Abstract
Detailed study of ac conductivity of “1-x-y (Bi0.5Na0.5)TiO3–x(Bi0.5K0.5TiO3)–y(Na0.5K0.5)NbO3 (BNT-BKT-KNN)” with x = 0.2 y = 0.01 for 25 °C ≤ T ≤ 350 °C and 40 Hz≤f ≤ 100kHz is presented. Below depolarization temperature (Td ∼ 80 °C), a temperature independent translational short range hopping conduction of bipolarons between Ti+3 and Ti+4 sites was observed. Above Td , σac , α and n were found to be both frequency and temperature dependent. Thermally activated hopping assisted by large polarons was seen in the frequency range 40 Hz≤f ≤ 10kHz; whereas, reorientational hopping of charge carriers (hopping between two charge defects) assisted by small polaron mechanism was evident in the high frequency region (10 kHz<f ≤ 100 kHz).
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