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.

MnO2-doped 0.985[Li0.04(Na0.545K0.46)0.96(Nb0.81Ta0.15Sb0.04)]O3+0.015KNbO3(0.985LNKNTS+0.015KNbO3)lead-free ceramics were fabricated by conventional solid state method to develop excellent dielectric andpiezoelectric properties. The result of X-ray diffraction patterns obviously indicated that all of thespecimen has pure perovskite structure without secondary phase. In addition, orthorhombic phase andcoexistance region of orthorhombic-tetragonal phase (MPB) were observed with amount of MnO2. Theoptimal values of ρ=4.70 g/cm3, d33=238 pC/N, kP=0.46, Qm=121, εr=849, and TC=225℃ were obtained at0.01 mol% MnO2 doped 0.985LNKNTS+0.015KNbO3 ceramics sintered at 990℃ for 5 h, respectively. Hence, it was indicated that the suitable amount of MnO2 could improve the electrical properties of0.985[Li0.04(Na0.545K0.46)0.96](Nb0.81Ta0.15Sb0.04)]O3+0.015KNbO3 ceramics.

[Li0.04(Na0.54K0.46)0.96](Nb1-0.04-XTaXSb0.04)O3 lead-free piezoelectric ceramics have been prepared by normal sintering at 1,100℃ for 5 h. X-ray diffraction analysis indicated that specimens demonstrate orthorhombic symmetry when Ta≤5 mol%. While transforming into tetragonal symmetry when x ≥ 20 mol%. These suggest that the orthorhombic and tetragonal phases co-exist in the ceramics with 5 mol% < Ta < 20 mol% at room temperature. All samples have high density, ranging from 4.46 to 4.79 g/cm3. As the result of SEM images, the grain growth was decreased with the increase of Ta substitution. The ceramics become ``softening``, leading to improvements in kp, ε r and d33, but a decrease in Qm. Excellent properties of kp= 0.46, d33= 293 pC/N, εr= 1,583 and Tc= 340℃ were obtained when Ta= 15 mol%

In this study, piezoelectric and dielectric properties of the (Na0.5K0.5)NbO3-(1-x)(Bi0.5Na0.5)TiO3- xBaTiO3 [NKN-(1-x)BNT-xBT] ceramics were investigated. The lead-free NKN-(1-x)BNT-xBT ceramics were fabricated by a conventional mixed oxide method. The results indicate that the addition of BaTiO3 significantly influences the sintering, microstructure, phase transition and electrical properties of NKN-BNT ceramics. A gradual change in the piezoelectric and dielectric properties was observed with the increase of BT contents. The dielectric constant, piezoelectric constant (d33) and electromechanical coupling factor (kp) increased at the morphotropic phase boundary (MPB). The d33=184 pC/N, kp=0.38, dielectric constant=1455 with dielectric loss value of less than 1% were obtained for the NKN-0.95BNT-0.05BT ceramics sintered at 1150℃ for 2h. These results demonstrate that the NKN-(1-x)BNT-xBT ceramics is an attractive candidate for lead-free piezoelectric materials.