Submicrometric NASICON ceramics with improved electrical conductivity obtained from mechanically activated precursors

Na3Si2Zr1.88Y0.12PO11.94 was for the first time synthesised using mechanically activated mixtures of (ZrO2)0.97(Y2O3)0.03, Na3PO4·12H2O and SiO2 aiming to lower the sintering temperature thus improving chemical homogeneity. The best result was obtained with powder mixtures activated in Teflon containers with partial amorphisation of the reactants attained after milling for 70 h at a maximum of 300 rpm, without significant contamination. The microstructure consists of 300-500 nm agglomerates of smaller grains with size in the range 50-100 nm. Dense, single phase ceramics with submicrometric grain size were obtained from the activated mixture after sintering at 1050 °C for 10 h. The ionic conductivity of these ceramics is 2.5×10−3 S cm−1 at room temperature, and 0.24 S cm−1 at 300 °C. These values are higher than those obtained with non-activated solid state reaction samples and amongst the highest reported in the literature.