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Reconstructive phase transition in (NH 4 ) 3 TiF 7 accompanied by the ordering of TiF 6 octahedra
Author(s) -
Molokeev Maxim,
Misjul S. V.,
Flerov I. N.,
Laptash N. M.
Publication year - 2014
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520614021192
Subject(s) - octahedron , tetragonal crystal system , bar (unit) , phase transition , crystallography , phase (matter) , chemistry , crystal structure , condensed matter physics , materials science , physics , organic chemistry , meteorology
An unusual phase transition P 4/ mnc → has been detected after cooling the (NH 4 ) 3 TiF 7 compound. Some TiF 6 octahedra, which are disordered in the room‐temperature tetragonal structure, become ordered in the low‐temperature cubic phase due to the disappearance of the fourfold axis. Other TiF 6 octahedra undergo large rotations resulting in huge displacements of the F atoms by 1.5–1.8 Å that implies a reconstructive phase transition. It was supposed that phases P 4/ mbm and could be a high‐temperature phase and a parent phase, respectively, in (NH 4 ) 3 TiF 7 . Therefore, the sequence of phase transitions can be written as → P 4/ mbm → P 4/ mnc →. The interrelation between (NH 4 ) 3 TiF 7 , (NH 4 ) 3 GeF 7 and (NH 4 ) 3 PbF 7 is found, which allows us to suppose phase transitions in relative compounds.