Theoretical and Experimental Study of (Ba,Sr)TiO3 Perovskite Solid Solutions and BaTiO3/SrTiO3 Heterostructures

The results of experimental and theoretical ab initio study of structural and piezoelectric properties of (Ba,Sr)TiO ₃ perovskite solid solutions are discussed and compared. Experimentally, plate-like (Ba,Sr)TiO ₃ particles were synthesized by the topochemical conversion in the molten salt from Bi ₄ Ti ₃ O ₁₂ template plates. All dimensions (side length ≈1 μm, thickness ≈200-400 nm) were well above the critical size necessary for observation of piezo- and ferroelectricity. The first-principles computations of the structural and electromechanical properties of solid solutions were performed with the CRYSTAL14 computer code within the linear combination of atomic orbitals approximation, using three advanced hybrid functionals of density functional theory. Different chemical compositions are considered for the ferroelectric and paraelectric phases. The calculated structural properties of solid solutions in tetragonal and cubic phases are in very good agreement with experimental data. Experimentally obtained and calculated band gaps are compared for cubic SrTiO ₃ and tetragonal BaTiO ₃ . BaTiO ₃ /SrTiO ₃ heterostructures were considered theoretically for different chemical compositions. The calculated piezoelectric properties of solid solutions and heterostructures in the ferroelectric phase are compared. It is predicted that both solid solutions and heterostructures improve the piezoelectric properties of bulk BaTiO ₃ , but solid solutions are more preferable for equal Sr concentrations.