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La9.33Ge6O26 pellets synthesized by a molten-salt method exhibit higher conductivity owing to the high density and the avoidance of La2GeO5.

Lanthanum silicates La 10 Si 6−x Mg x O 27−x (x = 0-0.4) were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore, an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of La 10 Si 6−x Mg x O 27−x (x = 0-0.4) suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La 10 Si 6 O 27 , and La 10 Si 5.8 Mg 0.2 O 26.8 exhibits the highest conductivity with a value of 3.0×10 −2 S •cm −1 at 700 • C. Such conductive behavior agrees well with the refined results. The corresponding mechanism has been discussed in this paper.