Oxide ion conductivity inLa(10)Si(6)O(27) and La10Ce6O27-based apatite oxid
es was investigated in this study. In spite of the low symmetry of the crys
tal lattice, both oxides exhibited high oxide ion conductivity over a wide
range of oxygen partial pressures. Oxide ion conductivity of La10Si6O27 was
increased by doping Sr fur La sites. On the other hand, it was found that
La10Ge6O27 also exhibited high oxide ion conductivity which is comparable w
ith that of La0.9Sr0.1Ga0.8Mg0.2O3 perovskite oxide. Arrhenius plots of the
oxide ion conductivity in La10Ge6O27 show a knee around 1000 K. However, t
he knee in the Arrhenius plot of conductivity disappeared by doping Sr for
La sites. Thus, the conductivity at low temperature was greatly enhanced by
doping Sr for La sites in La10Ge6O26. This may be due to stabilization of
the high temperature crystal phase. The electrical conductivities of Sr-dop
ed La10Si6O27 and La10Ge6O27 were almost independent of the oxygen partial
pressure from P-O2 = 1 to 10(-21) atm. This suggests that these materials a
re ionic over a wide P-O2 range. This study revealed that apatite oxide of
La10M6O27 (M - Si, Ge) is a new class of the fast oxide ion conductors. (C)
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