Impact of Ba²⁺ on Structure and Piezoelectric Properties of PMN–PZN–PNN–PT Ceramics Near the Morphotropic Phase Boundary

The effect of using Ba²⁺ to modify the structure and dielectric and piezoelectric properties of Pb_(1−x)Ba_x(Mg_1/3Nb_2/3)_m(Zn_1/3Nb_2/3)_y(Ni_1/3Nb_2/3)_nTi_zO₃(x = 0–0.15) ceramics near the morphotropic phase boundary has been investigated. It is found that increasing the content of Ba²⁺ leads to a sequence of structural transformations from heterophase state (tetragonal and pseudocubic phases) to a cubic state via an intermediate pseudocubic phase. The evolution of the dielectric and piezoelectric properties (sequences of transformations: normal ferroelectric →relaxor ferroelectric → paraelectric) is shown. It is stated that ceramics with x = 0.025–0.050 possess the optimal combination of functional parameters for use in low‐frequency receivers and actuators. They are characterized by high values of small‐signal and large‐signal piezoelectric coefficients d₃₃ of 621 pC/N and ~1500 m/V (at E = 5 kV/cm), respectively, and also by increased values of dielectric permittivity ε/ε₀ and tunability coefficient (К = [(ε/ε₀(E = 0) − ε/ε₀(E≠0))/ε/ε₀(E = 0)]·100%), equal to ~7000 and ~80%, respectively (at E = 20 kV/cm). It is shown that for the creation of high‐power piezoelectric transducers it is necessary to use ceramics with x = 0.125, which differs with high values of the mechanical quality factor Q_m and ε/ε₀ (1406 and 10 890, respectively).