Assessment of stability and protonic conduction in NASICON ceramics

NASICON-type Na3Si2Zr1.88Y0.12PO11.94 and Na3.2Si2.2Zr1.88Y0.12P0.8O11.94 ceramics were obtained by a standard ceramic route. The structural and microstructural analysis of materials processed under different conditions suggested that the amount of Na- and P-rich liquid phases formed during the high temperature sintering is smaller for Na3.2Si2.2Zr1.88Y0.12P0.8O11.94. Indeed, samples of this composition showed a considerably worse sinterability. Total conductivity values obtained as a function of the humidity content show no evidence for protonic conduction in NASICON between 373 and 473 K. Results obtained at lower temperatures are not conclusive due to the significant degradation of the electrolyte/electrode interfaces and surfaces in wet atmospheres.