Thermodynamic properties of liquid gallium from picosecond acoustic velocity measurements

Structural transitions in liquid semiconductor alloys: A molecular dynamics study with a neural network potential

Liquid-liquid phase transitions hold a unique and profound significance within condensed matter physics. These transitions, while conceptually intriguing, often pose formidable computational challenges. However, recent advances in neural network (NN) potentials offer a promising avenue to effectively address these challenges. In this paper, we delve into the structural transitions of liquid CdTe, CdS, and their alloy systems using molecular dynamics simulations, harnessing the power of an NN potential named LaspNN. Our investigations encompass both pressure and temperature effects. Through our simulations, we uncover three primary liquid structures around melting points that emerge as pressure increases: tetrahedral, rock salt, and close-packed structures, which greatly resemble those of solid states. In the high-temperature regime, we observe the formation of Te chains and S dimers, providing a deeper understanding of the liquid's atomic arrangements. When examining CdSxTe1-x alloys, our findings indicate that a small substitution of S by Te atoms for S-rich alloys (x > 0.5) exhibits a structural transition much different from CdS, while a large substitution of Te by S atoms for Te-rich alloys (x < 0.5) barely exhibits a structural transition similar to CdTe. We construct a schematic diagram for liquid alloys that considers both temperature and pressure, providing a comprehensive overview of the alloy system's behavior. The local aggregation of Te atoms demonstrates a linear relationship with alloy composition x, whereas that of S atoms exhibits a nonlinear one, shedding light on the composition-dependent structural changes.

Experimental Confirmation of the Universal Law for the Vibrational Density of States of Liquids

An analytical model describing the vibrational density of states (VDOS) of liquids has long been elusive, owing to the complexities of liquid dynamics. Nevertheless, Zaccone and Baggioli have recently developed such a model which was proposed to be the universal law for the vibrational density of states of liquids. Distinct from the Debye law, g(ω) ∝ ω², for solids, the universal law for liquids reveals a linear relationship, g(ω) ∝ ω, in the low-energy region. We have confirmed this universal law with experimental VDOS measured by inelastic neutron scattering on real liquid systems including water, liquid metal, and polymer liquids, and have applied this model to extract the effective relaxation rate for the short time dynamics for each liquid. The model has also been further evaluated in the prediction of the specific heat with comparison to existing experimental data as well as with values obtained by different approaches.

Picosecond Acoustics Technique to Measure the Sound Velocities of Fe-Si Alloys and Si Single-Crystals at High Pressure

We describe here a time resolved pump-probe laser technique—picosecond interferometry—which has been combined with diamond anvil cells (DAC). This method enables the measurement of the longitudinal sound velocity up to Mbar pressure for any kind of material (solids, liquids, metals, insulators). We also provide a description of picosecond acoustics data analysis in order to determine the complete set of elastic constants for single crystals. To illustrate such capabilities, results are given on the pressure dependence of the acoustic properties for prototypical cases: polycrystal (hcp-Fe-5 wt% Si up to 115 GPa) and single-crystal (Si up to 10 GPa).

Molecular Dual-Rotators with Large Consecutive Emission Chromism for Visualized and High-Pressure Sensing

Low-cost, stable, highly sensitive, and easy-to-equip fluorescent high-pressure sensors are always attractive in both industrial and scientific communities. Organic emitting materials with pressure-dependent bathochromisms usually exhibit prominent mechanoluminescence, due to disturbance of intermolecular packing. This hinders their applications in stable and robust pressure sensing. In this work, we have developed a mechanically stable organic molecular pressure sensor, caused by intramolecular consecutive rotations by pressure, which exhibit large and eye-detectable emission bathochromism from yellow-green to red fluorescence and can be used for 0-15 GPa pressure sensing. The emission bathochromism shows good linear relationship with pressure, exhibiting a high linear coefficient of 9.1 nm/GPa. Moreover, this molecular sensor exhibits high thermal and mechanical stabilities, indicating good potentials for robust and outdoor applications.