High ionic conductivity of ultralow yttria concentration yttria-stabilized zirconia thin films

This paper investigates the ionic conductivity of ultralow yttria concentration (<2 mol. %) yttria-stabilized-zirconia (YSZ) thin films synthesized by atomic layer deposition (ALD). With our ALD recipe, yttria is homogeneously distributed among zirconia, and its concentration is controlled by the pulse time of the yttrium precursor. High conductivity values are observed at test temperatures (400, 500, and 600 °C). 1.6YSZ exhibits a conductivity of 0.02 S cm⁻¹ at 600 °C and an activation energy of 0.98 eV. In order to relate the electrical property, atomic force microscope and x-ray diffraction are used to study the crystallinity and microstructure. The true size effect is considered to be responsible for the outstanding electrical property. Finally, the effects of YSZ thin film thickness and annealing process on their conductivities are studied. The true size effect is weakened by an increase in grain size from annealing or higher thickness, leading to reduced ionic conductivities.