Impact of in-plane anisotropic strains on the dielectric and pyroelectric properties of $Ba0.7Sr0.3TiO3$ thin films

A modified Landau-Devonshire phenomenological thermodynamic theory is used to describe the influence of in-plane anisotropic strains on the dielectric and pyroelectric properties of epitaxial $Ba0.7Sr0.3TiO3$ thin films grown on dissimilar tetragonal substrates. The in-plane anisotropic strain factor-temperature phase diagram is developed. The in-plane anisotropic strains play a crucial role in the dielectric and pyroelectric properties of BST thin films. The theoretical maximum dielectric tunability approaching 100% can be attained at the critical anisotropic strain factor corresponding to the structural phase transformation from $ca1$ to $a1$ phase. Moreover, the anisotropic strain factor has an opposite effect on the figure of merit and pyroelectric coefficient, respectively. Furthermore, in the case of isotropic strains, our theoretical results are well consistent with the experimental results.