Influence of Zn²⁺ doping on the morphotropic phase boundary in lead‐free piezoelectric (1 – x)Na₁/₂Bi₁/₂TiO₃‐xBaTiO₃

A series of morphotropic phase boundary (MPB) compositions of (1–x)Na₁/₂Bi₁/₂TiO₃‐xBaTiO₃ (x = 0.05, 0.055, 0.06, 0.065, 0.07), with and without 0.5 mol% Zn‐doping was synthesized using the solid‐state route. The samples were characterized using X‐ray diffraction, dielectric analysis, and electromechanical measurements (piezoelectric d₃₃ coefficient, coupling factor kp, mechanical quality factor Qm, and internal bias field Ebias). The increase in the ferroelectric‐relaxor transition temperature upon Zn‐doping was accompanied by a shift of the MPB toward the Na₁/₂Bi₁/₂TiO₃‐rich side of the phase diagram. Higher tetragonal phase fraction and increased tetragonal distortion were noted for Zn‐doped (1 – x)Na₁/₂Bi₁/₂TiO₃‐xBaTiO₃. In addition, ferroelectric hardening and the presence of an internal bias field (Ebias) were observed for all doped compositions. The piezoelectric constant d₃₃ and the coupling coefficient kp decreased by up to ∼30%, while a 4‐ to 6‐fold increase in Qm was observed for the doped compositions. Apart from establishing a structure–property correlation, these results highlight the chemically induced shift of the phase diagram upon doping, which is a crucial factor in material selection for optimal performance and commercialization.