Dielectric behavior of Bi_3.25la_0.75Ti ₃O₁₂ ferroelectric film

Dielectric and ac conductivity measurements, at frequencies from 100 Hz to 1 MHz, were carried out on lanthanum doped bismuth titanium (Bi _3.25La_0.75Ti₃O₁₂) ferroelectric films, in the temperature range of 25-600°C. In addition to a dielectric peak at 483°C attributed to the paraferroelectric phase transition, three dielectric relaxations were found at ∼250, ∼400, and ∼500°C, respectively. The dielectric relaxation ∼400°C can be eliminated by using both a higher sintering temperature and oxygen postannealing, and it can be induced again by a subsequent nitrogen postannealing process. The activity energy of the dielectric relaxation of this mode is estimated to be 1.89 eV, according to Arrhenius law. The dielectric relaxation ∼500°C is not influenced by sintering temperature but is influenced by the postannealing process. The intensity of this anomaly decreases after oxygen postannealing and then increases after nitrogen postannealing. The relaxation behavior of this dielectric relaxation is not in accordance with Arrhenius law but is in accordance with Vogel-Fulcher law, and the activity energy is calculated as 0.31 eV. Possible mechanisms for the observed dielectric relaxations ∼250, ∼400, and ∼500°C are proposed.