Dielectric, impedance and ferroelectric characteristics of c-oriented bismuth vanadate films grown by pulsed laser deposition

Abstract

Ferroelectric bismuth vandante, Bi₂VO_5.5 (BVO) thin films with layered perovskite structure were deposited by pulsed excimer laser ablation technique on (1 1 1) Pt/TiO₂/SiO₂/Si substrates. The polarization hysteresis (P versus E) studies on the BVO thin films at 300 K confirmed the remnant polarization (P_r) and coercive field (E_c) to be 5.6 µ C/cm² and 113 kV/cm, respectively. The same was corroborated via the capacitance-voltage measurements. The dielectric response and conduction mechanism of BVO thin films under small ac fields were analyzed using impendence spectroscopy. A strong low frequency dielectric dispersion (LFDD) was found to exist in these films, which was ascribed to the presence of the ionized space charge carriers such as oxygen ion vacancies and interfacial polarization. The room temperature dielectric constant and the loss (D) at 100 kHz were 233 and 0.07, respectively. The thermal activation energy for the relaxation process of the ionized space charge carriers was 0.85 eV. The frequency characteristics of BVO thin films under study showed universal dynamic response that was proposed by Jonscher for the systems associated with quasi-free charges.