Piezoelectric Properties in the Perovskite BiScO₃–PbTiO₃–(Ba,Sr)TiO₃ Ternary System

A new ternary system (1-x)BiScO₃–x{(1-y)PbTiO₃–y(Ba_0.294Sr_0.706)TiO₃} was studied in relation to morphotropic phase boundaries (MPB). Analogous to modified PZT ceramics, barium and strontium were introduced to the recently developed MPB (1-x)BiScO₃–xPbTiO₃ for x>0.60, in order to investigate Curie temperature and piezoelectric property variations. With increasing barium and strontium substitution up to y=0.3, the MPB line moved from x=0.64 to 0.70 and d₃₃ and k_p gradually decreased. X-ray diffraction phase analysis correlated the variations in piezoelectric properties showing a maximum in the compositions near rhombohedral–tetragonal phase boundary. Grain sizes were around 2 µm for all compositions and tetragonality decreased with the downward shifting of T_c in the range of 216–371°C. The frequency dependence of dielectric properties about the Curie maximum shows a dispersion in both ε' and tan δ. This relaxation behavior becomes more pronounced with increasing (Ba,Sr)TiO₃ content, and high Curie maximum temperatures T_max's are found compared to lead based perovskites with complex B-sites.