Correction and integration of solid-angle data from the azimuthally resolving 2D detector at ID06-LVP, ESRF.

The unique diffraction geometry of ESRF beamline ID06-LVP offers continuous static 2D or azimuthally resolving data collections over all accessible solid angles available to the tooling geometry. The system is built around a rotating custom-built Pilatus3 CdTe 900k-W detector from Dectris, in a configuration equivalent to three butted 300k devices. As a non-standard geometry, here the method of alignment, correction and subsequent integration for any data collected over all solid angles accessible, or over any azimuthal range contained therein, are provided and illustrated by parameterizing and extending existing pyFAI routines.

Hypervalent hydridosilicate in the Na-Si-H system.

Hydrogenation reactions at gigapascal pressures can yield hydrogen-rich materials with properties relating to superconductivity, ion conductivity, and hydrogen storage. Here, we investigated the ternary Na-Si-H system by computational structure prediction and synchrotron diffraction studies of reaction mixtures NaH-Si-H at 5-10 GPa. Structure prediction indicated the existence of various hypervalent hydridosilicate phases with compositions NaSiH (m = 1-3) at comparatively low pressures, 0-20 GPa.

Chemical Reactions and Phase Stabilities in the Si-Te System at High Pressures and High Temperatures.

Chemical reactions and phase stabilities in the Si-Te system at high pressures were explored using angle-dispersive synchrotron powder diffraction in a large-volume multianvil press together with density functional theory-based calculations. Cubic and rhombohedrally distorted clathrates, with the general formula Te@(SiTe) and wide compositional range, preceded by a hexagonal phase with the composition SiTe, are formed for different mixtures of Si and Te as starting materials. SiTe, with the structural formula Te(TeSi)(TeSi), is the very first chalcogenide with the MnSi-type structure.

Unconventional Route to High-Pressure and -Temperature Synthesis of GeSn Solid Solutions.

Ge and Sn are unreactive at ambient conditions. Their significant promise for optoelectronic applications is thus largely confined to thin film investigations. We sought to remove barriers to reactivity here by accessing a unique pressure, 10 GPa, where the two elements can adopt the same crystal structure (tetragonal, 4/) and exhibit compatible atomic radii.

An Unexpected Cubic Symmetry in Group IV Alloys Prepared Using Pressure and Temperature.

The cubic diamond (Fd m) group IVA element Si has been the material driver of the electronics industry since its inception. We report synthesis of a new cubic (Im m) group IVA material, a GeSn solid solution, upon heating Ge and Sn at pressures from 13 to 28 GPa using double-sided diamond anvil laser-heating and large volume press methods. Both methods were coupled with in situ angle dispersive X-ray diffraction characterization.

NaFeH and NaCoH: Hydrogen-Rich First-Row Transition Metal Hydrides from High Pressure Synthesis.

The formation of ternary hydrogen-rich hydrides involving the first-row transition metals TM = Fe and Co in high oxidation states is demonstrated from in situ synchrotron diffraction studies of reaction mixtures NaH-TM-H at 10 GPa. NaFeH and NaCoH feature pentagonal bipyramidal FeH and octahedral CoH 18-electron complexes, respectively. At high pressure, high temperature (300 < ≤ 470 °C) conditions, metal atoms are arranged as in the face-centered cubic Heusler structure, and ab initio molecular dynamics simulations suggest that the complexes undergo reorientational dynamics.

Na-Ni-H Phase Formation at High Pressures and High Temperatures: Hydrido Complexes [NiH] the Perovskite NaNiH.

The Na-Ni-H system was investigated by synchrotron diffraction studies of reaction mixtures NaH-Ni-H at around 5, 10, and 12 GPa. The existence of ternary hydrogen-rich hydrides with compositions NaNiH and NaNiH, where Ni attains the oxidation state II, is demonstrated. Upon heating at ∼5 GPa, face-centered cubic () NaNiH forms above 430 °C.

Exploring the Mg-Cr-H System at High Pressure and Temperature via in Situ Synchrotron Diffraction.

The complex transition metal hydride MgCrH has been previously synthesized using high pressure conditions. It contains the first group 6 homoleptic hydrido complex, [Cr(II)H]. Here, we investigated the formation of MgCrH by in situ studies of reaction mixtures of 3MgH-Cr-H at 5 GPa.

Nature of Hexagonal Silicon Forming via High-Pressure Synthesis: Nanostructured Hexagonal 4H Polytype.

Hexagonal Si allotropes are expected to enhance light absorption in the visible range as compared to common cubic Si with diamond structure. Therefore, synthesis of these materials is crucial for the development of Si-based optoelectronics. In this work, we combine in situ high-pressure high-temperature synthesis and vacuum heating to obtain hexagonal Si.

Unraveling Hidden Mg-Mn-H Phase Relations at High Pressures and Temperatures by in Situ Synchrotron Diffraction.

The Mg-Mn-H system was investigated by in situ high pressure studies of reaction mixtures MgH-Mn-H. The formation conditions of two complex hydrides with composition MgMnH were established. Previously known hexagonal MgMnH (h-MgMnH) formed at pressures 1.

Synthesis of Bulk BC8 Silicon Allotrope by Direct Transformation and Reduced-Pressure Chemical Pathways.

Phase-pure samples of a metastable allotrope of silicon, Si-III or BC8, were synthesized by direct elemental transformation at 14 GPa and ∼900 K and also at significantly reduced pressure in the Na-Si system at 9.5 GPa by quenching from high temperatures ∼1000 K. Pure sintered polycrystalline ingots with dimensions ranging from 0.

An Alternative Route to Pentavalent Postperovskite.

Two different high-pressure and -temperature synthetic routes have been used to produce only the second-known pentavalent CaIrO3-type oxide. Postperovskite NaOsO3 has been prepared from GdFeO3-type perovskite NaOsO3 at 16 GPa and 1135 K. Furthermore, it has also been synthesized at the considerably lower pressure of 6 GPa and 1100 K from a precursor of hexavalent Na2OsO4 and nominally pentavalent KSbO3-like phases.

The large volume press facility at ID06 beamline of the European synchrotron radiation facility as a High Pressure-High Temperature deformation apparatus.

We report here the newly developed deformation setup offered by the 20MN (2000T) multi-anvil press newly installed at sector 7 of the European synchrotron radiation facility, on the ID06 beamline. The press is a Deformation-DIA (D-DIA) type apparatus, and different sets of primary anvils can be used for deformation experiments, from 6 mm to 3 mm truncations, according to the target pressure needed. Pressure and temperature calibrations and gradients show that the central zone of the assemblies is stable.

Perovskite to postperovskite transition in NaFeF3.

The GdFeO3-type perovskite NaFeF3 transforms to CaIrO3-type postperovskite at pressures as low as 9 GPa at room temperature. The details of such a transition were investigated by in situ synchrotron powder diffraction in a multianvil press. Fit of the p-V data showed that the perovskite phase is more compressible than related chemistries with a strongly anisotropic response of the lattice metrics to increasing pressure.

Structures of dolomite at ultrahigh pressure and their influence on the deep carbon cycle.

Carbon-bearing solids, fluids, and melts in the Earth's deep interior may play an important role in the long-term carbon cycle. Here we apply synchrotron X-ray single crystal micro-diffraction techniques to identify and characterize the high-pressure polymorphs of dolomite. Dolomite-II, observed above 17 GPa, is triclinic, and its structure is topologically related to CaCO(3)-II.

The structural behaviour of LaF(3) at high pressures.

We have performed in situ X-ray diffraction, Raman scattering, pseudosymmetry analysis and quantum mechanical atomistic simulations of the structure and behaviour of LaF(3) at high pressure, up to and exceeding the phase transition pressure reported for the I4/mmm structure and Cmma symmetry proposed previously. We observe that the structure of LaF(3)-II is best described as being of anti-Cu(3)Ti-type (oP8, Pmmn, SG59), which is closely related to the I4/mmm structure obtained by simulation, through notional distortion, and is evidently similar to the Cmma symmetry by comparison of published diffraction data. We demonstrate that the models are also related to each other, and can be derived through pseudosymmetry searches.

Establishing the structure of GeS(2) at high pressures and temperatures: a combined approach using x-ray and neutron diffraction.

The change in structure of glassy GeS(2) with pressure increasing to [Formula: see text] at ambient temperature was explored by using in situ neutron and x-ray diffraction. Under ambient conditions, the glass structure is made from a mixture of corner- and edge-sharing Ge(S(1/2))(4) tetrahedra where 47(5)% of the Ge atoms are involved in edge-sharing configurations. The network formed by these tetrahedra orders on an intermediate range as manifested by the appearance of a pronounced first sharp diffraction peak in the measured total structure factors at a scattering vector k = 1.

Portable multi-anvil device for in situ angle-dispersive synchrotron diffraction measurements at high pressure and temperature.

A recently developed portable multi-anvil device for in situ angle-dispersive synchrotron diffraction studies at pressures up to 25 GPa and temperatures up to 2000 K is described. The system consists of a 450 ton V7 Paris-Edinburgh press combined with a Stony Brook ;T-cup' multi-anvil stage. Technical developments of the various modifications that were made to the initial device in order to adapt the latter to angular-dispersive X-ray diffraction experiments are fully described, followed by a presentation of some results obtained for various systems, which demonstrate the power of this technique and its potential for crystallographic studies.

Phase separation, crystallization and polyamorphism in the Y(2)O(3)-Al(2)O(3) system.

A detailed study of glass formation from aerodynamically levitated liquids in the (Y(2)O(3))(x)(Al(2)O(3))(1-x) system for the composition range 0.21≤x≤0.41 was undertaken by using pyrometric, optical imaging and x-ray diffraction methods.

Structural description of pressure-induced amorphization in ZrW2O8.

ZrW2O8 undergoes a high-pressure amorphization transition above 1.5 GPa to a phase which is recoverable to ambient conditions. Reverse Monte Carlo modeling of neutron and x-ray total scattering data from ZrW2O8 recovered from approximately 4 GPa shows that the large increase in density on pressurizing ZrW2O8 is accommodated within the structure by increased bonding between the WO4 tetrahedra.

Amorphous silica-like carbon dioxide.

Among the group IV elements, only carbon forms stable double bonds with oxygen at ambient conditions. At variance with silica and germania, the non-molecular single-bonded crystalline form of carbon dioxide, phase V, only exists at high pressure. The amorphous forms of silica (a-SiO2) and germania (a-GeO2) are well known at ambient conditions; however, the amorphous, non-molecular form of CO2 has so far been described only as a result of first-principles simulations.

Alternating sequence of ring and chain structures in sulphur at high pressure and temperature.

Sulphur is the subject of a renewed intensive research effort aiming at characterizing its complex phase diagram. Nonetheless, on reading recent literature on its high-pressure phases, a confused picture emerges where different techniques obtain different results. We have investigated the phase diagram of sulphur by X-ray diffraction at high pressures and temperatures (6-11 GPa and 300-1,000 K), and have observed a new occurrence of a molecular S6 phase, in addition to the previously described polymeric helical trigonal and tetragonal phases.