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Raman scattering and phase transitions in (NH 4 ) 3 TiF 7
Author(s) -
Gerasimova Y.V.,
Oreshonkov A.S.,
Laptash N.M.,
Krylov A.S.,
Aliev A.R.,
Roginskii E.M.
Publication year - 2018
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.5374
Subject(s) - raman spectroscopy , octahedron , tetrahedral symmetry , phase transition , raman scattering , chemistry , crystallography , lattice (music) , spectral line , hydrogen bond , tetrahedron , octahedral symmetry , analytical chemistry (journal) , crystal structure , ion , physics , condensed matter physics , molecule , optics , acoustics , chromatography , organic chemistry , astronomy , mechanics , rotational symmetry
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.