Angle-dispersive Synchrotron X-ray Diffraction Research Articles

Structure transition of multiferroic hexagonal TmMnO3 compound under high pressure

The high-pressure-induced structure transition in multiferroic hexagonal TmMnO3 (h-TmMnO3) has been investigated using an in situ angle-dispersive synchrotron X-ray diffraction technique in a diamond anvil cell. The experimental results show that the phase transition from ambient hexagonal to orthorhombic structure with space group Pbnm begins around 10.2 GPa. The Rietveld refinement method was used to determine the lattice parameters and lattice compressibility of the h-TmMnO3 compound from 0.8 to 28.6 GPa. The pressure evolution of average bond distances and bond angles between the Mn and O atoms in the ab-plane was obtained. The magnetic properties under different pressures as well as their effect on multiferroic properties are discussed using extrapolations from the empirical relation of magnetic order versus rare-earth ionic radius.

High-pressure behavior of β-Ga2O3 nanocrystals

Freestanding nanocrystalline β-Ga2O3 particles with an average grain size of 14 nm prepared by chemical method was investigated by angle-dispersive synchrotron x-ray diffraction in diamond-anvil cell up to 64.9 GPa at ambient temperature. The evolution of x-ray diffraction patterns indicated that nanocrystalline monoclinic β-Ga2O3 underwent a phase transition to rhombohedral α-Ga2O3. It was found that β- to α-Ga2O3 transition began at about 13.6–16.4 GPa, and extended up to 39.2 GPa. At the highest pressure used, only α-Ga2O3 was present, which remained after pressure release. A Birch–Murnaghan fit to the P-V data yielded a zero-pressure bulk modulus at fixed B0′=4: B0=228(9) GPa and B0=333(19) GPa for β-Ga2O3 and α-Ga2O3 phases, respectively. We compared our results with bulk β-Ga2O3, and concluded that the phase-transition pressure and bulk modulus of nanocrystalline β-Ga2O3 are higher than those of bulk counterpart.

Synchrotron X-ray Diffraction and Infrared Spectroscopy Studies of C60H18 under High Pressure

In situ high-pressure angle-dispersive synchrotron X-ray diffraction and high-pressure mid-infrared (IR) spectrum measurements of C60H18 were carried out up to 32 and 10.2 GPa, respectively. Our diffraction data indicated that the fcc structure of C60H18 was stable up to 32 GPa. The bulk modulus B0 was determined to be 21 ± 1.16 GPa, about 40% higher than that of C60. The C−H vibrations still existed up to 10.2 GPa, and the vibrational frequencies decreased with increasing pressure. IR-active vibrational frequencies and their corresponding eigenvectors of C60H18 were simulated by DMOL3. The effects of the hydrogen atoms attached to the fullerene molecular cage on the stability of the structure under high pressure are discussed.

Microstructure, residual strain, and eigenstrain analysis of dissimilar friction stir welds

A study of residual strains in aluminium-based dissimilar friction stir welds (FSWs) was performed by a novel approach that will be referred to as the Eigenstrain Reconstruction Method (ERM). The method is based on the theory of permanent inelastic strain (eigenstrain) as the basis for reconstructing full-field residual stress and strain states. The strain distributions evaluated by the angle-dispersive synchrotron X-ray diffraction were used to obtain the eigenstrain distributions by ERM. In order to build the FE eigenstrain model that forms the essential part of ERM implementation, the analysis of microstructure and diffraction peak profile (i.e., intensity and FWHM) was performed to understand the material mixing that occurred in the weld zone. The ERM approach allowed the approximate determination of the complete stress and strain state everywhere in the component. The resulting description is continuous, complete and consistent, in terms of satisfying the equilibrium, compatibility and boundary conditions. This is a significant improvement over the experimentally obtained raw data that only provides a limited knowledge of stress components at a number of selected measurement points, and over simple interpolation between these data points. It is concluded that ERM is a powerful tool for the analysis and use of full-field residual stress and strain distributions in engineering components and structures.

Pressure-induced structural transformations of the Zintl phase sodium silicide

The high-pressure behaviour of NaSi has been studied using Raman spectroscopy and angle-dispersive synchrotron X-ray diffraction. Our studies reveal a first structural transformation occurring at 8–10 GPa, followed by irreversible amorphisation, suggesting the formation of Si–Si bonds with oxidation of the Si − species and reduction of Na + to metallic sodium. We have combined our experimental studies with DFT calculations to assist in the analysis of the structural behaviour of NaSi at high pressure. [Display omitted]

Structural evolution during the dehydration of gypsum materials

AbstractThe dehydration of pure and waste gypsums has been examined using in situ synchrotron angledispersive X-ray diffraction. Pure gypsum was studied under a number of defined environments; various industrial waste gypsums were also studied under a common standard environment. It is found that the dehydration of gypsum to anhydrite proceeds via the hemihydrate and γ-anhydrite phases and the interplay and behaviour of these phases has been determined by full structural ‘Rietveld’ refinement. In the study of the pure gypsum system, the hemihydrate structure is shown to be preserved as water is lost. A ‘zero-water hemihydrate’ is observed before refinement in the higher symmetry γ-anhydrite cell is possible. The waste gypsum materials studied showed significant differences in the temperatures at which key transformation events occurred; these observations raise implications concerning the re-use of by-product gypsum materials. Finally, high temperature data are re-examined in the search for a variation of the anhydrite structure.

Size dependence of rutile TiO2 lattice parameters determined via simultaneous size, strain, and shape modeling

Simultaneous crystal structure, microstructure, and morphology modeling with convolution-based profile fitting of angle-dispersive synchrotron x-ray diffraction data was applied to retrieve the size-dependent lattice changes in nanocrystalline rutile TiO2. The dominant prismatic crystallite morphology was adequately modeled using the parallelepiped geometry. As with anatase TiO2, opposing trends of decreasing c and increasing a parameter, as well as lattice expansion with decreasing average crystallite size were observed. A correlation between Ti vacancy abundance and lattice volume increase suggests a possible causative link.

High-pressure phase transformations, pressure-induced amorphization, and polyamorphic transition of the clathrateRb6.15Si46

The type-I clathrate ${\text{Rb}}_{6.15}{\text{Si}}_{46}$ with partly empty cage sites has been studied up to 36 GPa using Raman spectroscopy, synchrotron x-ray diffraction in diamond-anvil cells, and ab initio total-energy and lattice-dynamics calculations. A first phase transition is observed at $13\ifmmode\pm\else\textpm\fi{}1\text{ }\text{GPa}$ and a ``volume collapse'' transition within the clathrate structure is then observed at $24\ifmmode\pm\else\textpm\fi{}1\text{ }\text{GPa}$. Pressure-induced amorphization into a high-density amorphous (HDA) state occurs above $P=33\ifmmode\pm\else\textpm\fi{}1\text{ }\text{GPa}$. The HDA form transforms into a low-density amorphous polymorph during decompression. During the compression study using angle dispersive synchrotron x-ray diffraction techniques we measured bulk modulus parameters for rocksalt-structured TaO, included adventitiously in the clathrate sample [${K}_{0}=293(3)\text{ }\text{GPa}$ and ${K}_{0}^{\ensuremath{'}}=5.4(3)$].

A high pressure x-ray diffraction study of titanium disulfide

A high pressure angle dispersive synchrotron x-ray diffraction study of titanium disulfide(TiS2)was carried out to pressures of 45.5 GPa in a diamond-anvil cell. We observed a phase transformationof TiS2 beginning at about 20.7 GPa. The structure of the high pressure phaseneeds further identification. By fitting the pressure–volume data to thethird-order Birch–Murnaghan equation of state, the bulk modulus,K0T, was determinedto be 45.9 ± 0.7 GPa with itspressure derivative, K′0T, being 9.5 ± 0.3 at pressures lower than 17.8 GPa. It was found that the compression behavior ofTiS2 is anisotropic along the different axes. The compression ratio of thec-axis is about ninetimes larger than the a-axis when pressures are lower than 1 GPa. It suddenly decreases to three times larger atpressures of about 3 GPa. This ratio shows a linear decrease with a slope of negative 0.048at pressures below phase transformation.

Size Dependence of Cubic to Trigonal Structural Distortion in Silver Micro- and Nanocrystals under High Pressure

Silver micro- and nanocrystals with sizes of ∼2−3.5 μm and ∼50−100 nm were uniaxially compressed under nonhydrostatic pressures (strong deviatoric stress) up to ∼30 GPa at room temperature in a symmetric diamond-anvil cell and studied in situ using angle-dispersive synchrotron X-ray diffraction. A cubic to trigonal structural distortion along a 3-fold rotational axis was discovered by careful and comprehensive analysis of the apparent lattice parameter and full width at half-maximum, which are strongly dependent upon the Miller index and crystal size.

Phase transitions and isothermal equations of state of epsilon hexanitrohexaazaisowurtzitane (CL-20)

The phase stability of epsilon hexanitrohexaazaisowurtzitane at high pressure and temperature was investigated using synchrotron angle-dispersive x-ray diffraction experiments. The samples were compressed at room temperature using a Merrill–Bassett diamond anvil cell. For high-temperature compression experiments a hydrothermal diamond anvil cell developed by Bassett was used. Pressures and temperatures of around 5 GPa and 175 °C, respectively, were achieved. The epsilon phase was determined to be stable under ambient pressure to a temperature of 120 °C. A phase transition to the gamma phase was seen at 125 °C and the gamma phase remained stable until thermal decomposition above 150 °C. Pressure-volume data for the epsilon phase at ambient and 75 °C were fitted to the Birch–Murnaghan formalism to obtain isothermal equations of state.

Experimental high pressure and high temperature study of the incorporation of uranium in Al-rich CaSiO 3 perovskite

The high ability of the Al-rich CaSiO 3 perovskite to contain large amounts of uranium (up to 4 at.% U) has been studied up to 54 GPa and 2400 K, using laser-heated diamond anvil cell (LH-DAC) and up to 18 GPa and 2200 K using a multi-anvil press (MAP). Both latter HP-HT techniques proved to be complementary and gave similar results, in spite of different heating modes (laser and furnace). Chemical reactions were characterized and described by electron probe microanalysis and analytical scanning electron microscopy while associated structural changes were precisely characterized by synchrotron angle dispersive X-ray diffraction and by X-ray micro-diffraction. The diffusion of uranium into the CaSiO 3 matrix was measured as a function of run duration and temperature. We obtain diffusion coefficients with the same order of magnitude (about 10 −16 m 2 s −1) than for those found in the literature. After this work, coupled cationic substitutions of Ca by U and Si by Al are proposed to generate new interesting crystallographic features for a CaSiO 3 perovskite: a higher compressibility, a tetragonal distortion along the c-axis with c/ a ratio >1, a different compression behaviour of c-axis relative to a-axis, and a perovskite structure quenchable to ambient P and T conditions. The tetragonal U-bearing aluminous CaSiO 3 perovskite is observed to remain stable at pressures up to 54 GPa, then in the ( P, T) range of the upper part of the lower mantle. The influence of the present results, in terms of both uranium and aluminium partitioning related to the coexisting mineral phases as the (Mg,Fe)SiO 3 perovskite, is discussed. Uranium provides approximately 25% of the total energy generated within the deep Earth through its radioactive decay. The location of this source within the deep mantle is fundamental to the understanding of the geodynamics and thermal behaviour of our planet. Since the tetragonal structure of the U-bearing Al-rich CaSiO 3 perovskite is expected to remain stable towards the base of the Earth's mantle, this latter phase is proposed to be the main storage mineral for heat producing actinides of the lower mantle.

X-ray diffraction study of molybdenum diselenide to 35.9 GPa

In situ high-pressure angle dispersive synchrotron X-ray diffraction studies of molybdenum diselenide (MoSe 2) were carried out in a diamond-anvil cell to 35.9 GPa. No evidence of a phase transformation was observed in the pressure range. By fitting the pressure–volume data to the third-order Birch–Murnaghan equation of state, the bulk modulus, K 0T, was determined to be 45.7±0.3 GPa with its pressure derivative, K′ 0T, being 11.6±0.1. It was found that the c-axis decreased linearly with pressure at a slope of −0.1593 when pressures were lower than 10 GPa. It showed different linear decrease with the slope of a −0.0236 at pressures higher than 10 GPa.

Self-diffusion in sodium under pressure revisited

The pressure–volume relation in sodium has been measured up to 100 GPa usinghigh-resolution angle-dispersive synchrotron x-ray diffraction (Hanfland et al 2002 Phys.Rev. B 65 184109). In the light of these data, we show that a model suggested long ago(e.g., Varotsos et al 1978 J. Phys. C: Solid State Phys. 11 L305–15) can satisfactorilyanswer the long-standing question of the variation of the diffusion coefficientD under pressureP, which resultedin a curved lnD versus P plot, in the frame of a single operating mechanism (monovacancies). This is achievedwithout using any adjustable parameters.

Nonlinear size dependence of anatase TiO2 lattice parameters

We characterized the size dependence of anatase TiO2 lattice parameters using Rietveld analysis of angle-dispersive synchrotron x-ray diffraction data obtained on a suite of nanocrystalline samples. The refined crystal structure and microstructure data suggest that for crystallites with size less than ∼10nm, the lattice parameters vary nonlinearly. Small lattice expansion, associated with possible increased Ti vacancy and lattice strain, at reduced crystallite size observed in our samples is in contrast to the lattice contraction behavior reported for “pure” anatase nanocrystals. The nonlinear, composition-dependent variation of anatase unit cell volume contrasts with the linear expansion behavior of rutile lattice at finite sizes.

Pressure-induced antifluorite-to-anticotunnite phase transition in lithium oxide

Using synchrotron angle-dispersive x-ray diffraction and Raman spectroscopy on samples of ${\mathrm{Li}}_{2}\mathrm{O}$ pressurized in a diamond anvil cell, we observed a reversible phase change from the cubic antifluorite ($\ensuremath{\alpha}$, Fm-3m) to orthorhombic anticotunnite ($\ensuremath{\beta}$, Pnma) phase at $50(\ifmmode\pm\else\textpm\fi{}5)\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ at ambient temperature. This transition is accompanied by a relatively large volume collapse of $5.4\phantom{\rule{0.3em}{0ex}}(\ifmmode\pm\else\textpm\fi{}0.8)%$ and large hysteresis upon pressure reversal (${P}_{\mathit{\text{down}}}$ at $\ensuremath{\sim}25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$). Contrary to a recent study, our data suggest that the high-pressure $\ensuremath{\beta}$-phase $({B}_{o}=188\ifmmode\pm\else\textpm\fi{}12\phantom{\rule{0.3em}{0ex}}\mathrm{GPa})$ is substantially stiffer than the low-pressure $\ensuremath{\alpha}$-phase $({B}_{o}=90\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.3em}{0ex}}\mathrm{GPa})$. A relatively strong and pressure-dependent preferred orientation in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}\mathrm{O}$ is observed. The present result is in accordance with the systematic behavior of antifluorite-to-anticotunnite phase transitions occurring in the alkali-metal sulfides.

High-Pressure-Induced Phase Transitions in Pentaerythritol: X-ray and Raman Studies

The high-pressure response of pentaerythritol crystals has been examined to 10 GPa in diamond-anvil cells using angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy. The results reveal two first-order phase transitions: one at 4.8 GPa from phase I, tetragonal I(), to phase II, orthorhombic Pnn2C2v10, with a small approximately 0.5% volume change, and the other at 7.2 GPa to phase III with an unknown crystal structure. We found that phase I exhibits a large crystallographic anisotropy which rapidly decreases with increasing pressure: the ratio of linear compressibilities between two primary crystal axes decreases from betao= 8.1 at 1 atm to betaP = 2.6 at 4 GPa. We suggest that this apparent decrease in crystal anisotropy is due to the disruption of hydrogen bonding in the (001) plane of phase I and eventually leads to an orthorhombic distortion from a quadrilateral network structure in phase I to a quasi one-dimensional structure in phase II. The crystal structure of phase III exhibits a disordered character, and it is likely a conformational variant of phase II.

Structural Refinement of the High‐Pressure Phase of Aluminum Trihydroxide: In situ High‐Pressure Angle Dispersive Synchrotron X‐Ray Diffraction and Theoretical Studies.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structural Refinement of the High-Pressure Phase of Aluminum Trihydroxide: In-Situ High-Pressure Angle Dispersive Synchrotron X-ray Diffraction and Theoretical Studies

In-situ high-pressure synchrotron angle-dispersive X-ray diffraction for gibbsite (aluminum trihydroxide) was performed at room temperature up to 20 GPa. A pressure-induced phase transition was observed at 2.6 GPa. The new high-pressure phase can be recovered at ambient pressure. Rietveld refinement shows that the new phase of Al(OH)(3) has an orthorhombic structure, spacegroup Pbca, and the lattice parameters at ambient condition are a = 868.57(5) pm, b = 505.21(4) pm, c = 949.54(6) pm, V = 416.67(6) x 10(6) pm(3) with Z = 8. The compressibility of gibbsite and the high-pressure polymorph was analyzed, and their bulk moduli were estimated as 49.8 +/- 1.8 and 81.0 +/- 5.2 GPa, respectively. First-principles calculations of the high-pressure phase were performed to determine the hydrogen positions and to confirm the structural stability of the new phase.

Isothermal equations of state of beta octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine at high temperatures

Isothermal pressure-volume equations of state of beta HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) at temperatures of 30, 100, and 140°C under both hydrostatic and nonhydrostatic compressions have been obtained using synchrotron angle-dispersive x-ray diffraction experiments. The samples were heated to the isotherm temperature and compressed up to 5.8GPa. At all temperatures HMX remained in the beta phase up to 5.8GPa. However, at 140°C upon decompression to ambient from nonhydrostatic pressures above 4GPa, HMX underwent a phase transition to the delta phase. The same transition was seen upon decompression to ambient from hydrostatic compression; however, parts of the sample remain in the β phase, resulting in a mixed-phase sample. The diffraction data were analyzed to yield unit-cell dimensions at each pressure, and further analyzed to yield thermal expansion, bulk modulus, and the pressure derivative of the bulk modulus.