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Sequence of phase transitions in (NH 4 ) 3 SiF 7 .
- Source :
-
Dalton transactions (Cambridge, England : 2003) [Dalton Trans] 2017 Feb 21; Vol. 46 (8), pp. 2609-2617. - Publication Year :
- 2017
-
Abstract
- Single crystals of silicon double salt (NH <subscript>4</subscript> ) <subscript>3</subscript> SiF <subscript>7</subscript> = (NH <subscript>4</subscript> ) <subscript>2</subscript> SiF <subscript>6</subscript> ·NH <subscript>4</subscript> F = (NH <subscript>4</subscript> ) <subscript>3</subscript> [SiF <subscript>6</subscript> ]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 <subscript>1</subscript> ) ↔ Pbam (Z = 4) (G <subscript>2</subscript> ) ↔ P2 <subscript>1</subscript> /c (Z = 4) (G <subscript>3</subscript> ) ↔ P1[combining macron] (Z = 4) (G <subscript>4</subscript> ) ↔ P2 <subscript>1</subscript> /c (Z = 8) (G <subscript>5</subscript> ). 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.
Details
- Language :
- English
- ISSN :
- 1477-9234
- Volume :
- 46
- Issue :
- 8
- Database :
- MEDLINE
- Journal :
- Dalton transactions (Cambridge, England : 2003)
- Publication Type :
- Academic Journal
- Accession number :
- 28157243
- Full Text :
- https://doi.org/10.1039/c6dt04874a