Dispersion of Relaxation Times in Impedance Measurements of Na_1−xK_xNbO₃ Mixed Ceramic

Sodium Potassium Niobate ceramic with perovskite structure has been prepared through solid state reaction using conventional double sintering method. The starting materials are mixed in the stoichiometric proportion. The compound is characterized through x-ray diffraction to ensure the formation of single phase. From this data, the lattice parameters are determined. The temperature dependence of the dielectric constant and loss factor are obtained over a wide frequency range. Both dielectric constant and loss factor show two peaks. The dielectric and loss peaks observed at lower temperature are found to be of less intensity. The second dielectric anomaly observed around 430°C is found to follow Curie-Weiss law. The curie constant ‘C’ is observed to be around 10 ⁵ °C. Impedance measurements are also made in the temperature range 30°C to 550°C in frequency range 500 Hz to 1 MHz. Dispersion of impedance with frequency show peaks, which vary both with temperature and frequency. The relaxation times are obtained from these peak frequencies. Activation energy of relaxation is calculated and the results are presented.

Keywords:

• Impedance spectroscopy
• ferroelectric
• perovskite
• dielectric

Acknowledgments

We thank DRDO, New Delhi for the financial support and G. Swaminathan, B.H.E.L. (R&D) Vikas nagar, Hyderabad for extending XRD facilities.

Paper originally presented at AMF-4, Bangalore, India, December 12–15, 2003