Vadim V. Brazhkin

TOROID TYPE HIGH-PRESSURE DEVICE: HISTORY AND PROSPECTS

The Toroid type high-pressure device and its predecessor, the Chechevitsa (lentil) type high-pressure device, are known to be used efficiently for the synthesis of new materials in recent decades. It was through the Chechevitsa device the first ultradense modification of silica, ‘stishovite’, was obtained. Both devices were essential for the industrial production of superhard materials in the USSR and other socialist countries. In 1980s, almost half of the world synthetic diamond and c-BN products were manufactured by these devices. However, the application of the Toroid device for examining the structure and physical properties of highly compressed substances has been considerably less appreciated. Meanwhile, the device has some unique features that have made possible 35-years of an extensive investigation of physical properties of substances at pressures up to 150 kbar, including electron transport and thermodynamic properties, elastic characteristics, viscosity, thermo-conductivity and other physical properties. Also, the device has been widely employed for structural X-ray and neutron diffraction studies of many materials. But it is not until recently that the convenience of the Toroid device for physical studies has been fully recognized. Through this recognition, the Toroid type device is today becoming increasingly popular among the researchers in the field of high pressures around the world.

New Kinds of Phase Transitions: Transformations in disordered Substances

Photo and list of participants. Preface. Dedication. Part I: New Phase Transitions: General Properties. The search for phase transitions in liquids: A personal account S.M. Stishov. New types of phase transitions: Phenomenology, concepts and terminology V.V. Brazhkin, et al. Cooperative disordering phase transitions C.A. Angell, S. Borick. Beyond fluid-fluid separation M.A. Anisimov. Liquid polymorphism in yttrium-aluminate liquids M.C. Wilding, P.F. Mcmillan. The inherent states of glassy systems and granular media A. Coniglio, et al. The liquid-vapor transition of mercury F. Hensel. Double-step potential models of fluids S.V. Buldyrev, et al. Kinetic slowing down in liquid water M. Sasai. A phase transition induced by water reorientation at electrode interfaces L. Blum, D.A. Huckaby. Master equation approach to configuration kinetics of non-equilibrium alloys K.D. Belashchenko, et al. Part II: Transitions in Liquids. Interrelationship of polyamorphism and the fragile-to-strong transition in liquid silica I. Saika-Voivod, et al. In-situ observation of a liquid-liquid transition in phosphorus Y. Katayama. Insulator-metal transitions in fluids and the Coulomb critical points A.A. Likalter. From liquid to amorphous germanium by molecular dynamics J.K. Bording, et al. Smeared first-order phase transition in melts Yu.S. Tveryanovich, V.L. Ugolkov. Equilibrium structural model for liquid water S.R. Dillon, R.C. Dougherty. Transitions in liquids: Examples and open questions V.V. Brazhkin, et al. Behaviors of liquid carbon at high pressure M. Togaya. Structural changes across phase transitions in disordered systems P. Jovari, L. Pusztai. Pressure-induced transformations in fluidiodine P. Postorino, et al. Pressure-temperature phase diagrams of Se and S in terms of the Patashinski model L. Son, et al. Part III: Water and Amorphous Ice. Unsolved problems of liquid water H.E. Stanley, et al. High-density amorphous ice and its phase transition to ice XII I. Kohl, et al. Structure and dynamics of confined water M.-C. Bellissent-Funel. Neutron diffraction study of water polymorphism M.A. Ricci, A.K. Soper. Liquid-vapour phase diagrams of water in nanopores I. Brovchenko, et al. Relaxations in supercooled confined water P. Gallo. Transformations, dynamics, and structures of amorphous ice D.D. Klug, et al. Pure water structure and hydration forces for protein folding T. Head-Gordon, et al. Dynamic properties of stretched water P.A. Netz, et al. Computer simulation of supercooled water and amorphous ices G.G. Malenkov. Part IV: Glasses and Amorphous Solids. Amorphous-amorphous phase transitions in group-IV semiconductors P.C. Kelires. Kinetics and non-ergodic nature of amorphous-amorphous transformations under pressure A.G. Lyapin, et al. Phase relations for water and ice in confined geometry J. Dore, et al. Energy landscapes and amorphous-amorphous transitions D.J. Lacks. Localized low-energy excitations in glasses V. Hizhnyakov, et al. Amorphous pressure-induced alloys V.F. Degtyareva. Part V: Puzzles. Monte Carlo study of the dynamic and static glass transitions in the 10-state Potts glass C. Brangian, et al. Transitions in simple liquids: Correlation function approach V.N. Ryzhov, E.E. Tareyeva. Phase transitions induced or suppressed by confinement J. Quintana, A. Robled

The phonon theory of liquid thermodynamics

Heat capacity of matter is considered to be its most important property because it holds information about systems degrees of freedom as well as the regime in which the system operates, classical or quantum. Heat capacity is well understood in gases and solids but not in the third main state of matter, liquids, and is not discussed in physics textbooks as a result. The perceived difficulty is that interactions in a liquid are both strong and system-specific, implying that the energy strongly depends on the liquid type and that, therefore, liquid energy can not be calculated in general form. Here, we develop a phonon theory of liquids where this problem is avoided. The theory covers both classical and quantum regimes. We demonstrate good agreement of calculated and experimental heat capacity of 21 liquids, including noble, metallic, molecular and hydrogen-bonded network liquids in a wide range of temperature and pressure.

Mechanical properties of the 3D polymerized, sp2–sp3 amorphous, and diamond-plus-graphite nanocomposite carbon phases prepared from C60 under high pressure

Mechanical properties (Vicker’s hardness, Young’s modulus, and fracture toughness coefficient) have been studied for the three-dimensionally polymerized, amorphous, and nanocrystalline diamond-plus-graphite composite carbon phases prepared from fullerite C60 by temperature treatment under pressure. The hardness was found to increase gradually with the synthesis temperature. The experimental values of hardness are well correlated with the density of samples regardless of the phase structural nature, displaying the same dependence as amorphous carbon films. It has been shown that the hardness and Young’s modulus of both polymerized crystalline and disordered phases, though not as high as those of diamond, are comparable to the properties of cubic BN, while fracture toughness coefficient can be higher than that for diamond. An unusual combination of high hardness and high plasticity has been established for strongly polymerized C60.

Thermodynamic behaviour of supercritical matter

Since their discovery in 1822, supercritical fluids have been of enduring interest and have started to be deployed in many important applications. Theoretical understanding of the supercritical state is lacking and is seen to limit further industrial deployment. Here we study thermodynamic properties of the supercritical state and discover that specific heat shows a crossover between two different regimes, an unexpected result in view of currently perceived homogeneity of supercritical state in terms of physical properties. We subsequently formulate a theory of system thermodynamics above the crossover, and find good agreement between calculated and experimental specific heat with no free-fitting parameters. In this theory, energy and heat capacity are governed by the minimal length of the longitudinal mode in the system only, and do not explicitly depend on system-specific structure and interactions. We derive a power law and analyse supercritical scaling exponents in the system above the Frenkel line.

Glassy dynamics under superhigh pressure.

Nearly all glass-forming liquids feature, along with the structural alpha-relaxation process, a faster secondary process (beta relaxation), whose nature belongs to the great mysteries of glass physics. However, for some of these liquids, no well-pronounced secondary relaxation is observed. A prominent example is the archetypical glass-forming liquid glycerol. In the present work, by performing dielectric spectroscopy under superhigh pressures up to 6 GPa, we show that in glycerol a significant secondary relaxation peak appears in the dielectric loss at P>3 GPa. We identify this beta relaxation to be of Johari-Goldstein type and discuss its relation to the excess wing. We provide evidence for a smooth but significant increase in glass-transition temperature and fragility on increasing pressure.

Heat capacity at the glass transition

A fundamental problem of glass transition is to provide a quantitative and microscopic explanation of the heat-capacity jump at the glass transition temperature Tg. Similar problems are also common to other disordered systems, including spin glasses. We propose that the jump of heat capacity at Tg takes place as a result of the change of the liquid’s elastic, vibrational, and thermal properties. In this theory, we discuss time-dependent effects of glass transition, and identify three distinct regimes of relaxation. Our approach explains a widely observed logarithmic increase of Tg with the quench rate and correlation of the heat-capacity jump with liquid fragility.

What separates a liquid from a gas

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

Bulk nanostructured carbon phases prepared from C60: approaching the 'ideal' hardness

New nanomaterials have been prepared by high-temperature treatment of fullerite C60 at moderate (0.1–1.5 GPa) pressures attainable for large-volume pressure apparatus. The structure, EELS spectra, Raman spectra, hardness and elastic moduli of these carbon substances have been studied. The materials have a high (90%) elastic recovery, fairly high hardness H~10–15 GPa and record values of the hardness-to-Young-modulus ratio H/E~0.22. The observed hardness is close to the ideal limit, which is associated with the nanostructure of the materials. This structure represents a combination of interlinked curved fragments of C60 molecules and nanographite nuclei.

Elastic constants of stishovite up to its amorphization temperature

Brillouin spectra of stishovite were measured up to the amorphization temperature (xa0K) using large (1xa0mm) defect-free single crystals. At room temperature the sound velocities extracted from the BLS yield all six elastic constants. The derived bulk modulus and the polycrystalline shear modulus of stishovite at ambient conditions are B = 316xa0GPa, G = 222xa0GPa. Between room temperature and 800xa0K only a small decrease of the elastic constants was observed. This is an indication that the amorphization process is not due to a soft, long-wavelength, acoustic phonon. Room-temperature Raman spectra from samples heated to close to the amorphization temperature show that amorphization occurs more rapidly on the (110) than on the (001) crystallographic face. These results, together with those of x-ray measurements from the literature, allow us to conclude that amorphization in stishovite is most likely a surface phenomenon initiated by large oscillations of the Si atoms within the crystal faces whose normals are perpendicular to the c-axis.