Microstructure and ionic conductivity of alternating-multilayer structured Gd-doped ceria and zirconia thin films

Multilayer thin film of Gd-doped ceria and zirconia have been grown by sputter-deposition on α-Al2O3 (0001) substrates. The films were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The Gd-doped ceria and zirconia layers had the fluorite structure and are highly textured such that the (111) plane of the films parallel to the (0001) plane of the α-Al2O3. The epitaxial relationship can be written as $$ ( 1 1 1)_{{{\text{ZrO}} ₂ /{\text{CeO}} ₂ }} //(000 1)_{{{\text{Al}}₂ {\text{O}}₃ }} $$ and $$ [ 1 1{-}2]_{{{\text{ZrO}}₂ /{\text{CeO}}₂ }} //[ - 2 1 10]_{{{\text{Al}}₂ {\text{O}}₃ }} $$ , respectively. The absence of Ce3+ features in the XPS spectra indicates that the Gd-doped ceria films are completely oxidized. The ionic conductivity of this structure shows great improvement as compared with that of the bulk crystalline material. This research provides insight on designing of material for low temperature electrolyte applications.