A correlation between piezoelectric response and crystallographic structural parameter observed in lead-free (1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 piezoelectrics

The structure of lead-free (1-x)(Bi0.5Na0.5)TiO3-xSrTiO3 (BNT-STx) ceramics was analyzed by the Rietveld method, using X-ray diffraction and neutron scattering data. The structural refinement results suggest that the crystal structure successively changes with SrTiO3 concentration, x, from the rhombohedral phase (x = 0.00) to rhombohedral and tetragonal (x = 0.10-0.30), tetragonal and cubic (x = 0.40-0.60), and finally cubic (x = 0.80-1.00) phases. Correlation between the charge sensor constant (d33) and the weighted off-center value (dw) was observed, which may be attributed to the increased dipole motion in the unit cell due to an increased tendency to respond to external stimulation. Furthermore, an improved charge sensor constant (d33) of 140 pC/N was observed for BNT-ST0.20, and a large strain of 0.25% and a d33* value of 443 pm/V were observed from x = 0.30.