Raman scattering of Sm and Eu-doped ceria thin films undergoing anelastic biaxial strain relaxation

We developed a method to monitor Raman spectra of thin films undergoing biaxial strain relaxation of 0.3-0.5% and applied it to sputtered films of 10 mol% Eu and Sm doped ceria. The method is based on comparison of... [ view full abstract ]

We developed a method to monitor Raman spectra of thin films undergoing biaxial strain relaxation of 0.3-0.5% and applied it to sputtered films of 10 mol% Eu and Sm doped ceria. The method is based on comparison of substrate-supported films under large compressive strain against 2 mm diameter self-supported films (membranes) prepared by partial substrate removal. The self-supported films were found to be strain-free. From the unit cell volume and Raman spectra acquired in the self-supported and the substrate-supported films, the Grüneisen parameter of the Raman mode was found to be 0.5±0.1, which is much lower than that acquired using hydrostatic compression. Our work strongly suggests that the Raman shift during an isothermal volume change of thin films contains both volume (quasi-harmonic) and anharmonic contributions, with the strong anelasticity of doped ceria being a dominant phenomenon contributing to the latter. This finding has implications on the understanding of anharmonicity effects in ionic conductors with large concentration of point defects and their relationship to strain and volume change.