Chemical and structural effects on ionic conductivity at columnar grain boundaries in yttria-stabilized zirconia thin films

This study elucidated the effects of coherence and chemical composition on ionic conductivity at columnar grain boundaries of 6 mol % Y2O3 doped ZrO2 (YSZ) thin films. The YSZ thin films were deposited with several orientation textures on MgO (100), Al2O3 (102), and SiO2-glass substrates using metal–organic chemical vapor deposition (MOCVD). Impedance measurements revealed the total ionic conductivity of the thin films. The activation energy of the ionic conduction of YSZ thin films on MgO or Al2O3 substrates was 90–120 kJ/mol. These films showed similar dependence that simply increased along with decreasing coherency at the columnar grain boundaries. However, that of YSZ thin films on SiO2 glass substrate showed dependence of the coherency at the columnar grain boundaries, but the value is higher than those of the films on MgO or Al2O3 substrates by more than 20 kJ/mol. Structural and compositional analyses clarified that the second phase of SiO2 is segregated at mid-gaps between columnar grain boundaries in YSZ thin films on a SiO2 glass substrate. Results show that two factors affect ionic conductivity at the columnar grain boundaries in YSZ thin films: structural coherency and the second phase of ionic insulator.