Dielectric Relaxation in K_0.5Na_0.5NbO₃-PVDF Composites

K_1−x Na _x NbO₃ is considered as an alternative system for lead-based functional ceramics widely used in transducers, sensors and actuators. In some applications however, the composites of electroactive ceramic and polymer, with low acoustic impedance and dielectric permittivity that can be tailored to various requirement, are more useful. We studied dielectric relaxation processes in polyvinylidene fluoride (PVDF) loaded with K_0.5Na_0.5NbO₃ powder in wide temperature and frequency range. The powder was prepared by solid state synthesis and characterized by HRTEM and NIR Raman spectroscopy. The dielectric response of (K_0.5Na_0.5NbO₃)_0.32(PVDF)_0.68 composite, of (0–3) connectivity, was found to be determined by the relaxation processes of the polymer matrix with an additional broad low-frequency anomaly at ∼ 305 K that we relate to a response of water absorbed by the shell of KNN grains.

Keywords:

• Composites
• dielectric spectroscopy
• lead-free

Acknowledgment

The work was supported by Grant 2 P03B 121 24 from the Committee of Scientific Researches in Poland, and by POLECER–Thematic European Network on Polar Electrocceramics G5RT-CT-2001-05024.

Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005; received for publication January 26, 2006.