New approach to improve the conductivity of apatite-type lanthanum germanate La9.33Ge6O26 as electrolyte for IT-SOFCs

Abstract

Apatite-type La_9.33Ge₆O₂₆ powders have been successfully synthesized by a facile molten-salt synthesis method, using NaCl as a eutectic salt. The morphology, structure and phase composition of the powders were examined. The results demonstrated that the apatite-type La_9.33Ge₆O₂₆ powders are homogeneous, nano-size, non-agglomerated and well crystallized particles, which are favorable to obtain highly dense pellets. Compared with the conventional methods, dense pellets have been successfully sintered at a relatively low temperature of 1100 °C, which inhibits the vaporization of GeO₂. The pellets exhibit a higher conductivity with a value of 2.4 × 10⁻² S cm⁻¹ at 850 °C, due to the high density and the avoidance of impurity La₂GeO₅. The main problems such as Ge volatility, agglomeration and crystallinity encountered in the conventional methods have been effectively solved via the molten-salt synthesis method. In addition, the related mechanism is also discussed in the present paper.