Effect of uniaxial stress on phase transitions and dielectric properties of potassium niobate ferroelectric single crystal

The uniaxial compression stress dependence of the phase transitions and dielectric properties of a potassium niobate (KNbO3) ferroelectric crystal were investigated using Landau-Ginsburg-Devonshire phenomenological theory. The results showed that (1) uniaxial stress along [001](c) could induce a spontaneous polarization change from the [001](c) direction to the [010](c) or [100](c) directions and from the [011](c), [101](c) directions to the [110](c) direction; (2) the cubic to tetragonal and the tetragonal to orthorhombic phase transition temperatures increased, while the orthorhombic to rhombohedral phase transition temperature decreased as the uniaxial stress was increased; and (3) spontaneous polarization increased as the uniaxial stress was increased for the tetragonal and orthorhombic phases. The uniaxial stress dependence of the dielectric susceptibility also showed that a flatter Gibbs free energy profile corresponds with a greater expandability, contractibility, and rotationality of the polarization (which indicates a higher dielectric susceptibility), while a steeper Gibbs free energy profile corresponds with a reduced expandability, contractibility, and rotation of the polarization (which indicates a lower dielectric susceptibility).