Influence of ytterbium- and samarium-oxides codoping on structure and thermal conductivity of zirconate ceramics

To increase operating temperature and improve performance of gas-turbine engines, it is urgently needed to develop new thermal barrier oxides with a lower thermal conductivity than 6–8 wt.% yttria-stabilized zirconia. (YbxSm1−x)2Zr2O7 (0 ≤ x ≤ 1.0) ceramics were synthesized by pressureless-sintered at 1700 °C for 10 h in air. The relative density, phase structure, morphology and thermal diffusivity coefficients of (YbxSm1−x)2Zr2O7 ceramics were investigated by the Archimedes method, X-ray diffraction, scanning electron microscopy and laser-flash method. Sm2Zr2O7 and (Yb0.1Sm0.9)2Zr2O7 ceramics exhibit a pyrochlore structure, while (YbxSm1−x)2Zr2O7 (0.3 ≤ x ≤1.0) ceramics have a defect fluorite-type structure. The thermal conductivities of (YbxSm1−x)2Zr2O7 ceramics first gradually decrease with increasing temperature, and then increase slightly above 800 °C due to the increased radiation contribution. YbSmZr2O7 ceramics have the lowest thermal conductivity over the entire temperature range, which is caused by the reduction of cation mean free path in ytterbium–samarium zirconate system.