Metastable ice VII at low temperature and ambient pressure

Klotz, Stefan; Besson, Jean; Hamel, G.; Nelmes, R. J.; Loveday, J. S.; Marshall, William G.

doi:10.1038/19480

Cited by 89 publications

(74 citation statements)

References 15 publications

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“…Insulating oP8 Na may be achieved experimentally if the oP8 phase can be compressed metastably. The technique of trapping phases outside of their stability fields by choosing an appropriate pressure-temperature path and compression rate is becoming increasingly common (22,23). The reflectivity in the visible energy range drops still further at the transition to the tI19 phase.…”

Section: Resultsmentioning

confidence: 99%

Anomalous optical and electronic properties of dense sodium

Lazicki

Goncharov

Struzhkin

et al. 2009

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

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Synchrotron infrared spectroscopy on sodium shows a transition from a high reflectivity, nearly free-electron metal to a lowreflectivity, poor metal in an orthorhombic phase at 118 GPa. Optical spectra calculated within density functional theory (DFT) agree with the experimental measurements and predict a gap opening in the orthorhombic phase at compression beyond its stability field, a state that would be experimentally attainable by appropriate choice of pressure-temperature path. We show that a transition to an incommensurate phase at 125 GPa results in a partial recovery of good metallic character up to 180 GPa, demonstrating the strong relationship between structure and electronic properties in sodium.high pressure ͉ infrared reflectivity ͉ metal-insulator transition T he alkali metals are often presented as textbook examples of simple metals. At low pressures they all take on very simple bcc and fcc crystal structures and display the free-electronlike metallic character predictable for monovalent compounds (1). However, recent work has shown that the application of pressure results in an unexpected variety of complex phenomena. These include the existence of low-symmetry and even incommensurate phases (2-10) and significant electronic changes leading to effects such as unusual melting behavior (10), Fermi-surface nesting (11), phonon instabilities (12), electron-phonon coupling and superconductivity (13,14), and transformations to poor metals or even insulators (9,(15)(16)(17)(18). Sodium is unique among the alkali metals because of its occupied electronic states; it differs from lithium by the presence of p states, and from the heavier alkalis by the absence of d states under compression. Its Fermi surface remains spherical up to 120 GPa, whereas in all other alkali metals the Fermi surface is significantly deformed by 7 GPa (12). It is the only alkali metal not predicted to date to become a superconductor under pressure (14). It exhibits the largest pressure-induced drop in melting temperature ever reported, dropping from Ϸ1,000 K to nearly room temperature at 120 GPa (10), and possessing crystal structures in the vicinity of the melting minimum with hundreds of atoms per unit cell (8). It has been suggested that an observed darkening of the metal (18) at a transition to an incommensurate phase at 125 GPa may signify the onset of semiconducting or insulating behavior suggested in theoretical studies for sodium (15,16). To address this, we have conducted synchrotron and conventional reflectivity measurements on sodium metal in the low-symmetry phases up to Ϸ180 GPa and performed first-principles calculations on the reported crystal structures. We demonstrate that a transition to an orthorhombic phase is accompanied by nearinsulating behavior and find that further (metastable) compression of this phase would result in a metal-insulator transition. Enhanced metallic behavior is partially recovered, however, in the incommensurate phase, in which valence charge density accumulates into quasi 1-dimensional cha...

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Section: Resultsmentioning

confidence: 99%

Anomalous optical and electronic properties of dense sodium

Lazicki

Goncharov

Struzhkin

et al. 2009

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

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“…Apart from ice VIII, our studied ices are proton disordered while ice VII has an additional oxygen disorder which distinguishes it from otherwise identical ice VIII [6]. This site disorder…”

Section: Introductionmentioning

confidence: 97%

“…[6]. Ice VIII was produced by cooling H 2 O at 3 GPa to 77 K and decompressing the sample to ambient pressure.…”

Section: Experimental Procedures and Calculationsmentioning

confidence: 99%

Oxygen disorder in ice probed by x-ray Compton scattering

et al. 2011

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Abstract.We use electron momentum density in ice as a tool to quantify order-disorder transitions by comparing Compton profiles differences of ice VI, VII, VIII and XII with respect to ice Ih. Quantitative agreement is found between theory and experiment for ice VIII, which is the most ordered phase. Robust signatures of the oxygen disorder are identified in the momentum density for the VIII-VII ice phase transition. The unique aspect of this work is the determination of the fraction n e of electron directly involved in phase transitions as well as the use of position space signatures for quantifying oxygen site disorder.

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“…Hemley et al 5 indicated that at 4 GPa and 80 K, HDA crystallizes into ice VII with further disorder, which they called ice VIIЈ. Later, Klotz et al 6 reported that a phase closely related to ice VI and possibly ice VIIЈ can be recovered to 0.1 MPa at temperatures below 95 K.…”

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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Metastable ice VII at low temperature and ambient pressure

Cited by 89 publications

References 15 publications

Anomalous optical and electronic properties of dense sodium

Anomalous optical and electronic properties of dense sodium

Oxygen disorder in ice probed by x-ray Compton scattering

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

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