A comparison study of the structural and mechanical properties of cubic, tetragonal, monoclinic, and three orthorhombic phases of ZrO2

Based on the optimized structures, the individual elastic stiffness constants Cij of three ambient pressure polymorphs including cubic (fluorite, Fm3¯m), tetragonal (P42/nmc) and monoclinic (baddeleyite, P21/c), as well as three high-pressure orthorhombic polymorphs containing ortho-I (brookite, Pbca), ortho-II (cotunnite, Pnma) and ortho-III (Pca21) phases of ZrO2 have been calculated by finite difference method. Accordingly, the mechanical properties of the polycrystalline aggregates including bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio υ and universal elastic anisotropy index AU have been predicted. It is found that, the ortho-II (Pnma), ortho-I (Pbca) and cubic phases have higher fracture strength, while the ortho-II (Pnma), ortho-III (Pca21) and cubic phases have higher yield strength and plastic strength. The ductility of the six polycrystalline ZrO2 phases decreases in the sequence of tetragonal, ortho-I (Pbca), ortho-II (Pnma), cubic, ortho-III (Pca21) and monoclinic. The elastic anisotropy of tetragonal (especially) and cubic ZrO2 is larger and prone to cause stress concentration and micro-cracks.