Polyhydric alcohols under high pressure: comparative ultrasonic study of elastic properties.

We carried out an experimental ultrasonic study of polyhydric alcohols with the general chemical formula CH(OH) with an increasing number of OH groups: glycerol ( = 3), erythritol ( = 4), xylitol ( = 5), sorbitol ( = 6). The baric and temperature dependences of the elastic characteristics of these substances in the crystalline and glassy states were studied both under isothermal compression up to 1 GPa and during the isobaric heating of 77-295 K. For glycerol, glasses were obtained at different cooling rates, glass-liquid transitions were studied at different pressures.

Remarkably Stable Glassy GeS Densified at 8.3 GPa: Hidden Polyamorphism, Contrasting Optical Properties, Raman and DFT Studies, and Advanced Applications.

Glassy GeS, densified at 8.3 GPa, exhibits a strongly reduced bandgap, predominantly tetrahedral Ge environment, enhanced chemical disorder and partial 3-fold coordination of both germanium and sulfur, assuming two possible reaction paths under high pressure: (i) a simple dissociation 2Ge-S ⇄ Ge-Ge + S-S and (ii) a chemical disproportionation GeS ⇄ GeS + S. The observed electronic and structural changes remain intact for at least seven years under ambient conditions but are gradually evolving upon heating.

Thermobaric history as a tool to govern properties of glasses: case of dipropylene glycol.

The elastic properties of high- and low-pressure glasses of dipropylene glycol were determined for the first time under conditions of isothermal compression up to 1 GPa at 77 K and isobaric heating of 77-300 K at 0.05 GPa and 1 GPa. A strong dependence of the elastic properties of glasses on their thermobaric history has been revealed: glasses obtained at high pressure have not only higher densities (3.

High-Pressure Synthesis of Cubic ZnO and Its Solid Solutions with MgO Doped with Li, Na, and K.

The possibility of doping ZnO in its metastable rock salt structure with Li, Na, and K intended to act as acceptor dopants was investigated. For the first time, MgZnO alloys and pure ZnO with a rock salt structure doped with Li, Na, and K metals was obtained by high-pressure synthesis from pure oxides with the addition of carbonates or acetates of the corresponding metals as dopant sources. Successful stabilization of the metastable rock salt structure and phase purity were confirmed by X-ray diffraction.

Local structure, thermodynamics, and melting of boron phosphide at high pressures by deep learning-driven ab initio simulations.

Boron phosphide (BP) is a (super)hard semiconductor constituted of light elements, which is promising for high demand applications at extreme conditions. The behavior of BP at high temperatures and pressures is of special interest but is also poorly understood because both experimental and conventional ab initio methods are restricted to studying refractory covalent materials. The use of machine learning interatomic potentials is a revolutionary trend that gives a unique opportunity for high-temperature study of materials with ab initio accuracy.

Benzophenone glass, supercooled liquid, and crystals: elastic properties and phase transitions.

The elastic properties of glass α- and β-modifications of benzophenone (CH)CO are determined for the first time by the ultrasonic method at high pressures up to 1 GPa and in the temperature range of 77 K< < 293 K. Four states of benzophenone are experimentally observed in the investigated temperature range of 77-293 K: glass, supercooled liquid, and α- and β-crystalline phases. The boundaries of phase transitions during isobaric heating are determined.

Setup for precision optical studies of supercritical fluids in a wide temperature range at high pressures up to 1 GPa.

A setup with a working volume of more than 10 mm has been fabricated to experimentally study the optical properties of gases, liquids, and solutions in a wide range of temperature (from 200 to 500 K) at hydrostatic pressures up to 1 GPa. The experimental parameters can be maintained with an accuracy of 0.1 K and 1.

Transient Mesoscopic Immiscibility, Viscosity Anomaly, and High Internal Pressure at the Semiconductor-Metal Transition in Liquid GaTe.

Gallium tellurides appear to be promising phase-change materials (PCMs) of the next generation for brain-inspired computing and reconfigurable optical metasurfaces. They are different from the benchmark PCMs because of sp gallium hybridization in both cubic GaTe and amorphous pulsed laser deposition (PLD) films. Liquid GaTe also shows a viscosity η() anomaly just above melting when η() first and only then starts decreasing.

The thermodynamics of pressurized methanol: A simple hydrogen-bonded liquid as a touchstone for experiment and computer simulations.

Methanol as a basic liquid and the simplest alcohol is widely used in industry and scientific experiments. However, there are still no reliable data on the thermodynamic properties of methanol at high pressure. Here, we present an experimental and computational study of the thermodynamic properties of liquid methanol under high pressure up to 15 kbar, which significantly exceeds previously reported pressures.

Ultrasonic study of 1-X adamantane (X = F, Cl, Br) compounds at high pressure and at order-disorder transitions.

We present an ultrasonic study of the elastic properties of 1-X adamantane (X = F, Cl, Br) during order-disorder and order-quasi-order transitions at various temperatures (77-305 K) and high pressures (up to 1 GPa). On the basis of our ultrasonic experiments, we studied for the first time the high-temperature (HT) 3, medium-temperature (MT) 4/, and low-temperature (LT) 42 phases of 1-fluoroadamantane at high pressures. The elastic properties of these phases at pressures up to 1 GPa at = 293 and 77 K, as well as at isobaric heating from 77 to 293 K, have been determined.

Universal interrelation between dynamics and thermodynamics and a dynamically driven "c" transition in fluids.

Our very wide survey of the supercritical phase diagram and its key properties reveals a universal interrelation between dynamics and thermodynamics and an unambiguous transition between liquidlike and gaslike states. This is seen in the master plot showing a collapse of the data representing the dependence of specific heat on key dynamical parameters in the system for many different paths on the phase diagram. As a result, the observed transition is path independent.

Phase transitions in 1-bromoadamantane compared to 1-chloroadamantane: similarities and unique features.

The elastic properties of 1-chloroadamantane and 1-Bromoadamantane in order-disorder and order-quasi-order phase transitions at temperatures in the range of 77-305 K and high pressures up to 1.1 GPa are studied by the ultrasonic method. The elastic moduli of halogenated adamantanes clearly indicate these transitions, demonstrating high capabilities of the ultrasonic method.

Extended Defects in Graphene and Their Contribution to the Excess Specific Heat at High Temperatures.

The recent experiments on fast (microsecond) pulse heating of graphite suggest the existence of sharp maximum (6500 K at 1-2 GPa) on its melting curve. To check the validity of these findings, we propose to investigate the accumulation of extended in-plane defects in graphene. Such defects would contribute to thermodynamic properties of graphene and impose the upper limit on its melting temperature.

Comparative study of the elastic properties of adamantane and 1-chloroadamantane at high pressure and different temperatures and at order-disorder transitions.

We present a comparative ultrasonic study of the elastic properties of adamantane and 1-chloroadamantane at high pressure (up to 1.4 GPa) and different temperatures (77-293 K) and at order-disorder transitions. The ultrasonic method provides complementary pictures of the order-disorder transitions in diamondoids under pressure.

Speed of sound from fundamental physical constants.

Two dimensionless fundamental physical constants, the fine structure constant α and the proton-to-electron mass ratio [Formula: see text], are attributed a particular importance from the point of view of nuclear synthesis, formation of heavy elements, planets, and life-supporting structures. Here, we show that a combination of these two constants results in a new dimensionless constant that provides the upper bound for the speed of sound in condensed phases, We find that [Formula: see text], where is the speed of light in vacuum. We support this result by a large set of experimental data and first-principles computations for atomic hydrogen.

Universal Effect of Excitation Dispersion on the Heat Capacity and Gapped States in Fluids.

The change in dispersion of high-frequency excitations in fluids, from an oscillating solidlike to a monotonic gaslike one, is shown for the first time to affect thermal behavior of heat capacity and the q-gap width in reciprocal space. With in silico study of liquified noble gases, liquid iron, liquid mercury, and model fluids, we established universal bilinear dependence of heat capacity on q-gap width, whereas the crossover precisely corresponds to the change in the excitation spectra. The results open novel prospects for studies of various fluids, from simple to molecular liquids and melts.

WB : Synthesis, Properties, and Crystal Structure-New Insights into the Long-Debated Compound.

The recent theoretical prediction of a new compound, WB, has spurred the interest in tungsten borides and their possible implementation in industry. In this research, the experimental synthesis and structural description of a boron-rich tungsten boride and measurements of its mechanical properties are performed. The ab initio calculations of the structural energies corresponding to different local structures make it possible to formulate the rules determining the likely local motifs in the disordered versions of the WB structure, all of which involve boron deficit.

Experimental and modeling evidence for structural crossover in supercritical CO_{2}.

The physics of supercritical states is understood to a much lesser degree compared to subcritical liquids. Carbon dioxide, in particular, has been intensely studied, yet little is known about the supercritical part of its phase diagram. Here, we combine neutron scattering experiments and molecular dynamics simulations and demonstrate the structural crossover at the Frenkel line.

Pronounced structural crossover in water at supercritical pressures.

There have been ample studies of the many phases of HO in both its solid and low pressure liquid states, and the transitions between them. Using molecular dynamics simulations we address the hitherto unexplored deeply supercritical pressures, where no qualitative transitions are thought to take place and where all properties are expected to vary smoothly. On the basis of these simulations we predict that water at supercritical pressures undergoes a structural crossover across the Frenkel line at pressures as high as 45 times the critical pressure.

Minimal quantum viscosity from fundamental physical constants.

Viscosity of fluids is strongly system dependent, varies across many orders of magnitude, and depends on molecular interactions and structure in a complex way not amenable to first-principles theories. Despite the variations and theoretical difficulties, we find a new quantity setting the minimal kinematic viscosity of fluids: , where and are electron and molecule masses. We subsequently introduce a new property, the "elementary" viscosity ι with the lower bound set by fundamental physical constants and notably involving the proton-to-electron mass ratio: , where is the proton mass.

Mechanism of universal conductance fluctuations.

Universal conductance fluctuations are usually observed in the form of aperiodic oscillations in the magnetoresistance of thin wires as a function of the magnetic field. If such oscillations are completely random at scales exceeding, their Fourier analysis should reveal a white noise spectrum at frequencies belowξB-1. Comparison with the results for 1D systems suggests another scenario: according to it, such oscillations are due to the superposition of incommensurate harmonics and their spectrum should contain discrete frequencies.

Experimental study of water thermodynamics up to 1.2 GPa and 473 K.

Water is the most common liquid on the Earth. At the same time, it is the strangest liquid having numerous anomalous properties. For this reason, although water was investigated in numerous studies, many questions still remain unanswered.

Extended short-range order determines the overall structure of liquid gallium.

Polyvalent metal melts (gallium, tin, bismuth, etc.) have microscopic structural features, which are detected by neutron and X-ray diffraction and which are absent in simple liquids. Based on neutron and X-ray diffraction data and the results of ab initio molecular dynamics simulations for liquid gallium, we examine the structure of this liquid metal at the atomistic level.

Direct Experimental Evidence of Longitudinal and Transverse Mode Hybridization and Anticrossing in Simple Model Fluids.

A significant number of key properties of condensed matter are determined by the spectra of elementary excitations and, in particular, collective vibrations. However, the behavior and description of collective modes in disordered media (e.g.

Pressure-Driven Chemical Disorder in Glassy AsS up to 14.7 GPa, Postdensification Effects, and Applications in Materials Design.

A small difference in energy between homopolar and heteropolar bonds and the glass-forming ability of pure chalcogens leads to unexpected trends in densification mechanisms of glassy chalcogenides compared to vitreous oxides. Using high-precision compressibility measurements and in situ high-energy X-ray diffraction up to 14.7 GPa, we show a new densification route in a canonical glass AsS.