Lanthanum oxide as a scavenging agent for zirconia electrolytes

The present work demonstrates that additions of lanthanum oxide can counter the negative grain boundary effects of relatively high silica contents in 8 mol% yttria-stabilized zirconia (YSZ). This can be predicted by thermodynamic analysis, showing strong affinity between silica and lanthanum oxide at typical sintering temperatures. Microstructural analysis revealed the onset of La- and Si-rich precipitates, and impedance spectroscopy confirmed a positive impact on grain boundary conductivity. Gradual oversaturation of lanthana in YSZ with decreasing temperature allows one to extend these effects by heat treatment at intermediate temperatures. This procedure enhances the positive effects of additions of lanthana on the specific grain boundary conductivity, while minimizing the negative impact on bulk conductivity.