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Anisotropic Thermal Expansion in CaAl4O7

Published online by Cambridge University Press:  31 January 2011

Koichiro Fukuda  and
Kaori Yamauchi
Koichiro Fukuda
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466–8555, Japan
Kaori Yamauchi
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466–8555, Japan
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Extract

Crystals of CaAl4O7 (space group C2/c) have been examined by high-temperature powder x-ray diffractometry to determine the change in unit-cell dimensions with temperature up to 1473 K. The lattice deformation induced by thermal expansion has been investigated by matrix algebra analysis to determine the directions and magnitudes of the principal distortions. During heating from 298 K, two of the three principal distortions, λ1 and λ2, invariably showed a positive thermal expansion, the magnitudes of which at 1473 K are respectively approximately 1.0% and approximately 0.8%. The direction of λ1 was nearly parallel to [304], and the λ2 axis invariably coincides with the crystallographic b axis. On the other hand, the distortion λ3 showed a negative thermal expansion below approximately 1173 K; the maximum contraction of approximately 0.2% occurred at approximately 673 K nearly along [207]. During further heating to 1473 K, λ3 showed, to the contrary, a positive expansion of approximately 0.2% nearly along [50, 16]. The negative thermal expansion along the λ3 axis substantially accounts for the mean linear thermal expansion being very low at temperatures below approximately 473 K.

Type
Articles
Information
Journal of Materials Research , Volume 17 , Issue 5 , May 2002 , pp. 1050 - 1054
Copyright
Copyright © Materials Research Society 2002

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