DEVELOPMENT OF LEAD-FREE PIEZOELECTRIC CERAMIC MATERIALS

近年来，无铅压电材料作为替代压电材料的新型环保材料备受关注。在众多无铅压电材料中，钛酸铋钠、（Bi_<1/2>Na_<1/2>）TiO_3 [BNT]基铁电陶瓷将是较好的候选材料。在伪三组分体系a(Bi_<1/2>Na_<1/2>)TiO_3-b KnbO_3-c l/2（Bi_2O_3）中，通过测定不同Bi <3+>离子改性量的增加或减少，研究了Bi <3+>离子改性量对bnt基固溶体介电、压电和铁电性能的影响。Sc_2O_3) (a +b +c =1) [KTNS (lOOa /lOOb /lOOc)]是一类新型无铅压电陶瓷。在KTNS （lOOa/lOOb/lOOc）体系中，加入l/2（Bi_2O_3）可以提高Bi^<3+>离子的含量。在a +b +c = 1的条件下，加入一定量的KnbO_3（增加b值）后，Sc_2O_3（增加c值）含量降低。压电测量结果表明，靠近BNT侧的KTNS陶瓷具有较高的机电耦合系数，k_<33>(=0.47)。其中，Bi^<3+>离子的改性量对k_<33>有影响。这些陶瓷似乎是无铅压电陶瓷的候选材料。为了获得较高的机电耦合系数k，减小矫顽力场E_c是很重要的。特别地，可以清楚地看到，修正的Bi^<3+>离子的数量对E_c有影响。随着Bi^<3+>离子修饰量的增加，E_c增大，极化困难，k_<33>相对较低。另一方面，当改性Bi^<3+>离子的数量减少时，E_c变低，易于极化，k_<33>相对较高。

Recently, lead-free piezoelectric materials have been attracting attention as new materials in place of PZT materials for environments. Among of many lead-free piezoelectric materials, bismuth sodium titanate, (Bi_<1/2>Na_<1/2>)TiO_3 [BNT]-based ferroelectric ceramics will be a superior candidate. In this research, the effects of the amount of modified Bi^<3+> ions on dielectric, piezoelectric and ferroelectric properties for the BNT-based solid solution were studied by measuring on various compositions with increasing or decreasing amount of modified Bi^<3+> ions in a pseudo-three-component system, a(Bi_<1/2>Na_<1/2>)TiO_3-b KnbO_3-c l/2(Bi_2O_3. Sc_2O_3) (a +b +c =1) [KTNS (lOOa /lOOb /lOOc)] as a new group of lead-free piezoelectric ceramics. In the KTNS (lOOa/lOOb/lOOc) system, Bi^<3+> ion content can be increased by adding an amount of l/2(Bi_2O_3. Sc_2O_3) (increasing c value) and decreased by adding an amount of KnbO_3 (increasing b value) under the condition of a +b +c = 1.Piezoelectric measurements show that the KTNS ceramics near the BNT side have a relatively high electromechanical coupling factor, k_<33> (=0.47). On particular, the amount of modified Bi^<3+> ions has an effect on k_<33>. These ceramics seem to be a candidate for lead-free piezoelectric ceramics. To attain a high electromechanical coupling factor, k, it is important to decrease the coercive field, E_c. In particular, it is clear that the amount of modified Bi^<3+> ions has an effect on E_c. When the amount of modified Bi^<3+> ions is increased, E_c becomes higher, making poling difficult and the k_<33> is the relatively low. On the other hand, when the amount of modified Bi^<3+> ions is decreased, the E_c becomes lower, making poling easy and the k_<33> is the relatively high.