Anomalous dielectric properties in (BaSr)TiO3 films fabricated by pulsed-laser deposition in N2 atmosphere

A high dielectric constant of 2500 at 10 kHz near room temperature was observed in (Ba0.5Sr0.5)TiO3 (BST) films prepared by pulsed-laser deposition (PLD) at 550 °C in N2 atmosphere. The dielectric constant is weakly temperature-dependent above 200 K. However, there is about one hundred fold drop below 200 K, which can be characterized by a thermally excited relaxation process. The temperature and frequency-dependent dielectric response of the film is very similar to that reported for the so-called 'colossal' dielectric constant material, such as CaCu3Ti4O12. The dielectric properties are sensitive to the metal contacts with different work functions, however insensitive to the film thicknesses. Such an anomalous dielectric response for the BST films is ascribed to the formation of the Schottky barrier between the metallic electrode and the film surface, and the existence of the mobile charges in the film as indicated by the frequency characteristics of dielectric constant changing as the applied dc bias.