The Ferroelectric Phase Transition and Modulated Valence Electrons in the Incommensurate Phase of Ammonium Tetrafluoroberyllate

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Palatinus, Lukas ; van Smaalen, Sander:
The Ferroelectric Phase Transition and Modulated Valence Electrons in the Incommensurate Phase of Ammonium Tetrafluoroberyllate.
In: Ferroelectrics. Bd. 305 (2004) Heft 1 . - S. 49-52.
ISSN 1563-5112
DOI: https://doi.org/10.1080/00150190490462388

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Abstract

The incommensurate structure of (NH 4 ) 2 BeF 4 is determined from single-crystal x-ray diffraction at T = 175 K. Comparison of this structure with the low-temperature structure shows the ferroelectric phase transition to correspond to the simultaneous development of local and global polarisations. The modulations of the electrons in the chemical bonds are made visible by the Maximum Entropy Method with the modulated structure as superspace prior.