Li/Ce/La共掺杂对CaBi_2Nb_2O_9陶瓷晶体结构及电学性能的影响

Li/Ce/La Multidoping on Crystal Structure and Electric Properties of CaBi_2Nb_2O_9 Piezoceramics

采用固相反应法制备(Li_(0.5)Ce_(0.25)La_(0.25))_xCa_(1-x)Bi_2Nb_2O_9铋层状结构压电陶瓷,分析多元稀土元素掺杂对CaBi_2Nb_2O_9(CBN)陶瓷晶体结构、微观形貌及电学性能的影响。Rietveld结构精修表明,多元稀土元素进入晶格内部形成固溶体,掺杂使晶体结构有由斜方晶系向四方晶系转变的趋势,反位缺陷中A位的Bi^(3+)具备6s2孤对电子,抑制这种变化趋势。SEM照片显示,掺杂主要抑制晶粒沿垂直c轴平面生长,这是由于稀土氧化物具备较高的熔点,在烧结过程中不易扩散。准同型相界附近,垂直b轴方向的a滑移面被打破,极化方向沿a轴和b轴,导致压电性能增强。其中,(Li_(0.5)Ce_(0.25)La_(0.25))_(0.17)Ca_(0.83)Bi_2Nb_2O_9陶瓷具备最优异的性能:居里温度为913℃,压电系数高达16.4 pC/N;经850℃退火2 h,其d33值为14.0 pC/N,约为原始值的85.4%。

(Li0.5Ce0.25La0.25)xCa1-xBi2Nb2O9 Aurivillius phase ceramics were prepared via conventional solid-state sintering route. The effects of co-substitution with different types of rare-earth elements on crystal structure, microstructure and electric properties were investigated. Rietveld-refinement analysis showed that the multiple rare earth elements embedded into the lattice point and formed corresponding solid solutions. The crystal structure tended to transform to tetragonal system from pristine orthorhombic system, whereas Bi3+ in A-site with 6s2 lone pair electrons suppressed this change. SEM images exhibited that the grain growth in the direction perpendicular to the c-axis was restrained, which could be attributed to the rare earth oxides' high melting point and low diffusion during the sintering process. Morphotropic phase boundary of a glide plane between orthorhombic system and pseudo-tetragonal system vanished, which generated spontaneous polarization along a and b axis and resulted in increase of piezoelectric properties. The obtained (Li0.5Ce0.25La0.25)0.17Ca0.83Bi2Nb2O9 ceramics performed optimal piezoelectric properties (d33=16.4 pC/N, Tc=913 ℃) and exhibited excellent thermal stability, remaining 85.4% of their initial d33 values after annealing at 850 ℃ for 2 h. All above results demonsrated that the multidoped materials are promising candidates for ultrahigh temperature applications.