Study On Preparation, Structure And Electric Properties Of NBT-based Lead-free Piezoelectric Ceramics

Bismuth Sodium Titanate (Na_0.5Bi_0.5)TiO₃ (abbreviated NBT) is a A-site complex perovskite-structure ferroelectric material, which is considered as one of the most promising lead-free piezoelectric materials that instead of lead electric ceramic materials. The phase transitions of NBT have a more complex sequence, and its phase transition is argumentative. In this thesis, NBT-based binary system, ternary system and the quaternary system of ceramic materials were prepared by the solid state reaction method. The phase transition process and application of NBT were discussed by phase structure and microstructure test and the electrical properties of materials.In the studied range, Na_0.5Bi_0.5TiO₃-xSrTiO₃ and Na_0.5Bi_0.5TiO₃-xCaTiO₃ ceramics were formed of a single perovskite structure.The introduction of SrTiO₃ can effectively refine the grain, while add CaTiO₃ will promote the sintering of ceramics. By the dielectric temperature characteristic curve and hysteresis loop of NBT-xST and NBT-xCT ceramics, the phase change of NBT material was proved to Rhombohedral ferroelectric phas-Orthogonal antiferroelectric phase-tetragonal paraelectric Phase.By calculating the frequency dispersion parameterΔT₁ and diffuse phase transition parameterΔT₂ of the low-temperature dielectric temperature characteristic curve of NBT-xCT ceramics, CaTiO₃ increase could enhance the relaxation properties.(1-x) (0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃)-xLiNbO₃ lead-free piezoelectric ceramics were prepared by the traditional electronic ceramic processing. The phase structure, microstructure, ferroelectric and dielectric properties were investigated. X-ray diffraction patterns indicated that all ceramics samples (0.02≤x≤0.08) formed stable rhombohedral perovskite structure. With the increasing of LiNbO3 amount, the coercive field declined obviously from 4.41KV·mm^-1 to 1.51KV·mm^-1. At the same time, the ferroelectric–antiferroelectric transition temperature moved significant form high temperature to low temperature and antiferroelectric–paraelectric transition peak was repressed obviously.BiFeO₃ was introduced to formation a quaternary solid solution compound with the morphotropic phase boundary of 0.7Na_0.5Bi_0.5TiO₃-0.2K_0.5Bi_0.5TiO₃-0.1Li_0.5Bi_0.5TiO₃ based and 0.852Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃-0.028Li_0.5Bi_0.5TiO₃ based ceramics. Within the experimental range, adding BiFeO3 could not change the phase structure of matrix materials, and could make the material easy to sintering by the grain size increased.With oxygen vacancieing, grain size and strong piezoelectric effect of Bi mechanism, the dielectric constantε_r of NBT-KBT-BT-xBF ceramics reduced and the hysteresis loop becomed plump gradually. The piezoelectric constant d33 andε_r of NBT-KBT-LBT-xBF ceramicsincreased firstly and then decreased.When x=0.05mol%, the maximum of d33 was 84pC / N,ε_r =3178.5, Tm= 376℃, tanδ= 0.04, showing a good overall performance.