Mechanical and thermal properties of fine-grained quasi-eutectoid (La1−xYbx)2Zr2O7 ceramics

A2B2O7-type rare earth zirconates have been intensively investigated as potential thermal barrier coating (TBC) materials due to their low thermal conductivities and high stability at high temperature. In this work, mixing La3+ and Yb3+ with a large difference in atomic radii at A site formed a quasi-eutectoid mixture of La2Zr2O7-rich pyrochlore phase and Yb2Zr2O7-rich fluorite phase. The competition between these two phases in grain growth effectively reduces the grain size down to 0.8-1 μm, giving rise to improved mechanical properties comparing with the single-phase materials, including a higher hardness, a higher fracture toughness and a lower elastic modulus. Furthermore, a significantly low thermal conductivity was found, as the small and heavy Yb3+ ions that dissolve in the La2Zr2O7-rich pyrochlore could “rattle” in the lattice and strongly scatter the heat-carrying phonons. Considering the comprehensively improved mechanical and thermal properties, the quasi-eutectoid (La1−xYbx)2Zr2O7 ceramic can be considered as a potential TBC material.