Pressure and temperature effects on the Γ, N and L-phonons in zirconium

Abstract

The effective potentials for the E_2g,-phonon at the T point of the Brillouin zone of hep Zr, the transverse N- and longitudinal L-phonons of bcc Zr are calculated for different pressures by the “frozen phonon” method. The temperature and pressure dependences of the phonon frequencies are studied within the framework of a modified pseudo-harmonic approximation. The results obtained are in good agreement with the experimental ones. The stability of the hep, bec and ω phases of zirconium at different temperatures and pressures is discussed.     

Going to 10 TPa: The Calculated Hugoniots for Cu,Ta, and Mo

The Hugoniot equations of state for shock compressed Cu, Ta, and Mo are calculated at pressures up to 4 TPa and then up to 10 TPa are obtained by extrapolation. The calculations are parameter-free in that the cold part of the Helmholtz free-energy is calculated using the first-principles full-potential linearized augmented plane wave method within the generalized gradient approximation, the thermal contribution to the Helmholtz free-energy due to the lattice oscillations is calculated using the recently developed classical mean-field potential approach, and that due to the thermal electrons is calculated using the one-dimensional numerical integration. The calculated results agree with the existing experimental values very well.     

High-pressure,high-temperature thermophysical measurements on liquid metals

Abstract

Metal-samples are investigated as pan of a submicrosecond resistive pulse heating system up to temperatures of about 10.000 K and ambient pressures up to 0.5 GPa. The measuremnts allow the determination of such thermophysical properties as heat capacity and the mutual dependences between enthalpy, electrical resistivity, temperature and volume. Up to now investigations have been done on the following elements: C, W, Re, Ta, Mo, Nb, Fe, Ni, Cu, Pb, In, and Hg. From the investigations at elevated pressures an estimation of the critical point data of the metals lead and indium can be given.     

Electron-Impact Fragmentographic Fluorescence Spectroscopy of Ethanol,Acetaldehyde, 1- and 2-Propanol and Acetone

Abstract

Gaseous ethanol, acetaldehyde, 1-propanol, 2-propanol and acetone at pressures of 2 × 10^?5 to 5 × 10^?4 torr were irradiated with electrons of energies 0-1000 eV. The visible-region fluorescence of the excited fragments was then measured. Studies included pressure dependence, electron energy dependence, threshold energy measurements, and excitation curve measurements. The aim of the research was to ascertain if molecules of similar structure could be differentiated by their spectra.     

High-Pressure Raman Study of Zincblende,Cinnabar, and Cmcm Phases Of ZnTe

Raman measurements of ZnTe have been performed at pressures up to 15 GPa. Frequencies, line widths, and intensities of first- and second-order Raman features of the zincblende phase (0-9.5 GPa) were studied in detail. In this note, we focus on the Raman spectra of the high-pressure cinnabar and Cmcm phases. In the transition regime from cinnabar to Cmcm (12.2 to 13.7 GPa) the Raman data indicate the possible existence of a new intermediate high-pressure phase.     

Dynamic compression: what it is,making metallic H and magnetic fields of Uranus and Neptune

ABSTRACT

Static compression is a well-known method to achieve very high pressures in ‘cold’ (degenerate) condensed matter. Because dynamic compression is adiabatic, it achieves both high pressures and temperatures, which are tunable by choice of pressure-pulse shape. Dynamic compression uses supersonic hydrodynamic variables, which are straight forward to measure, to achieve a wide range of extreme thermodynamic states in degenerate condensed matter. Because dynamic compression developed primarily in national laboratories, it is relatively unknown to a significant portion of the high pressure community. This paper is a brief review of (i) dynamic compression itself, (ii) its application to making metallic fluid H (MFH) and (iii) implications of data generated at extreme conditions with dynamic compression for understanding the unusual magnetic fields of Uranus and Neptune, which are made primarily by convection of semiconducting and MFH. Metallic hydrogen made under dynamic and static compression is compared.     

High-pressure,high-resolution NMR probe working at 400 MHZ

Abstract

A probe for obtaining high-resolution multinuclear NMR spectra at elevated pressures with a Bruker AM-400 spectrometer is described. The probe is designed for pressures up to 200 MPa and has been used between -40 to 150°C. We obtain routinely a resolution of about 1 Hz for proton (400 MHz) spectra using deuterium as an internal field lock. This probe is easily interchangeable with a commercial probe. We also describe a simple sample tube made of a 5 mm commercial NMR tube and a machinable glass cap with a total volume of about 1 cm³.     

Theoretical calculation for the equations of state and phase transitions of sodium and potassium hydrides

Abstract

The ionic overlap-compression model is used to calculate the equations of state, as well as the equilibrium properties, of sodium and potassium hydrides (NaH and KH). The present results agree with the experimental ones well. The NaC1-to-CsC1 phase transition pressures for both crystals are also determined. The agreement of the theoretical pressures (23.0 GPa for NaH and 4.9 GPa for KH) with the experimental measurements (29.3 GPa and 4 GPa) is rather good. The calculation shows that the effect of the zero-point vibration to the equilibrium properties and the transition pressures should not be ignored.     

Phase behavior of pure and mixed systems at high pressure

Abstract

Our knowledge of intermolecular potentials, equations of state theories, and methods of handling chemical reactions are at a stage where one can perform rigorous calculations on pure and mixture systems at high pressures and temperatures.     

Computational reconstitution of crystal structures and (p,T) phase diagrams of benzene C6H6 and hexachlorobenzene C6Cl6

Abstract

With a simplified dynamical model for molecular packing analysis, crystal and molecular structures of benzene C₆H₆ and hexachlorobenzene C₆H₆ were investigated. This model includes thermal motion and molecular deformation effects. Several crystalline structures have been found by the calculation. They are compared to experimental structures determined at various temperatures and pressures, by X-ray diffraction or neutron scattering. A schematic (p, T) phase diagram is suggested for each compound.     

Structural,elastic, thermodynamic and electronic properties of LuX (X = N,Bi and Sb) compounds: first principles calculations

ABSTRACT

The structural, electronic, elastic and thermodynamic properties of LuX (X = N, Bi and Sb) based on rare earth into phases, Rocksalt (B1) and CsCl (B2) have been investigated using full-potential linearized muffin-tin orbital method (FP-LMTO) within density functional theory. Local density approximation (LDA) for exchange-correlation potential and local spin density approximation (LSDA) are employed. The structural parameters as lattice parameters a₀, bulk modulus B, its pressure derivate B’ and cut-off energy (E_c) within LDA and LSDA are presented. The elastic constants were derived from the stress–strain relation at 0 K. The thermodynamic properties for LuX using the quasi-harmonic Debye model are studied. The temperature and pressure variation of volume, bulk modulus, thermal expansion coefficient, heat capacities, Debye temperature and Gibbs free energy at different pressures (0–50 GPa) and temperatures (0–1600 K) are predicted. The calculated results are in accordance with other data.     

Interactive Effects of Pressure,Temperature and Time on the Molecular Structure of Ovalbumin,Lysozyme and β-Lactoglobulin

The structure of three food proteins, ovalbumin, lysozyme and g -lactoglobulin were investigated when subjected to pressure, temperature and holding time. Structural effects were determined by the examination of circular dichroism spectra. Experiments were performed using pressures of up to 105 MPa, temperatures up to 79 °C and holding times of 30 minutes using experimental design methodology and compared with ultra high pressures (600 MPa). Examination of the spectra showed that the structure of the three proteins behaved differently to the processing conditions. g -lactoglobulin was found to be the least stable protein while lysozyme was the most stable protein. The higher pressure of 105 MPa was not sufficient to cause structural change when used at ambient conditions but when used in conjunction with raised temperatures and holding time, the applied energy was found to be sufficient to disrupt the protein structure.     

Electrical conductivity and thermal EMF of CsI at high pressures

Abstract

The pressure dependence of thermal EMF and the resistivity-temperature dependence of CsI has been measured at pressures 20-50 GPa. In CsI non-monotonous change of resistivity, thermal EMF and activation energy of charge carriers has been observed at pressures above 40 GPa. The sign of thermal EMF corresponds to the electron conductivity. At pressures below 47 GPa the resistivity-temperature dependence is of the type characteristic of non-degenerate semiconductors, at pressure above 49 GPa it is characteristic of degenerate semiconductors (or metals). The observed properties are connected probably with the continuous distortion of B2 to an hcp-like phase.     

Studies of crystallization process of silica and germania glasses at high pressure

Abstract

The process of crystallization of SiO₂ and GeO₂ glasses was studied using samples retrieved after heat treatment at high pressures up to 12GPa. Two different samples of fused quartz and silica gel were studied in order to compare SiO₂ glass structure. Upon heating beyond 400°C at fixed pressures under which stishovite, rutile-type phase, is thermodynamically stable, the SiO₂ glasses underwent crystallization into coesite and stishovite, without quartz. In the course of heating GeO₂ glass in the stability field of rutile-type phase, low-quartz-type phase appeared as an intermediate at pressures below 7GPa, whereas only rutile-type phase was observed at 12GPa. The crystallization sequences are discussed in terms of coordination numbers in the glass and crystalline states.     

A New Class of Low Compressibility Materials: Clathrates of Silicon and Related Materials

We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility, transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation. The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature of the guest atom. We address the implications for obtaining a metallic material as hard as diamond.     

Synthesis experiments on B-Sb,Ge-Sb,and Xe-Pd systems using a laser heated diamond anvil cell

Abstract

In an effort to synthesize B-Sb, Ge-Sb and Xe-Pd compounds under high pressure, the respective system was laser-heated in a diamond anvil cell at temperatures above 2500 K and up to a maximum pressure of 51 GPa. The product was characterized by X-ray diffraction using rotating anode and synchrotron radiation X-ray sources. No reaction was observed in any of these systems up to pressures of 32, 20 and 51 GPa, respectively. In the case of Ge-Sb, new peaks were observed in the pressurequenched samples, but they were identified with the known metastable phases of Ge. In this regard our results are contrary to the earlier work on Ge-Sb.     

Thorium: Phase transformations and equation of state to 300 GPa

Abstract

Equation of state and phase transformations of thorium metal have been investigated to 300 GPa at 300 K in a diamond anvil cell using energy dispersive X-ray diffraction employing synchrotron source. Phase transformations in the 70–100 GPa range indicative of 5f-electron bonding are observed and thorium metal is isostructural with its 4f counterpart cerium at ultra high pressures. The measured static equation of state of thorium to 300GPa (volume fraction V/V _o = 0.40) at 300K is given. At high pressures, the sd to f electronic transfer has significant influence on the measured equation of state of thorium.     

Physical principles of plastification of solid bodies under pressure and their application to hydrostatic treatment of materials

Abstract

An attempt is made to formulate the physical causes of the solid body plastification at deformation under high hydrostatic pressures. The nature of critical pressures above which the character of the given process changes qualitatively is discussed in this work.     

Infrared Spectra of Crystalline,Glassy and Liquid Methanol at High Pressures

Abstract

Mid-infrared spectra in the range 400–1800 cm^?1 of methanol samples in diamond anvil cells at ambient temperature and pressures up to 11 GPa are reported. The freezing pressure is confirmed to be 3.6 GPa, and the spectra of the resulting metastable glass are very similar to those of the liquid. When maintained at high pressure, the glass spontaneously transforms to an ordered crystalline phase which is stable over the range 3.6 to 11 GPa. Small changes in peak wavenumbers for 14 internal modes as a function of pressure are observed, indicating that distortion of the molecules is minimal. A slight decrease for the C-O-H bending mode is attributed to charge transfer from the molecular 0-H bond to the strengthening intermolecular hydrogen bond.     

First-principles study of structural,elastic, electronic and optical properties of RDX under pressure

ABSTRACT

The influences of pressure on structural, elastic, electronic and optical properties of α-RDX under pressure from 0 to 40?GPa have been investigated by performing first-principles calculations. The obtained structural parameters based on the GGA-PBE+G calculations are consistent with previous experimental values. The results of B/G, C₁₂-C₄₄ and Poisson's ratio show that α-RDX has changed to ductility under pressure between 0 and 5?GPa. The obvious rotation of NO₂ group in the equatorial position appears, especially in the range of pressure from 10 to 15?GPa, which influences the elastic and mechanical properties of α-RDX. Moreover, we find that the electrons of α-RDX become more active under higher pressure by comparing the curves of DOS under different pressure. Furthermore, the anisotropy of optical properties under different pressures has been shown.