Effects of dopant concentration and impurities on the conductivity of magnetron-sputtered nanocrystalline yttria-stabilized zirconia

Cubic yttria-stabilized zirconia (YSZ) films with yttria concentrations of 8.7, 9.9, and 11 mol% have been deposited by reactive pulsed DC magnetron from Zr–Y alloy targets. The overall microstructure and texture in the films showed no dependence on the yttria concentration. Films deposited at floating potential had a <111> texture. Single-line profile analysis of the 111 X-ray diffraction peak yielded a grain size of 18 nm and a microstrain of 2%, regardless of deposition temperature. Films deposited at 400 °C and selected bias voltages in the range from − 70 V to − 200 V showed a reduced grain size for higher bias voltages, yielding a grain size of 7 nm and a microstrain of 2.5% at a bias voltage of − 200 V with additional incorporation of argon. Furthermore, the effect of impurities on the ionic conductivity has been investigated, since Hf impurities were found in the samples with yttria concentrations of 8.7, and 9.9 mol%. Temperature-dependent impedance spectroscopy of the YSZ films, deposited at 400 °C and floating potential, showed no variation of the in-plane ionic conductivity with yttria concentration. However, for films deposited at 400 °C and a bias − 70 V, the in-plane ionic conductivity decreased systematically for samples with yttria concentrations of 8.7 and 9.9 mol% compared to the sample with 11 mol% yttria. This suggests that ionic conduction is not a purely bulk mechanism, but mainly related to the grain boundaries. The activation energy for oxygen ion migration was determined to be between 1.25 and 1.32 eV.