Structural Characterization of Na0.5K0.5NbO3 Ceramic Particles Classified by Centrifugal Separator

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Na0.5K0.5NbO3 (NKN)-based materials have been studied intensively as a lead-free candidate for piezoelectric application, but it has been well known that inhomogeneous microstructure often arises during the sintering process. In general, the “size effect” is well recognized in the electric property of dielectric materials. In this study, the size classification of NKN particles has been achieved by a wet-type centrifugal separation technique using one sample source fired at 1100 °C for 2 h to avoid the effect of heating conditions and to investigate the distribution of the crystallinity in the sample. The selected rotating rates successfully produced 6 kinds of the classified powders with different mean-particle sizes from 0.3 to around 40 μm (NKN-0.3 to NKN-38.9). Their crystallinity were characterized by the X-ray diffraction technique, and the refined crystal structures confirmed that a considerable change occurred in lattice parameters for the samples between NKN-0.3 and NKN-7.0, and that non linear variations in the Nb--O bond distance and the bond angle were also recognized in the samples between NKN-0.9 and NKN-2.4. The calculated $P_{\text{s}}$ was maximized to 35 μC/cm2 in NKN-2.4, and markedly decreased to 25 μC/cm2 in a particle with size exceeding 7.0 μm.
2011-09-25