Abstract: (Pb_x,Sr_1-x)_0.85Bi_0.1TiO₃thin films with perovskite structure were prepared on ITO glass substrate by a sol-gel method. XRD, SEM and impedance analyzer were respectively used to characterize the phase status, morphology and dielectric properties of the films. The results show that during the formation of (Pb_x,Sr_1-x)_0.85Bi_0.1TiO₃ thin films, nucleus of the perovskite phase are initially formed and then congregated together. These aggregated nucleus are then transformed as the perovskite-phase crystalline. And finally, the crystalline phase grows and separates gradually to form the perfect crystalline structure. The content of the perovskite phase formed in the thin film under rapid thermal process(RTP) is more than that formed in kinetic equilibrium under traditional heat treatment. It is due to the high active decomposed ions forming the perovskite phase directly when
heat-treated by RTP. The structure of the perovskite phase has a close relation to the ratio of Pb/Sr in the system because of the difference of radius between Pb²⁺ and Sr²⁺. The transformation temperature between cubic and tetragonal of the perovskite phase is increased as increasing Pb2+ whose radius is larger than that of Sr²⁺. It appears at room temperature when the content of Pb²⁺/Sr²⁺ is about 0.4/0.6. Meanwhile, the tetragonality of the perovskite phase is increased
with increasing Pb2+ ions. High tunability of the (Pb_x,Sr_1-x)_0.85Bi_0.1TiO₃ thin film is exhibited when the film composition is close to transformation point between paraelectric and ferroelectric. Pb²⁺ ions act as a dominant factor to affect the Curie point of the system and then to change tunability.

Key words: PST films, dielectric properties, sol-gel method, phase formation