Internal stress and the deformation phase transition in nanoscale barium-strontium titanate films

It has been established by varying the thickness of Ba0.8Sr0.2TiO3 heteroepitaxial films grown via the layer-by-layer mechanism on (100) MgO substrates that there is a critical film thickness (∼50 nm): the internal strain field in the films with a thickness below critical is much weaker than in the films with a thickness exceeding critical. Tensile and compressive stresses occur at thicknesses, respectively, below and above critical. The existence of critical thickness is confirmed by the X-ray diffraction data and Raman spectroscopy.