Issue 8, 2017

Sequence of phase transitions in (NH4)3SiF7


Single crystals of silicon double salt (NH4)3SiF7 = (NH4)2SiF6·NH4F = (NH4)3[SiF6]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) (G1) ↔ Pbam (Z = 4) (G2) ↔ P21/c (Z = 4) (G3) ↔ P[1 with combining macron] (Z = 4) (G4) ↔ P21/c (Z = 8) (G5). 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–H⋯F hydrogen bonds can be a driving force of the observed phase transitions.

Graphical abstract: Sequence of phase transitions in (NH4)3SiF7

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Article information

Article type
26 Dec 2016
18 Jan 2017
First published
18 Jan 2017
This article is Open Access
Creative Commons BY license

Dalton Trans., 2017,46, 2609-2617

Sequence of phase transitions in (NH4)3SiF7

S. V. Mel'nikova, M. S. Molokeev, N. M. Laptash, E. I. Pogoreltsev, S. V. Misyul and I. N. Flerov, Dalton Trans., 2017, 46, 2609 DOI: 10.1039/C6DT04874A

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