Mechanical properties of zirconia, doped and undoped yttria-stabilized cubic zirconia from first-principles

Density functional theory calculations investigate the mechanical properties of: cubic (c), tetragonal (t) and monoclinic (m) zirconia (ZrO₂); cubic yttria-stabilized zirconia (c-YSZ); c-YSZ doped with TiO₂, MnO₂, CaO and NiO. These find the elastic constants, elastic compliances, bulk, shear and Young's modulus for the three phases of zirconia together with the ideal strength of c-ZrO₂. The ideal strength of c-ZrO₂ for strain in the [ 100 ] direction (84.3 GPa) being significantly higher than in the [ 110 ] (30.5 GPa) and [ 111 ] directions (9.87 GPa) is attributed to change in the bond angle reducing the internal strain on the bonds. Adding Y₂O₃ to c-ZrO₂ decreases the ideal strength, particularly in the [100] direction, namely to respectively 11.1 and 28.8 GPa for 6.67 and 14.29 mol % Y₂O₃. Doping c-YSZ with TiO₂, MnO₂, CaO and NiO further reduces the ideal strength, with the lowest values for TiO₂ (7.16-7.88 GPa). The significant decrease in the ideal strength of c-YSZ and doped c-YSZ compared to c-ZrO₂ in the [100] direction is attributed to the weakening of the ZrO₂ framework by the oxygen vacancies.