The LGD energy of three ferroelectric phases as a function of temperature. The black squares represent the energy values based on and from the previous work (Ref. 11).
Polarization vs temperature in the single domain, where , in the tetragonal phase, in the orthorhombic phase, and in the rhombohedral phase.
Dielectric constants vs temperature in the single crystal. is along the polarization direction and and are along the two directions orthogonal to the polarization direction. For the tetragonal phase, . For the orthorhombic and rhombohedral phases, is along the  and  polarization directions. The squares represent the experimental values and the solid lines represent the calculated values by the thermodynamic free energy.
Spontaneous strain as a function of the temperature in .
Lattice constant vs temperature in the single crystal. The squares represent experimental values from Ref. 40. The solid lines represent calculated values through the present free energy. The dashed line represents pseudocubic lattice .
Phase diagram as a function of transition temperature and applied pressure for .
Dependence of the dielectric constant of on hydrostatic pressure at different temperatures.
Dependence of the dielectric constant on temperature under different hydrostatic pressures.
Piezoelectric coefficients vs applied electric field , , and , respectively, at room temperature.
The thermodynamic parameters used for fitting the LGD energy expansion coefficients.
The fitted LGD energy expansion coefficients for single crystal.
The values of polarization and dielectric constant for at room temperature .
Entropy and latent heat changes of at three ferroelectric phase transition points.
Piezoelectric coefficients under the applied electric field at room temperature .
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