This article is cited in 3 papers

Phase transitions

Structural transformations and the critical and noncritical parameters during the phase transition in the (NH$_4$)$_2$KWO$_3$F$_3$ oxyfluoride

M. S. Molokeev^a, S. V. Misjul<sup>b

a</sup> L. V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk
^b Siberian Federal University, Krasnoyarsk

Abstract: The structures of two phases of the (NH$_4$)$_2$KWO$_3$F$_3$ crystal have been determined from X-ray diffraction data obtained for a powder sample. The profile and structural parameters have been refined according to the procedure implemented in the DDM program. The results obtained have been discussed with invoking the group-theoretical analysis of the complete order parameter condensate, which takes into account the critical and noncritical atomic orderings and allows one to interpret the experimental data. It has been found that the symmetry transformation in the crystal can be schematically represented in the form
$$ Fm\bar{3}m \underset{(\eta,0,0,0,0,0)}{\overset{(10-10)(X_5^-)}{\longrightarrow}} Pmmn. $$
This transformation is accompanied by the ordering of WO$_3$F$_3$ polyhedra and the displacement of NH$_4$ and K ions.

Received: 13.01.2011

 English version: DOI: 10.1134/S1063783411080208

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