Microstructure-property modifications in plasma sprayed 20 wt.% yttria stabilized zirconia electrolyte by spark plasma sintering (SPS) technique

Spark plasma sintering (SPS) was adopted in this study as a rapid post-spray treatment for 20 wt.% yttria stabilized zirconia (YSZ) electrolytes prepared by the direct current (DC) plasma spray process. The lamellar microstructure in the as-sprayed samples was found to significantly reduce the ionic conductivity of the YSZ electrolytes. However, the ionic conductivity (at 1053 °C) increased sharply from 0.065 S/cm for the as-sprayed electrolyte to 0.122 S/cm for electrolyte post-spray treated through SPS at 1400 °C for 3 min. These phenomena were attributed to the microstructure transformation from lamellar structure of the as-sprayed samples to equi-axial type granular structure of the post-spray samples treated by SPS. Correspondingly, porosity reduced from ∼10.72% in as-sprayed coating to ∼1.38% in the SPS sample treated at 1400 °C for 3 min. Majority of the pores in the SPS sample were also found to have contracted to a narrow size range 0.03-1 μm. AC impedance spectroscopy demonstrated the effect of the microstructure modification among samples treated by SPS at temperature 1200, 1300, and 1400 °C for 3 min with the concomitant reduction of the resistivity, which is consistent with the microstructure changes of the YSZ electrolyte from lamellar structure to granular structure. Overall, the results show that SPS is an effective and rapid post-spray treatment to improve the relative density and electrical properties of plasma sprayed YSZ electrolytes.