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

摘要

Nanoscale 20 mol% gadolinia-doped ceria (GDC) thin films were prepared by RF sputtering on single crystal (0001) Al_2O_3 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.