Enhancement of ferroelectricity in the compositionally graded (Pb,Sr)TiO₃ thin films derived by a sol-gel process

The compositionally graded Pb_1-xSr _xTiO₃ (PST) films with a fine compositional gradient from Pb_0.6Sr_0.4TiO₃ to Pb_0.3Sr _0.7TiO₃ were fabricated on LNO-buffered Pt/Ti/SiO ₂/Si substrates by a sol-gel deposition method. The graded films crystallized into a pure perovskite structure and exhibited highly (1 0 0) preferred orientation after post-deposition annealing. Dielectric and ferroelectric properties were investigated as a function of temperature, frequency and direct current bias field. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range of 25-250 °C within which the dielectric constant showed weak temperature dependence. This compositionally graded thin film can result in a dielectric constant more than double and a remanent polarization at least two and a half times larger than conventional PST thin films. © 2005 Elsevier B.V. All rights reserved.