Refinement of the crystal structure of the high-temperature phase G 0 in (NH4)2WO2F4 (powder, X-ray, and neutron scattering)

D. M. Novak; L. S. Smirnov; A. I. Kolesnikov; V. I. Voronin; I. F. Berger; N. M. Laptash; A. D. Vasil'Ev; I. N. Flerov

doi:10.1134/S1063774513010240

Refinement of the crystal structure of the high-temperature phase G ₀ in (NH₄)₂WO₂F₄ (powder, X-ray, and neutron scattering)

D. M. Novak, L. S. Smirnov, A. I. Kolesnikov, V. I. Voronin, I. F. Berger, N. M. Laptash, A. D. Vasil'Ev, I. N. Flerov

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Abstract

The (NH₄)₂WO₂F₄ compound undergoes a series of phase transitions: G ₀ → 201, K → G ₁ → 160, and K → G ₂, with a significant change in entropy (ΔS ₁ ∼ Rln10 at the G ₀ → G ₁ transition), which indicates significant orientational disordering in the G ₀ phase and the order-disorder type of the phase transition. X-ray diffraction is used to identify the crystal structure of the G ₀ phase as rhombohedral (sp. gr. Cmcm, Z = 4), determine the lattice parameters and the positions of all atoms (except hydrogen), and show that [WO₂F₄]^2- ions can form a superposition of dynamic and static orientational disorders in the anionic sublattice. A determination of the orientational position of [NH₄]⁺ ions calls for the combined method of elastic and inelastic neutron scattering. Inelastic neutron scattering is used to determine the state of hindered rotation for ammonium ions in the G ₀ phase. Powder neutron diffraction shows that the orientational disorder of NH₄ ions can adequately be described within the free-rotation approximation.

Original language	English
Pages (from-to)	129-134
Number of pages	6
Journal	Crystallography Reports
Volume	58
Issue number	1
DOIs	https://doi.org/10.1134/S1063774513010240
State	Published - Jan 2013

Funding

The work at ORNL was supported by the DOE BES and managed by UT Battelle, LLC, for DOE under Contract DE AC05 00OR22725. The measurements at ANL were supported by the Office of General Sci ences on Energy, Division of Materials Science of the U.S. DOE (contract DE AC02 06CH11357).

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title = "Refinement of the crystal structure of the high-temperature phase G 0 in (NH4)2WO2F4 (powder, X-ray, and neutron scattering)",

abstract = "The (NH4)2WO2F4 compound undergoes a series of phase transitions: G 0 → 201, K → G 1 → 160, and K → G 2, with a significant change in entropy (ΔS 1 ∼ Rln10 at the G 0 → G 1 transition), which indicates significant orientational disordering in the G 0 phase and the order-disorder type of the phase transition. X-ray diffraction is used to identify the crystal structure of the G 0 phase as rhombohedral (sp. gr. Cmcm, Z = 4), determine the lattice parameters and the positions of all atoms (except hydrogen), and show that [WO2F4]2- ions can form a superposition of dynamic and static orientational disorders in the anionic sublattice. A determination of the orientational position of [NH4]+ ions calls for the combined method of elastic and inelastic neutron scattering. Inelastic neutron scattering is used to determine the state of hindered rotation for ammonium ions in the G 0 phase. Powder neutron diffraction shows that the orientational disorder of NH4 ions can adequately be described within the free-rotation approximation.",

author = "Novak, {D. M.} and Smirnov, {L. S.} and Kolesnikov, {A. I.} and Voronin, {V. I.} and Berger, {I. F.} and Laptash, {N. M.} and Vasil'Ev, {A. D.} and Flerov, {I. N.}",

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doi = "10.1134/S1063774513010240",

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AU - Novak, D. M.

AU - Smirnov, L. S.

AU - Kolesnikov, A. I.

AU - Voronin, V. I.

AU - Berger, I. F.

AU - Laptash, N. M.

AU - Vasil'Ev, A. D.

AU - Flerov, I. N.

PY - 2013/1

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N2 - The (NH4)2WO2F4 compound undergoes a series of phase transitions: G 0 → 201, K → G 1 → 160, and K → G 2, with a significant change in entropy (ΔS 1 ∼ Rln10 at the G 0 → G 1 transition), which indicates significant orientational disordering in the G 0 phase and the order-disorder type of the phase transition. X-ray diffraction is used to identify the crystal structure of the G 0 phase as rhombohedral (sp. gr. Cmcm, Z = 4), determine the lattice parameters and the positions of all atoms (except hydrogen), and show that [WO2F4]2- ions can form a superposition of dynamic and static orientational disorders in the anionic sublattice. A determination of the orientational position of [NH4]+ ions calls for the combined method of elastic and inelastic neutron scattering. Inelastic neutron scattering is used to determine the state of hindered rotation for ammonium ions in the G 0 phase. Powder neutron diffraction shows that the orientational disorder of NH4 ions can adequately be described within the free-rotation approximation.

AB - The (NH4)2WO2F4 compound undergoes a series of phase transitions: G 0 → 201, K → G 1 → 160, and K → G 2, with a significant change in entropy (ΔS 1 ∼ Rln10 at the G 0 → G 1 transition), which indicates significant orientational disordering in the G 0 phase and the order-disorder type of the phase transition. X-ray diffraction is used to identify the crystal structure of the G 0 phase as rhombohedral (sp. gr. Cmcm, Z = 4), determine the lattice parameters and the positions of all atoms (except hydrogen), and show that [WO2F4]2- ions can form a superposition of dynamic and static orientational disorders in the anionic sublattice. A determination of the orientational position of [NH4]+ ions calls for the combined method of elastic and inelastic neutron scattering. Inelastic neutron scattering is used to determine the state of hindered rotation for ammonium ions in the G 0 phase. Powder neutron diffraction shows that the orientational disorder of NH4 ions can adequately be described within the free-rotation approximation.

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Refinement of the crystal structure of the high-temperature phase G ₀ in (NH₄)₂WO₂F₄ (powder, X-ray, and neutron scattering)

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