Kirill Zhuravlev

High pressure single-crystal micro X-ray diffraction analysis with GSE_ADA/RSV software

GSE_ADA/RSV is a free software package for custom analysis of single-crystal micro X-ray diffraction (SCμXRD) data, developed with particular emphasis on data from samples enclosed in diamond anvil cells and subject to high pressure conditions. The package has been in extensive use at the high pressure beamlines of Advanced Photon Source (APS), Argonne National Laboratory and Advanced Light Source (ALS), Lawrence Berkeley National Laboratory. The software is optimized for processing of wide-rotation images and includes a variety of peak intensity corrections and peak filtering features, which are custom-designed to make processing of high pressure SCμXRD easier and more reliable.

Vibrational, elastic, and structural properties of cubic silicon carbide under pressure up to 75 GPa: Implication for a primary pressure scale

We present results of concomitant measurements of synchrotron x-ray diffraction (XRD), Brillouin, and Raman spectroscopy on the single crystal samples of cubic silicon carbide (3C-SiC) under quasi-hydrostatic pressures up to 65 GPa, as well as x-ray diffraction and Raman spectroscopy up to 75 GPa. We determined the equation of state of 3C-SiC and pressure dependencies of the zone-center phonon, elastic tensor, and mode Gruneisen parameters. Cubic SiC lattice was found to be stable up to 75 GPa, but there is a tendency for destabilization above 40 GPa, based on softening of a transverse sound velocity. By applying the concomitant density and elasticity measurements, we determined the pressure on the SiC sample without referring to any other pressure scale thus establishing a new primary pressure scale with a 2%–4% precision up to 65 GPa. We proposed corrections to the existing ruby and neon pressure scales, and also calibrated cubic SiC as a pressure marker for the x-ray diffraction and Raman experiments.

How “Hollow” Are Hollow Nanoparticles?

Diamond anvil cell (DAC), synchrotron X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS) techniques are used to probe the composition inside hollow γ-Fe(3)O(4) nanoparticles (NPs). SAXS experiments on 5.2, 13.3, and 13.8 nm hollow-shell γ-Fe(3)O(4) NPs, and 6 nm core/14.8 nm hollow-shell Au/Fe(3)O(4) NPs, reveal the significantly high (higher than solvent) electron density of the void inside the hollow shell. In high-pressure DAC experiments using Ne as pressure-transmitting medium, formation of nanocrystalline Ne inside hollow NPs is not detected by XRD, indicating that the oxide shell is impenetrable. Also, FTIR analysis on solutions of hollow-shell γ-Fe(3)O(4) NPs fragmented upon refluxing shows no evidence of organic molecules from the void inside, excluding the possibility that organic molecules get through the iron oxide shell during synthesis. High-pressure DAC experiments on Au/Fe(3)O(4) core/hollow-shell NPs show good transmittance of the external pressure to the gold core, indicating the presence of the pressure-transmitting medium in the gap between the core and the hollow shell. Overall, our data reveal the presence of most likely small fragments of iron and/or iron oxide in the void of the hollow NPs. The iron oxide shell seems to be non-porous and impenetrable by gases and liquids.

The Sm:YAG primary fluorescence pressure scale

Primary pressure determinations involve the measurement of pressure without recourse to secondary standard materials. These measurements are essential for ensuring the accuracy of pressures measured in gasketed high-pressure devices. In this study, the wavelength of optical fluorescence bands and the density of single crystal Sm-doped yttrium aluminum garnet Y3Al5O12 (Sm:YAG) have been calibrated as a primary pressure scale up to 58 GPa. Absolute pressures were obtained by integrating the bulk modulus determined via Brillouin spectroscopy with respect to volumes measured simultaneously by X-ray diffraction. A third-order Birch-Murnaghan equation of state of Sm:YAG yields V0 = 1735.15(26) A3, KT0 = 185(1.5) GPa, and K` = 4.18(5). The accompanied pressure-induced shifts of the fluorescence lines Y1 and Y2 of Sm:YAG were calibrated to the primary pressure, thus creating a highly accurate fluorescence pressure scale. These shifts are described as P = (A/B) * {[1 + (Δλ/λ0)]B − 1} with A = 2089.91(23.04), B = −4.43(1.07) for Y1, and A = 2578.22(48.70), B = −15.38(1.62) for Y2 bands, where ∆λ = λ − λ0, λ and λ0 are wavelengths in nanometer at pressure and ambient conditions. The sensitivity in the pressure determination of the Sm:YAG fluorescence shift is 0.32 nm/GPa, which is identical to that of the ruby scale. Sm:YAG can be considered elastically isotropic up to 58 GPa, implying insensitivity of the determined pressure to the crystallographic orientation under nonhydrostatic or quasi-hydrostatic conditions. The Sm:YAG fluorescence shift is apparently also independent of crystallographic orientation, in contrast to that of ruby. Since the Y fluorescence band of Sm:YAG is insensitive to temperature changes, this material is highly suitable for the measurement of pressure at elevated temperatures.

Structure of methane and ethane at high pressure

A. Goncharov, E. Stavrou , S. Lobanov , A. Oganov, V. Roisen, A. Chanyshev, K. Litasov, Z. Konopkova, K. Zhuravlev, V. Prakapenka Geophysical Laboratory, Carnegie Insitution of Washington, Washington DC, USA, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens, Greece, V.S. Sobolev Institute of Geology and Mineralogy SB RAS , Novosibirsk, Russian Federation, Department of Geosciences, State University of New York, Stony Brook, NY, United States, Petra III, P02.2, DESY, Hamburg, Germany, Center for Advanced Radiation Sources, University of Chicago, Chicago, IL, United States

High-pressure behavior of single-crystal and nanocrystalline ZnO studied with XRD and BS

-Single-crystal x-ray diffraction (XRD) and Brillouin spectroscopy (BS) are the most powerful technique for studies elastic and structural properties of materials at ambient conditions. At high-pressure, however, the single-crystal technique is restricted by limited angular access to the sample in the high pressure vessel and by the requirement of having a highquality thin crystal sustained in the desired pressure-temperature range [1]. As a result, in a number of cases at extremely high pressure and high temperature conditions, polycrystalline samples with various grain sizes are still the most routinely used for structure solution and physical property measurements. While effect of crystal size on structural and elastic properties of solid is well known at ambient condition the high pressure data is very limited [2]. In this work, we present a new approach in high pressure research employing the combination of BS with synchrotron XRD for characterization of ZnO in three crystalline forms: single-crystal, polycrystalline and nano-sized. The main reasons for using nano-structural materials in adition to single crystal and polycrystalline forms are to (1) reduce the anisotropy of samples probed with BS/XRD and (2) avoid significant effects on the Brillouin spectra due to the high sensitivity of acoustic velocities to crystallographic direction. The ability to perform simultaneous measurements of velocities and bulk modulus Ks (by BS), and the volume/density (by XRD) independent of any pressure standard in the same pressure-temperature environment provides essential information to resolve discrepancies between experimental data and theoretical calculations. First order phase transition from hexagonal (wurtzite, B4) to cubic (rock salt, B1) was observed with XRD technique in pressure range of 8-12 GPa for all samples associated with significant jump in density. At the same time the sound velocities show a slight softening of shear acoustic mode and quick raise after B4-B1 phase transition while longitudinal mode shows rather smooth behavior across the transition region. We were able to collect shear and longitudinal modes of ZnO up to 176 GPa, which is currently the highest known pressure where both Vs and Vp were measured simultaneously for known material structure and density. Important physical properties such as aggregate acoustic velocities, isothermal and adiabatic bulk and shear moduli, thermal expansion, structure, density, and other thermodynamic constants essential for understanding the nature of phase transition and compression mechanisms could be derived from combined studies single crystal and nanosized materials with BS and x-ray synchrotron techniques [3].