Preparation And Doping Modification Of BNT-based Lead-free Piezoelectric Ceramics

Bi_1/2Na_1/2TiO₃?BNT?–based lead-free piezoceramics have received extensive attention and considered to be a kind of promising environmental–friendly materials replacing for lead–containing materials using as piezoelectric actuators owing to their strong ferroelectricity and high strain. In this paper, complex ions, multiferroic materials and new component were selected as the dopants to dope BNT–based materials. All the samples were prepared by conventional solid-state reaction method. Moreover, the phase transition behavior at the MPB, and the relationship between the MPB composition, large piezoelectricity and high strain were disclosed. These works lay a theoretical and technical foundation for the high performance BNT–based lead–free piezoelectric ceramic materials. Several important conclusions can be summarized as follows:The effects of complex ions(Nd_1/2Ta_1/2)⁴⁺ and(Fe_1/2Nb_1/2)⁴⁺ doping BNT–based ceramics on phase structure and electrical properties were investigated. All the samples possessed pure perovskite structure regardless of doping(Nd_1/2Ta_1/2)⁴⁺ or(Fe_1/2Nb_1/2)⁴⁺. A reduction of small amount of oxygen vacancies, a significant effect in grain size due to the(Nd_1/2Ta_1/2)⁴⁺ doping, led to the enhancements of electrical properties of Bi_1/2Na_1/2Ti_1-x(Nd_1/2Ta_1/2)_xO₃ ceramics, and the optimized modification was x = 0.006. The electrical properties of modified samples were deteriorated with further doping?x ? 0.006?, owing to an increase in the concentration of oxygen vacancies. The BNT–NT ceramics with x = 0.006 was found to have a high remnant polarization?Pr? of 34.7 ?C/cm² and a piezoelectric constant(d₃₃) of 110 pC/N.(Bi_1/2Na_1/2)_0.935Ba_0.065Ti_1-x(Fe_1/2Nb_1/2)_xO₃ materials has a highest unipolar strain of 0.422% and corresponding normalized strain, d*33( = S_max/E_max) of 844 pm/V under an applied field of 50 kV/cm at x = 0.020. The highest strain originates from the coexistence of the ferroelectric and relaxor ferroelectric phase. It is observed that the unipolar strain of BNBT–0.02 FN is temperature insensitive and the d₃₃* maintains a high value of 600 pm/V at 90 oC.Multiferroic materials Sr₂ Zr MnO₆ and La₂CoMnO₆ were introduced into BNT–based system. Large normalized strain(d₃₃* = 597 pm/V) and high strain?0.388%? in(Bi_0.5Na_0.5)_0.935Ba_0.065TiO_3-xSr₂ZrMnO₆ materials were achieved at the composition of x = 0.0050. The grain shape and grain size strongly rest with the La₂CoMnO₆ content. The density and strain of this material have been enhanced by adding appropriate La₂CoMnO₆. Around critical composition?x = 0.005? at a driving field of 70 kV/cm, large unipolar strain of 0.22%(S_max/E_max = 328 pm/V) and high piezoelectric constant of 211 pC/N are obtained at room temperature. These results suggest that such a system is a promising lead-free candidate for electromechanical actuator applications.BNT-based materials doped with new solid solutions Al₆Bi₂O₁₂ and Sr₃FeNb₂O₉ to enhance their electrostrictive properties. Appropriate Al₆Bi₂O₁₂ doping into BNT–based ceramics induces the enhancement of piezoelectric and ferroelectric properties. Improved Pr = 32.8 ?C/cm², low E_c of 18.2 kV/cm, and high d₃₃ = 234 pC/N were observed at x = 0.005. Furthermore, electric field-induced strain was enhanced to its maximum value(S_max = 0.33%) with normalized strain(d₃₃* = S_max /E_max = 413 pm/V) at an applied electric field of 80 kV/cm for x = 0.010. Sr₃FeNb₂O₉ effectively diffused into the BNT–based system lattice to form a solid solution. A large EFIS of 0.35% was obtained at the critical composition of x = 0.009 which corresponds to a normalized strain(S_max/E_max) of 583 pm/V. A maximumvalue of piezoelectric constant?254 pC/N? was obtained for x = 0.006.