An enhancement in thermal stability of alumina doped YSZ by applying an electric field

The metastable tetragonal (t′) phase in YSZ exhibits significant thermal stability, high strength, excellent toughness and high temperature creep resistance (unlike stable tetragonal phase). Because of its properties, t′ phase YSZ would seem to be ideally suited for elevated temperature applications. However, stabilizing of the t′ phase is difficult due to its non-equilibrium nature. Electrical treatment is introduced as a method to stabilize metastable phases in zirconia material. Treatment consists of applying an external polarization (3 V) to the YSZ layer at high temperature (700 °C) for 20 min. This process results in a fully t′ phase YSZ with the appearance of t′′ phase within t′ domain boundaries. Arguments are put forth to explain this transformation from the thermodynamic and kinetic point of view.

► Oversaturating YSZ with alumina results in nucleation and growth of metastable phase.
► Electric field stabilizes the metastable phases of YSZ by lattice oxygen displacement.
► Metastable phase generates from transformation of tetragonal and cubic YSZ.
► YSZ constructed by metastable phases is promising for high temperature application.