Abstract
Rare earth oxides doped hafnia ceramics,with a formula of Hf0.76LnxY0.24-xO1.88 (Ln =Gd,Yb,Gd + Yb or La + Yb),were prepared by solid state sintering at 1500 ℃.The effects of the rare earth oxides on the microstructures,sintering resistance,and thermo-physical properties of the doped hafnia ceramics were investigated.Results show that the Gd-Y,Yb-Y or Gd-Yb-Y co-doped hafnia ceramics remain the same defect fluorite (F) structure,while the La-Yb-Y co-doped hafnia revealing coexistence of pyrochlore (P)and fluorite structures.Yb-Y co-doped samples exhibited much better sintering resistance compared with Gd-Y and Gd-Yb-Y co-doped samples.The coexistence of P and F phases is beneficial to improved sintering capability.The thermal conductivities of the Gd-Y,Yb-Y and Gd-Yb-Y doped samples are relatively lower (1.4-1.7 W m-1 K-1 at 1200 ℃),but for the La-Yb-Y co-doped samples,the thermal conductivity increases dramatically with temperature due to increased thermal radiation at high-temperature.The average thermal expansion coefficients (TECs) of the Gd-Y,Yb-Y and Gd-Yb-Y co-doped samples are as high as ～10.3 × 10-6 K-1 in temperature range between 200-1200 ℃.
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