  Zirconia ceramics have been known as a structural material with high fracture
toughness and strength since Garvie et al. discovered phase transformation
toughening in 1975 [1]. Although these mechanical properties are the most
excellent among the advanced ceramics, the toughness has not yet reached the
level of metallic materials. Here, we demonstrate for the first time that 2.9
mass% Y2O3-stabilized ZrO2s doped with Al2O3 greatly exceed the toughness of
conventional zirconia ceramics which is comparable to those of metallic
materials, even with slightly higher strength. The excellent mechanical
properties in the proposed ceramic materials will be useful for further
expanding the application of advanced ceramics to many engineering fields.
