Processing of Piezoelectric (Li,Na,K)NbO3 Porous Ceramics and (Li,Na,K)NbO3/KNbO3 Composites

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Porous Li0.06(Na0.5K0.5)0.94NbO3 (LNKN-6) ceramics with different pore volumes have been prepared using preceramic powder and phenol resin fiber (KynolTM) as a pore former. It was confirmed that the porous ceramics synthesized by the “two-stage firing method” suppressed the loss of alkali elements from the porous body during heat treatment. The porous LNKN-6 ceramics were then converted to LNKN-6/KNbO3 composites through soaking and heat treatment using a sol–gel precursor source composed of KNbO3 to form 3–3-type composites. The microstructure, dielectric, and piezoelectric properties of the porous LNKN-6 ceramics and LNKN-6/KNbO3 composites were characterized and compared. The LNKN-6/KNbO3 composites had a hollow structure whose pores in the region near the surface were filled and coated with KNbO3 precipitates; however, a large amount of residual air was trapped in the pores inside the composites. As a result, the LNKN-6/KNbO3 composites fabricated using 30 vol % KynolTM showed an enhanced piezoelectric voltage output coefficient ($g_{33}$) of $63.0\times 10^{-3}$ V$\cdot$m/N, compared with monolithic LNKN-6 ceramics having a $g_{33}$ of $30.2\times 10^{-3}$ V$\cdot$m/N.
2007-10-30