LiSrAlF6 with the LiBaCrF6-type structure

Titelangaben

Grzechnik, Andrzej ; Dmitriev, Vladimir ; Weber, Hans-Peter ; Gesland, Jean-Yves ; van Smaalen, Sander:
LiSrAlF6 with the LiBaCrF6-type structure.
In: Journal of Physics: Condensed Matter. Bd. 16 (2004) Heft 18 . - S. 3005-3013.
ISSN 1361-648X
DOI: https://doi.org/10.1088/0953-8984/16/18/001

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Abstract

The crystal structure of LiSrAlF 6 -III ( P 2 1 / c , Z = 4) occurring above 3.0 GPa at room temperature was studied with synchrotron angle-dispersive x-ray powder diffraction in a diamond anvil cell. It was solved by combining a global optimization and a topological analysis with the Rietveld method using rigid-body AlF 6 geometrical constraints. LiSrAlF 6 -III, related to LiBaCrF 6 ( P 2 1 / c , Z = 4), is built of deformed SrF 12 icosahedra within a three-dimensional framework of corner-sharing distorted AlF 6 octahedra and LiF 4 tetrahedra, whereas the low-pressure phases I ( ##IMG## http://ej.iop.org/images/0953-8984/16/18/001/cm176381ieqn1.gif {P\overline 3 1c} , Z = 2) and II ( P 2 1 / c , Z = 4) have cations exclusively in distorted octahedral coordinations. The pressure-induced changes of the coordination polyhedra in the series LiSrAlF 6 -I, LiSrAlF 6 -II to LiSrAlF 6 -III are similar to the differences in coordination polyhedra due to the increase of the ionic radii of the Sr 2+ and Ba 2+ cations in LiSrAlF 6 -I and ##IMG## http://ej.iop.org/images/0953-8984/16/18/001/cm176381ieqn2.gif {{\mathrm {LiBaM''F_{6}}}} ( ##IMG## http://ej.iop.org/images/0953-8984/16/18/001/cm176381ieqn3.gif {{\mathrm {M''=Al}}} , Ga, Cr, V, Fe, or Ti) at ambient conditions. These observations are discussed on the basis of the high-pressure high-temperature systematics in AB 2 X 6 compounds.