Structure and ionic conductivity of nanoscale gadolinia-doped ceria thin films

Nanoscale 20 mol% gadolinia-doped ceria (GDC) thin films were prepared by RF sputtering on single crystal (0001) Al2O3 substrates. The films were polycrystalline with columnar grains that were very highly textured along the (111) direction. A moderate amount of lattice strain was observed when the thickness was less than 81 nm, similar to the grain size. Impedance spectroscopy measurements between 300 °C and 650 °C demonstrated that GDC thin films achieved highest conductivity at 81 nm thickness. The activation energy was ≈ 0.75 eV when thickness was under 81 nm but increased as the thickness increased above 81 nm. Constant conductivity values for all samples as the oxygen partial pressure varied between 10− 3 atm and 1 atm demonstrated that the conductivity was predominantly ionic.