The fluctuation of dielectric and piezoelectric properties and the DC poling field dependence of ferroelectric properties were investigated to intend for practical use and to evaluate the mechanism of domain alignment in lead-free ceramics of the forms of (l-x)(Na_(0.5)Bi_(0.5))TiO3-x(K_(0.5)Bi_(0.5))TiO3 (x=0.08-0.28) 0.79(Na_(0.5)Bi_(0.5))TiO3-0.20(K_(0.5)Bi_(0.5))TiO3-0.01Bi(Fe_(0.5)Ti_(0.5))O3 and (1-x)(Na_(0.5)Bi_(0.5))TiO3-xBaTiO3 (x=0.03-0.11). It was found that there were two kinds of fluctuation from the results to evaluate dielectric loss (tan8); one comes from chemical compositions and another is due to the manufacturing processes such as firing process. For the compositions for improvement of tan8, it was though that the substitution by (K_(0.5)Bi_(0.5))TiO3-Bi(Fe_(0.5)Ti_(0.5))O3 for (Na_(0.5)Bi_(0.5))TiO3, especially Bi(Fe_(0.5)Ti_(0.5))O3, played an important role in reducing tanS. In addition, tan8 could be improved by BaTiO3 substitution for (Na_(0.5)Bi_(0.5))TiO3 in the case of the small amount of up to x=0.11. For the manufacturing process, since there is a linear relation between tan8 and relative dielectric constant (ε_r), it was found that the firing process affects the fluctuation of tan8 in individual samples of the same firing lot. From DC poling field (E) dependence of ferroelectric properties, asymmetrical shapes in piezoelectric constants vs ±E caused by nonuniform mobility of domain alignment upon the application of positive and negative poling fields were observed in the small amount substitution by (K_(0.5)Bi_(0.5))TiO3 (x≤0.11) and BaTiO3 (x≤0.03). On the other hand, symmetrical shapes in piezoelectric constants vs ±E were observed in higher piezoelectricity with lower frequency constant accompanied with typical domain clamping. The effects to improve tanS by Bi(Fe_(0.5)Ti_(0.5))O3 and by BaTiO3 substitutions for (Na_(0.5)Bi_(0.5))TiO3 were also proved by the measurement of P-E hysteresis loops.
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