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Вид документа : Статья из журнала Шифр издания :
Автор(ы) : Molokeev M. S., Misjul S. V., Flerov I. N., Laptash N. M.
Заглавие : Reconstructive phase transition in (NH4)3TiF7 accompanied by the ordering of TiF6 octahedra
Место публикации : Acta Crystallogr. B: Wiley-Blackwell, 2014. - Vol. 70. - P.924-931. - ISSN 0108-7681, DOI 10.1107/S2052520614021192. - ISSN 1600-5740 Примечания : This study was supported by Russian Fund of Basic Research, project No. 12-02-00056 a
Предметные рубрики: CRYSTAL-STRUCTURE NEUTRON-DIFFRACTION POWDER DIFFRACTION FLUORIDES DISORDER MECHANISM PATHWAYS COMPLEX LI3THF7 ALPHA Ключевые слова (''Своб.индексиров.''): reconstructive phase transition--ammonium heptafluorotitanate--order-disorder transition Аннотация: An unusual phase transition P4/mnc →Pa3 has been detected after cooling the (NH4)3TiF7 compound. Some TiF6 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 TiF6 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 P4/mbm and Pm3m could be a high-temperature phase and a parent phase, respectively, in (NH4)3TiF7. Therefore, the sequence of phase transitions can be written as Pm3m → P4/bm → P4/mnc → Pa3. The interrelation between (NH4)3TiF7, (NH4)3GeF7 and (NH4)3PbF7 is found, which allows us to suppose phase transitions in relative compounds.
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