Journal of the Ceramic Society of Japan, Supplement
Online ISSN : 1349-2756
ISSN-L : 1349-2756
Journal of the Ceramic Society of Japan, Supplement 112-1, PacRim5 Special Issue
Session ID : 9
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Crystal Structure and Electrical Conductivity of Pyrochlore-type Composition Systems, A2B2O7
Hanako NISHINONaoto MATSUNAGAKatsuyoshi KAKINUMAHiroshi YAMAMURAKatsuhiro NOMURA
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Abstract
The relationship between the crystal phase and the electrical conductivity was investigated for the pyrochlore-type composition systems, A2B2O7 (A3+=Rare earth element, B4+=Zr, Ce) and their solid solution systems. The crystal phase of these systems varied among rare-earth C-type, fluorite- and pyrochlore-type phases depending on both the lattice constant and the cationic radius ratio (rA/rB), where rA and rB denote ionic radii of A- and B-sites in the pyrochlore-type composition, respectively. The lattice constant decreased with increasing the Zr content in the A2(Zr1-xCex)2O7 (A=La, Sm and Yb) systems. Even if the oxygen vacancy concentration was kept constant in all sample systems, the electrical conductivity changed in the wide range. The oxide-ion conductivity increased in proportion to the unit cell free volume in the fluorite-type phases with or without rare-earth C-type superstructure, and decreased sharply in the pyrochlore-type phase range because of the ordering of oxygen vacancy.
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© 2004 The Ceramic Society of Japan
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