Electrical properties of silica-doped 3 mol% yttria-stabilized tetragonal zirconia

Inconsistent opinions in the literature on the impact of silica on the conductivity of Y2O3–ZrO2 system become a motivating reason to reinvestigate this matter. Too low a value of the grain boundaries’ conductivity in the case of 3YSZ (3 mol% yttria-stabilized zirconia) is a fundamental barrier to using this material in the solid oxide fuel cell technology. The presence of silica is considered as the main cause of blocking effect on grain boundaries. The main purpose of this study involved the synthesis of nanomaterials, 3YSZ, with the addition of restricted amounts of silica. Two series of samples were prepared and sintered at the temperatures of 1073 and 1473 K. Then the obtained materials were tested for their phase composition, microstructure and electrical properties (based on analysis of the impedance spectra). The SEM microphotograph analysis indicated the decrease in the grain sizes of zirconia with the addition of SiO2. Moreover, X-ray diffraction measurements showed the beginning of formation of zirconium silicate at 1473 K. The detailed investigation of microstructures and electrical properties shows that the two factors reported in the literature have an influence on grain boundary conductivity—grains sizes and the amount of introduced silica. Presented studies shows that up to temperature in which silica reacts with zirconia to form zircon (ZrSiO4), its presence actually improves the grain boundaries conductivity due to decrease in particle size of YSZ (pinning effect). The blocking effect of silica at the grain boundaries begins to play a greater role causing the formation of glassy layers at a higher temperature.