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Crystal structures of room- and low-temperature phases in oxyfluoride (NH4)2KWO3F3

Published online by Cambridge University Press:  01 March 2012

M. S. Molokeev ,
A. D. Vasiliev  and
A. G. Kocharova
M. S. Molokeev
Affiliation:
L. V. Kirensky Institute of Physics, SB RAS, Krasnoyarsk 660036, Russia
A. D. Vasiliev
Affiliation:
L. V. Kirensky Institute of Physics, SB RAS, Krasnoyarsk 660036, Russia
A. G. Kocharova
Affiliation:
L. V. Kirensky Institute of Physics, SB RAS, Krasnoyarsk 660036, Russia
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Abstract

Crystal structures of (NH4)2KWO3F3 at 298 K and 113 K were solved from X-ray powder diffraction data and refined by the Rietveld technique. The compound is isostructural with elpasolite K2NaAlF6 at room temperature with space group Fm-3m, a=8.95850(5) Å, V=718.961(7) Å3, Z=4, Dx=3.363 g/cm3, and MW=364.02. The structure was refined over 18 parameters to Rwp=12.6%, Rp=10.9%, Rexp=5.03%, and RB=3.27% from 40 independent reflections. (NH4)2KWO3F3 was transformed upon cooling to a ferroelastic monoclinic phase with space group P21/n, a′=6.3072(3) Å, b′=6.3028(3) Å, c′=8.9882(3) Å, β′=90.242(2)°, V=357.30(3) Å3, Z=2, and Dx=3.383 g/cm3. The low-temperature structure at 113 K was refined over 28 parameters to Rwp=20.9%, Rp=21.3%, Rexp=12.5%, and RB=6.93% from 453 independent reflections.

Keywords

structure determinationRietveld analysispowder diffractionphase transitionoxyfluoride
Type
Technical Articles
Information
Powder Diffraction , Volume 22 , Issue 3 , September 2007 , pp. 227 - 230
Copyright
Copyright © Cambridge University Press 2007

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