Thermal Expansion of Ln 6 WO 12 ( Ln = Y , Ho , Er , Yb ) and Ln 2 WO 6 ( Ln = Gd , Dy , Ho ) – an In Situ Synchrotron X‐ray Diffraction Study
The thermal expansion ( TE ) behavior of cubic and rhombohedral Ln 6 WO 12 (Ln = Y, Ho, Er, Yb) and monoclinic Ln 2 WO 6 (Ln = Gd, Dy, Ho) was investigated by synchrotron X‐ray diffraction from room temperature to approximately 1500°C. The volumetric and lattice parameter expansions were measured fo...
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Published in | Journal of the American Ceramic Society Vol. 97; no. 8; pp. 2496 - 2505 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
01.08.2014
|
Online Access | Get full text |
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Summary: | The thermal expansion (
TE
) behavior of cubic and rhombohedral
Ln
6
WO
12
(Ln = Y, Ho, Er, Yb) and monoclinic
Ln
2
WO
6
(Ln = Gd, Dy, Ho) was investigated by synchrotron X‐ray diffraction from room temperature to approximately 1500°C. The volumetric and lattice parameter expansions were measured for all compositions in both systems, and the respective expansion coefficients were derived and fitted over the observed temperature range with a second‐order polynomial. The relative
TE
evolution along the unit cell edges in each phase was described from a crystallographic perspective, with the reasons for
TE
dynamics explained in terms of the fundamental constituent units of the structure. Analysis of the TE ellipsoid of the monoclinic
Ln
2
WO
6
revealed a continuous change in both its shape and orientation, with the latter effect strongly manifested in the (010) plane. A noticeable reversal of the relative expansion rates between
a
, and
b
and
c
lattice parameters was attributed to the rotation of the ellipsoid cross section in this plane, bringing the larger of the two eigenvectors closer to
a
, while the smaller one to
c
. Investigating the structural dynamics of the constituent layers in
Ln
2
WO
6
suggested that the bridging role of the Ln polyhedron centered on the only general position in the unit cell may be the reason for the rotating
TE
ellipsoid. |
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ISSN: | 0002-7820 1551-2916 |
DOI: | 10.1111/jace.12962 |