Sequence of phase transitions in (NH 4 ) 3 SiF 7

Single crystals of silicon double salt (NH ) SiF = (NH ) SiF ·NH F = (NH ) [SiF ]F were grown and studied by the methods of polarization optics, X-ray diffraction and calorimetry. A sequence of symmetry transformations with the temperature change was established: P4/mbm (Z = 2) (G ) ↔ Pbam (Z = 4) (...

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Published in:Dalton transactions : an international journal of inorganic chemistry 2017-02, Vol.46 (8), p.2609-2617
Main Authors: Mel'nikova, S V, Molokeev, M S, Laptash, N M, Pogoreltsev, E I, Misyul, S V, Flerov, I N
Format: Article
Language:English
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Summary:Single crystals of silicon double salt (NH ) SiF = (NH ) SiF ·NH F = (NH ) [SiF ]F were grown and studied by the methods of polarization optics, X-ray diffraction and calorimetry. A sequence of symmetry transformations with the temperature change was established: P4/mbm (Z = 2) (G ) ↔ Pbam (Z = 4) (G ) ↔ P2 /c (Z = 4) (G ) ↔ P1[combining macron] (Z = 4) (G ) ↔ P2 /c (Z = 8) (G ). Crystal structures of different phases were determined. The experimental data were also interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account critical and noncritical atomic displacements. Strengthening of the N-HF hydrogen bonds can be a driving force of the observed phase transitions.
ISSN:1477-9226
1477-9234
DOI:10.1039/C6DT04874A