Local structural motifs and extended-range order in liquid and solid ammonia under pressure

Guthrie, Malcolm; Tulk, C. A.; Molaison, Jamie J.; Santos, A. M. dos

doi:10.1103/physrevb.85.184205

Cited by 12 publications

(16 citation statements)

References 39 publications

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“…**** The principal peak in the measured neutron diffraction pattern for liquid ammonia also sharpens with increasing density as packing constraints become more important. 192 The extended-range ordering for this system is described by using eqn (21).…”

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confidence: 99%

Identifying and characterising the different structural length scales in liquids and glasses: an experimental approach

Salmon

Zeidler

2013

Phys. Chem. Chem. Phys.

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The structure of several network-forming liquids and glasses is considered, where a focus is placed on the detailed information that is made available by using the method of neutron diffraction with isotope substitution (NDIS). In the case of binary network glass-forming materials with the MX 2 stoichiometry (e.g. GeO 2 , GeSe 2 , ZnCl 2 ), two different length scales at distances greater than the nearest-neighbour distance manifest themselves by peaks in the measured diffraction patterns. The network properties are influenced by a competition between the ordering on these ''intermediate'' and ''extended'' length scales, which can be manipulated by changing the chemical identity of the atomic constituents or by varying state parameters such as the temperature and pressure. The extended-range ordering, which describes the decay of the pair-correlation functions at large-r, can be represented by making a pole analysis of the Ornstein-Zernike equations, an approach that can also be used to describe the large-r behaviour of the pair-correlation functions for liquid and amorphous metals where packing constraints are important. The first applications are then described of the NDIS method to measure the detailed structure of aerodynamically-levitated laser-heated droplets of ''fragile'' glass-forming liquid oxides (CaAl 2 O 4 and CaSiO 3 ) at high-temperatures (B2000 K) and the structure of a ''strong'' network-forming glass (GeO 2 ) under pressures ranging from ambient to B8 GPa. The high-temperature experiments show structural changes on multiple length scales when the oxides are vitrified. The high-pressure experiment offers insight into the density-driven mechanisms of network collapse in GeO 2 glass, and parallels are drawn with the high-pressure behaviour of silica glass. Finally, the hydrogen-bonded network of water is considered, where the first application of the method of oxygen NDIS is used to measure the structures of light versus heavy water and a difference of C0.5% is found between the O-D and O-H intra-molecular bond lengths. The experimental data are best matched by using path integral molecular dynamics simulations with a flexible anharmonic water model, and the results support a competing quantum effects model for water in which its structural and dynamical properties are governed by an offset between intra-molecular and inter-molecular quantum contributions.

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confidence: 99%

Identifying and characterising the different structural length scales in liquids and glasses: an experimental approach

Salmon

Zeidler

2013

Phys. Chem. Chem. Phys.

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“…They showed that the density increase between ambient and 1 GPa has a large effect on the structure, disrupting the 3D network of H-bonds although preserving the tetrahedral H-bonding scheme around a given molecule. In ammonia, the comparison between the structure at ambient and 1 GPa did not show a strong difference in the short-range structure, however a substantial increase of the spatial correlations at large distance was found [12].…”

Section: Introductionmentioning

confidence: 78%

“…The situation is less clear-cut in the liquid phase. Evidence for hydrogen bonding have been obtained from neutron diffraction [9][10][11][12], elastic [13,14] and inelastic x-ray scattering [15] experiments, as well as from theoretical simulations [16][17][18][19][20]. The N-N pair distribution function at 277 K obtained by the x-ray diffraction experiment of Ref.…”

Section: Introductionmentioning

confidence: 99%

“…Again, this is in sharp contrast with the case of liquid water where the solvation structure of a molecule is determined primarily by hydrogen bonding interactions. Except for the recent work of Guthrie et al [12], all previous experimental studies of the structure of liquid ammonia have been carried out at or near ambient pressure. For water, several neutron [21,22] and x-ray diffraction experiments [23,24] have been reported to pressures of several GPa.…”

Section: Introductionmentioning

confidence: 99%

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Structure of liquid ammonia at high pressures and temperatures

et al. 2019

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The structure of liquid ammonia (NH3) is investigated from 1 to 6.3 GPa and up to 800 K by means of synchrotron x-ray diffraction (XRD) and ab initio molecular dynamics (AIMD) simulations. The XRD data are used to extract the molecular structure factor S mol (Q), pair distribution function (PDF) g mol (r), and the density of NH3. There is an excellent agreement between present S mol (Q) and g mol (r) at our lowest density and those reported in reference neutron experiments. Our densities agree better with the equation of state of Tillner-Roth et al. [1] than with more recent equation of state (EoS) models. The experimental structure factor and PDF are well reproduced by AIMD simulations using either the BLYP or the PBE exchange-correlation functional. The shapes of S mol (Q) and g mol (r) vary little over the investigated pressure range and suggest a compact liquid with weak orientational correlations between molecules, which is corroborated by the coordination number varying from 12.7 to ∼14. The simulations are used to study the evolution of the site-site pair distribution functions, which reveals that the number of H-bonds per molecule (between 1.5 and 2) do not evolve with density, and that the distribution of H atoms around N atoms becomes more and more anisotropic with pressure.

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“…In a large portion of polar molecules also non-bonding valence electron pairs of the central atom may complicate the situation. The structure of solid NH 3 (there are several temperature and pressure depended phases of the compound) is presented (Guthrie et al 2012) in Fig. 6.…”

Section: Effect Of Attractive Intermolecular Interactionsmentioning

confidence: 99%

Structure-related melting and boiling points of inorganic compounds

Šíma

2015

Found Chem

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The paper is aimed at rationalizing relationships between the structure of inorganic compounds in condensed phases and their melting and boiling points. It is documented that the main factor governing both points is their molecular or polymeric nature. In case of polymeric ionic compounds, the higher actual charge bearing by the ions involved, the higher their melting/boiling points. In case of covalent polymers, the value of both points increases with polymer dimensionality (1D ? 2D ? 3D polymers) and with the number and energy of the respective covalent bonds. In case of molecular compounds, both points depend on the weight and shape of molecules, the presence of hydrogen bonds, and electric quadrupole moment.

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Local structural motifs and extended-range order in liquid and solid ammonia under pressure

Cited by 12 publications

References 39 publications

Identifying and characterising the different structural length scales in liquids and glasses: an experimental approach

Identifying and characterising the different structural length scales in liquids and glasses: an experimental approach

Structure of liquid ammonia at high pressures and temperatures

Structure-related melting and boiling points of inorganic compounds

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