Improved Structural Properties in Homogeneously Doped Sm_0.4Ce_0.6O_2-δ Epitaxial Thin Films: High Doping Effect on the...

The study of ionic materials on nanometer scale is of great relevance for efficient miniaturized devices for energy applications. The epitaxial growth of thin films can be a valid route to tune the properties of the materials and thus obtain new degrees of freedom in materials design. High crystal quality SmCe_1-O_2-δ films are here reported at a high doping level up to x = 0.4, thanks to the good lattice matching with the (110) oriented NdGaO₃ substrate. X-ray diffraction and transmission electron microscopy demonstrate the ordered structural quality and absence of Sm segregation at the macroscopic and atomic level, respectively. Therefore, in epitaxial thin films, the homogeneous doping can be obtained even with the high dopant content not always approachable in bulk form, getting even an improvement of the structural properties. In situ spectroscopic measurements by X-ray photoemission and X-ray absorption show the O 2p band shift toward the Fermi level, which can favor the oxygen exchange and vacancy formation on the surface when the Sm doping is increased to x = 0.4. X-ray absorption spectroscopy also confirms the absence of ordered oxygen vacancy clusters and further reveals that the 5d e_g and t_2g states are well separated by the crystal field in the undistorted local structure even in the case of a high doping level up to x = 0.4.