Ferroelectric phase transitions and electromechanical properties of barium titanate and lead titanate crystals under uniaxial and shear stresses: A thermodynamic analysis

Ferroelectric phase transitions and electromechanical properties of BaTiO₃ (BT) and PbTiO₃ (PT) crystals under uniaxial and shear stresses are investigated using the Landau-Devonshire phenomenological approach. The results show that (1) the Curie temperature of BT and PT crystals increases with increasing stress; (2) at room temperature, no ferroelectric-ferroelectric phase transition is induced by uniaxial stress along the [1 0 0]_c direction for the PT crystal, while the orthorhombic phase is the ultimate stable state for BT and PT crystals under uniaxial stress along the [0 0 1]_c direction and shear stress; (3) shear stress induces a temperature-independent morphotropic phase boundary in tetragonal phase BT and PT crystals; (4) the dielectric and piezoelectric properties are closely related to the phase transition induced by external stresses, where nonlinearity is observed owing to higher order terms of free energy.