Showing papers in "High Pressure Research in 1996"
TL;DR: Calibration methods and software have been developed for single crystal diffraction experiments, using both approaches for calibrate, and apply corrections, to obtain accurate angle and intensity information.
Abstract: Detector systems introduce distortions into acquired data. To obtain accurate angle and intensity information, it is necessary to calibrate, and apply corrections. Intensity non-linearity, spatial distortion, and non-uniformity of intensity response, are the primary considerations. It is better to account for the distortions within scientific analysis software, but often it is more practical to correct the distortions to produce ‘idealised’ data. Calibration methods and software have been developed for single crystal diffraction experiments, using both approaches. For powder diffraction experiments the additional task of converting a two-dimensional image to a one-dimensional spectrum is used to allow Rietveld analysis. This task may be combined with distortion correction to produce intensity information and error estimates. High-pressure experiments can introduce additional complications and place new demands on software. Flexibility is needed to be able to integrate different angular regions se...
4,884 citations
TL;DR: In this article, a diamond-anvil cell was used to compress a sample of quartz at room temperature in a diamond anvil cell without a medium to maximum pressures of 31 to 213 GPa and was studied by energy-dispersive synchrotron X-ray diffraction.
Abstract: α-Quartz was compressed at room temperature in a diamond-anvil cell without a medium to maximum pressures of 31 to 213 GPa and was studied by energy-dispersive synchrotron X-ray diffraction Broad peaks observed in a previous high-pressure diffraction study of silica glass are evident in the present study of quartz compression, providing in situ confirmation of pressure-induced amorphization above 21 GPa The 21-GPa crystalline-crystalline (quartz 1–11) transformation previously observed on quasihydrostatic compression of quartz is found to also occur under the current nonhydrostatic conditions, at the identical pressure With nonhydrostatic compression, however, new sharp diffraction lines are observed at this pressure The measurements show the coexistence of at least one amorphous and two crystalline phases above 21 GPa and below 43 GPa The two crystalline phases are identified as quartz II and a new, high-pressure silica phase The high-pressure phases, both crystalline and amorphous, can be
61 citations
TL;DR: A phase transition from portlandite to Ca(OH)2 I (portlandite) at high pressure and temperature has been confirmed, using in situ x-ray diffraction in a multianvil high pressure device (DIA).
Abstract: A phase transition from Ca(OH)2 I (portlandite) to Ca(OH)2 II at high pressure and temperature has been confirmed, using in situ x-ray diffraction in a multianvil high pressure device (DIA). The structure was determined at 9.5 GPa and room temperature from data collected after heating the sample at 300°C at 7.2 GPa in a diamond anvil cell. Both the Le Bail fit and preliminary Rietveld refinement suggest that the new phase, which reverts to Ca(OH), I during pressure release, has a structure related to that of baddeleyite (ZrO1); it is monoclinic (P21/c) with a= 4.887(2), b= 5.834(2), c = 5.587(2), β = 99.74(2)°. The coordination number of Ca increases from six to seven (5 + 2) across the transition. At 500°C, the phase boundary is bracketed at 5.7 ± 0.4 GPa by reversal experiments performed in the DIA.
33 citations
TL;DR: In this paper, the capability of x-ray diffraction with high spatial resolution is most fundamental for probing microscopic samples at the maximum P-T and for minimizing the effect of gradients.
Abstract: Ultrahigh pressures and temperatures in diamond-anvil cells are achieved at the expense of reducing sample volume. The capability of x-ray diffraction with high spatial resolution is most fundamental for probing microscopic samples at the maximum P-T and for minimizing the effect of gradients. Polychromatic synchrotron radiation with energy dispersive x-ray diffraction is ideal for the development of new classes of structural microprobes. Primary x-ray beams down to 3 microns can be produced with microbeam slit systems and microfocusing optical devices. The microprobe can be routinely used for a variety of high-pressure experiments, including single-crystal x-ray diffraction above 50 GPa, polycrystal-line diffraction above 300 GPa, deviatoric strain measurements, and diffraction at simultaneous high pressure and temperature.
33 citations
TL;DR: In this article, a multi-anvil apparatus combined with a synchrotron-radiation source was used to measure the densities of crystalline and liquid tellurium.
Abstract: We have developed a new method for density measurements by means of X-ray absorption under high pressure and high temperature using a multi-anvil apparatus combined with a synchrotron-radiation source. To overcome the effect of the variation of the sample thickness under pressure, a sapphire ball was put in the sample capsule as a calibrant of the thickness, and the intensity of the transmitted X-ray beam was measured as a function of the sample position. The densities of crystalline and liquid tellurium were measured up to 5 GPa and up to 700°C. Discontinuous changes in the density at the Te I-Te 11 transition and at the melting were clearly observed.
27 citations
TL;DR: In this article, the results of a synchrotron X-ray diffraction study on the crystal structures of Bi 111 and Bi 111′ which have been known to form under high pressure but have, for a long time, been unsolved.
Abstract: This paper reports the results of a synchrotron X-ray diffraction study on the crystal structures of Bi 111 and Bi 111′ which have been known to form under high pressure but have, for a long time, been unsolved. Powdered samples were compressed in a cubic-type multi-anvil press, MAXID, and diffraction data were collected using an Imaging Plate with monochromatized radiation of an energy of 49.7 keV. It was possible to identify at 3.8 GPa forty-eight reflections for Bi I11 in the sin / δ range from 1.6 nm−1 to 5.6 nm−1, which were indexed in terms of a tetragonal unit cell with a=0.8659 nm and c═ O·4238 nm (2=10). Analysis based on the observed intensities of the reflections led to a structure in which atoms form a distorted body-centered cubic lattice. It is of the same type as the structure of the high pressure phase of antimony Sb 11. When pressure was increased across the suggested transition pressure 4.3 GPa between Bi III and Bi III′ to 6.6 GPa, no change in the diffraction pattern was obser...
27 citations
TL;DR: The maximum pressure within which these gem anvil cells could generale was 16.7 GPa in cubic-zirconia anvil cell and 25.8 GPA in sapphire anvilcell, respectively.
Abstract: In analogy with the bevelled diamonds in diamond anvil cells, some transparent gems are used as anvils for generating static ultrahigh pressure. The maximum pressure within which these gem anvil cells could generale was 16.7 GPa in cubic-zirconia anvil cell and 25.8 GPa in sapphire anvil cells, respectively.
23 citations
TL;DR: The European Synchrotron Radiation Facility (ESRF) is the first high-energy, high-brilliance synchron radiation source in operation today and it is ideally suited to high pressure research.
Abstract: The European Synchrotron Radiation Facility (ESRF) is the first high-energy, high-brilliance synchrotron radiation source in operation today and it is ideally suited to high pressure research. Whit...
21 citations
TL;DR: The theoretical background of the maximum entropy method when it is applied to restore the electron or nuclear densities from diffraction data is described and a few results for simple structures with typical types of chemical bonding are presented.
Abstract: The theoretical background of the maximum entropy method (MEM) when it is applied to restore the electron or nuclear densities from diffraction data is described. In MEM, the concept of “entropy” is introduced to deal with any incompleteness in an observation in a proper way. An incompleteness causes some ambiguities in the results to some extent. The essence of the method is to find a solution which necessarily agrees with the observation, leaving the measure of ambiguities (entropy) maximum. A few results for simple structures with typical types of chemical bonding are also presented.
17 citations
TL;DR: In this article, measurements under hydrostatic pressure on tetrahedrally-bonded semiconductors were performed by two-and three-photon spectroscopy.
Abstract: The present article reviews measurements under hydrostatic pressure on the tetrahedrally-bonded semiconductors CuCI, CuBr, ZnO, ZnS, ZnSe, ZnTe, Cds, and AgGaS2, by two-photon spectroscopy and on the alkali halides NaC1, KBr, KI, and RbI by two- and three-photon spectroscopy. It is shown that these nonlinear techniques yield a much higher precision than linear spectroscopy in the determination of the pressure dependence of the electronic band gap. Additionally, it is often possible to determine the pressure dependence of other parameters of the electronic band structure like exciton binding energy, spin-orbit coupling, crystal-field interaction, and Luttinger parameters. In the case of the alkali halides with their rather large band gaps there is a further advantage of three-photon spectroscopy, namely that pressure-cell windows need only be transparent for photons of one third of the band gap energy.
16 citations
TL;DR: In this paper, the electron density between adjacent iodine molecules has been shown to gradually increase with increasing pressure; also, a two-dimensional network is formed at a density level of 0.2 e/A3 at around 16 GPa.
Abstract: A direct observation of the electron density of solid iodine has been attempted in order to study the electron-density delocalization process due to pressure-induced metallization. A high-accuracy x-ray powder diffraction measurement was carried out with a diamond anvil cell and an imaging plate on a synchrotron-radiation source. The maximum entropy method was employed to analyze the data and to obtain electron-density maps under pressures up to 20 GPa. The electron density between adjacent iodine molecules has been shown to gradually increase with increasing pressure; also, a two-dimensional network is formed at a density level of 0.2 e/A3 at around 16 GPa.
TL;DR: Neutron diffraction was until recently confined to pressures below ∼ 3 GPa, which limited the high-pressure structural information that is available for a wide range of phenomena for which neutron diffraction is the technique of choice.
Abstract: Neutron diffraction was until recently confined to pressures below ∼ 3 GPa. This restricted range has limited the high-pressure structural information that is available for a wide range of phenomena for which neutron diffraction is the technique of choice. But now the recently-developed Paris-Edinburgh cell can achieve pressures up to ∼ 30 GPa with a sample volume large enough to allow accurate structural studies with neutrons. After a period of development of the neutron scattering techniques needed to obtain the best possible results using the cell, a variety of successful structural studies have been performed. These illustrate the value of neutron diffraction in important areas such as locating hydrogen and other low-Z atoms in structures, the measurement of accurate structural pressure dependence and the examination of the changes in atomic thermal motion with pressure.
TL;DR: In this paper, a diamond anvil cell was used to perform high-pressure 57Fe Mossbauer spectroscopy with synchrotron radiation and a pressure-induced magnetic hyperfine interaction at 57Fe in SrFeO2, 97 has been detected at 44 GPa and 300 K for the first time by a quantum-beat modulation of the decay rate after collective nuclear excitation by the synchoretron pulse.
Abstract: Using a diamond anvil cell, high-pressure 57Fe Mossbauer spectroscopy has been performed with the nuclear forward scattering of synchrotron radiation. A pressure-induced magnetic hyperfine interaction at 57Fe in SrFeO2, 97 has been detected at 44 GPa and 300 K for a first time by a quantum-beat modulation of the decay rate after collective nuclear excitation by the synchrotron pulse. The basic concept and method used to detect nuclear forward scattering with synchrotron radiation are discussed.
TL;DR: In this article, the phase transition in praseodymium and lanthanum under pressure was studied using a synchrotron powder X-ray diffraction technique using an imaging plate detector.
Abstract: Phase transitions in praseodymium and lanthanum under pressure have been studied using a synchrotron powder X-ray diffraction technique. A structure refinement of the distorted fcc phase of Pr using diffraction data collected with an imaging plate (IP) detector demonstrate that among some possible structures the rhombohedral structure with space group R3m best reproduces the observed diffraction pattern. The distorted fcc-fcc phase transition in La was observed as a function of the temperature at 23 GPa using a CCD-based detector. A five-minute exposure sufficiently long to measure the intensities of very weak superlattice reflections from the distorted fcc phase, which has been found to transform to the fcc phase at 550 K. The performance of the IP and a CCD-based detector are compared and their future developments discussed.
TL;DR: In this article, the temperature dependence of the equilibrium solubility of hBN and cBN in the supercritical ammonia up to 4.2 GPa have been calculated using phenomenological thermodynamic models.
Abstract: The temperature dependence of the equilibrium solubility of hBN and cBN in the supercritical ammonia up to 4.2 GPa have been calculated using phenomenological thermodynamic models. Experimental data on hBN solubility in ammonia in the temperature range of 850 to 1500 K have been used for the determination of the interaction parameters of the regular solutions' model for the liquid phase. It was shown that the experimental data on cBN solubility in ammonia in the whole experimental p, Region can be best expressed by using the value of ΔHtr= −16200 J/mol for the hBN → cBN transformation enthalpy, that was found earlier by fluorine combusfiion calorimetry. The results obtained are in good agreement with the equilibrium p, T-phase diagram of boron nitride.
TL;DR: In this article, the reduced structure factor S(Q) of KCl under high pressure was found to increase with the coordination number of nearest-neighbor ions in KCl with pressure.
Abstract: Energy-dispersive X-ray diffraction experiments of molten KCl under high pressure have been carried out by using synchrotron radiation. The diffraction profiles of molten KCl were acquired just above the melting temperature of KCl up to 4 GPa. The reduced structure factor S(Q)'s for molten KCl do not show any change in their primary features, except for a gradual increase in the first peak intensity with increasing pressure. This implies that molten KCl does not show a first-order phase transition, such as the B1-B2 transition, found in solid KCl, but that the local structure in molten KCl must be changed by compression. According to a molecular-dynamics simulation, this change of S(Q) can be explained by a continuous increase in the coordination number of the nearest-neighbor ions in molten KCl with pressure.
TL;DR: In this paper, the Gibbs free energy calculations demonstrate that efficient packing more than close packing is the reason of their stability, and that these compounds offer interesting issues for the physical chemistry at high pressure and astrophysical implications for outer planets.
Abstract: Four compounds of simple molecular systems have already been observed at high pressure: He(N2)1 1, Ne(He)2, Ar(H2)2 and (O2)3 (H2)4 They have been characterized by a combination of visual, Raman and energy dispersive measurements. Yet, the direct x-ray determination of their space-groups remains an experimental challenge. Gibbs free energy calculations demonstrate that efficient packing more than close packing is the reason of their stability. Finally, those compounds offer interesting issues for the physical chemistry at high pressure and astrophysical implications for outer planets.
TL;DR: In this article, techniques such as leBail extraction, soft restraints, and rigid body refinement were discussed with application to analysis of high pressure neutron powder diffraction data, and the results showed that these techniques can be used to extract the maximum useful information from the data.
Abstract: X-ray and neutron powder diffraction data obtained from samples contained within high pressure cells are generally of lower quality than data collected from samples at ambient conditions. The far smaller sample size as well as possible contamination of the pattern by the pressure cell means that Rietveld refinement techniques must be adapted to extract the maximum useful information from the data. These problems become paramount as larger structures at high pressure are attempted. Techniques such as “leBail extraction”, “soft restraints” and “rigid body refinement” will be discussed with application to analysis of high pressure neutron powder diffraction data.
TL;DR: In this paper, the synthesis of polycyclic strained molecules from norbornadiene and quadricyclane is described, which uses high pressure and involves concerted [2 + 2+2+2] or [2+ [sgrave]2+[sgrave]- processes in the first step followed by Diels-Alder cycloadditions of the primary cycloadducts 4a, 4b, 5a, 5b with cyclopen-tadiene, 1,3-cyclohexadiene.
Abstract: The synthesis of polycyclic strained molecules from norbornadiene and quadricyclane is described. The procedure uses high pressure and involves concerted [2+2+2] or [2+[sgrave]2+[sgrave]2] processes in the first step followed by Diels-Alder cycloadditions of the primary cycloadducts 4a, 4b, 5a, 5b with cyclopen-tadiene, 1,3-cyclohexadiene, furan, cycloheptatriene. The spectral NMR data of the new polycyclic molecules are given.
TL;DR: In this article, the Raman spectra of the layered compound, AsI3, were reported for samples at ambient temperature and at pressures up to 8 GPa, and evidence for a possible crystallographic phase transition near 1.6 GPa was presented.
Abstract: Raman spectra of the layered compound, AsI3, are reported for samples at ambient temperature and at pressures up to 8 GPa. Changes in the number of peaks, their frequencies, relative intensities and spectral widths as a function of pressure are briefly described, and evidence for a possible crystallographic phase transition near 1.6 GPa is presented. The two As-I stretching frequencies initially decrease with increasing pressure, as a result of charge-transfer effects, but above 4.5 GPa show the more typical increase with pressure exhibited by all other normal modes.
TL;DR: Using angle-dispersive diffraction techniques and synchrotron radiation, this article made a detailed re-examination of the high-pressure behavior of a number of core II-VI, III-V and group IV semiconductors.
Abstract: Using angle-dispersive diffraction techniques and synchrotron radiation, we have made a detailed re-examination of the high-pressure behaviour of a number of core II-VI, III-V and group IV semiconductors. Despite much previous work on these materials, the good resolution afforded by angle-dispersive techniques, and the high-sensitivity of the image-plate area detector have yielded many new results which reveal that the accepted structural systematics have to be modified quite substantially. In this paper, we summarise the newly emerging structural systematics, and use the results to show how access to full 2-d powder patterns has proved essential in determining correct crystal structures.
TL;DR: The diamond-like amorphous carbon phase was obtained by means of detonation compression of mixtures of an explosive with soot or graphite as discussed by the authors, and the pycnometric density of powders after compression and treatment in boiling acids achieved 3.42 g/cm3.
Abstract: The diamond-like amorphous carbon phase was obtained by means of detonation compression of mixtures of an explosive with soot or graphite. The pycnometric density of powders after compression and treatment in boiling acids achieved 3.42 g/cm3. The X-ray and TEM study showed that fine-grained crystalline and nanocrystalline diamond was also present in the samples in addition to the diamond-like amorphous phase.
TL;DR: In this paper, the temperature and pressure dependence of internal and external vibrations of crystalline S6 were investigated by means of conventional Raman spectroscopy, using a high pressure diamond anvil cell.
Abstract: We have investigated by means of conventional Raman spectroscopy the temperature and pressure dependence of internal and external vibrations of crystalline S6 For the low temperature measurements we used chemically prepared S6, for the high pressure experiments we produced S6, from p-S in a high pressure diamond anvil cell We systematically measured the temperature and pressure dependence of frequencies and intensities of internal and external modes and improved the mode assignment
TL;DR: In this article, electrical resistivity measurements have been carried out on bulk Ge-Te-Se glasses in a Bridgman anvil system, and the resistivity of the Ge-te-Se samples is found to decrease continuously with increasing pressure, with the metallization occurring around 8 GPa.
Abstract: Electrical resistivity measurements have been carried out on bulk Ge-Te-Se glasses in a Bridgman anvil system The resistivity of the Ge-Te-Se samples is found to decrease continuously with increasing pressure, with the metallization occurring around 8 GPa Ge20TexSe80-x glasses (10 ≤×≤ 50) with the mean co-ordination number Zav=24 exhibit a plateau in resistivity up to about 4 GPa pressure, followed by a continuous decrease to metallic values On the other hand, Ge10TexSe90-x glasses (10 ≤×≤ 40) having Zav=22, exhibit a smaller plateau (only up to 1 GPa), followed by a decrease in resistivity with pressure This subtle difference in the high pressure resistivity of Ge-Te-Se glasses with Zav<24 and Zav ≥ 24 can be associated with the changes in the local structure of the chalcogenide glasses with composition
TL;DR: In this paper, perovskite oxides were synthesized in a belt-type reaction cell, where in situ generation of high oxygen pressure was made by the thermal decomposition of KCIO3.
Abstract: New Ir(VI) containing perovskite oxides, (ALa)LiIrO6-δ,(A ˭ Ca,Sr,Ba) were synthesized in a belt-type reaction cell, where in situ generation of high oxygen pressure was made by the thermal decomposition of KCIO3. The crystal structure and their oxygen stoichiometry depend on the A cation species (Ca, Sr, Ba) in the same preparation conditions. The long range magnetic interaction was not observed in the stoichiometric(BaLa)LiIrO6, by the magnetic susceptibility measurements. Complex paramagnetic behavior of SrLaLiIrO5.82, and CaLaLiIrO5.62 is attributed to the partial formation of pentavalent iridium (+ V) characterized by a T-ground term.
TL;DR: In this paper, the authors describe a number of in situ high pressure x-ray diffraction work for radonium and thorium actinides at synchrotrons and neutron facilities.
Abstract: Uranium and thorium have sufficiently low radioactive dose rates to allow their study at synchrotrons and neutron facilities. Correspondingly, numerous compounds of these two actinides have been studied under pressure by synchrotron x-ray diffraction. The maximum pressures reached were on the order of 60-80 GPa, and 300 GPa in one case. The situation is much more difficult for all other actinides. Their high level of radioactivity has up to now prevented their study at synchrotrons, except in a few special cases. In contrast, all actinide metals available in sufficient quantities, and a large number of compounds of highly radioactive actinides, have been studied in highpressure laboratory facilities. Recent examples of in situ high pressure x-ray diffraction work will be described.
TL;DR: In this paper, the helium-gas pressure system at the Intense Pulsed Neutron Source (IPNS) with the Special Environment Powder Diffractometer (SEPD) was introduced and the results for TIBa2CuO6+8, and La2−x, Srx, CuO4−8 are briefly reviewed.
Abstract: High-pressure neutron-diffraction experiments using the time-of-flight (TOF) method are presented. We first introduce the helium-gas pressure system at Argonne's Intense Pulsed Neutron Source (IPNS) with the Special Environment Powder Diffractometer (SEPD). The results for TIBa2CuO6+8, and La2−x, Srx, CuO4–8 are briefly reviewed. We then introduce the present situation in Japan. We have been developing a high-pressure system on high-resolution powder diffractometer (HRP) which was much improved recently and renamed VEGA at KEK. The best resolution of 0.45% was obtained at VEGA. The preliminary results for YBa2, Cu4O8, and HgBa2, CuO4+8, are presented and compared with the SEPD data.
TL;DR: In this paper, the magnetic structure of a low-carrier Kondo-lattice system CeAs was determined and a softening of the crystalline electric field excitations was observed.
Abstract: We have determined the magnetic structure of a low-carrier Kondo-lattice system CeAs, and have observed a softening of the crystalline electric field excitations. Despite the prediction of a recent magnetic polaron model in which CeAs and CeP are expected to show a stacking order of T7 and T8 layers, CeAs does not show such a stacking structure under pressure. The ordering in the intermediate phase is a regular ferromagnetic order and that of the low-temperature phase is a canted type-I AF.
TL;DR: In this article, the lattice dynamics of monoatomic solids, consisting of many-electron atoms in very strong magnetic fields, are investigated at high pressures within the Kadomtzev's approach.
Abstract: Lattice dynamics of monoatomic solids, consisting of many-electron atoms in very strong magnetic fields, is investigated at high pressures. Consideration is done within the Kadomtzev's approach. Vibrational spectra of face-centered cubic lattice of neon are calculated for some directions of high symmetry in the Brillouin zone.
TL;DR: Combined x-ray absorption spectroscopy (XAS) and X-ray diffraction experiments on powders, both in the dispersive mode, may enable the determination of structural parameters as a function of pressure.
Abstract: Combined x-ray absorption spectroscopy (XAS) and x-ray diffraction experiments (EDX) on powders, both in the dispersive mode, may enable the determination of structural parameters as a function of pressure. After phase transitions, it may even be possible to determine the structure of the high pressure phases. The EDX enables the determination of the cell parameters, and eventually the space group from the systematic extinctions. On the other hand, the XAS provides information on the local environment of an atomic species, i.e., the coordination number and the first (eventually even second) neighbour distances with a high precision. The combination of these two techniques has been successfully used to determine the high pressure structure of ZnTe and HgTe. We present here recent results obtained on the high pressure properties of chalcopyrites and of berlinites. Finally, recent developments and future possibilities with the new synchrotron sources are presented.