Thermal Diffusivity of Partially and Fully Stabilized (Yttria) Zirconia Single Crystals

Abstract

Laser flash measurements of thermal diffusivity of ZrO 2 single crystals partially and fully stabilized with Y 2 O 3 were compared with measurements for polycrystalline cubic ZrO 2 , and single crystals and polycrystals of Al 2 O 3 and MgAl 2 O 4 . In general, the thermal diffusivities of the ZrO 2 materials examined initially decrease with increasing temperature, although significantly less than for the Al 2 O 3 and MgAl 2 O 4 materials. The diffusivity subsequently rises with increasing temperature for the single crystals of ZrO 2 but not for polycrystalline cubic ZrO 2 , with this increase for ZrO 2 crystals occurring at much lower temperatures than for Al 2 O 3 and MgAl 2 O 4 crystals. As the ZrO 2 materials went from fully stabilized with 20 wt% Y 2 O 3 to partially stabilized with 5 wt% Y 2 O 3 , the room‐temperature diffusivity increased from 0.70x10 ‐6 to 0.97x10 ‐6 m 2 /s. This indicated that the lattice defects, which increase with Y 2 O 3 content, are more important sources of phonon scattering than are the precipitates which appear at lower Y 2 O 3 compositions. On the other hand, at 1000°C the diffusivity of the fully cubic ZrO 2 crystals with 20 wt% Y 2 O 3 was 1.10x10 ‐6 m 2 /s while that of the partially stabilized ZrO 2 crystals with 5 wt% Y 2 O 3 was 1.05x10 ‐6 m 2 /s. The increased diffusivity at higher temperatures can be attributed to radiative heat transfer, with the lower relative diffusivity of the partially stabilized crystals resulting from photon scattering by the precipitate structures present.