arXiv subjects

Y. B. Lebed

Publications and source records attributed to Y. B. Lebed.

8 recordsLinked to original sources

arXiv2025

Extended defects in hard disk system and melting criteria

The hard sphere model is widely used in description of fluids and solid media as a zero approximation to real systems. Despite the uniqueness of the model, few analytical results are known for it, both for the 2D and 3D cases. In present research we have investigated melting of the hard disk system by considering accumulation of extended defects of a certain type in the crystaline phase, and jamming of the disk packing. It results in formulation of melting criteria with lower and upper bounds on volume ratio at melting transition: $25/21 \le V/V_0 \le 5/4$. It was found that, in full agreement with the Berezinskii-Kosterlitz-Thouless-Halperin-Nelson-Young theory, the 2D crystal melts into anisotropic liquid. The second transition, which is the transition between anisotropic and isotropic liquid has volume ratio $5/4 \le V/V_0 \le 13/9$.

cond-mat.soft↗

arXiv2024

The precision of molecular dynamics simulations and what we can learn from it?

We have investigated by molecular dynamics method the influence of a finite number of particles used in computer simulations on fluctuations of thermodynamic properties. As a case study, we used the two-dimensional Lennard-Jones system. 2D Lennard-Jones system, besides being an archetypal one, is a subject of long debate, as to whether it has continuous (infinite-order) or discontinuous (first-order) melting transition. We have found that anomalies on the equation of state (the van-der-Waals or Myer-Wood loops) previously considered a hallmark of the first order phase transition, are at best at the level of noise, since they have the same magnitude as the amplitude of pressure fluctuations. So, they could be regarded as statistically unsignificant effect. Also, we estimated inherent statistical noise, present in computer simulations, and came to conclusion, that it is larger, than predicted by statistical physics, and the difference between them (called algorithmic fluctuations) is possibly due to the computer-related issues. It was demonstrated that these fluctuations in principle could be observed in real-life physical experiments which would lead to practical resolution of The Matrix hypothesis.

cond-mat.stat-mech↗

arXiv2023

Phenomenological model of supercooled liquid as a possible resolution of the Kauzmann paradox

The diverging relaxation time in approaching hypothetical ideal glass transition is a subject of hot debate. In the current paper we demonstrate, how diverging relaxation time and turning excess entropy to zero (which is an essence of Kauzmann's paradox) can be avoided, using as an example the model molecular glassformer, propylene carbonate. For this purpose we compare its thermodynamic and dielectric relaxation properties, both known from the literature. The agreement between two sets of data can be achieved, if we suppose, that enthalpy of supercooled liquid propylene carbonate is governed by activation law, and relaxation time follows double exponential law. We propose the generalized Adam-Gibbs law to reconcile this two dependencies, and qualitatively discuss its implications.

cond-mat.soft↗

arXiv2023

Planar defects as a way to account for explicit anharmonicity in high temperature thermodynamic properties of silicon

Silicon is indispensable in semiconductor industry. Understanding its high-temperature thermodynamic properties is essential both for theory and applications. However, first-principle description of high-temperature thermodynamic properties of silicon (thermal expansion coefficient and specific heat) is still incomplete. Strong deviation of its specific heat at high temperatures from the Dulong-Petit law suggests substantial contribution of anharmonicity effects. We demonstrate, that anharmonicity is mostly due to two transverse phonon modes, propagating in (111) and (100) directions, and can be quantitatively described with formation of the certain type of nanostructured planar defects of the crystal structure. Calculation of these defects' formation energy enabled us to determine their input into the specific heat and thermal expansion coefficient. This contribution turns out to be significantly greater than the one calculated in quasi-harmonic approximation.

cond-mat.mtrl-sci↗

arXiv2021

Dielectric constant of disordered phases of the smallest monoalcohols : evidence for the hindered plastic crystal phase

With gradual temperature increase in premelting regions of solid phase of methanol and high pressure phase of ethanol, and using novel procedure of separation of electrode polarization effects, we are able to register the contribution of relaxation process to low-frequency dielectric constant. This contribution is about half the liquid's dielectric constant near temperature of solidification , and is almost an order of magnitude higher than reported earlier for ambient pressure phase of methanol. As opposed to dielectric constant of water at ambient pressure, which does not change much during crystallization, our finding indicates the hindrance of molecule rotation in orientationally disordered phases of monoalcohols. Similar dielectric responses of ambient pressure methanol and high-pressure phase of ethanol imply existence of hindered plastic crystal phase of ethanol (not observed at low pressures). We also have found some dynamic disorder in nominally fully ordered phase of these monoalcohols ($α$-phase of methanol and low-pressure phase of ethanol), the contribution of this disorder being dependent on external conditions (e.g. temperature), and increasing at approaching the order-disorder transition. On the other hand, the amplitude of dielectric responce in hindered plastic crystal phases is almost independent of temperature.

cond-mat.mtrl-sci↗

arXiv2018

Organic crystalline polymers: structural properties and way to synthesis under high pressure

We consider different structures, which can be obtained by polymerization of aromatic organic molecules under high pressures. These 2D and 3D covalently bonded organic polymers and their functionalization can pave the way to production of energy storage and conversion devices. High-pressure synthesis might serve as a useful hint for production of these structures and their functionalized analogs by means of wet chemical synthesis.

cond-mat.mtrl-sci↗

arXiv2013

Phase transformations in methanol at high pressure measured by dielectric spectroscopy technique

Dielectric response in methanol measured in wide pressure and temperature range ($P < 6.0$ GPa; 100 K $ $ 1.2 GPa $T < 270$ K. In the intermediate P-T region $P \approx 3.4-3.7$ GPa $T \approx 260-280$ K a set of complicated structural transformations occurs involving four methanol crystalline structures. At higher pressures within a narrow range $P \approx 4.3-4.5$ GPa methanol can be obtained in the form of fragile glass ($T_g \approx 200$ K, $m_p \approx 80$ at $P= 4.5$ GPa) by relatively slow cooling.

cond-mat.mtrl-sci↗

arXiv2011

Electrotransport and magnetic properies of Cr-GaSb spintronic materials synthesized under high pressure

Electrotarnsport and magnetic properties of new phases in the system Cr-GaSb were studied. The samples were prepared by high-pressure (P=6-8 GPa) high-temperature treatment and identified by x-ray diffraction and scanning electron microscopy (SEM). One of the CrGa$_2$Sb$_2$ phases with an orthorhombic structure $Iba2$ has a combination of ferromagnetic and semiconductor properties and is potentially promising for spintronic applications. Another high-temperature phase is paramagnetic and identified as tetragonal $I4/mcm$.

cond-mat.mtrl-sci↗