High-pressure Diffraction

High-pressure Crystallography, ed. A. Katrusiak and P. McMillan, NATO Science Series 2, 2003, vol. 140. 

Norlund Christensen and J.C. Hanson, Inorg. Chem., 1999, 38, 1216-1221. 

High-pressure Techniques in Chemistry and Physics, ed. W. B. Holzapfel and N. S. Isaacs, Oxford University Press, Oxford, 1997. 

Local Structure from Total Scattering and Atomic Pair Distribution Function (PDF) Analysis 

Department of Physics and Astronomy, 4268 Biomedical Phys. Sciences Building, Michigan State University, East Lansing, MI 48824, USA 

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Varga T, Wilkinson AP, Angel RJ (2(X)3) Huorinert as a pressure—transmitting medium for high-pressure diffraction smdies. Rev Sci Instmm 74 4564... 

Boldyreva EV (2008) High-pressure diffraction studies of molecular organic solids a personal view. Acta Cryst A 64 218-231... 

Jamieson J C, Lawson A W and Nachtreib N D 1959 New device for obtaining X-ray diffraction patterns from substances exposed to high pressures Rev. Sc/, instrum. 30 1016... 

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

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

A.I. Kolesnikov, A.M. Balagurov, I.O. Bashkin, V.K. Fedotov, V.Yu. Malyshev, G.M. Mironova, E.G. Ponyatovsky, A Real-Time Neutron Diffraction Study of Phase Transitions in the Ti-D System after High Pressure Treatment, J. Phys. Condensed Matter 5 5045 (1993). 

Takemura and co-workers31 have shown by optical measurements, X-ray diffraction and micro-DTA measurements that the high-pressure phase is liquid-crystalline, and that... 

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]. 

Thomas and co-workers [277] reported that irradiation of (382) with a 450 W high-pressure mercury lamp brought about photocyclisation to a constrained analogue (394). The structure of the product was elucidated through NMR and X-ray diffraction analysis. The compound retained high affinity for the CBi receptor (Xj = 48 nM) and good selectivity over the CB2 receptor (K[ — 3,340 nM). 

Note 41,57 neutron diffraction 43 high pressure 52 single crystal neutron diffraction. 

The behavior of cristobalite PON has been studied as a function of pressure. No in situ evidence for pressure-induced amorphization was noticed. Whereas cristobalite Si02 displays four crystalline phases up to 50 GPa (195), PON remains in a cristobalite phase (193, 196). By using Raman spectroscopy and synchrotron X-ray diffraction, Kingma et al. (193, 197) observe a displacive transformation below 20 GPa to a high-pressure cristobalite-related structure, which then remains stable to at least 70 GPa. The high value of the calculated bulk modulus (71 GPa) (196) is indicative of the remarkable stiffness of the phase. 

Several methods are also available for determination of the isothermal compressibility of materials. High pressures and temperatures can for example be obtained through the use of diamond anvil cells in combination with X-ray diffraction techniques [10]. kt is obtained by fitting the unit cell volumes measured as a function of pressure to an equation of state. Very high pressures in excess of 100 GPa can be obtained, but the disadvantage is that the compressed sample volume is small and that both temperature and pressure gradients may be present across the sample. 

More recent quantum-based MD simulations were performed at temperatures up to 2000 K and pressures up to 30 GPa.73,74 Under these conditions, it was found that the molecular ions H30+ and OH are the major charge carriers in a fluid phase, in contrast to the bcc crystal predicted for the superionic phase. The fluid high-pressure phase has been confirmed by X-ray diffraction results of water melting at ca. 1000 K and up to 40 GPa of pressure.66,75,76 In addition, extrapolations of the proton diffusion constant of ice into the superionic region were found to be far lower than a commonly used criterion for superionic phases of 10 4cm2/s.77 A great need exists for additional work to resolve the apparently conflicting data. 

Figure 24. X-ray diffraction pattern (in the inset the 2D image) of the polyethylene sample recovered by the laser-assisted high-pressure reaction in the pure liquid monomer. The two measured sharp lines nicely fit the polymer diffraction pattern having a orthorhombic cell (Pnam) defined by the lattice parameters reported in the figure.

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