Nature of phase transitions in ammonium oxofluorovanadates, a vibrational spectroscopy study of (NH4)(3)VO2F4 and (NH4)(3)VoF(5)

Описание

Тип публикации: статья из журнала

Год издания: 2017

Идентификатор DOI: 10.1016/j.saa.2017.01.004

Ключевые слова: Ammonium oxofluorovanadates, Order-disorder, Dynamics, Phase transitions, Infrared, Raman, PACS, 7830.-j, 78.30.Ly

Аннотация: Two ammonium oxofluorovanadates, (NH4)(3)VO2F4 and (NH4)(3)VOF5, have been investigated by temperature-dependent infrared and Raman spectroscopy methods to determine the nature of phase transitions (PT) in these compounds. Dynamics of quasioctahedral groups was simulated within the framework of semi-empirical approach, which justifПоказать полностьюied the cis-conformation of VO2F43- (C-2v) and the C-4v geometry of VOF53-. The observed infrared and Raman spectra of both compounds at room temperature (RT) revealed the presence at least of two crystallographically independent octahedral groups. The first order PT at elevated temperatures is connected with a complete dynamic disordering of these groups with only single octahedral state. At lower temperatures, the octahedra are ordered and several octahedral states appear. This PT is the most pronounced in the case of (NH4)(3)VOF5, when at least seven independent VOF53- octahedra are present in the structure below 50 K, in accordance with the Raman spectra. Ammonium groups do not take part in PTs at higher and room temperatures but their reorientational motion freezes at lower temperatures. (C) 2017 Published by Elsevier B.V.

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Издание

Журнал: SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY

Выпуск журнала: Vol. 176

Номера страниц: 106-113

ISSN журнала: 13861425

Место издания: OXFORD

Издатель: PERGAMON-ELSEVIER SCIENCE LTD

Авторы

  • Gerasimova Yu. V. (Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Lab Mol Spect, Krasnoyarsk 660036, Russia; Siberian Fed Univ, Inst Engn Phys & Radio Elect, Krasnoyarsk 660079, Russia)
  • Oreshonkov A.S. (Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Lab Mol Spect, Krasnoyarsk 660036, Russia; Siberian Fed Univ, Inst Engn Phys & Radio Elect, Krasnoyarsk 660079, Russia)
  • Laptash N.M. (FEB RAS, Inst Chem, Lab Opt Mat, Vladivostok 690022, Russia)
  • Vtyurin A.N. (Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Lab Mol Spect, Krasnoyarsk 660036, Russia; Siberian Fed Univ, Inst Engn Phys & Radio Elect, Krasnoyarsk 660079, Russia)
  • Krylov A.S. (Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Lab Mol Spect, Krasnoyarsk 660036, Russia)
  • Shestakov N.P. (Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Lab Mol Spect, Krasnoyarsk 660036, Russia)
  • Ershov A.A. (Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Lab Mol Spect, Krasnoyarsk 660036, Russia; Siberian Fed Univ, Inst Engn Phys & Radio Elect, Krasnoyarsk 660079, Russia)
  • Kocharova A.G. (Fed Res Ctr KSC SB RAS, Kirensky Inst Phys, Lab Mol Spect, Krasnoyarsk 660036, Russia)

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