Diffraction at high pressure

Banus, M.D., X-Ray Diffraction at High Pressures, High Temp-High Press. 1, 483-515(1969). 

Diffraction at high pressure also provides an opportunity to measure some combinations of elastic moduli directly, because the pressure is a stress which results in a strain that is expressed as a change in the unit cell parameters. The compressibility of any direction in the crystal is directly related to the components of the elastic compliance tensor by ... 

I thank Nancy Ross, Ulrich Bismayer, Tiziana Boffa-Ballaran, Jennifer Kung and Ronald Miletich for various collaborations, all of which contributed to this chapter. John Loveday kindly provided material on neutron diffraction at high pressures, and Don Isaak material on RUS. In addition Tiziana Boffa-Ballaran, Michael Carpenter, Simon Redfem, and Ekhard Salje made helpful comments and suggestions for improvement of the original manuscript. 

Angel RJ, Ross NL, Wood IG, Woods PA (1992) Single-Crystal X-Ray-Diffraction At High-Pressures with Diamond-Anvil Cells. Phase Transit 39 13-32... 

Singh AK, Mao HK, Shu JF, Hemley RJ (1998b) Estimation of single-crystal elastic moduli from polycrystalline X-ray diffraction at high pressure Application to FeO and iron. Phys Rev Lett 80 2157-2160... 

R. M. Brugger, R. B. Bennion, T. G. Worlton, and W. R. Myers, Neutron diffraction at high pressures, Trans. Amer. Cryst. Assoc. 5, 141-154 (1969). 

Since the vibrational spectra of sulfur allotropes are characteristic for their molecular and crystalline structure, vibrational spectroscopy has become a valuable tool in structural studies besides X-ray diffraction techniques. In particular, Raman spectroscopy on sulfur samples at high pressures is much easier to perform than IR spectroscopical studies due to technical demands (e.g., throughput of the IR beam, spectral range in the far-infrared). On the other hand, application of laser radiation for exciting the Raman spectrum may cause photo-induced structural changes. High-pressure phase transitions and structures of elemental sulfur at high pressures were already discussed in [1]. 

Macchi P, Casati N, Marshall WG, Sironi A (2010) The a and p forms of oxalic acid di-hydrate at high pressure a theoretical simulation and a neutron diffraction study. CrystEngComm 12 2596-2603... 

Casati N, Macchi P, Sironi A (2005) Staggered to eclipsed conformational rearrangement of [Co2(CO)g(PPh3)2] in the solid state an X-ray diffraction study at high pressure and low temperature. Angew Chem 44 7736-7739... 

There are four principal methods of determining crystal structures at high pressures employing powders or single-crystals, using X-rays or neutrons. Here 1 will give a brief review of the relevant diffraction techniques and analysis methods used with each technique, focusing on recent developments. 

The following four examples have been chosen to illustrate the variety of different crystal structures now being found in simple materials at high pressure, and the quality of diffraction information that was necessary to solve the crystal... 

Once Te-III was identified as incommensurate, subsequent analysis was conducted on the previously-collected powder-diffraction data using the formalism of 4D superspace [234], and the JANA2000 software for structure refinement [235]. The Rietveld refinement of the incommensurate Te-III diffraction profile is shown in Fig. 9, and the modulated structure is shown in Fig. 10. Tellurium was only the second element found to have a modulated crystal structure at high-pressure, the... 

Variable-temperature X-ray diffraction studies of crystalline substances are useful in the study of phase transitions, thermal expansion and thermal vibrational amplitudes of atoms in solids. Similarly, diffraction studies at high pressures are employed to examine pressure-induced phase transitions. Time-resolved X-ray diffraction studies (Clark Miller, 1990) will be of great value for examining reactions and other transformations. 

Bohanon et al. [86] studied heneicosanoic acid (which contains 21 carbon atoms) and Lin et al. [87] studied this material with particular reference to the effect of pH and the presence of divalent cations in the subphase. The former authors made use of in-plane diffraction (method 2 above) and obtained first order and second order diffraction peaks. They were able to show that, at high pressures ( r=35 mN m-1), at low pH (pH = 2) and at temperatures in the region of 0-5 °C, the material packs into a distorted hexagonal structure with the tilt towards the nearest neighbours. However, in the region 5-10°C the tilt is towards the next nearest neighbours. In the latter study [87] in-plane diffraction was studied as a function of pH and the presence of Ca2+ or Cu2+ in... 

A further requirement for a pressure sensor is the stability of the host lattice at high pressures and temperatures. This requirement strongly narrows the range of possible candidates for high-pressure sensors. From X-ray diffraction experiments under pressure, it was found that YAG is stable at least up to 69 GPa at room temperature (Liu and Vohra, 1993). This is one of the reasons why doped YAG was chosen by many researchers as a promising host for pressure calibrants. 

Glazkov, V.P., Zhukov, V.P., Somenkov, V.A., Shil shtein, S.Sh. (1997) Neutron diffraction investigation of C60 fullerene and C60F4S Fluorine-fullerene at high pressure, Poverhnost (Surface) 7, 45-49 (in Russian). 

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