New oxygen ion conductors have been prepared by substituting Ga3+ for Ge4+ in Nd4GeO8, Zn2+ and
Mg2+ for Ga3+ in Nd3GaO6, and Ca2+ and Sr2+ for Nd3+ in Nd3GaO6. A combustion technique using
ethylenediamine tetraacetic acid has been developed to synthesize these materials at ∼900 °C, leading to
powders with spherical particles of about 100−200 nm. The green pellets obtained through the combustion-synthesized powders could be sintered to ∼98% at 1250 °C. It was found that Nd4Ge1
-
x
Ga
x
O8
-
x
/2 are
formed up to x = 0.10, Nd3Ga1
-
x
M
x
O6
-
x/2 (M = Zn, Mg) up to x = 0.03, and Nd3(1
-
x)M‘3
x
GaO6
-
3
x
/2 up
to x = 0.03 and 0.015 for M‘ = Ca and Sr, respectively. These relatively small substitution rates induce
a significant increase in oxygen ion conductivity (σ800
°
C = 0.2 × 10-2 S cm-1 for Nd4Ge0.9Ga0.1O7.95;
σ800
°
C = 0.5 × 10-2 and 0.4 × 10-2 S cm-1 for Nd3Ga0.97M0.03O5.985 with M = Zn and Mg, respectively,
and σ800
°
C = 0.6 × 10-2 and 0.7 × 10-2 S cm-1 for Nd2.91Ca0.09GaO5.955 and Nd2.955Sr0.045GaO5.9775,
respectively) with respect to pure Nd4GeO8 (σ800
°
C = 2.8 × 10-4 S cm-1) and pure Nd3GaO6 (σ800
°
C =
2.7 × 10-4 S cm-1).