Breaking the Trade‐Off Relationship Between Thermal Conductivity and Toughness of Ferroelastic Oxide Ceramics via a High‐Density Dislocation Strategy

ABSTRACT The trade‐off relation between thermal conductivity and fracture toughness limits applications of brittle ceramic thermal insulation materials, and we propose that the high‐density dislocation engineering acts as an effective strategy to synergistically reduce thermal conductivity and enhance toughness. The spark plasma sintering (SPS) and heat treatments introduce high‐density dislocations (10 8 ∼10 10 mm −2 ) into the ferroelastic YTaO 4 /Y 3 TaO 7 ceramic composites as thermal insulation materials. The effects of high‐density dislocations on reducing thermal conductivity and enhancing toughness are elucidated from the phonon relaxation time and crack propagation behaviors, respectively. The high‐density dislocations produce large lattice strains to reduce phonon relaxation time, and the lowest thermal conductivity reaches 1.32 W·m −1 ·K −1 . The interfacial enhancements, ferroelastic domains, and high‐density dislocations synergistically boost the toughness to 5.0 MPa·m 1/2 , and the increment is higher than 50%. The effects of high‐density dislocations on toughness and thermal conductivity are revealed from an atomic scale, and the proposed high‐density dislocation strategy breaks the trade‐off relationship between thermal conductivity and toughness for brittle ceramic thermal insulation materials.