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Neutron structures of ammonium tetrafluoroberyllate
Srivastava1, Klooster, Koetzle
1Department of Physics, Indian Institute of Technology, Kanpur 208016, India.
Acta Crystallographica. Section B, Structural Science
|August 6, 2000
Summary
Hydrogen bonding drives ferroelectricity in ammonium tetrafluoroberyllate. Neutron diffraction reveals ion rotations and shifts, creating a superlattice and strengthening hydrogen bonds in the ferroelectric phase.
Area of Science:
- Crystallography
- Solid-state chemistry
- Materials science
Background:
- Ferroelectricity in ammonium tetrafluoroberyllate ((NH(4))(2)BeF(4)) is attributed to hydrogen bonding.
- Previous X-ray studies lacked precision for determining hydrogen atom positions.
Purpose of the Study:
- To accurately determine hydrogen atom positions in ammonium tetrafluoroberyllate.
- To elucidate the structural changes associated with the transition from paraelectric to ferroelectric phases.
Main Methods:
- Neutron diffraction was employed to determine the crystal structures.
- Structures were analyzed for both the paraelectric and ferroelectric phases.
Main Results:
- Both tetrafluoroberyllate (BeF(4)(2-)) and ammonium (NH(4)(+)) ions rotate and shift from mirror planes during the phase transition.
- This movement breaks mirror-plane symmetry, forming a superlattice with a doubled a axis.
- Intra-chain and inter-chain molecular movements occur along the polar c axis, enhancing hydrogen bonding.
Conclusions:
- Neutron diffraction provides precise structural data for understanding ferroelectricity in (NH(4))(2)BeF(4).
- The observed ion dynamics and structural rearrangements directly correlate with the onset of ferroelectricity and stronger hydrogen bonding.