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Home  >  Journal list  >  Journal of the Ceramic Society of Japan, Supplement 112-1, PacRim5 Special Issue  >  Vol.112  9. Electronic and Ionic Conductors  >  pp.S738-S741

Journal of the Ceramic Society of Japan, Supplement 112-1, PacRim5 Special Issue
<<Previous article Vol.112  9. Electronic and Ionic Conductors   pp.S738 - S741 Next article>>

Crystal Structure and Electrical Conductivity of Pyrochlore-type Composition Systems, A2B2O7

Hanako NISHINO1), Naoto MATSUNAGA1), Katsuyoshi KAKINUMA1), Hiroshi YAMAMURA1) and Katsuhiro NOMURA2)
1) Department. Applied Chemistry, Faculty of Engineering, Kanagawa University
2) National Institute of Advanced Industrial Science and Technology-Kansai


  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.


Keyword:
Oxide-ion conductivity, Fluorite-type structure, Pyrochlore-type structure, Rare earth C-type structure, Raman spectra

Received: August 09, 2003
Accepted: December 10, 2003 , Published online: September 29, 2004
Copyright (c) 2004 The Ceramic Society of Japan

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