This article is cited in 4 papers

Phase transitions

Influence of the substitution of the central Me atom in ammonium oxyfluorides on phase transitions: IR spectroscopy study

A. N. Vtyurin, Yu. V. Gerasimova, N. P. Shestakov, A. A. Ivanenko

L. V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk

Abstract: Comparative investigations of infrared absorption spectra of ion-molecular crystals of the ammonium-containing oxyfluorides (NH$_4$)$_3$WO$_3$F$_3$ and (NH$_4$)$_3$MoO$_3$F$_3$ have been performed. It has been found that the parameters of the vibrational spectra exhibit anomalies in the ranges of internal vibrations of the MeO$_3$F$_3$ octahedral groups and ammonium ions near the phase transition temperatures. A comparative analysis of the IR spectra allows us to affirm that the studied phase transition in (NH$_4$)$_3$WO$_3$F$_3$ is primarily associated with the ordering of octahedral groups, whereas in (NH$_4$)$_3$MoO$_3$F$_3$, it is mainly due to the ordering of ammonium groups and the distortion of ammonium ions by the crystal environment.

Received: 30.08.2010

 English version: Physics of the Solid State, 2011, 53:4, 840–844

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