Material constants of barium titanate thin films

The nonlinear properties of barium titanate lead to changes in the material constants of the linear equations for the piezoelectric effect in thin films. The behavior of the material constants of single-crystal barium titanate thin films at room temperature has been studied as a function of the misfit strain in terms of the Landau potential of the phenomenological theory. Most of material constants exhibit anomalies at the interfaces with variations in the strain. In the $r$ phase, some elastic and electroelastic constants reach an extremum. The obtained results indicate lines of the search for obtaining films with necessary properties.