Pressure dependence of Raman linewidths in ices VII and VIII

Besson, J. M.; Kobayashi, Michihiro; Nakai, T.; Endo, S.; Pruzan, Ph.

doi:10.1103/physrevb.55.11191

Cited by 23 publications

(15 citation statements)

References 37 publications

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“…In particular, while no Raman activity is expected in clean samples below 360 cm −1 , a broad band systematically appears at low frequency in ceramics [17,19], twice-peaked around 250 and 320 cm −1 , with an intensity which differs from sample to sample of a same bulk composition [17]. We attribute this band to a high density of states of disorder-activated acoustic phonons, in analogy to what is found, e.g., in ice VII [20]. Having shown that the vibrational spectra of B 4 C can be consistently interpreted in terms of a carbon atom occupying one of the polar sites, we consider now its elastic properties, which have recently attracted some interest [10].…”

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confidence: 63%

Atomic Structure and Vibrational Properties of IcosahedralB4CBoron Carbide

et al. 1999

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The atomic structure of icosahedral B4C boron carbide is determined by comparing existing infra-red absorption and Raman diffusion measurements with the predictions of accurate ab initio lattice-dynamical calculations performed for different structural models, a task presently beyond X-ray and neutron diffraction ability. By examining the inter-and intra-icosahedral contributions to the stiffness we show that, contrary to recent conjectures, intra-icosahedral bonds are harder.

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confidence: 63%

Atomic Structure and Vibrational Properties of IcosahedralB4CBoron Carbide

et al. 1999

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“…Besson et al (28) observed a roughly parabolic behavior of the υ 1 vibron line width in D 2 O ices VII and VIII with a clear minimum at ∼13 GPa, implying increased disorder above this pressure. Meanwhile, measurements of the VII-VIII transition temperature by Pruzan et al (29,30) show that this begins to decrease markedly between 10 and 18 GPa (being constant below this pressure).…”

Section: Resultsmentioning

confidence: 99%

Neutron diffraction observations of interstitial protons in dense ice

Guthrie

Boehler

Tulk

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The motif of distinct H 2 O molecules in H-bonded networks is believed to persist up to the densest molecular phase of ice. At even higher pressures, where the molecule dissociates, it is generally assumed that the proton remains localized within these same networks. We report neutron-diffraction measurements on D 2 O that reveal the location of the D atoms directly up to 52 GPa, a pressure regime not previously accessible to this technique. The data show the onset of a structural change at ∼13 GPa and cannot be described by the conventional network structure of ice VII above ∼26 GPa. Our measurements are consistent with substantial deuteron density in the octahedral, interstitial voids of the oxygen lattice. The observation of this "interstitial" ice VII form provides a framework for understanding the evolution of hydrogen bonding in ice that contrasts with the conventional picture. It may also be a precursor for the superionic phase reported at even higher pressure with important consequences for our understanding of dense matter and planetary interiors.crystallography | high pressure | water A ll of the some 16 phases of crystalline ice documented to date exhibit a tetrahedrally coordinated structure in which each molecule is H-bonded to four neighbors in an extended network. Above ∼2 GPa, the phase diagram contains just two, closely related, molecular phases: orientationally disordered ice VII and its ordered low-temperature analog ice VIII (1). Both phases have body-centered, close-packed oxygen sublattices with cubic and tetragonal symmetry, respectively. Infrared spectroscopy has provided evidence for bond symmetrization in ice VII-meaning covalent and H-bonds become geometrically equivalent, and ice becomes a simple oxide-starting around 60 GPa (2-4). Meanwhile, X-ray diffraction indicates the persistence of a closely body-centered cubic (bcc) oxygen sublattice up to at least 210 GPa (5-9). At the highest pressures, this system has been studied extensively by numerous experimental techniques [including infrared (3-4, 10) and Raman spectroscopy (2, 11), Brillouin scattering (12), and other optical techniques (13) as well as computational theory (e.g., refs. 14-18 and references therein)]. These efforts, spanning almost 50 years, have led to a consensus view that ice VII moves gradually toward a symmetric H-bonded phase (ice X) across a broad pressure range with protons essentially localized between neighboring O-atoms on network sites. However, the positions of the hydrogen nuclei have not been determined directly at pressures sufficient to significantly change the molecular geometry from that found in common ice Ih (19). In addition, the nature of the proposed intermediate states between ices VII and X remains uncertain (11,20), and changes in ices VII and VIII themselves have been suggested by anomalies in X-ray (5,7,8,21,22) and spectroscopic (12,22,23) data beginning as low as 13-14 GPa.In contrast to other techniques, neutron diffraction can resolve the location of deuterons (D) directly within the l...

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“…A possible transition near 2-3 GPa in ice VIII ͑referred to as ice VIIIЈ͒ has been reported on the basis of neutron diffraction, 7 Raman, 8 and far-infrared ͑FIR͒ measurements. 9 Theoretical calculations suggest that the ice VIII transition could arise from differences in the way that the hydrogenbonded network relaxes relative to the non-hydrogen-bonded structure.…”

Section: Introductionmentioning

confidence: 99%

High-pressure x-ray diffraction and Raman spectroscopy of ice VIII

Yoshimura

Stewart

Somayazulu

et al. 2006

The Journal of Chemical Physics

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In situ high-pressure/low-temperature synchrotron x-ray diffraction and optical Raman spectroscopy were used to examine the structural properties, equation of state, and vibrational dynamics of ice VIII. The x-ray measurements show that the pressure-volume relations remain smooth up to 23 GPa at 80 K. Although there is no evidence for structural changes to at least 14 GPa, the unit-cell axial ratio c∕a undergoes changes at 10–14 GPa. Raman measurements carried out at 80 K show that the νTzA1g+νTx,yEg lattice modes for the Raman spectra of ice VIII in the lower-frequency regions (50–800cm−1) disappear at around 10 GPa, and then a new peak of ∼150cm−1 appears at 14 GPa. The combined data provide evidence for a transition beginning near 10 GPa. The results are consistent with recent synchrotron far-IR measurements and theoretical calculations. The decompressed phase recovered at ambient pressure transforms to low-density amorphous ice when heated to ∼125K.

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Pressure dependence of Raman linewidths in ices VII and VIII

Cited by 23 publications

References 37 publications

Atomic Structure and Vibrational Properties of IcosahedralB4CBoron Carbide

Atomic Structure and Vibrational Properties of IcosahedralB4CBoron Carbide

Neutron diffraction observations of interstitial protons in dense ice

High-pressure x-ray diffraction and Raman spectroscopy of ice VIII

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