Piezoelectric materials, which convert mechanical energy into electrical signals, are widely used in various industrial applications such as sensors, actuators, and energy harvesting devices. This study aims to enhance the performance of Pb(Mg_1/3Nb_2/3)O₃-Pb(Al_1/2Nb_1/2)O₃-Pb(Zr_0.52Ti_0.48)O₃ (PMN-PAN-PZT) piezoelectric ceramics by investigating the effects of varying PAN and PMN content and adding Nb₂O₅ on their piezoelectric properties. The results show that with 2 mol% of PMN and PAN, the morphotropic phase boundary (MPB) region exhibits the highest piezoelectric properties. Additionally, excess Nb₂O₅ positively influenced the piezoelectric properties, maximizing electro-mechanical coupling factor (k_p=63%, d₃₃=440 pC/N). These findings contribute to developing next-generation high-performance piezoelectric materials, with potential for improved efficiency and performance in various industries.

Morphotropic phase boundary (MPB), which is a special boundary that separates two or multiple different phases in the phase diagram of some ferroelectric ceramics, is an important concept in identifying physics that includes piezoelectric responses. MPB, which had not been discovered in organic materials until recently, was discovered in poly(vinylidene fluoride-co- trifluoroethylene (P(VDF-TrFE)), resulting from a molecular approach. The piezoelectric coefficient of P(VDF-TrFE) in this MPB region was achieved up to -63.5 pC N^-1, which is about two times as large as the conventional value of -30 pC N^-1 of P(VDF-TrFE). An order-disorder arrangement greatly affects the rise of the piezoelectric effect and the ferroelectric, paraelectric and relaxor ferroelectric of P(VDF-TrFE), so the arrangement and shape of the polymer chain is important. In this review, we investigate the origin of negative longitudinal piezoelectric coefficients of piezoelectric polymers, which is definitely opposite to those of common piezoelectric ceramics. In addition to the mainly discussed issue about MPB behaviors of ferroelectric polymers, we also introduce the consideration about polymer chirality resulting in relaxor ferroelectric properties. When the physics of ferroelectric polymers is unveiled, we can improve the piezoelectric and pyroelectric properties of ferroelectric polymers and contribute to the development of next-generation sensor, energy, transducer and actuator applications.

The (Na0.52K0.44)(Nb0.9Sb0.06)O3-0.04dLiTaO3 (NKNS-LT) ceramics with various Cu2O concentration were prepared by the conventional solid state reaction method. The Cu2O content was varied in the range of 0.1~0.4 wt%. The effects of Cu on microstructure, crystallographic phase transition, and piezoelectric properties were investigated. The material with perovskite structure had a tetragonal phase (T1) when Cu2O concentration was less than 0.3 wt% and it transformed to another tetragonal phase (T2) when the Cu2O amount was greater than 0.3 wt%. The phase boundary between T1 and T2 phases appeared at around 0.3 wt% of Cu2O concentration. The piezoelectric properties were shown the maximum values at the composition of the phase boundary. The electro-mechanical coupling factor (kp) was 0.42 and the piezoelectric charge constant (d33) was 245 pC/N at the 0.3 wt% of Cu2O concentration.