Design of lead-free piezoelectric ceramics via domain control and its application to actuator

含铅压电材料PbTiO3、PbTiO3、PbTiO3等被广泛用作传感器和执行器。这些压电体虽然具有高性能，但因含铅而造成严重的环境污染。开发性能优良的无铅压电材料已被实际应用所催促。与PZT类似，(Na，K)NbO_3是铁电体(KNbO_3)和反铁电体(NaNbO_3)的混合物，具有很高的介电/压电性能。因此，(Na，K)NbO_3基固溶体具有与(Na，K)NbO_3相同的钙钛矿结构，并且它们之间可以形成完全的固溶体。采用放电等离子烧结法，克服了材料烧结性差的缺点，获得了相对密度大于96%的样品。雅高…根据介电常数的测量结果，建立了各固溶体的相图。结果表明，对于(1-x)(Na，K)NbO_3-xA_2O_3(A=Ba，Sr，Ca)固溶体，立方-四方相(C-T)、四方-正交相(T-O)和三方相变温度(T-O)随x的增加而迅速降低，其中T-O相变温度(t&lt；c2&gt；)的下降幅度大于C-T相变温度(t&lt；c1&gt；)。此外，t&lt；c2&gt；只是x的函数，几乎与a无关。因此，在x~0.05处存在一个普适的T/O同态相界。机电耦合系数k_p和压电常数d_t；33&gt；在x~0.05附近达到最大值。结果表明，(Na，K)NbO_3基固溶体中压电性能提高的机制是在x~0.05处形成的T/O MPB。所研制的无铅压电材料的最高性能为：k_p~43%，d_t；33&gt；~220pc/N(A=Ba，Ca，x=0.05)。为了验证所研制的无铅压电材料是否可以应用于驱动器，用0.95(K_&lt；0.5&gt；Na_&lt；0.5&gt；)NbO_3-0.05BaTiO_3材料制作了双压电驱动器。结果表明，执行器相对于直流电压的位移和谐振频率与理论值吻合较好。较少

Lead-containing piezoelectrics PbTiO_3, Pb(Zr,Ti)O_3 and so on have been widely used as sensors and actuators. Though these piezoelectrics possess high performance, they also cause serious environmental pollution due to lead containing. To develop lead-free piezoelectrics with superior properties has been urged by the practical usage. Similar to PZT, (Na,K)NbO_3 is a combination of a ferroelectric (KNbO_3) and an antiferroelectric (NaNbO_3), and has been reported to possess high dielectric/piezoelectric properties. Thus, it is anticipated that the (Na,K)NbO_3-based solid solutions would show excellent piezoelectricity.Barium titanate (BaTiO_3), strontium titanate (SrTiO_3), and calcium titanate (CaTiO_3) have the same perovskite structure as (Na,K)NbO_3 and a complete solid solution can be formed between them. By using the Spark-Plasma-Sintering method, the poor sinterability of the materials has been overcome, and samples with relative density higher than 96% have been obtained. Accor … More ding to the dielectric constant measurement results, a phase diagram is established for each solid solution. It is found that, for (1-x)(Na,K)NbO_3-xA TiO_3 (A=Ba, Sr, and Ca) solid solution, the cubic-tetragonal (C-T), the tetragonal- orthorhombic (T-O), and the orthorhombic-rhombohedra phase transition temperatures rapidly decrease with increasing x. The T-O phase transition temperature (t_<c2>) decreases more sharply than the C-T phase transition temperature (t_<c1>) does. Moreover, t_<c2> is only a function of x and almost independent of A. Therefore, there exists a universal T/O morphotropic phase boundary (MPB) at x〜0.05. The electromechanical coupling coefficients k_p and the piezoelectric constant d_<33> maximize at around x〜0.05. It is suggested that the mechanism responsible for the enhanced piezoelectric properties in the (Na,K)NbO_3-based solid solutions is the T/O MPB formation at x〜0.05. The highest performance for the developed piezoelectrics is k_p〜43% and d_<33>〜220pC/N (A=Ba, Ca and x=0.05).To verify if the developed lead-free piezoelectrics could be applied to actuator, a bimorph type actuator has been manufactured using the 0.95(K_<0.5>Na_<0.5>)NbO_3-0.05BaTiO_3 composition. It is found that the displacement of the actuator against DC voltage and the resonance frequency correspond well to the theoretical value. Less