Mechanical properties at the nanometer scale of GDC and YSZ used as electrolytes for solid oxide fuel cells

The Young's modulus (E), hardness (H) and fracture toughness (K-IC) of various compositions of gadolinia doped-ceria (GDC, GdxCe1-xO2-x/2, 0.1 <= x <= 0.2) and yttria-stabilized zirconia (YSZ, Y0.08Zr0.92O1.96) electrolytes were investigated by nanoindentation. All samples were produced by the sol-gel method, formed by uniaxial pressure and sintered at 1400 degrees C. In order to determine the mechanical properties, a Berkovich diamond tip was employed at applied loads of 5, 10, 30, 100 and 500 mN. The results were interpreted by the Oliver-Pharr method and values of K-IC were determined using the method of Palmqvist cracks. The residual imprints were observed by field emission scanning electron microscopy. The results obtained showed that the H, E and K-IC of GDC decreased with increasing gadolinia concentration, due to the oxygen vacancies generated by the dopant addition. As a result, the mechanical properties of GDC were significantly lower than those of YSZ electrolyte. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.