The effect of powder grain size on the microstructure and electrical properties of 8 mol% Y2O3-stabilized ZrO2

Abstract

To improve the electrical properties of an 8 mol% yttria-stabilized zirconia (8YSZ) electrolyte, nanocrystalline (10–100 nm) 8YSZ powders were synthesized via a hydrothermal method followed by heat treatment at temperatures ranging from 800 °C to 1200 °C. Note that all the powders maintained the single-cubic phase structure, as observed via the results of the XRD and Raman spectra. Moreover, the annealing procedure of the powders caused the yttrium concentration of the surface to slightly increase, as observed via X-ray photoelectron spectroscopy (XPS). Moreover, according to the morphology shown in the SEM images and the electrochemical impedance spectroscopy (EIS), the powder grain size had an effect on the microstructure of the electrolytes fabricated via the conventional sintering method. In addition, it further influenced the relative density and conductivity of the electrolytes, which both first increased and then decreased with the increase in the powder grain size in the range of 10–100 nm. This showed that the powders with 50–80 nm grain size exhibited the best performance since it was not easy to induce grain coarsening in ceramics. The electrolyte sintered by these powders showed uniform and hexagonal grains with a mean size of 0.97 μm and a relative density of over 99%. Because of a large sum of grain boundaries and point defects, the electrolyte had a good conductivity of 174.1 mS cm⁻¹ at 1000 °C measured by the four-probe DC method. In addition, the activation energy (0.955 eV) is lower than that for other samples; this suggests that 8 mol% Y₂O₃-stabilized ZrO₂ has more advantages at lower working temperatures for SOFCs.