Relaxation behaviour induced by oxygen vacancies of barium strontium titanate at high temperatures

The dielectric properties and electrical conduction of Ba _1-xSr_xTiO₃ (x = 0.2, 0.25, 0.3) ceramics have been investigated in the temperature range 25-400 °C and the frequency range 100 Hz-1 MHz. The broad dielectric peaks ε′(f), tanδ(T), tan δ(f) and the distribution parameter β are all indicative of a typical relaxation behaviour existing above 200 °C for all compositions. With increasing Sr content, more grain boundaries acting as 'electrical barriers' lead to the conductivity decreasing and the activation energy E_a = 0.88-0.96 eV for different compositions indicates that the oxygen vacancies acting as 'polarons' under the external ac electric field lead to the relaxation behaviour.