Processing and electrical properties of NASICON prepared from yttria-doped zirconia precursors

This work reports on the synthesis and characterization of NASICON obtained from solid state reaction between SiO2, Na3PO4·12H2O and two types of zirconia: monoclinic ZrO2 and yttria-doped tetragonal phase (ZrO2)0.97(Y2O3)0.03. Powders and dense samples were characterized by SEM, XRD and DTA. Electrical conductivity was measured by impedance spectroscopy. Results obtained with different NASICON samples showed a significant role of composition and processing conditions on the electrical properties. Dense yttria-doped samples were obtained at a lower temperature than the undoped material. The electrical conductivity, close to 2×10−3 S cm−1 at room temperature, is significantly higher than the value obtained with the material prepared from pure ZrO2. Attempts to compensate the charge unbalance due to replacement of Y3+ for Zr4+ with additions of Na+ failed. Instead, a drop in electrical conductivity due to an enhancement of the grain boundary impedance was observed. Formation of monoclinic zirconia and glassy phases along the grain boundary were responsible for this effect. Results suggest a major role of microstructure on electrical properties rather than composition.