Tunable dislocations overcome mechano-functional tradeoff in perovskite oxides.

Recent advancements in dislocation engineering are reshaping the traditional view towards ceramics being brittle. Here, we use KTaO3 (KTO), a perovskite oxide that is newly discovered with room-temperature bulk plasticity, and demonstrate that the seeded dislocations can effectively tune both mechanical and functional properties. We uncover a brittle-ductile-brittle (BDB) transition: low dislocation densities lead to brittle failure, intermediate densities (∼1014 m-2) enable superior compression plastic deformation capacity with strains over 20%, and high dislocation densities (∼1015 m-2) induce brittle fracture again. This dislocation density-dependent non-monotonic mechanical response challenges the traditional behavior of ceramics and offers design opportunities. Furthermore, dislocation densities can monotonically decrease thermal conductivity, revealing a tradeoff between mechanical strength and functionality. The findings reveal a critical threshold of dislocation density in optimizing the performance of functional oxides, and provide a framework for using dislocations to design advanced materials where mechanical durability and enhanced functionality are intertwined.