A design of backing seat and gasket assembly in diamond anvil cell for accurate single crystal x-ray diffraction to 5 GPa

Abstract

We designed a new cell assembly of diamond anvil cells for single crystal x-ray diffraction under pressure and demonstrate the application of the cell to the crystallographic studies for ice VI and ethanol high-pressure (HP) phase at 0.95(5) GPa and 1.95(2) GPa, respectively. The features of the assembly are: (1) the platy anvil and unique-shaped backing seat (called as "Wing seat") allowing the extremely wide opening angle up to ±65°, (2) the PFA-bulk metallic glass composite gasket allowing the easy attenuation correction and less background. Thanks to the designed assembly, the R(int) values after attenuation corrections are fairly good (0.0125 and 0.0460 for ice VI and ethanol HP phase, respectively), and the errors of the refined parameters are satisfactory small even for hydrogen positions, those are comparable to the results which obtained at ambient conditions. The result for ice VI is in excellent agreement with the previous study, and that for ethanol HP phase has remarkable contributions to the revision to its structure; the H12 site, which makes gauche molecules with O1, C2, and C3 sites, may not exist so that only trans conformers are present at least at 1.95(2) GPa. The accurate intensities using the cell assembly allow us to extract the electron density for ethanol HP phase by the maximum entropy method.

Single Crystal Growth of High-Pressure Phases of Ice and Salt Hydrate Far Below the Original Melting Point by Mixing Alcohol: Crystal Structure Determination of Magnesium Chloride Heptahydrate

“…Absorption by diamond anvils was corrected manually in the listed reflections, and the structure parameters were refined by SHELXL 13 . The initial structure of ice VI was from Komatsu et al 11 determined by single-crystal x-ray diffraction and that of MgCl2•7H2O was derived by the direct method using SIR2014 14 . The hydration number of MgCl2•7H2O was also determined from the derived structure with the minimal R1 factor.…”

“…An inner gasket made of perfluoroalkoxy alkanes (PFA) was inserted in the sample space to keep a single crystal at the centre position in the sample space. It prevents the incident and/or diffracted x-ray beams from travelling through the metal gasket 11 . Eight cartridge heaters were used to heat the DAC in order to enhance the crystal growth of a single crystal of MgCl2•7H2O with controlling pressure using a gearbox ( Figure S1).…”

“…The increment in alcohol concentration in the liquid shifted the liquid-solid phase boundary to higher pressure. Structural analyses of ice VI have already been conducted from x-ray 11,15 and neutron 16,17 diffraction studies, so that we do not deal with it in detail. In the case of ice VI obtained at around 2 GPa from ME41 mixed solution, its unit-cell volume decreased by 4 % compared with the ice VI from pure water at around 1 GPa.…”

Crystal structure of a high-pressure phase of magnesium chloride hexahydrate determined byin-situX-ray and neutron diffraction methods

“…Some set-ups were modified for single-crystal X-ray diffraction. A modified backing seat, which has three cutouts with an opening of 60 , was placed towards the detector to increase the number of observable Bragg reflections (Komatsu et al, 2011). An SUS 301 stainless plate with a hole of diameter of 0.4 mm was used as a gasket.…”

High pressure neutron and X-ray diffraction at low temperatures

“…Options include the use of a beryllium backing plate, or a harder support with a conical aperture for the beam. There are other alternative geometries still being suggested [88]. In specific cases where the beam must be passed radially between the anvils, the gasket material must have a low atomic number; beryllium, boron [89] or cubic boron nitride composite gaskets are used.…”