Stress relaxation effects in ferroelectric thin films and superlattices

This paper provides a review of a systematic micro-Raman scattering study on stress effects in heteroepitaxial (Ba(1-x)Sr(x))TiO(3) thin films and BaTiO(3)/SrTiO(3) superlattices grown on (001)MgO substrates. The evolution of stresses in heteroepitaxial (Ba(0.7)Sr(0.3)) TiO(3)/(001)MgO thin film was studied in partially unsupported and completelyfree-standing areas of the film in a side-view backscattering geometry. The E(TO) soft mode was used for estimations of local stresses in the thin film. Our experiments revealed stress relaxation and the gradient of the tetragonal distortion in the partially unsupported ferroelectric thin film. It is shown that thermoelastic strain arising due to the difference between the thermal expansion coefficients of the film and the substrate is the primary effect, which governs the domain structure and induces enhanced tetragonality in the film studied. In BaTiO(3)/SrTiO(3) superlattices the E(TO(1)) soft mode exhibited enhanced upward shift due to significant two-dimensional clamping caused by the lattice mismatch of the constituting layers. Relaxation of two-dimensional stresses with increasing the stacking periodicity of the superlattices was observed.