Processing and electrical properties of NASICON prepared from yttria-dopedzirconia precursors

This work reports on the synthesis and characterization of NASICON obtained from solid state reaction between SiO2, Na3PO4. 12H(2)O and two types of z irconia: monoclinic ZrO2 and yttria-doped tetragonal phase (ZrO2)(0.97)(Y2O 3)(0.03) Powders and dense samples were characterized by SEM, XRD and DTA. Electrical conductivity was measured by impedance spectroscopy. Results obt ained with different NASICON samples showed a significant role of compositi on and processing conditions on the electrical properties. Dense yttria-dop ed samples were obtained at a lower temperature than the undoped material. The electrical conductivity, close to 2x10(-3) S cm(-1) at room temperature , is significantly higher than the value obtained with the material prepare d from pure ZrO2, Attempts to compensate the charge unbalance due to replac ement of Y3+ for Zr4+ With additions of Na+ failed. Instead, a drop in elec trical conductivity due to an enhancement of the grain boundary impedance w as observed. Formation of monoclinic zirconia and glassy phases along the g rain boundary were responsible for this effect. Results suggest a major rol e of microstructure on electrical properties rather than composition. (C) 2 001 Elsevier Science Ltd, All rights reserved.