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

The compositionally graded Pb1−xSrxTiO3 (PST) films with a fine compositional gradient from Pb0.6Sr0.4TiO3 to Pb0.3Sr0.7TiO3 were fabricated on LNO-buffered Pt/Ti/SiO2/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.