The structure of deuterium in vycor

Wang, Y.; Snow, W. M.; Sokol, P. E.

doi:10.1007/bf00754516

Cited by 27 publications

(15 citation statements)

References 29 publications

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“…The ͑102͒ reflection is missing: the ͑103͒ reflection is extremely broadened, but can be still identified. Analogous observations have been made in neutron diffraction studies on H 2 and D 2 in Vycor glass, 11,12 where in fact the similarity to a hcp pattern was even lesser. Recently, we have shown that the differences between the bulk hcp diffraction pattern and the diffraction pattern of the confined solid N 2 in 50 Å pores can be reasonably well explained by finite size and stacking faults.…”

Section: A Nitrogensupporting

confidence: 75%

SolidN2and CO in nanoporous glasses

1999

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N 2 and CO condensed into nanoporous glasses have been investigated by vapor pressure measurements and x-ray diffraction as a function of temperature and fractional filling. The pore material is stable with respect to bulk condensation for any fractional filling. The adsorbate on the pore walls has to be distinguished from the capillary condensate in the center of the pores. This distinction can be made not only in the liquid, but also in the solid state. The solid capillary condensate is quasi-hcp at higher temperatures. N 2 remains in this state down to the lowest temperatures, even in pores as large as 130 Å diameter, whereas CO transforms into the orientationally ordered Pa3 phase. On heating an orientationally disordered intermediate phase with a fcc center-of-mass lattice is observed. ͓S0163-1829͑99͒08941-9͔

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Section: A Nitrogensupporting

confidence: 75%

SolidN2and CO in nanoporous glasses

1999

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“…In some cases, such as Hg in Vycor [8], the structure of the confined solid is identical to that of the bulk while in other cases, such as H 2 O and D 2 in Vycor [9,10], confinement stabilizes new structures not present in the bulk. Confinement can also suppress crystalline order, such as O 2 in xerogel [11], resulting in a glassy solid phase.…”

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confidence: 89%

New Disorder Induced Phase Transitions of Classical Rare Gases in Porous Vycor Glass

1998

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We report the results of x-ray diffraction studies of Ar and Kr confined in Vycor glass. The freezing and melting temperatures of both Ar and Kr were suppressed well below their bulk freezing points. On solidification, both samples crystallized in a disordered hexagonal close packed structure similar to that observed in molecular dynamics simulations of confined solids. A new solid-solid phase transition is observed at a reduced temperature of T ͞T f ഠ 0.5 when confined to Vycor. Below this temperature the disordered hexagonal closed packed structure coexists with the fcc structure.[S0031-9007 (98)06675-7] PACS numbers: 61.43.Gt, 61.10.NzThe effects of finite size and confinement on gases, liquids, and solids adsorbed in mesoporous materials, such as porous glasses and zeolites, is a topic of current interest for classical and quantum systems. For example, in classical systems the liquid-gas transition is enhanced with respect to the bulk [1,2] while the liquid-solid transition is suppressed [2,3]. Hysteresis, which appears to be a stable thermodynamic behavior, is also introduced into these transitions. Quantum transitions show equally dramatic behavior. For example, the superfluid transition of 4 He in Vycor is substantially suppressed while the critical exponents remain unchanged. However, confinement in aerogel results in only a small suppression but substantially different critical exponents [4,5]. 3 He, on the other hand, has superfluid phases in high porosity aerogels [6,7], but not in lower porosity confining geometries.Microscopic structural studies of materials confined to mesoporous media have only recently been undertaken, and a variety of different behaviors have been reported. In some cases, such as Hg in Vycor [8], the structure of the confined solid is identical to that of the bulk while in other cases, such as H 2 O and D 2 in Vycor [9,10], confinement stabilizes new structures not present in the bulk. Confinement can also suppress crystalline order, such as O 2 in xerogel [11], resulting in a glassy solid phase. Confinement has not, however, been observed to introduce new phase transitions in any systems that have been studied to date.In this Letter, we report x-ray diffraction studies of Ar and Kr adsorbed in Vycor. As in many other systems, a suppression of the liquid-solid transition hysteresis between freezing and melting is observed. On freezing, both Ar and Kr are observed to form a disordered hexagonal close packed (dhcp) structure, characterized by random plane stacking, in contrast to the bulk fcc structure. A new phase transition, which is absent from the bulk phase diagram, occurs at roughly half of the freezing temperature below which both Kr and Ar exhibit coexistence of the dhcp and fcc phases. This solid-solid structural phase transition is repeatable on cycling and no appreciable hysteresis is observed. Thus, the coexistence phase appears to be a true disorder-induced thermodynamic phase, rather than a metastable phase.The confining media used in these studies was Vycor glass. Vy...

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“…Diffraction studies on simple molecules such as H 2 , 18 D 2 , 19 Kr, Xe, 20 O 2 , 21 and CO 2 ͑Ref. 22͒ in Vycor have revealed that the solidified capillary condensates are crystalline in the sense that some Bragg peaks, which are, of course, broadened due to finite-size effects, do exist in the diffraction patterns.…”

Section: Introductionmentioning

confidence: 99%

Adsorption-desorption isotherms and x-ray diffraction of Ar condensed into a porous glass matrix

1999

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Ar condensed into a porous glass matrix has been investigated by simultaneous measurements of adsorptiondesorption isotherms and x-ray diffraction patterns as function of the pore filling above and below the melting point. The chemical-potential-temperature phase diagram has been established. It is consistent with a firstorder phase transition between the adsorbate state and the capillary condensed state, above and below the melting temperature. The adsorbate and the capillary condensed state can also be distinguished in the diffraction patterns. A consistent picture of the structure and the thermodynamics is obtained.

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The structure of deuterium in vycor

Cited by 27 publications

References 29 publications

SolidN2and CO in nanoporous glasses

SolidN2and CO in nanoporous glasses

New Disorder Induced Phase Transitions of Classical Rare Gases in Porous Vycor Glass

Adsorption-desorption isotherms and x-ray diffraction of Ar condensed into a porous glass matrix

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