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-xBaTiO(3) (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 d(33) coefficient, coupling factor k(p), mechanical quality factor Q(m), and internal bias field E-bias). 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-xBaTiO(3). In addition, ferroelectric hardening and the presence of an internal bias field (E-bias) were observed for all doped compositions. The piezoelectric constant d(33) and the coupling coefficient k(p) decreased by up to similar to 30%, while a 4- to 6-fold increase in Q(m) 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.