Experimental and DFT insight into the influence of Yb3+doping on phase structure, thermophysical and mechanical properties of (Sm1-xYbx)2Zr2O7 ceramics

In this study, a series of (Sm1-xYbx)2Zr2O7 (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) ceramics were synthesized by solid state reaction, and their phase structure, thermophysical properties, and mechanical properties were investigated. The results showed that (Sm1-xYbx)2Zr2O7 (x = 0, 0.1) exhibited pyrochlore structure, while (Sm1-xYbx)2Zr2O7 (x = 0.3, 0.5, 0.7, 0.9, 1) possessed defective fluorite structure. The thermal conductivity of (Sm1-xYbx)2Zr2O7 ceramics initially decreased with the increases of Yb3+ doping fraction, but subsequently increased when x exceeded 0.3. The lowest thermal conductivity of (Sm0.7Yb0.3)2Zr2O7 achieved was 1.341 W m-1 K-1 at 800 degrees C. Differential scanning calorimetry (DSC) results and thermogravimetric analysis (TGA) confirmed that (Sm0.7Yb0.3)2Zr2O7 possessed high thermal phase stability. Moreover, (Sm0.7Yb0.3)2Zr2O7 had a Vickers hardness of 9.084 GPa and a fracture toughness of 1.886 MPa m1/2, exhibiting good resistance to deformation and crack propagation. The density functional theory (DFT) calculation results suggested that the declined thermal conductivity is due to the lattice distortion. And the variation in fracture toughness is related to the reduced lattice parameter and uneven bond strength within RE-O and Zr-O following the substitution of Yb3+ on Sm3+. These findings indicate that (Sm0.7Yb0.3)2Zr2O7 possesses high phase stability and favorable thermophysical and mechanical properties, highlighting its great potential as a thermal barrier coating (TBC) material.