This article is cited in 4 papers

Phase transitions

Processes of ordering of structural elements, critical and noncritical parameters of phase transitions in the (NH$_4$)$_3$WO$_3$F$_3$ crystal

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 structure of the low-temperature triclinic phase of the (NH$_4$)$_3$WO$_3$F$_3$ crystal has been determined and the structure of the cubic phase of this crystal has been refined from data of an X-ray diffraction experiment performed 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 obtained experimental data. It has been found that the symmetry transformation in the crystal can be schematically represented in the following form: $Fm\bar3m(Z=4)\to P\bar1(Z=1)\to P\bar1(Z=6)$. This transformation is accompanied by the complete ordering of WO$_3$F$_3$ polyhedra and the displacement of NH$_4$ ions.

Received: 05.05.2011
Accepted: 28.06.2011

 English version: Physics of the Solid State, 2012, 54:1, 155–165

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