Experimental study of the thermal conductivity of metal oxides co-doped yttria stabilized zirconia

Doping of yttria stabilized zirconia (YSZ) with metal oxides has been reported to have the potential of increasing the thermal insulation capability and phase stability of YSZ at higher application temperatures. In order to select the dopant oxides, it is important to understand the effects of the dopants, in terms of the ionic radius, mass, and valence, on various thermal and mechanical properties of the doped YSZ. In this study, a series of metal oxides, tantalum pentoxide (Ta2O5), niobium pentoxide (Nb2O5), scandium oxide (Sc2O3), ytterbium oxide (Yb2O3) and cerium oxide (CeO2) were incorporated to 7YSZ (7 wt% yttria) by mechanical alloying and sintering; the thermal conductivity changes of the doped 7YSZ were investigated. The oxide dopants that exist as defect clusters within the zirconia lattice structure played an important role in reducing the thermal conductivity of the ternary oxide system. Yb2O3 co-doped 7YSZ exhibited the most significant effect on reducing the thermal conductivity while CeO2 co-doped 7YSZ showed marginal effect. The measured results were also found to be consistent with that obtained from a semi-empirical thermal conductivity model established based on the assumption of defect clusters acting as the phonon scattering centers.