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Crystal structure of lanthanum oxyorthosilicate, La2SiO5

Published online by Cambridge University Press:  01 March 2012

Koichiro Fukuda ,
Tomoyuki Iwata  and
Eric Champion
Koichiro Fukuda
Affiliation:
Department of Environmental and Materials Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Tomoyuki Iwata
Affiliation:
Department of Environmental and Materials Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Eric Champion
Affiliation:
Science des Procédés Céramiques et de Traitements de Surface, Université de Limoges, UMR CNRS 6638, 123 Avenue Albert Thomas, 87060 Limoges Cedex, France
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Abstract

The crystal structure of La2SiO5 was refined from laboratory X-ray powder diffraction data (CuKα1) using the Rietveld method. The crystal structure is monoclinic (space group P21∕c,Z=4) with lattice dimensions a=0.93320(2) nm, b=0.75088(1) nm, c=0.70332(1) nm, β=108.679(1)°, and V=0.46687(1) nm3. The final reliability indices were Rwp=7.14%, RP=5.52%, and RB=3.83%. There are two La sites in the structural model, La1 and La2. La1 is ninefold coordinated to oxygen, forming a tricapped trigonal prism with a mean La1-O distance of 0.263 nm. The La2O7 coordination polyhedron is a distorted capped octahedron with a mean La2-O distance of 0.251 nm. The La1O9 polyhedra share faces and the La2O7 polyhedra share edges, forming two sets of sheets that alternate parallel to the (100) plane. These sheets are linked through SiO4 tetrahedra and non-silicon-bonded oxygen atoms to form a three-dimensional structure. This compound is isomorphous with the low-temperature (X1) phases of R2SiO5 (R=Y and Gd). The volumes of RO9 polyhedra steadily increase with increasing ionic radius of R, from Y3+ to Gd3+ to La3+, which causes substantial volumetric expansion of the crystals.

Keywords

lanthanum oxyorthosilicatecrystal structurepowder diffractionRietveld refinement
Type
Technical Articles
Information
Powder Diffraction , Volume 21 , Issue 4 , December 2006 , pp. 300 - 303
Copyright
Copyright © Cambridge University Press 2006

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