Cation mobility in Y2O3- and CaO-stabilised ZrO2 studied by tracer diffusion and mechanical spectroscopy

Internal friction measurements of polycrystalline tetragonal ZrO2(2.8 mol% Y2O3), YSZ-2.8, and of polycrystalline cubic ZrO2(7.8 mol% Y2O3), YSZ-7.8, show a high temperature background which is characterised by an activation enthalpy of DeltaH(m) = 6.5 +/- 0.7 eV (YSZ-2.8) and DeltaH(m) = 5.3 +/- 0.5 eV (YSZ-7.8). We obtained about the same activation enthalpies in tracer diffusion studies of Zr-96 (DeltaH(Zr) = 6.3 eV for YSZ-2.8 and DeltaH(Zr) = 5.1 eV for YSZ-7.8). Therefore, the high temperature background is attributed to Zr- or Y-diffusion. For single crystals with higher Y2O3-concentrations, the background is much smaller and obscured by a phase transition peak. In ZrO2-CaO (CSZ) an internal friction maximum with DeltaH(R) = 4.0 eV and a frequency factor close to the Debye - frequency was observed for concentrations from 12.4 mol% CaO to 16.8 mol% CaO. It is assigned to the reorientation of Schottky-defects, e.g. cation vacancy - Ca pairs. The activation enthalpies for the long range tracer diffusion (DeltaH(Ca) = 5.1 eV and DeltaH(Zr) = 5.3 eV) are significantly higher than for the internal friction maximum where only local cation jumps are monitored. This may be due to the formation of vacancy complexes.