| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2005: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 2004: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
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
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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
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