Energy dispersive x-ray diffraction of micro-crystals at ultrahigh pressures

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.     

Single crystal x-ray diffraction with a synchrotron source in a mdac at low temperature

Abstract

A new diamond anvil cell and a helium flow cryostat have been developed for x-ray diffraction on single crystals at low temperatures and high pressures using the white radiation of a synchrotron beam. This novel instrument especially enables continuous change of sample temperature and pressure without any adjustment of alignment. A minimum temperature of 46 K has been reached.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’, Daresbury Laboratory 20-21 July 1991     

Orthorhombic to tetragonal phase transition in high TC superconductor YBa2Cu3O7-y and NdBa2Cu3O7-z under high pressure

Abstract

X-ray powder diffraction measurements for YBa₂Cu₃O_7-y and NdBa₂Cu₃O_7-y were made at the intense synchrotron radiation source under high pressure up to 5 GPa. These samples were wrapped tightly in platinum foil to avoid deoxidizing atmosphere. The orthorhombic to tetragonal transition temperature increases with pressure in both samples. These results are discussed on the basis of the disordering of the oxygen atoms on the chain sites.     

Melting and thermal expansion of iron in uniformly laser-heated diamond anvil cells

Abstract

A technique is described to laser heat samples uniformly under hydrostatic pressure conditions to over 2500 K and 400 kbar with very high accuracy in P and T. I re-measured the melting curve of iron by this technique and obtained excellent agreement with my earlier work using resistive wire heating (Boehler 1986). P-V-T measurements on γ-iron to 200 kbar and 2000 K using synchrotron radiation leads to a strong decrease of the thermal expansion coefficient with pressure, (?lnα/?lnV)_T = 6.5. The zero pressure bulk modulus K₀ decreases with temperature by 0.33 kbar deg^?1. This Yields densities of iron at conditions in the Earth's core which are consistent with shock compression measurements. The potiential of studying mineralogical phase transitions by this method is described.     

Synchrotron x-ray-diffraction study of α-cristobalite at high pressure and high temperature

Abstract

Energy-dispersive x-ray diffraction using synchrotron radiation was carried out on α-cristobalite to 3 GPa and 350°C in a cubic anvil press. A cascading structural phase transition occurred beyond 0.61 GPa at room temperature. The transition was accompanied by a splitting of most of the a-cristobalite reflections: the (111) reflection at 0.61 GPa through the (211) reflections at 2.13 GPa, with many other lines between. The pressure of this transition decreased with increasing temperature.     

X-ray absorption spectroscopy and high pressure

Abstract

The difficulties of the adaptation of high pressure to x-ray absorption are presented. The advantages of the energy-dispersive geometry are discussed as well as the future improvements expected with the new synchrotron radiation sources.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’, Daresbury Laboratory 20-21 July 1991     

High-pressure Mössbauer spectroscopy with nuclear forward scattering of synchrotron radiation

Abstract

Using a diamond anvil cell, high-pressure ⁵⁷Fe Mössbauer spectroscopy has been performed with the nuclear forward scattering of synchrotron radiation. A pressure-induced magnetic hyperfine interaction at ⁵⁷Fe in SrFeO_{2, 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.     

Rietveld analysis for energy dispersive x-ray diffraction under high pressure with synchrotron radiation

Abstract

A new program has been developed for the conversion of energy-dispersive x-ray diffraction spectra obtained from powder samples at high pressure in a diamond anvil cell (DAC) into conventional pseudo angle-dispersive data. The program is compatible with a conventional Rietveld program. This allows the determination of the structural parameters of the samples investigated. Results of a synchrotron radiation study of polycrystalline SrFCl in the tetragonal phase at high pressure are presented.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’, Daresbury Laboratory 20-21 July 1991     

High pressure studies at the photon factory

Abstract

The Photon Factory has unique features from the point of view of high pressure research. Six beamlines have been used for high pressure experiments, two of which were constructed as dedicated beamlines for large high pressure devices. Various kinds of high pressure studies, such as powder and single crystal x-ray diffraction and absorption experiments, have been carried out on these beamlines by more than 30 user groups, including foreign visitors. Two types of high pressure apparatuses are most frequently used. One is the large volume high pressure devices (MAX80 and MAX90) combined with high energy and/or high brightness synchrotron radiation. The other is a system combining the diamond anvil cell with a 2-dimensional detector, the IMAGE PLATE. Many improvements have been made both in the high pressure techniques and the diffraction measurement methods.

Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for High Pressure Crystallography’. Daresbury Laboratory 20-21 July 1991     

Equations of state of MgO at high pressure and temperature

Abstract

A synchrotron X-ray diffraction study on MgO has been done at simultaneous high pressure and temperature. The lattice parameter of MgO has been measured up to a static pressure of 6 GPa and a temperature of 1273 K, using a large volume pressure cell and energy-dispersive synchrotron X-ray powder diffraction. The compression was made following six high-temperature isotherms. A Vinet equation of state was used to fit the experimental P-V-T data. The Vinet's model compares very well with the experimental data above the Debye temperature (760 K) and allows the use of MgO as an alternative internal pressure calibrant for experiments at high temperature.     

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 Mössbauer spectroscopy using synchrotron radiation and radioactive sources

A high-pressure ⁵⁷Fe Mössbauer study of SrFeO₃ up to 74 GPa has been performed with diamond-anvil-cell (DAC) using synchrotron radiation and a radioactive point source of ⁵⁷Co in Rh. SrFeO₃ is known as a typical cubic perovskite with a high-valence state of Fe⁴⁺ and shows metallic conductivity at 0.1 MPa down to 4.2 K. Applying an external high pressure, SrFeO₃ has not shown any structural transformation up to 74 GPa keeping an Fe⁴⁺ state but the Néel temperature increases up to 300 K at 18 GPa. The external high pressure may induce the ferromagnetism in SrFeO₃ by a decrease of the interatomic distance of Fe or an increase of the d-band width. ⁵⁷Fe Mössbauer measurements under externally applied longitudinal magnetic field using radioactive ⁵⁷Co in Rh source and also nuclear forward scattering measurements with a linearly polarized synchrotron radiation under external magnetic field indicate the existence of the pressure induced ferromagnetism in SrFeO₃. In this work we compare high-pressure Mössbauer spectroscopy using synchrotron and radioactive sources and summarize the advantages and disadvantages of each method.     

Pressure-induced structure change of molten KCl

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.     

X-ray Diffraction Study of Cd 0.8 Zn 0.2 Te Under High Pressure and Temperature

Energy dispersive X-ray diffraction using synchrotron radiation has been used to study phase transformations of Cd 0.8 Zn 0.2 Te under high pressure and temperature. We confirm the presence of a cinnabar phase between the zinc-blende and rock-salt phases. But contrary to the results in CdTe, this intermediate phase is found to be stable only on pressure decrease and in a narrower pressure and temperature range. Single-phase cinnabar patterns are obtained only at 300 and 373 K. At 673 K and above, even on pressure decrease, no evidence of the cinnabar phase is found. In this temperature range, a phase segregation phenomenon is observed in the zinc-blende phase during the zinc-blende transition in both upstroke and downstroke, and the retrieved sample at ambient conditions presents a double pattern corresponding to two different Zn contents.     

A system for doing low temperature-high pressure single crystal X-ray diffraction with a synchrotron source

Abstract

A new diamond anvil cell and a helium flow cryostat have been developed for X-ray diffraction on single crystals at low temperatures and high pressures using white radiation of a synchrotron beam. This novel instrument especially enables continuous change of temperature and pressure of the sample without any adjustment of alignment. Automatic search for diffraction peaks can be performed since less than 30 pm eccentricity can be maintained during the rotation of the cell in the cryostat and the rotation of the cryostat on the goniometer head. The minimum temperature reached is 46 K. Measurements of solid 4He at 11.8 GPa are presented which confirm the stability of the hcp phase on this isobar.     

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.     

Thermoelastic behaviour of hexagonal graphite-like boron nitride

Abstract

A synchrotron X-ray diffraction study on hexagonal graphite-like boron nitride (h-BN) was performed under high pressures and temperatures. From the measured P-V-Trelation for h-BN (with a three-dimensional ordering parameter P₃ = 0.9) in the temperature range from 298 to 1273 K and up to 6.7 GPa, the thermoelastic parameters are derived by fitting a modified high temperature Birch-Murnaghan equation of state. The results are: bulk modulus B₀[GPa] = 27.6-0.0081(T[K]-298) and its pressure derivative B¹ = 10.5 + 0.0016(T [K] - 298). These values are for samples with P₃ = 0.9 and are quite different for samples with different values of the order parameter. This parameter is shown to have a leading role in the determination of the thermoelastic properties of h-BN, which explains and reconciles the differences between previous results.     

High-Pressure Phase Relationships for FeS

Phase relationships for FeS polymorph have been studied at the pressure of 16-20 GPa and temperature of 300-1350 K by in situ X-ray observation using a large volume high-pressure apparatus and a synchrotron radiation. Contrary to Fei's prediction [1], we found the stability field of NiAs-type phase of FeS extending at least to 18 GPa. Results of in situ X-ray observation correspond with the NiAs-hexagonal phase boundary determined by Kusaba et al . [2, 3]. Assuming the straight NiAs-hexagonal phase boundary, we estimate that the NiAs-hexagonal-liquid triple junction is located at 39.5 GPa and 2300 K.     

Current progress and future developments in sychrotron radiation instrumentation for high-pressure research including the esrf programme

Abstract

The field of synchrotron radiation instrumentation and techniques for high-pressure research is reviewed. Current state-of-the-art, recent developments, main directions of progress and areas with the greatest need for further developments are discussed. Large volume devices, diamond-anvil cells, temperature variation, detectors, all diffraction techniques and dispersive x-ray absorption are covered. Theplanned ESRF high-pressure facilities and programme are presented.     

Optics and beamlines for high-pressure research at the european synchrotron radiation facility

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. White-beam and monochromatic diffraction techniques are being optimized in particular for structural studies of low-Z materials and poor scatterers generally, the best example being hydrogen single crystals at very high pressures. Most high pressure measurements are carried out on a versatile beamline equipped with a wiggler and an undulator. Focusing and image plates are used in all monochromatic angle-dispersive studies. The success of the high pressure programme has so far been achieved on a non-optimized beamline, but the next phase of the programme needs an optimized facility. A beamline is being constructed to fully exploit the intrinsic qualities of this unique source and insertion devices for high pressure studies. Its main design concepts are presented.