The analysis of the efficiency of excitation ofSurface Acoustic Waves (SAWs) surface acoustic waves (SAW) in the heterostructure “barium strontium titanateFilm film—single-crystal silicon substrate” is carried out for different directions of wave propagation. The study is performed within the framework of the Landau thermodynamic theory, which allows analyzing the stressed state of the ferroelectric barium strontium titanate film using the example of the Ba0.8Sr0.2TiO3 (BST08) heterostructure. Depending on the deposition technology, such a filmFilm can be in three phases: paraphase, c-phase and aa-phase. The last two phases are characterized by the presence of polarization, the vector of which is either directed along the normal to the film plane (c-phase) or lies in the film plane (aa-phase). The efficiency of SAW excitation in the above heterostructure is theoretically studied. It is shown that the most efficient excitation occurs in the aa-phase when the spontaneous polarization vector lies in the filmFilm plane and is directed diagonally to the coordinate axes, and the wave propagates along the direction of the spontaneous polarization vector. Based on the nonlinear model of phase transitionsPhase transition, linearization is performed and linearized equations of the piezoelectric effect are constructed for solid solutions of barium—strontium titanate. Based on these equations, the dependence of material constants on the value of forced deformationDeformation um is calculated.