Study On Property Improvement Of Bismuth Layered Structure Lead-free Piezoelectric Ceramics By Ionic Substitution

Bismuth layered-structure lead-free piezoelectric ceramics materials possess higher Curie temperature and favorable anti-fatigue performance, therefore, they have extensive application prospect in high-temperature piezoelectric and ferroelectric memory. As for the shortcoming that single bismuth layered materials have difficulty in practical utilization, this paper adopted solid solution and ionic substitution to improve the electrical properties of the materials, and did some research on the relation among material structure properties, dielectric properties, ferroelectric and piezoelectric properties, which provided guiding significance for preparing ferroelectric materials with high-performance and practicality.This paper adopted conventional ceramic fabrication process and successfully prepared the ceramic system of (SrBi₂Ta₂O₉)_x(Bi₃TiTaO₉)_1-x. This system formed a single orthogonal crystal system with bismuth layer-structure, the more introduction of SBT, the bigger sizes of grain and the more highly improved of crystallinity, meanwhile, the grain size trends to be consistent. When x=0.6mol, the ceramics has =131.6516,tan =0.01273, showing excellent dielectric properties at room temperature. Because of the crystal ionic radius of A position increase and ionic polarization decrease, the Curie temperature of ceramics decreased with the increasing content of SBT(x=0.6,Tc=450℃).For the first time, (BaTiO₃)_x(SrBi₂Ta₂O₉)_1-x(0.05≤x≤0.3) ceramics have been prepared by solid solution with bismuth layer structure and perovskite structure. When x≤0.2, a single phase of bismuth layered-structure was obtained, but when x=0.3, the tetragonal phase was formed. The ceramic samples formed solid solution with bismuth layer structure and perovskite structure coexistence by SEM. The has litter relation with frequence in 1 kHz¹00 kHz and the tan was less than 6.0×10^-3. All samples possessed the characteristic of diffuse phase transition, frequency dispersion and large degree of diffuseness , showing that the ceramics are typically relaxor ferroelectrics.With the content of BT increase, the Curie temperature of ceramic samples was up to 650℃, which are much higher than the Curie temperature of BT(T_c=130℃)and SBT(T_c=335℃).When x=0.1mol, the ceramics has =200, tan =0.00376,d₃₃=12pC/N at room temperature,showing excellent integrated properties.The method of ionic substitution was also adopted in this article. The Ca²⁺, in A position of CaBi₄Ti₄O₁₅, was substituted by Ba²⁺ that in the same main group.And the formed system of Ca_1-xBa_xBi₄Ti₄O₁₅ was a four-layer bismuth layer-structure.With the substitution increase, the degree of orthogonal distortion and the Curie temperature of ceramic samples decreased, meanwhile the dielectric and ferroelectric properties were improved.The Na⁺, in A position of Na_0.5Bi_4.5Ti₄O₁₅, is substituted by K⁺ which in the same main group, all the samples formed the single bismuth layered-structure, with the increasing content of K⁺, the lattice distortion was enlarged and the crystallinity was improved. Due to the easy volatilization during sintering process, the vacancies of K and Bi in reactant ratio were increased, which prevent Curie temperature varies with the content of K+, all the four samples were at 660℃. The dielectric loss peaks appeared a relaxation peak at low temperature , according to the Arrhenius equation fitting,the relaxation process was caused by the thermal motion of oxygen vacancies.