interest because, like metals and graphene, they are good electronic conductors but with the particularity that they have a marked hydrophilic character. Having a structural organization and properties close to those of clay minerals (natural silicates typically with a lamellar morphology), they are sometimes referred to as "conducting clays" and exhibit colloidal, surface and intercalation properties also similar to those of clay minerals. The present contribution aims to inform and discuss the nature of MXenes in comparison with clay phyllosilicates, taking into account their structural analogies, outstanding surface properties and advanced applications. The current in-depth understanding of clay minerals may represent a basis for the future development of MXene-derived nanoarchitectures. Comparative examples of the preparation, and studies on the properties and applications of various nanoarchitectures based on clays and MXenes have been included in the present work.

Extended X-ray absorption fine structure of dynamically-compressed copper up to 1 terapascal

Large laser facilities have recently enabled material characterization at the pressures of Earth and Super-Earth cores. However, the temperature of the compressed materials has been largely unknown, or solely relied on models and simulations, due to lack of diagnostics under these challenging conditions. Here, we report on temperature, density, pressure, and local structure of copper determined from extended x-ray absorption fine structure and velocimetry up to 1 Terapascal. These results nearly double the highest pressure at which extended x-ray absorption fine structure has been reported in any material. In this work, the copper temperature is unexpectedly found to be much higher than predicted when adjacent to diamond layer(s), demonstrating the important influence of the sample environment on the thermal state of materials; this effect may introduce additional temperature uncertainties in some previous experiments using diamond and provides new guidance for future experimental design.

Imaging velocity interferometer system for any reflector (VISAR) diagnostics for high energy density sciences

Two variants of optical imaging velocimetry, specifically the one-dimensional streaked line-imaging and the two-dimensional time-resolved area-imaging versions of the Velocity Interferometer System for Any Reflector (VISAR), have become important diagnostics in high energy density sciences, including inertial confinement fusion and dynamic compression of condensed matter. Here, we give a brief review of the historical development of these techniques, then describe the current implementations at major high energy density (HED) facilities worldwide, including the OMEGA Laser Facility and the National Ignition Facility. We illustrate the versatility and power of these techniques by reviewing diverse applications of imaging VISARs for gas-gun and laser-driven dynamic compression experiments for materials science, shock physics, condensed matter physics, chemical physics, plasma physics, planetary science and astronomy, as well as a broad range of HED experiments and laser-driven inertial confinement fusion research.

Pressure-induced structural phase transitions of zirconium: anab initiostudy based on statistical ensemble theory

Recently, we put forward a direct integral approach to solve the partition function with ultrahigh efficiency and precision, which enables the rigorous ensemble theory to investigate phase behaviors of realistic condensed matters and has been successfully applied to the phase transition of vanadium metal (Ninget al2022J. Phys.: Condens. Matter34425404). In this work, the approach is applied to the structural phase transitions of zirconium metal under compressions up to 160 GPa and ultrahigh calculation precision is achieved. For the obtained equation of state with pressure over 40 GPa, the deviations from latest experiments are within0.7%and the computed transition pressure ofα→ωis 6.93 GPa, which is about five times larger than previous theoretical predictions and in excellent agreement with the measured range of 5-15 GPa. Our results support the argument that there is no existence of the isostructural phase transition of Zr metal that was asserted by recent experimental observations.

The Electronic Spectrum of Si2. J Phys Chem Lett 2022;13:7624-7628. [PMID: 35951547 DOI: 10.1021/acs.jpclett.2c02200]

The optical spectrum of Si₂⁺ is presented. The two electronic band systems observed near 430 and 270 nm correspond to the two lowest optically allowed transitions of Si₂⁺ assigned to ⁴Σ_u^-(I) ← X⁴Σ_g^- and ⁴Σ_u^-(II) ← X⁴Σ_g^-. The spectra were measured via photodissociation spectroscopy of mass-selected ions at the level of vibrational resolution, and the determined spectroscopic constants provide detailed information about the geometric and electronic structure, establishing molecular constants of this fundamental diatomic cation that enable astrophysical detection on, for example, hot rocky super-Earth-like exoplanets.