Doping-induced disappearance of ice II from water’s phase diagram

Shephard, Jacob J.; Slater, Ben; Hart, M. J.; Bull, Craig L.; Bramwell, S. T.; Salzmann, Christoph G.

doi:10.1038/s41567-018-0094-z

Cited by 30 publications

(53 citation statements)

References 30 publications

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“…The neutron diffraction patterns collected during the compression are shown in Figure 2(b) anddisplayed a cascade of phase transitions from ice Ih → ice III → ice V → ice XII → ice VI → ice VIII / VII. Remarkably, and in line with our previous study,17 the formation of ice II was fully suppressed due to the presence of the ND4F.…”

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confidence: 93%

“…[7][8]24 To complement these efforts, we have recently begun to investigate the effect of ammonium fluoride (NH4F) doping with respect to inducing hydrogen disorder in hydrogen-ordered phases of ice. 17 The expected hydrogen disordering effect of NH4F doping is shown schematically in Figure 1(c) for the case of the hydrogen-ordered planar square ice. In ref.…”

mentioning

confidence: 94%

“…15 (c) Schematic illustration of the hydrogen disordering effect of NH4F doping on the hydrogen-ordered square ice. 8,17 Due to the constraints of the ice rules, the molecular reorientation of water molecules in ice is a difficult process and only possible in the presence of mobile point defects that locally break the ice rules. In the case of ices III and VII, the concentration of intrinsic point defects is sufficient so that the hydrogen-ordering phase transitions to ices IX and VIII can be observed upon cooling.…”

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Ammonium Fluoride as a Hydrogen-Disordering Agent for Ice

et al. 2019

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The removal of residual hydrogen disorder from various phases of ice with acid or base dopants at low temperatures has been a focus of intense research for many decades. As an antipode to these efforts, we now show using neutron diffraction that ammonium fluoride (NH4F) is a hydrogendisordering agent for the hydrogen-ordered ice VIII. Cooling its hydrogen-disordered counterpart ice VII doped with 2.5 mol% ND4F under pressure leads to a hydrogen-disordered ice VIII with ~31% residual hydrogen disorder illustrating the long-range hydrogen-disordering effect of ND4F.The doped ice VII could be supercooled by ~20 K with respect to the hydrogen-ordering temperature of pure ice VII after which the hydrogen-ordering took place slowly over a ~60 K temperature window. These findings demonstrate that ND4F-doping slows down the hydrogenordering kinetics quite substantially. The partial hydrogen order of the doped sample is consistent with the antiferroelectric ordering of pure ice VIII. Yet, we argue that local ferroelectric domains must exist between ionic point defects of opposite charge. In addition to the long-range effect of NH4F-doping on hydrogen-ordered water structures, the design principle of using topological charges should be applicable to a wide range of other 'ice-rule' systems including spin ices and related polar materials. IntroductionWater's phase diagram has been explored for more than a century leading to the discovery of 17 crystallographically distinct phases of ice so far. [1][2][3][4][5] The water molecules in the various phases of ice are fully hydrogen-bonded which gives rise to 4-fold connected networks following the 'twoin-two-out' ice rules with respect to the donation and acceptance of hydrogen bonds. 6-8 Based on this building principle, a wide range of network topologies can be observed ranging from the high-symmetry ice Ih network with only six-membered rings and the highly complex ice V/XIII network to the two interpenetrating individual networks of ice VII/VIII. [6][7][8] Within the constraints of the ice rules, 9 the water molecules can display orientational disorder and such phases are categorized as hydrogen-disordered. In fact, all phases of ice that can be crystallized from liquid water display hydrogen disorder as can be seen in Figure 1(a). In the case of ices Ih, Isd, IV, VI, VII and XII, full hydrogen disorder is observed in neutron diffraction in the form of half-occupied deuterium sites. [10][11][12][13] Ices III and V on the other hand display partial hydrogen order and some of the fractional occupancies deviate significantly from ½. 13 As required by the third law of thermodynamics, the various hydrogen-disordered phases are expected to transform to their corresponding hydrogen-ordered counterparts upon cooling as long-range orientational order of the water molecules is established. Figure 1(b) shows the crystal structures of the hydrogen-disordered ice VII and its hydrogen-ordered counterpart ice VIII.

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confidence: 93%

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confidence: 94%

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confidence: 99%

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Ammonium Fluoride as a Hydrogen-Disordering Agent for Ice

et al. 2019

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“…Here, the arrows on the Ti ions forming the dimer are directed inwards in the Ti tetrahedron. As shown by the blue arrows in Fig.8(d It is known that the phase transition occurs by the impurity in ice [29]. By introducing a tiny amount of NH + 4 and Cl − ions, the ice II phase changes into the ice III phase having a large entropy owing to many kinds of the H 2 O configuration.…”

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confidence: 96%

Nanoscale ice-type structural fluctuation in spinel titanates

et al. 2018

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In the spinel titanate MgTi 2 O 4 , the tetragonal phase collapses upon substitution of a tiny amount of Mg ions at the Ti site, and the cubic phase with the geometrical frustration is resurrected. The atomic pair distribution function (PDF) and the extended x-ray absorption fine structure (EXAFS) reveal the nanoscale structural fluctuation, in which the Ti atomic displacement has the two-in two-out configuration in the cubic phase. We argue that the geometrical frustration plays an essential role in the collapse of the tetragonal phase and the resultant nanoscale ice-type structural fluctuation.

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“…In ref. 92 it was found that this ice phase completely disappeared, and instead was replaced by the hydrogen disordered phases III and V, if a small amount of ammonium fluoride was added to the ice. The very special properties of ice II were even suggested to be the reason for the anomalies of the phase diagram of water.…”

Section: Possible Implications For Bulk Watermentioning

confidence: 99%