Dielectric relaxation of Sr1–1.5xBixTiO3 sol-gel thin films

Abstract

The dielectric response of Sr1–1.5xBixTiO3 films (0.002 ≤ x ≤ 0.167), prepared by sol-gel and deposited on Si/SiO2/TiO2/Pt substrates, is analyzed as a function of frequency and temperature. The hysteretic behavior of the polarization versus the electric field is studied as well. Between 100 Hz and 1 MHz, the real part of the dielectric permittivity ɛ′ exhibit a relaxation between ∼60 and 260 K, shifting to high temperatures with increasing the Bi content. In the imaginary part of the dielectric permittivity ɛ′′ of these films two relaxations are induced by Bi doping below the temperature of the ɛ′ relaxation. The first relaxation observed in films with 0.002 ≤ x ≤ 0.10 follows the Arrhenius law with an activation energy of U = 64–80 meV and a preexponential term τ0 = (0.3–10.8) × 10−14 s almost independent on the Bi content and is ascribed to the individual hopping of dipoles created by the off-center Bi ions. The second relaxation observed in the films with 0.04 ≤ x ≤ 0.167 is described by the Vögel–Fulcher relation with U = 2–38 meV, τ0 = 5 × 10−10–5 × 10−6 s and a freezing temperature Tf = 50–102 K, increasing with Bi content, and is attributed to the presence of polar clusters of interacting Bi ions. Slim P(E) hysteresis loops are observed at low temperatures, confirming the appearance of a polar state. The effect of Bi incorporation in ST films is qualitatively the same as the relaxorlike behavior observed in Bi-doped ST ceramics and the dissimilarities are explained based on the influence of the substrate and by a higher homogeneity of the dopant distribution in the sol-gel derived films.