Effect of in-plane strain anisotropy on (011) epitaxial BaTiO3 and PbTiO3 thin films

Misfit strain phase diagrams of single-domain (011) epitaxial BaTiO3 and PbTiO3 thin films are computed using a thermodynamic phenomenological approach. In the case of (001) epitaxial films, the two orthogonal in-plane misfit strains are equivalent. For (011) epitaxial films, however, the two substrate constraints exert quantitatively different influences due to crystal anisotropy. Effects of preferential strain relaxation and arbitrary in-plane strains are investigated, and similarity and contrast of BaTiO3 and PbTiO3 phase diagrams are revealed. Impact of anisotropy of in-plane constraint on polarization, dielectric and piezoelectric properties is explored, and the calculated structural transitions and out-of-plane lattice strain are compared with relevant theoretical and experimental data reported in the literature.