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

• Nanoscale 20 mol% GDC thin films were fabricated by magnetron sputtering.
• Insensitivity to oxygen partial pressure verified the conductivity as ionic.
• Conductivity changed from grain- to grain boundary-control as thickness increased.
• A moderate amount of lattice strain seemed to decrease the ionic conduction.

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.