Space charge effect in ferroelectric (K0.50Na0.50)(2)(Sr0.75Ba0.25)(4)Nb10O30 ceramics

The effects of space charges on the ferroelectric properties of (K0.50Na0.50)(2)(Sr0.75Ba0.25)(4)Nb10O30 (KNSBN) ceramics have been investigated in the temperature range between 30 degrees C and 800 degrees C. For samples aged at room temperature or poled at temperatures above the Curie point (T-c similar to 208 degrees C) in order to induce space-charge polarization, we have observed a broad dielectric peak at around 650 degrees C, a negative depolarization current above 650 degrees C, and a variation of the activation energy at 650 degrees C. This behavior above T-c may be interpreted in terms of mobile space charges such as A-site vacancies or oxy vacancies which may be formed during the sintering process at high temperatures (similar to 1300 degrees C). The experimental results are discussed in connection with the interaction between the polarities of domain and space charges.