LAUSR

Abstract Yttria-stabilised zirconia (YSZ) is a promising electrolyte for SOFCs and gas sensors. In this study, the particle size of a co-precipitated 5 mol% yttria-stabilised zirconia (5YSZ) powder was refined from 10.47 μm to 130 nm via high-energy ball milling to improve its sinterability and ionic conductivity. The ball milling process increased the specific surface area of the 5YSZ powder from approximately 11 to 22 m2∙g-1. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) results indicated that the 5YSZ crystallites decomposed into irregular shapes with the evolution of point, linear, and planar defects. An increase in the milling duration increased the number of oxygen defects in the 5YSZ powder, as revealed by the X-ray photoelectron spectroscopy results. The tetragonal-to-monoclinic phase transformation occurring in the powder was investigated by X-ray diffraction, Raman spectroscopy, HRTEM, and selected-area electron diffraction pattern analyses. The ball-milled powders could be easily densified, but the presence of too many crystal defects and the large fraction of the m-ZrO2 phase were detrimental to the further densification of the 5YSZ powders. In spite of the high sintering temperature (1500 °C) used in this study, the maximum relative density of 99.67% could be achieved for the powder ball-milled for 60 min at the rotor speed of 1500 rpm. Moreover, the ionic conductivity of 5YSZ was improved significantly from 20.6 to 36.2 mS•cm-1 (850 °C) after the high-energy ball milling process.