Layered YSZ/SCSZ/YSZ electrolytes for intermediate temperature SOFC Part I: Design and manufacturing

(Sc₂O₃)0.1(CeO₂)_0.01(ZrO ₂)_0.89 (SCSZ) ceramic electrolyte has superior ionic conductivity in the intermediate temperature range (700-800 °C), but it does not exhibit good phase and chemical stability in comparison with 8 mol% Y ₂O₃-ZrO₂ (YSZ). To maintain high ionic conductivity and improve the stability in the whole electrolyte, layered structures with YSZ outer layers and SCSZ inner layers were designed. Because of a mismatch of coefficients of thermal expansion and Young's moduli of SCSZ and YSZ phases, upon cooling of the electrolytes after sintering, thermal residual stresses will arise, leading to a possible strengthening of the layered composite and, therefore, an increase in the reliability of the electrolyte. Laminated electrolytes with three, four, and six layers design were manufactured using tape-casting, lamination, and sintering techniques. After sintering, while the thickness of YSZ outer layers remained constant at ~30 μm, the thickness of the SCSZ inner layer varied from ~30 μm for a Y-SC-Y three-layered electrolyte, ~60 μm for a Y-2SC-Y four-layered electrolyte, and ~120 μm for a Y-4SC-Y sixlayered electrolyte. The microstructure, crystal structure, impurities present, and the density of the sintered electrolytes were characterized by scanning and transmission electron microscopy, X-ray and neutron diffraction, secondary ion mass spectroscopy, and water immersion techniques.