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Polar and non‐polar structures of NH 4 TiOF 3
Author(s) -
Boytsova O.,
Dovgaliuk I.,
Chernyshov D.,
Eliseev A.,
O'Brien P.,
Sutherland A. J.,
Bosak A.
Publication year - 2019
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576718016606
Subject(s) - anatase , crystallography , polar , thermal decomposition , phase (matter) , crystal structure , decomposition , chemistry , crystal (programming language) , diffraction , materials science , powder diffraction , transformation (genetics) , stereochemistry , physics , optics , organic chemistry , catalysis , photocatalysis , astronomy , computer science , programming language , gene , biochemistry
Ammonium oxofluorotitanate, NH 4 TiOF 3 , is probably the best known precursor for the synthesis of anatase mesocrystals. Transformation of NH 4 TiOF 3 into TiO 2 through thermal decomposition, accompanied by hydrolysis, preserves some structural features of the precursor. Currently, any discussion of the mechanism of this transformation is difficult, as the exact crystal structure of the starting compound is not available and no intermediate structures are known. This article describes the outcome of single‐crystal and powder X‐ray diffraction studies, revealing the existence of two polymorphs of the parent NH 4 TiOF 3 at different temperatures. A second‐order phase transition from the polar Pca 2 1 α phase (1), stable at room temperature, to the Pma 2 β phase (2) above ∼433 K has been demonstrated. The direction of the pseudo‐fourfold axis in NH 4 TiOF 3 coincides with the orientation of the fourfold axis of anatase mesocrystals, consistent with a topotactical transformation.