Domain structures and toughening mechanism in Al₂O₃ matrix ceramic composites dispersed with piezoelectric LiTaO₃

LiTaO₃/Al₂O₃ ceramic composites were fabricated by hot pressing and pressureless sintering, respectively, to investigate the effect of piezoelectric secondary phase on the properties of structural ceramics. Phase constitution, microstructure and mechanical properties of the ceramic composites were studied. LiTaO₃ could stably coexist with Al₂O₃ during sintering. LiTaO₃ phase was located at the grain boundaries of Al₂O₃ matrix fabricated by different processing routes. Domain structures were clearly seen in LiTaO₃, confirming that LiTaO₃ remained hexagonal ferroelectric phase. About 5 vol.%LiTaO₃/Al₂O₃ ceramic composite prepared by pressureless sintering at 1300 °C showed an increase in fracture toughness. Energy dissipation due to domain switching was suggested as a toughening mechanism. With the increasing of LiTaO₃ content, the domain switching toughening mechanism was decompensated by the decreased relative density of LiTaO₃/Al₂O₃ ceramic composites. For LiTaO₃/Al₂O₃ ceramic composites prepared by hot pressing at 1500 °C, the bending strength decreased because of the increased grain size of Al₂O₃ matrix. The toughening effect due to domain switching was also decompensated by the coarsening of Al₂O₃ matrix grains, the weaker net-like LiTaO₃ phase and the weaker bonding strength between LiTaO₃ phase and Al₂O₃ matrix.