ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The crystal structure of RbH3(SeO3)2 has been determined in the low-temperature phase (space group P21) with neutron diffraction. The crystal undergoes an improper ferroelectric phase transition at 158 K and the unit cell is doubled below the transition temperature. This transition is induced by the condensation of a soft mode at the Brillouin zone boundary. Imposing the symmetry of the soft-mode eigenvector on the static displacements from the high-temperature positions (space group P212121) results in a reduction, by a factor of four, of the number of positional parameters required to describe the low-temperature structure. The crystal is constructed of two types of chains consisting of SeO3 groups connected by hydrogen bonds, and the order parameter for the transition is shown to be the rigid rotations of the SeO3 tetrahedra belonging to one type of chain. The atomic displacements necessary to produce the observed spontaneous polarization are shown to be too small to be observed in the present experiment, and the precise mechanism responsible for the spontaneous polarization remains unknown.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739478000509
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