Synthesis and characterization of strontium and magnesium doped lanthanum gallate via steric entrapment synthesis

Development of more efficient fuel cells and sensors requires cost-effective solid state electrolytes with high ionic conductivity. Lanthanum gallate doped with magnesium and strontium (LSGM) is among the most promising materials, but it is a real challenge to produce this compound with high phase purity and good microstructure. We produce high phase purity LSGM1020 (La0.9Sr0.1Ga0.8Mg0.2O2.85) by steric entrapment synthesis (SES) with polyacrylamide polymer, using a ratio cationic charge / number of monomers equal to 2:1. The doping process is split into two steps to make the formation of LaGaO3 phase easier. After calcination at 1300°C up to 93% pure phase is obtained. Ball milling of powders between the two steps of the synthesis further improves the phase purity. Phase pure material is obtained by conventional sintering in air at 1350-1450°C or by Spark Plasma Sintering (SPS) at 1250°C applying a 50 MPa pressure: SPS permits to obtain 96% relative density independent of the temperature. Therefore the combination of two-steps SES synthesis and SPS sintering allows at the same time to improve phase purity and density and to reduce the sintering temperature by 100-200°C. Ionic conductivity of conventionally sintered LSGM (measured by impedance spectroscopy) is 0.037 S/cm at 750°C, higher than for SPS sintered LSGM.