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

Gerasimova Y.V.; Oreshonkov A.S.; Laptash N.M.; Vtyurin A.N.; Krylov A.S.; Shestakov N.P.; Ershov A.A.; Kocharova A.G.

doi:10.1016/j.saa.2017.01.004

Инд. авторы:	Gerasimova Y.V., Oreshonkov A.S., Laptash N.M., Vtyurin A.N., Krylov A.S., Shestakov N.P., Ershov A.A., Kocharova A.G.
Заглавие:	Nature of phase transitions in ammonium oxofluorovanadates, a vibrational spectroscopy study of (NH4)(3)VO2F4 and (NH4)(3)VoF(5)
Библ. ссылка:	Gerasimova Y.V., Oreshonkov A.S., Laptash N.M., Vtyurin A.N., Krylov A.S., Shestakov N.P., Ershov A.A., Kocharova A.G. Nature of phase transitions in ammonium oxofluorovanadates, a vibrational spectroscopy study of (NH4)(3)VO2F4 and (NH4)(3)VoF(5) // SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY. - 2017. - Vol.176. - P.106-113. - ISSN 1386-1425.
Внешние системы:	DOI: 10.1016/j.saa.2017.01.004; PubMed: 28088082; WoS: 000394074700014;
Реферат:	eng: 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 justified 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.
Ключевые слова:	AG4V2O6F2; OXYFLUORIDES; CATHODE MATERIAL; CRYSTAL-STRUCTURE; ORIENTATIONAL DISORDER; ROOM-TEMPERATURE; SILVER DENSITY PHASE; IMPLANTABLE CARDIOVERTER-DEFIBRILLATORS; (NH4)(2)MOO2F4; 7830.-j; PACS; Raman; Infrared; Phase transitions; Dynamics; Order-disorder; Ammonium oxofluorovanadates; 78.30.Ly; (NH4)(3)MOO3F3;
Издано:	2017
Физ. характеристика:	с.106-113