Abstract
Recently it was found that in the lead-free (1-x)BaZr0.2Ti0.8O3-xBa0.7Ca0.3TiO3 (BZT-xBCT) system, the highest piezoelectric d33 coefficient appears at the tetragonal (T) – orthorhombic (O) phase boundary rather than the O – rhombohedral (R) phase boundary, but the physical origin of it is still unclear. In this work we construct the phase diagram of the BZT-xBCT system using a generic sixth-order Landau free energy polynomial and calculate the energy barrier (EB) for direct domain switching between two variants of the stable low-symmetry ferroelectric phase. We find that the EB at the T-O phase boundary is lower than that at the O-R phase boundary and EB may serve as a rigorous quantitative measure of the degree of polarization anisotropy through Landau potential. The calculations may shed some light on the physical origin of the highest piezoelectric coefficients as well as the softest elastic compliance at the T-O phase boundary observed in experiments.
Highlights
Using a generic six-order Landau free energy polynomial we show that the energy barriers (EBs) is the smallest and so is the polarization anisotropy at the T-O phase boundary
At composition C1 that is in the R phase field and away from the R-O phase boundary, the energy surface has minima located along the C directions and maxima located along the C directions, as shown in Fig. 2(a) for C1
A generic sixth-order Landau free energy polynomial is formulated for BZT-xBCT and the phase diagram constructed agrees well with the experimentally measured one
Summary
In this work we construct the phase diagram of the BZT-xBCT system using a generic sixth-order Landau free energy polynomial and calculate the energy barrier (EB) for direct domain switching between two variants of the stable low-symmetry ferroelectric phase.
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