Stress effects on ferroelectric and fatigue properties of Nd- and La-doped Bi4Ti3O12 thin films

The ferroelectric properties of ${\mathrm{Bi}}_{3.15}{\mathrm{Nd}}_{0.85}{\mathrm{Ti}}_3{\mathrm{O}}_{12}$ and ${\mathrm{Bi}}_{3.25}{\mathrm{La}}_{0.75}{\mathrm{Ti}}_3{\mathrm{O}}_{12}$ thin films under applied uniaxial stress were investigated. It was observed in both films that the remnant polarization $\left(P_r\right)$ increased with tensile stress, while it decreased with compressive stress. On the contrary, the coercive field $\left(E_c\right)$ decreased with the stress changing from maximum compression to maximum tension. Fatigue behavior of the films was improved under either compressive or tensile stress compared with zero stress (free state). These results can be well explained in the scenario of domain reorientation under stress; however, the polarization-strain coupling mechanism could not be simply ruled out.