Showing papers in "High Pressure Research in 1995"
TL;DR: In this article, the equilibrium phase diagram for boron nitride has been plotted, which differs from the generally accepted Bundy-Wentorfs one, and the threshold pressure of cBN crystallization can be reduced from 4 down to 2 GPa with the supercritical fluids present.
Abstract: From recent experimental data on BN thermodynamic propeties, the equilibrium phase diagram for boron nitride has been plotted, which differs from the generally accepted Bundy-Wentorfs one. At atmospheric pressure cubic boron niride has been shown to be a thermodynamically stable modification up to temperatures of 1600 K, which drastically changes the established notions of BN polymorphism, based on assumed analogy of phase diagrams for carbon and boron nitride. These studies have shown that according to the proposed equilibrium phase diagram the threshold pressure of cBN crystallization can be reduced from 4 down to 2 GPa with the supercritical fluids present, which opens new fields for developing methods for cBN low-pressure synthesis.
46 citations
TL;DR: In this article, a new magnetic state with partial moment reorientation has been detected in hematite α-Fe2O3, at pressures above 2.5-3 GPa.
Abstract: High-intensity low-background neutron diffraction and high-pressure anvil technique have been used in the studies of magnetic materials up to the pressures of 10 GPa (sapphire anvils) and 24.5 GPa (diamond anvils) in the temperature range 1.5–300 K. Results of powder and single-crystal experiments are reported. A new magnetic state with partial moment reorientation has been detected in hematite α-Fe2O3, at pressures above 2.5–3 GPa. Incommensurate and commensurate phases in TbD2+x (x=0, 0.2), have been studied, stabilization of the incommensurate phase was found under pressure. The magnetic phase diagram of UAs has been determined, a sequence of magnetic structures (AF IA double-k, AF I double-k, AF I single-k) was observed at low temperatures when pressure was increased.
39 citations
TL;DR: In this paper, free surface velocity profiles of high-purity titanium samples under shock-wave loading were performed to study the dynamic strength and phase transition parameters of high purity titanium samples.
Abstract: Measurements of free surface velocity profiles of high-purity titanium samples under shock-wave loading were performed to study the dynamic strength and phase transition parameters. The peak pressu...
27 citations
TL;DR: The Paris-Edinburgh cells have been used over the past few years to obtain fully refinable neutron diffraction patterns by time-of-flight measurements on large volume powder samples up to 10 GPa at ambient temperature.
Abstract: The Paris-Edinburgh cells have been used over the past few years to obtain fully refinable neutron diffraction patterns by time-of-flight measurements on large volume powder samples up to 10 GPa at ambient temperature. The use of this type of instrument can be extended to i) higher pressures, well above 20 GPa, ii) experiments at low and high temperature iii) the study of samples which are liquids or gases at ambient, and iv) to the study of single crystals in the angular dispersive mode.
22 citations
TL;DR: Using accurate electronic-structure, interatomic-potential, and statistical methods, first-principles theoretical equations of state (EOSs) have been developed for the prototype metals Al, Cu, Mo, and... as mentioned in this paper.
Abstract: Using accurate electronic-structure, interatomic-potential, and statistical methods, first-principles theoretical equations of state (EOSs) have been developed for the prototype metals Al, Cu, Mo, ...
19 citations
TL;DR: In this article, the compressibility of synthetic polycrystalline NiO was studied in a diamond anvil cell at room temperature utilizing two different X-ray sources: a standard film with a conventional Xray source and the energy dispersive Xray diffraction (EDXRD) method with synchrotron radiation.
Abstract: The compressibility of synthetic polycrystalline NiO was studied in a diamond anvil cell at room temperature utilizing two different X-ray sources. A standard film with a conventional X-ray source and the energy dispersive X-ray diffraction (EDXRD) method with synchrotron radiation were used for data acquisition. In the film method, the sample was compressed in a 4:1 methanol to ethanol solution up to 7 GPa with ruby fluorescence as a pressure calibrant. In the energy dispersive method, NiO powder was mixed with gold and compressed in two different conditions: gasketed and ungasketed up to 30 GPa. In the gasketed run, water was used as the pressure transmitting medium while gold was used as pressure calibrant in both runs. Hydrostatic compression of NiO in both diffraction methods yields a bulk modulus (K o) of 187 ± 7 GPa assuming K′ = 4. The compression of gasketed NiO of the synchrotron experiment, however, showed an obvious break at pressure exceeding 4 GPa due to the loss of hydrostaticity. ...
15 citations
TL;DR: In this article, a new neutron spectrometer for investigations of elastic and inelastic neutron scattering on polycrystal microsamples under high pressure in diamond and sapphire anvils cells is described.
Abstract: A new neutron spectrometer for investigations of elastic and inelastic neutron scattering on polycrystal microsamples under high pressure in diamond and sapphire anvils cells is described. The spectrometer is operating at the IBR-2 pulsed reactor at JINR. The time-of-flight method and ring-shaped multicounter detector are used to register the scattered neutrons. Parameters and methodical peculiarities of the device and the examples of experimental studies are given.
15 citations
TL;DR: In this paper, the first time that Freon-11 has been used as a hydrostatic pressure transmitting medium was described and the results of the investigation on the influence of pressure upon the structure of the YBaCuO HTSC obtained by means of the powder diffraction method.
Abstract: The design of a titanium-zirconium clamped cylinder-piston type pressure cell for neutron diffraction investigations under hydrostatic pressure up to 10 kbars without supports is described. It is the first time that Freon-11 has been used as a hydrostatic pressure transmitting medium. The following results carried out at the room temperature are presented: the discovery of the transition from I to 111 phase in a LiKSO4 single crystal and the results of the investigation on the influence of pressure upon the structure of the YBaCuO HTSC obtained by means of the powder diffraction method.
13 citations
TL;DR: In this article, the authors studied the pressure dependence of the crystal structure of a powder sample of HgBa2CaCu2O6.3 in the pressure range of 0 to 3.6 GPa, using the DN-12 time-of-flight diffractometer at the IBR-2 pulsed reactor and a sapphire anvil cell chamber.
Abstract: The pressure dependence of the crystal structure of a powder sample of HgBa2CaCu2O6.3 (Tc=123 K) was studied in the pressure range of 0 to 3.6 GPa, using the DN-12 time-of-flight diffractometer at the IBR-2 pulsed reactor and a sapphire anvil cell chamber. At P=O the results are in a good accordance with the published data. At P=3.0 and 3.6 GPa the best fit of the experimental data was achieved using the structural model with apical oxygen disordered in the (a, b) plane. The compressibility values of the lattice constants and selected bonds were calculated from the structural data. The highest absolute value of compressibility was found for the distance between the Ba and O atom layers.
13 citations
Abstract: The development of appropriate procedures to maximise data quality and to make accurate data corrections is vital if reliable structural data are to be obtained at high pressure As a result, the development of the Paris-Edinburgh high-pressure neutron cell has included considerable effort on neutron-scattering techniques The procedures developed are described, and their importance in obtaining accurate structural information at high pressure is illustrated by recent results
12 citations
TL;DR: In this paper, the electronics structure, the charge distribution and the total energy of hexagonal titanium diboride are calculated using non-local pseudopotentials in both the local density approximation (LDA) and the generalized gradient expansion approximation (GGA).
Abstract: The electronics structure, the charge distribution and the total energy of hexagonal titaniumdiboride are calculated using non-local pseudopotentials in both the local density approximation (LDA) and the generalized gradient expansion approximation (GGA). In the LDA we obtain a = 3.023 A, c = 3.166 A and Bo = 271. GPa. For these quantities the GGA values are slightly lower and both compare well with experiment. We also determined selected elastic constants by fitting the total energies to a quadratic surface in the lattice parameters. Using strains that do not break the hexagonal symmetry we obtain C11 + C12 = 777.GPa, C13 = 83. GPa and C33 = 568. GPa. Again slightly lower values are obtained using the GGA. These values agree well with a recent experiment.
TL;DR: In this article, the results of experimental studies and thermodynamic calculations of melting diagrams of the 3-d transition metal-carbon systems are discussed and the theoretical and experimental results which complement the earlier available data are presented.
Abstract: The results of experimental studies and thermodynamic calculations of melting diagrams of the 3-d transition metal-carbon systems are discussed in this paper. The authors present their theoretical and experimental results which complement the earlier available data. The Fe-Ni-C, Fe-Co-C, and Mn-Ni-C systems are shown to be suitable for diamond synthesis at relatively low p, T-parameters.
TL;DR: In this paper, an application of the sapphire anvils technique to the study of vibrational spectra of hydrogen-containing systems by inelastic neutron scattering under high pressure is described.
Abstract: In this paper application of the sapphire anvils technique to the study of vibrational spectra of hydrogen-containing systems by inelastic neutron Scattering under high pressure is described. The experiments were performed with the DN-12 time-of-flight spectrometer at the IBR-2 pulsed reactor in Dubna. The structural changes and pressure dependence of the libration and lattice modes in NH4Cl were studied up to 40 kbar. The results give some evidence of the NH4 + ion instability.
TL;DR: In this article, the design and general description of diamond anvil cells, developed for neutron diffraction studies of powder and single crystal samples, are given and some aspects of high pressure neutron diffusion experiments are discussed.
Abstract: Design and general description of diamond anvil cells, developed for neutron diffraction studies of powder and single crystal samples, are given. Some aspects of high pressure neutron diffraction experiments are discussed.
TL;DR: The first synthesis of stishovite, a high-density form of silica, is described by the author, Sergei Stishov as discussed by the authors, who was a graduate student at Moscow State University in geochemistry in the period 1960-1962, and developed an interest in the interior of the Earth and its constituents.
Abstract: The first synthesis of stishovite, a high-density form of silica, is described by the author, Sergei Stishov. Stishov was a graduate student at Moscow State University in geochemistry in the period 1960–1962, and developed an interest in the problem of the interior of the Earth and its constituents. He decided to look for the high-pressure phase of silica predicted by Francis Birch in 1952. Stishov was able to perform experiments with a high-pressure apparatus at the Institute of High-pressure Physics in Moscow, and in 1961 he obtained the new phase. The scientific politics that followed included attempts by others to take credit for Stishov's discovery, controversy over the naming of the new phase, and Stishov's eventual separation from the Institute. An epilogue and some material of historical interest are appended.
TL;DR: An in situ X-ray diffraction study of the high-pressure ζ-phase evidenced a fct Ti sublattice as mentioned in this paper, where H atoms are displaced to octahedral sites, and the energy of H optic peak (at ∼ 75 meV) is half that in other Ti-H phases where H occupy tetrahedral sites.
Abstract: An in situ X-ray diffraction study of the high-pressure ζ-phase evidenced a fct Ti sublattice. In the fco X-phase quenched under pressure, H atoms are displaced to octahedral sites, and the energy of H optic peak (at ∼ 75 meV) is half that in other Ti-H phases where H occupy tetrahedral sites. Phase transformations on heating of x-TiH(D)∼0.75 were studied by neutron diffraction, small angle and inelastic neutron scattering (INS). Bound multiphonons were observed in the INS spectra of ordered γ-TiH(D).
TL;DR: In this article, the structure of UAI2 at ambient pressure is of MgCu2 type with space group Fd3m and UAI4 has been found to undergo a structural transition at ∼ 11 GPa.
Abstract: The UAI2, UAI2, AND UAI4 compounds have been studied by high pressure X-ray diffraction up to a maximum pressure of ∼ 35 GPa. The compressibility behaviour of UAI2 has been found to be consistent with the itinerant 5f states, whereas that of UAI2 and UAI4, indicate a more localized nature. Further, UAI2 has been found to undergo a structural transition at ∼ 11 GPa and the structure of the high pressure phase has been identified to be of MgNi2 type with space group P63/mmc. The structure of UAI2 at ambient pressure is of MgCu2 type with space group Fd3m. From the electronic considerations, for instance, free electrons per atom ratio e/a, it is anticipated that it may transform back to MgCu2 type structure at still higher pressures. On similar considerations, it is expected that most of the AB2 type Laves phase compounds of the ‘f’ electron systems may undergo the structural sequence: MgCu2 – MgZn2 (or MgNi2) – MgCu2 due to increased delocalization of their ‘f’ electron states.
TL;DR: In this paper, inelastic scattering of neutrons using anvils technique was used to study the lattice dynamics of graphite at high pressures. But the results were limited to hexagonal-axis-polarized phonons in the strongly anisotropic layered crystal lattice, and it was shown that the pressure effect resulting in a contraction of interlayer distances gives rise to a monotonous hardening of the measured frequencies.
Abstract: Lattice dynamics of graphite at high pressures is studied by inelastic scattering of neutrons using anvils technique. Pressure dependence of frequencies for hexagonal-axis-polarized phonons in the strongly anisotropic layered crystal lattice of graphite has been measured up to 60 kbar. It is shown that the pressure effect, resulting in a contraction of interlayer distances, gives rise to a monotonous hardening of the measured frequencies. An investigated longitudinal acoustic branch does not change its sinusoidal shape under pressure while the continuous evolution from quasi-twodimensional to three-dimensional behavior is found for a transverse acoustic branch. It is pointed out that the observed higher rate of pressure variations of the lattice dynamics parameters as compared to the structural anisotropy can reflect changes of the crystal potential in graphite related to an available high-pressure phase transformation from the layered to more isotropic lattice.
TL;DR: In this paper, the phase transformations in sulfur for pressures up to 10 GPa were investigated by time resolved Raman spectroscopy and the transition to the photosensitive phase p-S was stimulated by the blue laser line between 3 and 9 GPa.
Abstract: We investigate the phase transformations in sulfur for pressures up to 10 GPa by time resolved Raman spectroscopy. The transition to the photosensitive phase p-S is stimulated by the blue laser line between 3 and 9 GPa. The kinetics of this transition as derived from the time evolution of the intensities of characteristic Raman excitations shows the typical features of an activated first order phase transition. This transformation proceeds via a disordered (amorphous) intermediate state. Above 9 GPa a further phase change to S, is kinetically characterized and follows similar rules i.e. the integral intensities of selected S, Raman lines exhibit a sigmoidal time dependence. In both high pressure phases a broad Raman excitation between 800 and 1000 cm−1 is observed.
TL;DR: In this article, a pressure-temperature phase diagram of Sb melt has been studied and four new triple points connected with the transformations in Sb melts were detected, and a general rule concerning the triple points at the p-T diagrams of the melts is determined.
Abstract: Pressure-temperature phase diagram of Sb melt has been studied. Liquid antimony was found to have four regions separated from each other by the sharp jumps of volume and electrical conductivity. Four new triple points connected with the transformations in Sb melt were detected. Kinetics of the transitions is discussed. Comparison of p-T diagrams of liquid and solid Sb is presented. A general rule concerning the triple points at the p-T diagrams of the melts is determined.
TL;DR: In this article, a combination of lanthanide catalysis and high pressure is highly beneficial in the Diels-Alder addition of ethyl vinyl ether to unsaturated keto compounds, particularly appropriate for the synthesis of sterically congested dihydropyrans.
Abstract: Combination of lanthanide catalysis and high pressure is highly beneficial in the Diels-Alder addition of ethyl vinyl ether to unsaturated keto compounds. The method is particularly appropriate for the synthesis of sterically congested dihydropyrans. The activation volumes of catalyzed and thermal hetero-Diels-Alder reactions do not differ significantly. This means conservation of the pericyclic character of the process.
TL;DR: In this article, the crystal structure of ThS2, ThSe2 and US2 has been investigated for pressure up to 60GPa using x-ray powder diffraction, and the results indicate that its high-pressure phase has a monoclinic structure.
Abstract: The crystal structure of ThS2, ThSe2 and US2 has been investigated for pressure up to 60GPa using x-ray powder diffraction. The bulk moduli are 175(10), 155(10) and 155(20) GPa, respectively. A pressure-induced phase transformation occurs at about 40 GPa for ThS2, 30 GPa for ThSe2 and 15 GPa for US2. The results for ThSe2 indicate that its high-pressure phase has a monoclinic structure. The same structure is compatible with the observed high-pressure spectra of ThS2 and US2. However, the crystal system assignment is less certain for these compounds.
TL;DR: In this paper, a simple charge-transfer scheme is used to relate the evolution of the tilt angle π of NiO6 octahedra to the decrease of the metal insulator temperature with external pressure.
Abstract: The modifications of the crystallographic structure of PrNiO3 associated to the decrease of the metal insulator temperature TM-I with external pressure (Pmax ≈ 5 kbar) have been investigated by means of neutron powder diffraction. The most interesting finding is the unexpected evolution of the tilt angle π of the NiO6 octahedra which, in contrast to the results reported for other isostructural compounds, decreases under pressure. A simple charge-transfer scheme is used to relate the evolution of ≈ to the decrease of TM-I upon pressure.
TL;DR: A high pressure cell with profiled anvils for neutron diffraction investigations has been designed and tested in this article, where the matrices of the cell are made of alloyed aluminium oxide ceramic.
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
TL;DR: In this paper, the ISIS pulsed neutron scattering facility in high pressure vibrational spectroscopy studies using incoherent inelastic neutron scattering (INS) has been discussed and an interesting scientific example is given to demonstrate the usefulness of this technique.
Abstract: In recent years there have been significant developments at the ISIS pulsed neutron scattering facility in high pressure vibrational spectroscopy studies using incoherent inelastic neutron scattering (INS). By using suitable collimation and shielding techniques it has been possible to extend the available pressure range and so open up new areas of science to a technique which has significant advantages over the more traditional I-R and Raman scattering spectroscopies. The experimental details are discussed and an interesting scientific example is given to demonstrate the usefulness of this technique.
TL;DR: In this article, high pressure experiments up to 5 kbar on quasi one-dimensional singlet ground state and the induced magnetic moment systems AFeX3 and TIFeCl3 are reported.
Abstract: Uniform high pressure experiments up to 5 kbar on quasi one-dimensional singlet ground state and the induced magnetic moment systems AFeX3 are reported. The pressure-induced changes in the magnetic ordering vector are related to induced structural phase transitions. The anisotropic compression of the lattice may give rise to induced moment formation in the CsFeX3 compounds. Inelastic neutron scattering experiments show that the anisotropic compression effect on the magnetic excitations is not visible. However, structural changes show a marked effect on the magnetic excitation spectrum. Predictions are made for the magnetic excitation spectra of the induced moment systems RbFeCl3 and TIFeCl3.
TL;DR: In this article, the authors showed the possibility of using a titanium-zirconium high pressure cell for small angle neutron scattering and measured the SANS curves with the help of this setup to illustrate the capabilities of the method.
Abstract: The experiments which were carried out showed the possibility of using a titanium-zirconium high pressure cell for small angle neutron scattering. We report on some curves measured by SANS with the help of this setup to illustrate the capabilities of the method.
TL;DR: In this article, a scheme for the experimental varification of some models describing the evolution of deformation structures in geological materials in dependence on various erxternal conditions (high pressures, temperatures, various loadings, etc.) acting on a sample is proposed.
Abstract: This paper suggests a classification of texture in quartzitic rocks. Possible mechanisms of texture formation and their relation to tectonic processes are discussed. A scheme for the experimental varification of some models describing the evolution of deformation structures in geological materials in dependence on various erxternal conditions (high pressures, temperatures, various loadings, etc.) acting on a sample is proposed. To investigate “in situ” the mechanisms of texture formation in rocks, high pressure devices are under construction. They will be built of a special Ti − Zr alloy, which has zero coherent scattering lenght and therefore is well suited for neutron diffraction investigations. Two different devices are proposed. The first one allows neutron diffraction measurements of sample volumes up to 4 cm3, a hydrostatic pressure of 1, 5 GPa, a temperature of 300° C, and uniaxial compression up to 50 kN. Pressure temperature and axial load are measured inside the chamber. Besides during ...
TL;DR: In this article, the authors measured the structural changes in irradiated superconductors under pressure and found that the value of dTc/dP is high (1.5 =bar).
Abstract: Pressure-induced structural changes in irradiated YBa2cu3Ox (x=6.95) and uninradiated (x=6.91,6.54,6.39) samples have been measured by neutron powder diffraction in a hydrostatic liquid pressure cell. Tc has been measured for irradiated superconductors under pressure. The value of dTc/dP is found to be high (1.5 =bar). Increase in Tc is associated with charge transfer between the CuO2 planes and CuO chains which is reflected by anisotropy of crystal lattice compression.