Raman scattering and phase transitions in (NH 4 ) 3 TiF 7

Raman spectra of (NH 4 ) 3 TiF 7 within spectral range 10–3,400 cm −1 at temperatures 8–370 K are recorded, which revealed 2 phase transitions at temperatures T 1  = 355 K and T 2  = 283 K. First principles calculations of lattice dynamics and assignment of the observed lines to specific vibrational...

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Bibliographic Details
Published in:Journal of Raman spectroscopy 2018-07, Vol.49 (7), p.1230-1235
Main Authors: Gerasimova, Y.V., Oreshonkov, A.S., Laptash, N.M., Krylov, A.S., Aliev, A.R., Roginskii, E.M.
Format: Article
Language:English
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Summary:Raman spectra of (NH 4 ) 3 TiF 7 within spectral range 10–3,400 cm −1 at temperatures 8–370 K are recorded, which revealed 2 phase transitions at temperatures T 1  = 355 K and T 2  = 283 K. First principles calculations of lattice dynamics and assignment of the observed lines to specific vibrational types are performed. The first phase transition is classified as an “order–disorder” one. Manifestation of 97 cm −1 vibration (mixed translational [NH 4  + F7]) evidences the creation of the hydrogen bond between ammonium group and free fluorine atom, indicating to reconstructive type of phase transition an T 2  = 283 K. The emergence of a large number of vibrational lines in Raman spectra at low temperatures proves symmetry lowering of NH 4 tetrahedra with the simultaneous ordering of TiF 6 octahedra.
ISSN:0377-0486
1097-4555
DOI:10.1002/jrs.5374