Dielectric and piezoelectric properties in the BiScO₃-PbTiO ₃-PbO·SnO₂ ternary system

The effect of Sn substitution on the dielectric and piezoelectric properties of BiScO₃-PbTiO₃ was investigated in the ternary system, (1 - x){(1 - y)BiScO₃-yPbO·SnO ₂}-xPbTiO₃ (x = 0.43-0.63, y = 0.25-0.75). The ferroelectric phase transition temperature near morphotropic phase boundary (MPB) decreased with increasing Sn content from 450°C (x, y = 0.64, 0) down to ∼250°C for the composition with x, y = 0.46, 0.75. Piezoelectric activity (d₃₃ = 460-465 and k_p = 0.54) in Sn-substituted MPBs remained at similar levels to the pure 0.46BiScO₃-0.64PbTiO ₃ MPB, with Sn content of up to y = 0.5. However, further Sn-additions lead to decreased electromechanical performance and the formation of secondary phases such as SnO₂. Broad temperature dependence of the permittivity near the ferroelectric phase transition was assessed by a diffuseness parameter δ, which generally decreased with firing temperature in the range of 1050-1250°C. The temperature of the permittivity maximum (T_max) increased with measuring frequency, a characteristic consistent with relaxor ferroelectric materials.