Electrostrain Enhancement at Tricritical Point for BaTi_1−xHf_xO₃ Ceramics

The maximum electromechanical property of piezoelectric ceramic is normally achieved at morphotropic phase boundary. Herein, we found that a maximum electrostrain is obtained in single rhombohedral phase region at the tricritical point (which is a single rhombohedral phase at room temperature) for BaTi_1−xHf_xO₃ ceramics. The mechanism for electrostrain enhancement at tricritical point (TTP) was uncovered by analyzing its crystallographic feature. The results show that TTP (x = 0.11) exhibits largest electrostrain (S = 0.063%) at room temperature. And the TTP reveals a maximum crystallite size (66.3 nm) and minimum lattice strain (0.7 × 10⁻⁴). Further Raman results demonstrate a lowest Raman intensity occurs at TTP, which confirmed the specific crystallographic behavior. Therefore, a minimum lattice strain-induced low elastic energy could lower landau free energy, which is responsible for electrostrain enhancement at TTP. This work may provide a new insight for understanding and designing large electromechanical ceramics.