镧掺杂PMN-PT陶瓷在准同型相界处的相组成调控

采用两步预烧工艺制备Pb_{0.962 5}La_0.025(Mg_1/3Nb_2/3)_1-zTi_zO₃(z=0.28、0.29、0.30、0.31)陶瓷,其准同型相界(MPB)的化学组成位于PbTiO₃含量为0.29 mol和0.30 mol附近。选取准同型相界两侧的化学组成,制备四方晶相Pb(Mg_1/3Nb_2/3)_0.66Ti_0.34O₃和三方晶相Pb_1-1.5xLa_x(Mg_1/3Nb_2/3)_1-yTi_yO₃(x=0.083 3~0.041 7,y=0.206 7~0.273 3)陶瓷粉体。将两种晶相粉体按照设计比例(三方晶相摩尔分数w=0.3、0.4、0.5、0.6)混合,干压成型,烧结成化学组成相同、晶相占比不同的Pb_{0.962 5}La_0.025(Mg_1/3Nb_2/3)_0.70Ti_0.30O₃陶瓷。研究了晶相组成对陶瓷压电性能、介电性能、铁电性能的影响。结果表明,高温烧结后,陶瓷中的三方晶相和四方晶相占比与配料比基本一致。当w=0.5时,1 250 ℃烧结陶瓷中三方晶相与四方晶相含量占比分别为0.47、0.53,晶粒平均尺寸为(5.24±0.23) μm,相对密度为96.76%。陶瓷的压电应变常数d₃₃、径向机电转换系数k_p、厚度机电转换系数k_t、相对介电常数ε_r、剩余极化强度P_r和场致应变系数S(1 Hz、3.5 kV/mm)分别为1 014 pC/N、0.67、0.64、10 955、24 μC/cm²和0.21%。该方法可人为调控化学组成位于准同型相界的陶瓷的晶相占比。

Phase Composition Tuning of Lanthanum-Doped PMN-PT Ceramics at Morphotropic Phase Boundary

The Pb_{0.962 5}La_0.025(Mg_1/3Nb_2/3)_1-zTi_zO₃ (z=0.28, 0.29, 0.30, 0.31) piezoelectric ceramics were synthesized by two-step pre-sintering process. The morphotropic phase boundary (MPB) of ceramics was found at 0.29 mol and 0.30 mol of PbTiO₃.Selecting the chemical composition on both sides of morphotropic phase boundary, and the tetragonal phase Pb(Mg_1/3Nb_2/3)_0.66Ti_0.34O₃ powder and rhombohedral phase Pb_1-1.5xLa_x(Mg_1/3Nb_2/3)_1-yTi_yO₃ (x=0.083 3~0.041 7, y=0.206 7~0.273 3) powder rhombohedral phase were prepared, respectively. Two crystal phase powders (rhombohedral phase mole fraction w=0.3, 0.4, 0.5, 0.6) were mixed and pressed into disks. The ceramics with the same chemical compositionand different crystal phase proportion of Pb_{0.962 5}La_0.025(Mg_1/3Nb_2/3)_0.70Ti_0.30O₃ were sintered. The effect of crystal phase ratio on the piezoelectric, dielectric, and ferroelectric properties of ceramics were investigated. The results show that the rhombohedral and tetragonal phase ratios of ceramics are pasically the same as the proportion of ingredients. For the sample with w=0.5, the rhombohedral and tetragonal phase ratios of ceramics sintered at 1 250 ℃ is about 0.47, 0.53, respectly. The average grain size is (5.24±0.23) μm. The relative density of ceramics is 96.76%. The piezoelectric constant d₃₃, planner electromechanical coefficient k_p, thickness electromechanical coefficient k_t, relative permittivity ε_r, remnant polarization P_r, and field-induced strain S (1 Hz, 3.5 kV/mm) of ceramics are 1 014 pC/N, 0.67, 0.64, 10 955, 24 μC/cm², and 0.21%, respectively. For the chemical composition near MPB, the rhombohedral and tetragonal phase ratios of ceramics could be tuned artificially via this method.