Electric-field-dependent mechanical and electrical properties of barium strontium titanate films for tunable device applications

Developing the novel electric field tunable, reconfigurable, adaptive and frequency-agile microwave devices with specific properties involves technological and scientific activities in the studying of material properties. Measurements of its properties could be a difficult and expensive issue, especially when it concerns thin-film ferroelectrics. Their electromechanical properties change significantly under applied DC bias field. The material coefficients of barium strontium titanate thin films are still unknown; therefore, it is expedient to carry out their calculations. In the present paper, the linear equations of piezoelectric effect have been written for thin barium strontium titanate films under DC bias electric field in paraelectric phase (induced piezoelectric effect) based on the grand potential of Landau theory of phase transitions. The dependence of material constants for thin films of Ba0.65Sr0.35TiO3 (BST65) on the applied planar field at different lattice misfit strains has been studied for this phase. All induced piezoelectric moduli show extreme behavior during field alteration. Elastic moduli show similar abnormal behavior. The alterations increase as misfit strain is approaching the critical value.