Oxygen vacancy induced dielectric relaxation studies in Bi4-xLaxTi3O12 (x=0.0, 0.3, 0.7, 1.0) ceramics

In the present work, oxygen vacancy induced dielectric relaxations were studied for Lanthanum substituted Bi4-xLaxTi3O12 (x = 0.0, 0.3, 0.7, 1.0) ceramics. X-ray diffraction patterns reveal the formation of single phase orthorhombic structure in all the samples. The partial substitutions of lanthanum ions were found to significantly influence the grain morphology of the sintered ceramics. Temperature dependent dielectric measurements indicate a well-defined dielectric constant peak around 150 A degrees C, with strong frequency dispersion. This dielectric anomaly was attributed to the Maxwell-Wagner space charge relaxation phenomenon related to oxygen vacancies. The space charges related to oxygen vacancies were confirmed by annealing the samples in oxidative atmosphere. The electrical modulus analysis shows that the samples exhibit non-Debye type relaxation behavior. Doubly ionized oxygen vacancies were found to influence the relaxation behaviour at higher temperature. The observed dielectric relaxation as a function of temperature and frequency were explained on the basis of oxygen vacancies.