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Title:
The crystal structure of synthetic simmonsite, Na2LiAlF6
Authors:
Ross, Kirk C.; Mitchell, Roger H.; Chakhmouradian, Anton R.
Affiliation:
AA(Department of Geology, Lakehead University, 955 Oliver Road, , Ont., P7B 5E1, Thunder Bay, Canada), AB(Department of Geology, Lakehead University, 955 Oliver Road, , Ont., P7B 5E1, Thunder Bay, Canada), AC(Department of Geological Sciences, University of Manitoba, , Man., R3T 2N2, Winnipeg, Canada)
Publication:
Journal of Solid State Chemistry, Volume 172, Issue 1, p. 95-101.
Publication Date:
04/2003
Origin:
ELSEVIER
Abstract Copyright:
(c) 2003 Elsevier Science (USA)
DOI:
10.1016/S0022-4596(02)00137-8
Bibliographic Code:
2003JSSCh.172...95R

Abstract

The structure of the synthetic fluoroperovskite, Na2LiAlF6 (simmonsite), has been determined by powder X-ray diffraction using the Rietveld method of structure refinement. The compound adopts space group P21/n [#14; /a=5.2842(1); /b=5.3698(1); c=7.5063(2)Å /β=89.98(1)° /Z=4), and is a member of the cryolite (Na2NaAlF6) structural group characterized by ordering of the B-site cations (Li, Al) and tilting of the BF6 octahedra according to the tilt scheme a-b-c+. Rotations of the B-site polyhedra are less (ΦLi=14.9° ΦAl=17.0°) than those found in cryolite (ΦNa=18.6 ΦAl=23.5°) because of the larger difference in the ionic radii of the /B-site cations in cryolite as compared to those in simmonsite. Na at the /A-site is displaced from the special position resulting in 10- and 8-fold coordination in simmonsite and cryolite, respectively. By analogy with the synthetic compound, naturally occurring simmonsite is considered to adopt space group P21/n /(#14) and not the P21(#4) or P21/m(#11) space groups.
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