The development of piezoelectric ceramics characterized by both large piezoelectric response and high-temperature stability is imperative for the advancement of practical electromechanical devices. However, existing high-performance piezoelectric ceramics often encounter compromised temperature stability because ferroelectric phase transitions occur within low-temperature regions. In this work, we focused on Sm-doped Pb(Ni_1/3Nb_2/3)O₃–PbZrO₃–PbTiO₃ (PNN–PZT:Sm) ceramics with a tetragonal (T)-phase structure to achieve the desired combination of high piezoelectricity and high temperature stability. The results indicate that 2 mol% Sm-doped samples exhibit a large piezoelectric constant (d₃₃) of 575 pC/N, an effective piezoelectric strain coefficient (d₃₃^*) of 890 pm/V, and a high ferroelectric-to-paraelectric phase transition temperature (T_m) of 279 °C. Remarkably, d₃₃ experiences only a 2.6% variation over the temperature range of 30–250 °C, while d₃₃^* changes by 8% within the temperature range of 30–180 °C. Microstructural and domain structure analyses suggest that Sm-doping effectively reduces the grain size, leading to a decreased domain size, thereby achieving excellent electromechanical properties. The superior temperature stability is attributed to the suppressive effect of Sm-doping on the R–T ferroelectric phase transition. These studies suggest that Sm-doping represents an effective strategy for achieving the collaborative optimization of piezoelectricity and temperature stability through grain and domain engineering techniques for perovskite ferroelectric materials.

(K,Na)NbO₃ (KNN)-based piezoelectric materials are candidates for replacing Pb-based materials. However, the piezoelectric properties of existing KNN-based single crystals are still inferior to those of Pb-based relaxor ferroelectric single crystals. Moreover, the piezoelectric response mechanism of KNN-based single crystals remains unclear. In this study, (Li,K,Na)(Nb,Sb,Ta)O₃:Mn (KNNLST:Mn) single crystals with an excellent piezoelectric coefficient d₃₃ of approximately 778 pC/N were prepared. Systematically studies of intrinsic and extrinsic piezoelectric responses have revealed that the high d₃₃ of KNNLST:Mn single crystals is related to the shear piezoelectric response of a single-domain state and irreversible domain wall motion of the engineering domains. Furthermore, the effect of the orthorhombic (O)-tetragonal (T) phase boundary on intrinsic and extrinsic piezoelectric response is systematically studied, and the impact mechanism is elucidated. The results indicate that a lower dielectric response and elastic constant limit the intrinsic shear piezoelectric response of KNNLST:Mn single crystals, and approaching the O–T phase boundary can enhance both intrinsic and extrinsic piezoelectric responses. This study improves our understanding of the structure-performance relationship in KNNbased single crystals and offers insights for optimizing piezoelectric properties in KNN-based materials.