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Updated: Mar 8, 2026
08:12
Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films
Published on: September 8, 2017
10.2K
Sequence of phase transitions in (NH4)3SiF7
S V Mel'nikova1, M S Molokeev2, N M Laptash3
1Laboratory of Crystal Physics, Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, 660036, Russia. msmolokeev@mail.ru.
Dalton Transactions (Cambridge, England : 2003)
|February 4, 2017
Summary
Researchers studied ammonium hexafluorosilicate fluoride crystals, revealing multiple phase transitions driven by hydrogen bonds. These structural changes were analyzed using advanced crystallographic and calorimetric techniques.
Area of Science:
- Solid State Chemistry
- Crystallography
- Materials Science
Background:
- Ammonium hexafluorosilicate fluoride ((NH4)3SiF7) is a complex salt exhibiting interesting structural properties.
- Understanding its phase transitions is crucial for potential applications in materials science.
Purpose of the Study:
- To investigate the structural phase transitions of single crystals of (NH4)3SiF7.
- To determine the sequence of symmetry transformations and crystal structures at different temperatures.
- To elucidate the driving forces behind these phase transitions.
Main Methods:
- Single crystal growth.
- Polarization optics.
- X-ray diffraction.
- Calorimetry.
- Group-theoretical analysis of order parameters.
Main Results:
- A sequence of five distinct crystallographic phases and their symmetry transformations (P4/mbm ↔ Pbam ↔ P21/c ↔ P1̄ ↔ P21/c) were identified with temperature changes.
- Crystal structures for the different phases were determined.
- Experimental data were interpreted using group-theoretical analysis, considering atomic displacements.
Conclusions:
- The observed phase transitions in (NH4)3SiF7 are driven by the strengthening of N-HF hydrogen bonds.
- The study provides a comprehensive understanding of the complex structural behavior of this silicon double salt.
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