Effect of mechanical stress on phase stability and polarization states in ferroelectric barium titanate and lead titanate

The effect of normal and shear stress on phase transitions in BaTiO₃ and PbTiO₃ has been investigated using a modified Landau–Ginzburg–Devonshire phenomenological model based on assumption of constant stress boundary conditions. Stress–temperature phase diagrams have been developed, and the influence of stress on polarization stability has been analyzed. The results show monoclinic phases with various polarization states absent in stress-free BaTiO₃ may exist under uniaxial, biaxial, anisotropic three-dimensional, and shear stress conditions. For PbTiO₃, our calculations show that, under normal stress new phases cannot be generated and the only stable ferroelectric phase has tetragonal symmetry, but under shear stress orthorhombic, rhombohedral, and monoclinic phases can be stabilized.