High pressure X-ray studies of palladium hydride and deuteride

Abstract

The palladium hydride and deuteride have been investigated in the diamond anvil cell up to 35 GPa using energy dispersive x-ray diffraction method. The search for the neutrons in the case of PdD up to the highest pressure reached was unsuccessful.     

Ceramic high pressure cell with profiled anvils for neutron diffraction investigations (up to 7 GPa)

Abstract

A high pressure cell with profiled anvils for neutron diffraction investigations has been designed and tested. The matrices of the cell are made of alloyed aluminium oxide ceramic. The reliable working pressure range of the cell is up to 7 GPa at a sample volume of 64 mm³. The cell attenuates the neutron flux not more than four times, with the transmission of the cell very slightly depending on neutron wavelength.     

High pressure raman study of PbMoO4

Abstract

Raman spectra of PbMoO₄ have been measured up to 31 GPa in a diamond anvil cell (DAC). Two new phases were found at 10 and 16 GPa pressures at room temperature.     

Effect of pressure and interstitial atoms on magnetic properties of LuFe11Ti Intermetallics

Magnetisation and magnetocrystalline anisotropy of the LuFe₁₁Ti intermetallics have been studied under pressure up to 1.2 GPa in temperatures from 5 K to 350 K using a miniature CuBe pressure cell and a SQUID magnetometer. A decrease of Fe-moment under pressure is compatible with the increase of Fe-moment in hydride and nitride of LuFe₁₁Ti. A complex dependence of magnetocrystalline anisotropy on volume of the elementary crystal cell of LuFe₁₁Ti and its hydride and nitride has been observed.     

Dependence of the annihilation pressure of ruby R-line fluorescence on the laser exciting wavelength

Abstract

Using solid argon as pressure medium, quasi-hydrostatic pressure was obtained at room temperature in the diamond cell up to 90 GPa. The mechanism of the disappearance of ruby R lines and the applicability of ruby pressure scale under quasi-hydrostatic pressure above 100 GPa was discussed. The deviation of every pressure measured at nine positions in the cell per mean pressure was less than 1.5% at pressure below 80 GPa.     

X-ray difffraction studies on samarium up to one megabar pressure

Abstract

High—pressure crystal structure studies have been performed on Sm up to 100 GPa using synchrotron x-radiation and a diamond anvil cell. The structural sequence Sm-dhcp-fcc-dist.fcc has been confirmed. There is no evidence of any volume collapse. The bulk modulus and its pressure derivative have been determined (B₀ = 30.7 GPa, B₀’ = 2.5).     

Pressure dependence of crystal structure and molecular packing in anthracene

Anthracene molecular crystal has been investigated up to a pressure of 10.5 GPa at room temperature using variable shape variable size Monte Carlo simulations in an isothermal–isobaric ensemble. We have reported various structural quantities, such as cell parameters and unit cell volume, as a function of pressure and compared them with the experimental results [J. Chem. Phys. 119, 1078 (2003)]. The pressure dependence of angles θ, δ and χ which describe the relative packing of molecules in the crystal has been calculated. We report that anthracene molecular crystal does not exhibit any first order phase transition up to a pressure of 10.5 GPa which is consistent with the experimental observations by Oehzelt et al. [Phys. Rev. B 66, 174104 (2002)]. The calculated equation of state (EOS) has been fitted to a Murnaghan-type EOS with good agreement. The calculated bulk modulus and the pressure derivative of bulk modulus are 8.2 GPa and 8.9 respectively which are in agreement with the experimentally calculated values.     

Crystal Structure Transformations of Rare-Gas Solids Under Pressure

Pressure-induced structural changes in solid krypton (Kr) and xenon (Xe) have been studied using angle dispersive X-ray diffraction in a diamond-anvil cell (DAC) up to 50 GPa. The analysis of the results shows that in solid Kr (Xe) the phase transition from fcc to hcp starts below 3.2 GPa (1.5 GPa). Albeit the hcp/fcc ratio increases under pressure, both phases coexist up to the highest pressure reached in this study. Room temperature (RT) equations of state (EOS) are determined.     

High-Pressure Ultrasonic Measurements on Single Crystal

Elastic properties of single crystalline germanium have been determined up to 6 GPa. All three elastic constants and their pressure derivative have been obtained by transit time measurements in a large volume cell. Comparison with previously published data fully validate the proposed set-up. The design of this set-up allows simultaneous in situ ultrasonic and X-ray diffraction measurements.     

Micro-raman at very high pressure and variable temperature

Abstract

We have designed a mechanical coupling between a spectrometer and a cryostat which allows the use of a microoptical system placed at the entrance of the spectrometer. Micro-Raman investigations are performed with a membrane diamond anvil cell placed inside the cryostat. The capability of this setup is illustrated with results obtained on benzene at 10 K up to 33 GPa.     

Low temperature high-pressure crystallization and fluid phase equilibria in the systems Ar + CHF3 and N2 + CHF3

Abstract

An optical autoclave for phase studies on mixtures in the temperature range from 80 to 373 K and for pressures up to 200 MPa is described. The cell is fitted with sapphire windows and employs magnetic stirring. Measurements are performed according to the synthetical (e.g. by visual observation) or analytical method (e.g. by sampling and online gaschromatography). Results for the crystallization and fluid phase equilibria of the binary systems nitrogen + trifluoromethane and argon + trifluoromethane from 110 K to 230 K and up to 200 MPa are presented and discussed in comparison with other N₂- and CHF₃-systems.     

High pressure assisted 1,3-dipolar cycloadditions: Synthesis of silylated triazoles from heteroaryl azides

Abstract

The 1,3-dipolar cycloaddition of 2- and 3-benzothiopheneazide with (trimethyl-sily1)acetylene to yield 1,2,3-triazoles has been studied at pressures up to 1GPa. The kinetics as a function of pressure was followed interfacing a diamond anvil cell to a FTIR spectrometer. Alike with aryl azides, the rate of reaction was found to increase logarithmically with pressure with a yield close to quantitative.     

Gas pressure cell for electroluminescence and photoconductivity measurements

Abstract

High-pressure studies of electroluminescence and photoconductivity are commonly carried out using liquid pressure systems. The wider application of a gas pressure system (with its substantial advantages) in this kind of studies is limited by the difficulties in the construction of a suitable sample cell. Such a cell, in addition to electric and optical access, must be provided with a high-pressure inlet, and the overall dimension of the cell should allow it to fit most standard cryostats. In this paper a high gas pressure optical cell is described which enables electroluminescence or photoconductivity measurements at pressures up to 1.0 GPa and at temperatures down to 1K.     

Hierarchy of critical exponents of currents on -simplex fractals

Using the symmetry of ( d +1)-simplex fractals with decimation number b =2, the current distribution has been determined. Then using the renormalization group technique, based on the independent Schur's invariant polynomials of current distributions, the multifractal spectrum of even moments of current distributions has been evaluated analytically up to order six for an arbitrary value of d. Also the scaling exponents of order 8 and order 10 have been calculated numerically up to d =30. Received: 19 November 1997 / Revised: 21 January 1998 / Accepted: 9 February 1998     

Implementation of a sapphire cell with external electrodes for laser excitation of a forbidden atomic transition in a pulsed E-field

We demonstrate the production of an electric field inside a high temperature cesium vapor cell with external electrodes. This external control of the electric field, which is not possible with a glass cell in presence of a cesium vapor, is achieved using a cell made of sapphire, and is of particular interest for our ongoing Parity Violation experiment. We describe the main components and the implementation on the set-up, including the pulsed high voltage generator. With pulse duration not exceeding 200 ns the system provides a reversible longitudinal E-field of up to 2 kV/cm in the vapor at a density of ∼ 2×10¹⁴ at/cm³ without discharge. Atomic signals attest the application of the electric field in the cell, with the predicted value. Further improvements obtained with sapphire cells are also presented. Received 15 September 2000     

Effect of high pressure on raman spectra of T1-based superconducting crystals

Abstract

Raman spectra for two members of the high-Tc superconductor family T1_m Ba₂ Ca₂ cuo_6+m were measured at pressure up to 3 0 GPa. It is shown that pressure induces nonuniform deformation of the unit cell. Analysis of Raman shifts indicates the applicability of a Gruneisen model for these high-Tc superconductors. As evidenced by the absence of changes of the Raman spectra, no phase transitions occur in the pressure range studied.     

Xanes and raman spectroscopy under pressure of bromobenzene

Abstract

The behaviour of bromobenzene (BBe) compressed in a diamond anvill cell up to 30 GPa was studied by XANES and Raman spectroscopy. The liquid-solid transition and a solid-solid transition were observed at 0.9 GPa and 9 GPa respectively. Above 24 GPa, an irreversible transformation occurs to a solid orange-yellow compound which can be recovered at zero pressure. The polymerization mechanism, in connection with the occurence of Br-bonded Sp² and Sp³ carbons in the solid compound, is discussed.     

Splitting of libration mode frequencies in the vicinity of orientation phase transition in NH4Br

Abstract

Vibrational spectra of NH₄Br at high pressures up to 4·5GPa have been studied by means of incoherent inelastic neutron scattering using sapphire anvil high pressure cell technique. Libration mode splitting was investigated in the vicinity of the orientation phase transition (P_tr = 2·7 GPa) and this effect disappears if pressure is less or higher than P_tr. This effect is explained in terms of two-well asymmetric potential.     

Magnetoelectric effect and toroidal ordering in Ga2−x FexO3

The field dependence of the magnetoelectric effect and longitudinal magnetostriction of Ga_2−x Fe_xO₃ single crystals is studied in magnetic fields up to 200 kOe in the temperature range from 4.2 to 300 K. It is shown that the magnetoelectric effect in these materials is determined mainly by the toroidal moment T and is not related to magnetostriction, as was previously theorized. A new method for determining the toroidal moment by measuring the electric polarization in a strong magnetic field is proposed. The value of the toroidal moment of the unit cell in Ga_1.15Fe_0.85O₃ is calculated: T=(T _a ,0,0), where T _a =24.155μ _B Å per unit cell. Experimental data are analyzed using a theory of toroidal spin ordering, which gives good agreement with experiment. Zh. éksp. Teor. Fiz. 114, 263–272 (July 1998) Deceased.     

High pressure X-ray diffraction experiments on NpS and PUS up to 60 GPa

Abstract

Neptunium and plutonium monosulfides were studied under high pressure up to ～60 GPa using a diamond anvil cell in an energy dispersive X-ray diffraction facility. The compounds, of cubic rock salt structure type at ambient pressure, do not show any crystallographic phase transition in the domain of investigation. From the pressure-volume relationship, we determined bulk moduli of 92 and 120 GPa with pressure derivatives of 4.6 and 4.1 for NpS and PUS respectively.