Phase transitions in (Ba0.7Sr0.3)TiO3/(001)MgO thin film studied by Raman scattering

Polarized Raman spectra of heteroepitaxial (Ba0.7Sr0.3)TiO3 thin film deposited on the (001)MgO substrate have been studied in the broad temperature range from 30 to 1300 K. Our results show that the ferroelectric-paraelectric phase transition is markedly shifted to higher temperatures with respect to the bulk ceramics of the same composition. Because of the two-dimensional compressive stresses imposed on the film by the substrate, the symmetry of the paraelectric phase is found to be tetragonal well above the Curie temperature. Near the deposition temperature (1173 K), the thermoelastic compressive stresses vanish and Raman response suggests nearly cubic symmetry. Raman measurements below room temperature show clearly that the phase transition to the rhombohedral phase is completely suppressed and only one phase transition from the tetragonal to the monoclinic phase is revealed at similar to150 K. (C) 2003 American Institute of Physics.