Enhanced mechanical properties and atomic-scale mechanisms of ferroelastic domain switching for GdNbO₄-La₂Zr₂O₇ materials

Optimization of mechanical properties in La₂Zr₂O₇ (LZO) ceramics, composites and coatings is an on-going requirement for their practical application. Herein, the contribution of monoclinic (La, Gd)NbO₄ (m-LGNO) enhancement of fracture toughness by ∼56% reveals its capability to be a prominent toughening agent. Due to the ferroelastic nature of LGNO, ferroelastic switching takes place within the stress concentrated regions, giving rise to significant strain energy relaxation. Atomic-scale evidence reveals that ferroelastic 94°/86° domain switching can occur, yielding merged 94° domains and newly formed 86° domains. The relevant strains induced by ferroelastic domain switching are quantified up to 8.06% and 6.20% in shear and normal strain, respectively. Such domain switching strains highlight their contribution to accommodate external mechanical loading for the 50 mol% GNO-LZO composite. The results indicate that the unique ferroelastic nature and 94°/86° ferroelastic domain switching in m-LGNO cooperatively provide a significant toughening effect.