Volume compression of thallium to 45 GPa

Abstract

High-pressure structural transition and volume compression for thallium were investigated to 45 GPa in a diamond anvil cell using the angular dispersive X-ray diffraction technique. Except for the known polymorphic transition at 3.7 GPa, no other structural change was observed in this pressure range. The equation of state of the high pressure phase has been obtained: its initial bulk modulus, B₀ = 33.1 GPa, is lower by 10% than that of the hexagonal phase at normal pressure.     

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.     

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.     

Photoluminescence of InGaAs/GaAs strained-layer quantum well structures under high pressure

Abstract

Measurements of the photoluminescence (PL) of strained In_0.2Ga_0.8As/GaAs and In_0.15Ga_0.85As/GaAs quantum well structures together with the PL from bulk GaAs, in a diamond anvil cell show that the pressure coefficient of the ground confined state in the wells depends upon well width (L_Z). In the thinnest wells, the coefficient is closer to that of the bulk GaAs (10.7 meV/kbar), as expected. However, in the widest wells the coefficients tend to values (9.5meV/kbar for the 15% alloy and 9.1meV/kbar for the 20% alloy) that are significantly lower than the pressure coefficient of unstrained In_0.53Ga_0.47As (10.9meV/kbar). It is found that the low pressure coefficients can not be explained by the change in uniaxial stress with pressure due to a difference in bulk moduli between the barrier and well.     

Comparison of the Raman pressure shift and the Raman temperature shift of benzene and diamond with the ruby soale

Abstract

In order to serve as substitute for the pressure ruby scale at high temperature, the breathing mode of bemsens (990 cm^?1) and the first order Raman mode of diamond (1333 cm^?1) have been studied as a function of pressure and temperature in the range of 0–15 GPa and 25–400°C. The diamond and bensene Raman frequency shifts are shoft to be of valuable use as a pressure scale at high temperature. A further advantage of bensene is to remain a suitable pressure transmitting medium up to 350°C and 15 GP.     

High Pressure Instrumentation: Low and Negative Pressures

Much work on semiconductors, soft solids and biological materials does not require the megabar capability of the diamond anvil cell; a few accurate kbar being all that may be required. Work in this range poses its own challenges, to make the experiments routine, safe and reliable, and well-calibrated. We contrast diamond anvil cells working at what for them is very low pressure, with traditional bombs working at what for them is dangerously high pressure. We describe our preferred solution, a single-diamond cell, and demonstrate its use with Raman data from ethanol under low pressure. Negative hydrostatic pressure cannot be obtained by traditional methods. However, we present data showing the Raman spectrum of ethanol apparently at the negative pressure of m 3 kbar.     

Peculiarities of phase transitions when synthesizing diamond in high pressure apparatus of various types

Abstract

The influence of P, T-parmeters and duration of heat when synthesizing diamond in high pressure apparatus both of recessed anvil-type and cylindrical type (belt-type) on properties of diamond powders was studied. The dependence of pressure in reaction cells on temperature of force elements of apparatus in initial state and on efficiency of high pressure production in a reaction cell before heating was shown.     

Single crystal EXAFS at high pressure

Abstract

We present a new technique for structure characterization under high pressure conditions. The use of an undulator beam of the third-generation ESRF source of synchrotron radiation has enabled the first single crystal EXAFS experiments at high pressure using a diamond anvil cell as pressure generator. Taking advantage of the linear polarization of X-rays the technique becomes an orientation-selective probe of the local structure of materials. We describe the principle of the technique and some applications.     

On compressibility of osmium metal

On the basis of the high-pressure diamond anvil cell experiments on Os metal, Cynn et al. [Phys. Rev. Lett. 88, 135701-1 (2002)] have reported that this metal has lower compressibility than diamond. In the present work we have reanalysed the experimental data of Cynn et al. We find that the bulk moduli of Os and diamond are close to each other, implying that Os metal is as incompressible as diamond, but not more so. Our first principles total energy calculations using the full potential linearised augmented plane wave method on Os and diamond also suggest the same results.     

HIGH pressure structural investigations of zirconium using LMTO method

Abstract

The structural energy differences have been calculated for zirconium as a function of pressure at zero temperature using the Andersen force theorem and the linear muffin tin orbital method. The structures included are the following: α (hcp), the room temperature room pressure phase, ω- a three atom simple hexagonal, bcc and fcc. Our calculations show that the bcc structure would become energetically most favourable above 11 GPa. This results is in agreement with well known correlation between the crystal structure and the d-electron population in transition metals at normal volume. The diamond anvil cell based high pressure x-ray diffraction experiments are in progress to verify this result.     

Further study of the difference in nitrogen aggregation among (111) and (100) growth sectors of synthetic diamonds

Abstract

Single nitrogen atoms in synthetic diamond crystals aggregate in pairs by heat treatment under high pressure after electron irradiations. We find that the rate constants of nitrogen aggregation in the (111) growth sectors grown by the various solvents are about ten times greater than those of the (100) growth sectors. Furthermore the rate constant of nitrogen aggregation of the same sector is almost the same value. (shown Table-1). We have considered a few reasons for this fact. It may be accurate that a form of nitrogen atoms contained in (111) growth sectors of an as-grown diamond differs from that in (100) grown sectors and that the former accelerates nitrogen aggregation. Consequently we propose one nitrogen migration and aggregation model.     

High pressures: Recent trends in materials science

Abstract

Pressure was developed during the 20th century. The most important illustration of the use of high pressure in Materials Science was the synthesis of diamond at the beginning of the fifties.

This contribution will describe the main scientific research axis developed these last years and based on high pressure (synthesis of new materials, stabilization of specific structures, crystal-growth, preparation of finely divided materials…).

In parallel some industrial developments will be analyzed.

In conclusion, the potential of high pressure will be sketched for the near future.     

Metastable carbon allotropes in picosecond-laser-modified diamond

In this paper, we report on the bulk modifications of type IIa single-crystal diamond with visible 10-ps pulses (at λ = 532 nm) and microstructural changes characterized by the appearance of several ‘unidentifiable’ vibrational modes in the frequency range of 1000–1400 cm^?1 in the Raman spectra of laser-modified diamond. It is found that the new Raman modes are strongly pronounced in the spectra of high-stress regions in immediate proximity to the bulk microstructures in the absence of the G mode at ~1580 cm^?1 characteristic of the sp² phase. The high internal stresses are determined from the splitting of the triply degenerate diamond Raman line. The revealed structure transformation is localized within a narrow bulk layer near the bulk microstructures formed, and the stress relaxation is found to result in disappearance of the detected vibrational modes in the spectra. It is suggested that the formation of bulk regions with a sp³ carbon structure consisting of Z-carbon and hexagonal diamond is responsible for the appearance of new Raman modes in the spectra of laser-modified diamond. These findings evidence that the stress-assisted formation of novel metastable carbon phases or defect structures occur in the course of bulk modification of diamond with ps-laser pulses. In addition, we report the results of simulations of internal stresses in the system ‘graphitized cylinder-in-diamond’ to show (1) the effect of the mechanical properties of laser-modified diamond on the resulting stresses and (2) formation of bulk microscopic regions with high stresses of >10 GPa, i.e., the conditions at which various sp³ carbon allotropes and defect structures become more stable than graphite.     

Phase Diagrams and Synthesis of Diamond

For reasons of phase equilibria, the lowest temperatures T min , above which at high pressures the diamond crystallization from melt solutions is allowable in terms of thermodynamics, have been found for a number of metal-carbon systems. In the Ta-C and Nb-C systems, the diamond synthesis is possible at temperatures below T min , while to synthesize diamond in the Mg-Zn-C system, the temperatures much higher than T min , are required because of the necessity to overcome the kinetic difficulties.     

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.     

Influence of Synthesis and Composition conditions on Strength Characteristics of Synthetic Carbonado-Type Diamonds

Polycrystalline diamonds carbonado were synthesized under pressure 6.0-12.0 GPa. Ni-Cr-Mo alloy and pure Ni were used as the catalysts. The strength was tested by static compression technique according to GOST 9206-80. Diamond powders APK 4 with the grit size 500/400 and 400/315 were made by crushing of the bulk polycrystalline samples and this diamond powders were under investigation. Influences of the synthesis pressure and the chemical treatment on strength of diamond carbonado were studied.     

Elastic properties of ultrahard fullerites

The elastic properties of C₆₀ fullerite samples synthesized under pressure P=13.0 GPa at high temperatures were investigated using acoustic microscopy. The velocities of longitudinal (c _L=17–26 km/s) and transverse (c _T=7.2–9.6 km/s) elastic waves in the samples were measured. It was established that the longitudinal sound velocity of ultrahard fullerites is higher than that of any other known solid. The bulk modulus of these ultrahard samples is higher than that of diamond and reaches a value greater than 1 TPa. The high bulk modulus, the relatively large shear moduli, and the substantial Poisson ratio indicate that the structure of the ultrahard fullerites is fundamentally different from that of diamond. Zh. éksp. Teor. Fiz. 114, 1365–1374 (October 1998)     

Phase diagram of GaAs

Abstract

Optical measurements in the diamond anvil cell (DAC) as well as thermodynamics, show cubic GaAs I to be unstable at 300 K, at 13 GPa. The thermodynamic phase line from GaAs I to the high pressure (H.P.) form(s) is at 11 ± 2 GPa. Large hyteresis makes the actual I→II transition observable only at 17.5 ± 1 GPa.