Thermodynamic properties and electrical conductivity of strongly correlated plasma media

We study thermodynamic properties and the electrical conductivity of dense hydrogen and deuterium using three methods: classical reactive Monte Carlo (REMC), direct path integral Monte Carlo (PIMC) and a quantum dynamics method in the Wigner representation of quantum mechanics. We report the calculation of the deuterium compression quasi-isentrope in good agreement with experiments. We also solve the Wigner-Liouville equation of dense degenerate hydrogen calculating the initial equilibrium state by the PIMC method. The obtained particle trajectories determine the momentum-momentum correlation functions and the electrical conductivity and are compared with available theories and simulations

Hole crystallization in semiconductors

When electrons in a solid are excited to a higher energy band they leave behind a vacancy (hole) in the original band which behaves like a positively charged particle. Here we predict that holes can spontaneously order into a regular lattice in semiconductors with sufficiently flat valence bands. The critical hole to electron effective mass ratio required for this phase transition is found to be of the order of 80.Comment: accepted for publication in J. Phys. A: Math. Ge

Investigation of the Degree of Local Structural Similarity between the Parent-liquid and Children-crystal States for a Model Soft Matter System

We investigate the degree of local structural similarity between the parent-liquid and children-crystal states for a model soft-matter system of particles interacting through the harmonic-repulsive pair potential. At different pressures, this simple system crystallizes into several significantly different crystal structures. Therefore, the model is well suited for addressing the question under consideration. In our studies, we carefully analyze the developments of the pair and triple correlation functions for the parent-liquid as the pressure increases. In particular, these considerations allow us to address the similarities in the orientational orderings of the corresponding liquid and solid phases. It is demonstrated that the similarities in the orientational ordering between the two states extend beyond the first and second neighbors. Currently, it is widely accepted that orientational ordering is important for understanding the behaviors of liquids, supercooled liquids, and the development of detailed theories of the crystallization process. Our results suggest that, up to a certain degree, it might be possible to predict the structures of the children-solids from studies of the parent-liquids. Our results raise anew a general question of how much insight into the properties of the liquid-state can be gained from drawing a parallel with the solid-state. © 2021 Elsevier B.V.This document is the results of the research project funded by the Russian Science Foundation (RNF-grant 18-12-00438).This work was supported by the Russian Science Foundation (grant 18-12-00438). We gratefully acknowledge access to the following computational resources: Supercomputing Center of Novosibirsk State University (http://nusc.nsu.ru), the federal collective usage center "Complex for Simulation and Data Processing for Mega-science Facilities" at NRC "Kurchatov Institute" (http://ckp.nrcki.ru/), supercomputers at Joint Supercomputer Center of Russian Academy of Sciences (http://www.jscc.ru), and ?Uran? supercomputer of IMM UB RAS (http://parallel.uran.ru)

Structure of the Simple Harmonic-Repulsive System in Liquid and Glassy States Studied by the Triple Correlation Function

An efficient description of the structures of liquids and, in particular, the structural changes that happen with liquids on supercooling remains to be a challenge. The systems composed of soft particles are especially interesting in this context because they often demonstrate non-trivial local orders that do not allow to introduce the concept of the nearest-neighbor shell. For this reason, the use of some methods, developed for the structure analysis of atomic liquids, is questionable for the soft-particle systems. Here we report about our investigations of the structure of the simple harmonic-repulsive liquid in 3D using the triple correlation function (TCF), i.e., the method that does not rely on the nearest neighbor concept. The liquid is considered at reduced pressure (P = 1.8) at which it exhibits remarkable stability against crystallization on cooling. It is demonstrated that the TCF allows addressing the development of the orientational correlations in the structures that do not allow drawing definite conclusions from the studies of the bond-orientational order parameters. Our results demonstrate that the orientational correlations, if measured by the heights of the peaks in the TCF, significantly increase on cooling. This rise in the orientational ordering is not captured properly by the Kirkwood's superposition approximation. Detailed considerations of the peaks' shapes in the TCF suggest the existence of a link between the orientational ordering and the slowdown of the system's dynamics. Our findings support the view that the development of the orientational correlations in liquids may play a significant role in the liquids' dynamics and that the considerations of the pair distribution function may not be sufficient to understand intuitively all the structural changes that happen with liquids on supercooling. In general, our results demonstrate that the considerations of the TCF are useful in the discussions of the liquid's structures beyond the pair density function and interpreting the results obtained with the bond-orientational order parameters. © 2020 IOP Publishing Ltd.This work was supported by the Russian Science Foundation (Grant 18-12-00438). We gratefully acknowledge access to the following computational resources: Supercomputing Center of Novosibirsk State University (http://nusc.nsu.ru), the federal collective usage center ‘Complex for Simulation and Data Processing for Mega-science Facilities’ at NRC ‘Kurchatov Institute’ (http://ckp.nrcki.ru/), supercomputers at Joint Supercomputer Center of Russian Academy of Sciences (http://jscc.ru), and ‘Uran’ supercomputer of IMM UB RAS (http://parallel.uran.ru)

Effect of Mechanical Activation on Ti3AlC2 Max Phase Formation under Self-Propagating High-Temperature Synthesis

In this study, we have investigated the effect of various mechanical activation (MA) modes on phase and structure formation in powder mixtures made up to produce Ti3AlC2 MAX phase. The optimal MA duration has been established which results in the maximum heat release under SHS due to accumulation of structural defects leading to the growth of internal energy. The effect of MA on the character and kinetics of combustion front propagation has been investigated. It was shown that following pretreatment of a powder mixture in a planetary ball mill, the combustion mode changes from stationary to a pulsating combustion and, consequently, the combustion rate decreases. The burning-out of the sample is partial and with interruptions (depressions). Force SHS-pressing technology was used for obtaining of compacted samples with homogeneous structure based on Ti3AlC2

Features of Structural and Phase Transformations in Mo–Si–B and Сr–Al–Si–B Systems During Self-Propagating High-Temperature Synthesis

This study is dedicated to investigation of the combustion mechanisms during the SHS of ceramic materials in multicomponent Mo–Si–B and Cr–Al–Si–B systems. It is concluded that the following processes are defined the SHS for Si-rich Mo–Si–B compositions: Si melting, its spreading over the surfaces of the solid Mo and B particles, followed by B dissolution in the melt, and formation of intermediate Mo3Si phase film. The subsequent diffusion of Si into Mo results in the formation of MoSi2 grains and MoB phase forms due to the diffusion of Mo into B-rich melt. The formation of MoB phase for B-rich compositions may occur via gas-phase mass transfer of MoO3 gaseous species to B particles and B2O2 to Mo particles. In Cr–Al–Si–B system firstly, the Al–Si eutectic mixture undergoes contact melting followed by formation of the reactionary surface as the eutectic melt spreads over the Cr and B particles surface. An increase in Al content increases the proportion of the Al–Si eutectic melt. The dissolution of Cr particles in this melt becomes the rate-limiting stage of the combustion process. The melt is saturated with these elements followed by crystallization of CrB and Cr(Si,Al)2 grains. In the Cr- and B-rich areas and low melt concentration, the formation of CrB may occur via gas-phase mass transfer of B2O2 gaseous species to Cr particles. Consecutive formation of chromium and molybdenum borides and silicides is established by means of dynamic X-ray diffraction analysis. Compact ceramic samples were produced using forced SHS pressing technique. Their structural investigations were conducted by XRD and SEM

Phase Transition in Strongly Degenerate Hydrogen Plasma

Direct fermionic path-integral Monte-Carlo simulations of strongly coupled hydrogen are presented. Our results show evidence for the hypothetical plasma phase transition. Its most remarkable manifestation is the appearance of metallic droplets which are predicted to be crucial for the electrical conductivity allowing to explain the rapid increase observed in recent shock compression measurments.Comment: 1 LaTeX file using jetpl.cls (included), 5 ps figures. Manuscript submitted to JETP Letter

Влияние частичного замещения титана его гидридом на структуру и свойства жаропрочного сплава TNM-B1, полученного методом горячего изостатического прессования СВС-порошка

This paper investigates the influence of partial substitution of titanium by its hydride on the microstructure and mechanical properties of TNM-B1 alloy obtained by powder metallurgy technology. The impact of the Ti:TiH2 ratio in the reaction mixture and heat treatment modes on the microstructure and mechanical properties of TNM-B1+1%Y2O3 alloy, obtained using high-energy ball milling (HEBM), selfpropagating high-temperature synthesis (SHS), and hot isostatic pressing (HIP) methods, has been examined. It was observed that a 10 % substitution of titanium with its hydride in the reaction mixtures reduces the oxygen content in SHS products from 1 % to 0.8 % due to the generation of a reducing atmosphere during the decomposition of TiH2 in the combustion wave. When the Ti : TiH2 ratio is 90 : 10, highest mechanical properties of TNM-B1+1%Y2O3 alloy were achieved: a compressive strength (σu) of 1200±15 MPa and a yield strength (YS) of 1030±25 MPa. An increase in the proportion of TiH2 results in a higher content of oxygen impurity, leading to the formation of Al2O3, which reduces the strength and ductility of the material. With additional heat treatment of TNM-B1+1%Y2O3 alloy, the globular structure transforms into a partially lamellar one, leading to an increase in σu by 50–300 MPa, depending on the TiH2 content. This attributed to a decrease in the average grain size and a reduction in dislocation mobility during deformation.В работе исследовано влияние частичного замещения титана его гидридом на микроструктуру и механические свойства сплава TNM-B1, полученного по технологии порошковой металлургии. Рассмотрено влияние соотношения Ti:TiH2 в реакционной смеси и режимов термообработки на микроструктуру и механические свойства сплава TNM-B1+1%Y2O3, полученного с использованием методов высокоэнергетической механической обработки (ВЭМО), самораспространяющегося высокотемпературного синтеза (СВС) и горячего изостатического прессования (ГИП). Установлено, что 10 %-ное замещение титана его гидридом в реакционных смесях позволяет уменьшить содержание кислорода в СВС-продуктах с 1 до 0,8 % благодаря созданию восстановительной атмосферы при разложении TiH2 в волне горения. При соотношении Ti : TiH2 = = 90 : 10 достигнуты максимальные механические свойства сплава TNM-B1+1%Y2O3: прочность при сжатии σв = 1200±15 МПа и предел текучести σ0,2 = 1030±25 МПа. Рост доли TiH2 увеличивает содержание примесного кислорода, приводящего к образованию Al2O3, который снижает прочность и пластичность материала. За счет дополнительной термообработки сплава TNM-B1+1%Y2O3 глобулярная структура преобразуется в частично ламеллярную, что приводит к увеличению σв на 50– 300 МПа в зависимости от содержания TiH2. Получаемый эффект обусловлен уменьшением среднего размера зерен и снижением подвижности дислокаций при деформации