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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. (Some figures may appear in colour only in the online journal) [ABSTRACT FROM AUTHOR]

The effects of hydrostatic and one-dimensional (1D) compression pressure on the phase transition of perovskite ferroelectric crystal were comparably investigated via the measurement of polarization Pr with respect to applied pressure and the Landau–Devonshire (LD) phenomenological approach. The results showed that hydrostatic pressure can induce ferroelectric-to-paraelectric phase transition, while 1D compression can stablize the ferroelectric phase. This phenomenon was very different from the phase transitions of metal crystals, such as iron. In the framework of LD phenomenological theory, this phenomenon is believed to be associated with the strong anisotropy and electromechanical coupling which exists in ferroelectrics under high pressure. On the other hand, the piezoelectric stress coefficient e31 and piezoelectric strain coefficient dh for PIN-PMN-PT crystal were obtained as  −2.9 C m−2 and 80 pC N−1, respectively. [ABSTRACT FROM AUTHOR]