Nonlinear behaviors of the compositionally graded (Ba,Sr)TiO3 thin films derived by a sol-gel process

The compositionally graded Ba1-xSrxTiO3 films with a fine compositional gradient from BaTiO3 to Ba0.70Sr0.30TiO3 were fabricated on LaNiO3-buffered Pt-Ti-SiO2-Si substrates by a sol-gel deposition method. After post-deposition annealing the graded films crystallized into a pure perovskite structure with their crystalline orientation and surface morphology closely related to the deposition sequence of the film layers. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range from -35degreesC to 190degreesC. Instead both the dielectric constant and dielectric loss showed negligible temperature dependence. The tunability of up-graded and down-graded films was about 35% and 37%, respectively, at an applied field of 300 kV/cm and measurement frequency of 1 MHz. The improved temperature stability from this type of compositionally graded material is beneficial to applications requiring a wide range of operating temperatures, thereby eliminating the need for environmental controls. (C) 2004 American Institute of Physics.