Engineering of the Curie temperature of epitaxial Sr1−xBaxTiO3 films via strain

Abstract

The impact of strain on the structural and electrical properties of epitaxial Sr1−xBaxTiO3 films grown on single crystalline DyScO3 (110), TbScO3 (110), and GdScO3 (110) substrates is presented. X-ray diffraction measurements demonstrate that all films are grown epitaxially. The tensile in-plane strain is only partially compensated by a contraction of the out-of-plane lattice parameter. As a result, the volume of the unit cell of the Sr1−xBaxTiO3 film increases due to the tensile strain, and the resulting Poisson ratio of the film is ν ≈ 0.33, which is larger than but still close to the literature values of ν ≈ 0.23 for unstrained defect-free SrTiO3. The Curie temperature derived from the temperature dependence of the in-plane dielectric response leads to a strain-temperature phase diagram for the epitaxial Sr1−xBaxTiO3 films. The experimental data show a deviation from the linear dependence predicted by the Landau thermodynamic theory for large strain (>1.2%). However, using the equilibrium thermodynamic analysis, we can demonstrate that this deviation arises from the relaxation of the strain due to defect formation in the film. The result reveals that in addition to the nominal misfit strain, the defect formation strongly affects the effective strain and, thus, the dielectric response of epitaxially grown ferroelectric films.