Solid-Solution Structure and Piezoelectric Property of KNbO3 Ceramics Doped with Small Amounts of Elements

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  • Kakimoto Ken-ichi
    Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology
  • Masuda Izumi
    Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology
  • Ohsato Hitoshi
    Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology

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  • Solid-Solution Structure and Piezoelectric Property of KNbO<sub>3</sub> Ceramics Doped with Small Amounts of Elements

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Abstract

The origin of the improvement of the ferroelectric and piezoelectric properties of KNbO3 ceramics by the addition of small amounts of La and Fe has been investigated. The La/Fe-codoped KNbO3 ceramics formed a single (K1−xLax)(Nb1−xFex)O3 solid solution, and their unit-cell volume decreased significantly with an x of 0.002 mol, while they recovered at x=0.004. In this region, the lattice parameters of the a-b basal plane decreased and the elongation in the c direction toward apical oxygen in NbO6 octahedra occurred. These results were correlated with the enhanced polarization and piezoelectric properties measured for the x=0.002 specimen. The x=0.002 specimen demonstrated a kt of 0.48 which corresponds to approximately 70% of the kt value predicted for a KNbO3 single crystal as its maximized property. Furthermore, La/Fe-codoped KNbO3 ceramics with MnO2 addition were prepared to observe the effect of multivalent ion (Fe and Mn) doping into the KNbO3 structure on the properties. Synchrotron near-edge X-ray absorption spectroscopy (XANES) study revealed a mixture of k-edge spectra consisting of Mn4+/Mn3+/Mn2+, while Fe3+ maintained its valence state. The influence of valence fluctuation on the ferroelectric and piezoelectric properties of KNbO3 ceramics was discussed.

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