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

摘要

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.percent yttria-stabilized zirconia. (Yb_xSm_(1-x))_2Zr_2O_7 (0 < = x < = 1.0) ceramics were synthesized by pressureless-sintered at 1700 deg C for 10 h in air. The relative density, phase structure, morphology and thermal diffusivity coefficients of (Yb_xSm_(1-x))_2Zr_2O_7 ceramics were investigated by the Archimedes method, X-ray diffraction, scanning electron microscopy and laser-flash method. Sm_2Zr_2O_7 and (Yb_(0.1) Sm_(0.9))_2Zr_2O_7 ceramics exhibit a pyrochlore structure, while (Yb_xSm_(1-x))_2Zr_2O_8 (0.3 < = x < = 1.0) ceramics have a defect fluoritc-type structure. The thermal conductivities of (Yb_xSm_(1-x))_2Zr_2O_7 ceramics first gradually decrease with increasing temperature, and then increase slightly above 800 deg C due to the increased radiation contribution. YbSmZr_2O_7 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.