Lattice dynamics of stishovite from powder inelastic X‐ray scattering

Abstract

[1] We have retrieved the full lattice dynamics of stishovite, SiO 2 , by a combination of powder inelastic x-ray scattering (IXS) and ab initio calculations. The extracted dispersion curves are confirmed by experiments on a single crystal. Thereby we have shown that IXS powder measurements over a large range of momentum transfers allow an unambiguous validation of lattice dynamics models, which then in turn can be used to derive elastic and thermodynamic properties. The proposed method can be extended to high pressure measurements on in situ synthesized samples and promises to be a valuable tool in studies of materials for which no single crystals can be obtained.

High-pressure phase behavior of SrCO3: an experimental and computational Raman scattering study

“…As is nearly always the case, the theoretical spectrum is 223 systematically shifted, and here we have scaled the computed Raman shifts by 6%. This is a typical value re-224 quired to achieve a good agreement between experiment and theory (Bosak et al 2009). The Raman spectra of 225 the three carbonates in Fig.…”

New insights into the lattice dynamics ofα-quartz

“…Contrary to the example of stishovite [29], the polycrystalline spectra are not structured enough to serve as a definitely discriminating test for the calculation, so they must be completed by single crystal studies. …”

“…This shortcoming can be overcome by exploring a large Q-range, from the low Q-limit to the VDOS limit, especially where the spectral shape varies with momentum transfer due to -though relaxed -selection rules. Thus, additional constraints beyond the VDOS are provided for the lattice dynamics modeling [21,29].…”

Density functional theory based calculations for high pressure research

“…The linear response approach allows one to compute LO/ TO splitting. With DFT-based models, it is possible to compute frequencies and intensities of Raman (Porezag and Pederson, 1996;Milman et al, 2009), infrared (Porezag andPederson, 1996;, inelastic neutron scattering (Ryan et al, 2011) and inelastic X-ray scattering (Winkler et al, 2008b;Bosak et al, 2009) spectra. Commonly, the IR absorption spectrum of a powder is obtained from samples embedded in a matrix such as KBr.…”

“…The first four data sets have been determined experimentally from Brillouin light scattering (Weidner et al, 1982;Brazhkin et al, 2005;Jiang et al, 2009) and from high frequency ultrasound resonance spectroscopy (Yoneda et al, 2012). Bosak et al (2009) employed inelastic X-ray scattering data to rescale DFT-GGA results. The DFT-based data with different xc-functionals confirm the often made observations that LDA gives an upper bound for the tensor components, GGA-PBE or RPBE a lower bound and that the results of PBESOL and WC-based calculations are in between the two extremes.…”