Synthesis of apatite type La10−xSrxSi6O27−0.5x powders for IT-SOFC using sol–gel process

• High purity and crystallinity apatite phase La10Si6O27 with and without Sr-doping has been synthesized.
• The involved parameters have been investigated, resulting in an optimized synthesis process.
• The most economic heat treatment to synthesize pure phase LSO has been found at 800 °C for 2 h in calcination step.
• The conductivity of 38.3 mS cm−1 at 600 °C represents therefore a suitable candidate for low temperature SOFC applications.

Apatite-type lanthanum silicates draw researchers' attention due to their good performance as electrolyte materials for IT-SOFC (intermediate temperature solid oxide fuel cells). In this paper we present the synthesis of Sr-doped La10Si6O27 obtained by optimizing a water-based sol–gel process. The relevant synthesis parameters have been investigated to get pure, highly crystalline powders. The mechanisms occurring in the sol–gel reactions are discussed to improve the process of the sol formation. Using this optimized sol–gel process, pure apatite powders have been obtained by calcination from a temperature as low as 800 °C for 2 h and characterized using scanning electron microscopy and X-ray diffraction. The sintering treatment was performed at the temperature of 1500 °C leading to well-crystallized electrolytes likely to be used in fuel cell applications. Ionic conductivities have been measured in order to investigate the effect of the Sr-doping. The results show that the ionic conductivity is thermally activated and its value lies between 3 × 10−2 and 1 × 10−6 S cm−1 at 873 K as function of the composition and powder preparation conditions.