Abstract Analysis of correlations between various physical properties solids provides a formulation simple criteria applicable to the search for new superhard materials. The prospects synthesis substances with key elastic moduli, whose values approach or even exceed those diamond are also discussed. We introduce concept ideal hardness and strength, which relates materials corresponding mechanical characteristics, concepts that less unambiguously determined depend on conditions measurements....

Strongly interacting, dynamically disordered and with no small parameter, liquids took a theoretical status between gases solids the historical tradition of hydrodynamic description as starting point. We review different approaches to well recent experimental work, propose that do not need classifying in terms their proximity or any categorizing for matter. Instead, they are unique system own class notably mixed dynamical state contrast pure states gases. start explaining how...

It is generally agreed that the supercritical region of a liquid consists one single state (supercritical fluid). On other hand, we show here liquids in this exist two qualitatively different states: ``rigid'' and ``nonrigid'' liquids. Rigid to nonrigid transition corresponds condition $\ensuremath{\tau}\ensuremath{\approx}{\ensuremath{\tau}}_{0}$, where $\ensuremath{\tau}$ relaxation time ${\ensuremath{\tau}}_{0}$ minimal period transverse quasiharmonic waves. This defines new dynamic...

We discuss the fluid state of matter at high temperature and pressure. review existing ways in which boundary between a liquid quasigas above critical point are discussed. show that proposed 'thermodynamic' continuation boiling line, 'Widom line', exists as line near only, but becomes bunch short lines higher temperature. subsequently propose new 'dynamic' separating gas-like fluid. The dynamic is related to different types particle trajectories diffusion mechanisms liquids dense gases....

We have studied in situ the kinetics of amorphous-amorphous coordination transformation ${\mathrm{GeO}}_{2}$ glass and initial stage vitreous ${\mathrm{SiO}}_{2}$ up to 9 GPa by volume vs time measurements using precise strain-gauge technique. The dependence at all pressure points was found obey logarithmic law, which distinguishes observed from that ordinary transitions crystals. first evidence anelastic behavior quasistatic equation state $P\ensuremath{\approx}6--7$ for 2--3 glass, i.e.,...

Recently, we have proposed a new dynamic line on the phase diagram in supercritical region, Frenkel line. Crossing corresponds to radical changes of system properties. Here, focus dynamics model Lennard-Jones and soft-sphere fluids. We show that location can be rigorously quantitatively established basis velocity autocorrelation function (VAF) mean-square displacements. VAF is oscillatory below at low temperature, monotonically decreasing above high temperature. Using this criterion,...

Heat capacity of matter is considered to be its most important property because it holds information about system's degrees freedom as well the regime in which system operates, classical or quantum. understood gases and solids but not third main state matter, liquids discussed physics textbooks a result. The perceived difficulty that interactions liquid are both strong system-specific, implying energy strongly depends on type that, therefore, can calculated general form. Here, we develop...

The locus of extrema (ridges) for heat capacity, thermal expansion coefficient, compressibility, and density fluctuations model particle systems with Lennard-Jones (LJ) potential in the supercritical region have been obtained. It was found that ridges different thermodynamic values virtually merge into a single Widom line at T < 1.1T(c) P 1.5P(c) become practically completely smeared 2.5T(c) 10P(c), where T(c) P(c) are critical temperature pressure. ridge capacity approaches close to...

Supercritical fluids are widely used in a number of important technological applications, yet the theoretical progress field has been rather moderate. Fairly recently, new understanding liquidlike and gaslike properties supercritical come to fore, particularly with advent Widom Frenkel lines that aim demarcate different physical on phase diagram. Here, we report results computational study carbon dioxide, one most chemical industry. We response functions ${\mathrm{CO}}_{2}$ state calculate...

Abstract Phase transitions in crystalline substances are a major field of study high-pressure physics. The sequences structural transformations and the boundaries separating different phases have been established for majority elements under high pressure temperatures. Though both electron taking place crystals should also be present liquid state, such questions as metallization dielectric liquids, nature short-range order reconstruction, presence states, thermodynamic description melts,...

We outline the current state of experimental study and basic ideas for describing phase transitions in topologically disordered condensed matter, such as liquids amorphous solids. Reviewing briefly molten elementary substances under pressure, we pay primary attention to results liquid Se, S, P also those that have not been represented previous publications, mainly oxides B2O3 GeO2. The data reveal possibility rather sharp transformations relatively simple are smoothed at high temperatures....

The present review covers the production of new materials under high pressures. A primary limitation on use pressures higher than 1 GPa is a small volume and mass produced material. Therefore, despite an extremely wide range high-pressure synthesized substances with unique properties, synthesis commercial scale applied up to now only obtain superhard materials, this real treasure today's industry. At same time, experiments often give material scientists hint at what intriguing can exist in...

We propose a new simple way to evaluate the effect of anharmonicity on system's thermodynamic functions such as heat capacity. In this approach, contribution all potentially complicated anharmonic effects constant-volume capacity is evaluated by one parameter only, coefficient thermal expansion. Importantly, approach applicable not only crystals but also glasses and viscous liquids. To support proposal, we perform molecular dynamics simulations several crystalline amorphous solids well...

Standard ways to distinguish between the two phases don’t apply at high pressure and temperature. But a look medium’s microscopic behavior makes it possible discriminate liquid gas everywhere on phase diagram.

A fundamental problem of glass transition is to provide a quantitative and microscopic explanation the heat-capacity jump at temperature ${T}_{g}$. Similar problems are also common other disordered systems, including spin glasses. We propose that heat capacity ${T}_{g}$ takes place as result change liquid's elastic, vibrational, thermal properties. In this theory, we discuss time-dependent effects transition, identify three distinct regimes relaxation. Our approach explains widely observed...

In the framework of van der Waals model, analytical expressions for locus extrema (ridges) heat capacity, thermal expansion coefficient, compressibility, density fluctuation, and sound velocity in supercritical region have been obtained. It was found that ridges different thermodynamic values virtually merge into single Widom line only at T < 1.07T(c), P 1.25P(c) become smeared 2T(c), 5P(c), where T(c) P(c) are critical temperature pressure. The behavior Batschinski lines pseudo-Gruneisen...

A new dynamic line, the Frenkel has recently been proposed to separate supercritical state into rigid-liquid and nonrigid gaslike fluid. The location of line on phase diagram is unknown for real fluids. Here we map three important systems: CO(2), H(2)O, CH(4). This provides an demarcation these systems, that separates two distinct physical states with liquidlike properties. We find can have a similar trend as melting above critical pressure. Moreover, discuss relationship between unexplained...

Recent research suggests that the supercritical state consists of liquidlike and gaslike states where particle dynamics key system properties are qualitatively different. We report experimental evidence structural crossover in neon at pressure temperature conditions significantly exceeding critical point values: $250\phantom{\rule{0.16em}{0ex}}{P}_{c}$ $6.6\phantom{\rule{0.16em}{0ex}}{T}_{c}$. The results show a medium-range order structure evidenced by change factor with pressure. also...

Abstract Although the understanding of excitation spectra in fluids is great importance, it still unclear how different methods spectral analysis agree with each other and which them suitable a wide range parameters. Here, we show that problem can be solved using two-oscillator model to analyze total velocity current spectra, while considered methods, including maxima single mode analysis, yield rough results become unsuitable at high temperatures wavenumbers. To prove this, perform...

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

Reports published in the last 25 years on synthesis of carbon-based materials significantly superior to diamond hardness and elastic properties have been critically examined, three groups recently appearing myths analyzed. The first group concerns possibility producing with bulk moduli much higher than that diamond. second “experimentally measured” hardness, which is Myths third state quantum confinement effects supposedly provide “theoretical” foundations for a several-fold increase...