Phase transition behavior and mechanical properties of (1-x)(Bi1/2Na1/2)TiO3-xSrTiO3 lead-free piezoelectric ceramics

- A ferroelectric to ergodic relaxor phase transition occurred with increasing ST concentration of the BNST ceramics.
- The BNST with 25 mol% ST showed the highest strain due to the electric-field-induced phase transition from ergodic relaxor to ferroelectric phase.
- The elastic compliance values of the BNST ceramics gradually decreased with increasing ST concentration.
- All tensors of elastic compliance values of BNST ceramics are almost half of those of commercial PZT-based ceramics.

Lead-free (1-x)(Bi1/2Na1/2)TiO3-xSrTiO3 (BNST, 0 ≤ x ≤ 0.25) ceramics were prepared by a conventional solid-state reaction. The effect of increasing the concentration of SrTiO3 (ST) on the phase transition behavior was investigated using x-ray diffraction patterns, field-induced polarization, and strain curves. As the ST concentrations increased, a ferroelectric to ergodic relaxor phase transition occurred. At x = 0.25, the highest strain was observed despite the piezoelectric charge constant being the lowest, and the ferroelectric and ergodic relaxor phases seemed to coexist. In order to investigate the mechanical properties of BNST ceramics, the resonance and antiresonance frequencies of various vibration modes were obtained, and the various tensors of elastic compliances were subsequently calculated. Because the resonance and antiresonance frequencies of the ergodic relaxor piezoceramics cannot be easily identified due to the absence of a remanent polarization and strain after the removal of the electric field, some tensors of elastic compliance of BNST with x = 0.25 were obtained by extrapolation of the compliance variation as a function of ST concentrations.