Low temperature Sol Gel deposition of lead scandium tantalate (Pb(Sc0.5Ta0.5)O3) thin films

This study reports research into the preparation of lead scandium tantalate (PST: Pb(Sc0.5Ta0.5)O3) thin films. The object of the project was to deposit thin films of this material at a relatively low temperature e.g. 500 deg. C for possible future pyroelectric applications. The thin films have been deposited using the Sol Gel method and the effect of the deposition conditions e.g. composition, preparation, firing method etc. on the crystallisation behaviour of the thin films has been carefully investigated. The crystallite phase and texture of the deposited thin films were characterised using X-Ray Diffraction (XRD) analysis and the surface morphology and thickness were investigated by means of Scanning Electron Microscopy (SEM) observations. Also the dielectric and pyroelectric properties of some of the thin films produced were measured and compared with the investigations reported in the literature on this subject. The XRD analysis showed that the thin films fired at a high temperature mainly consist of a perovskite phase strongly oriented in a (111) direction. It was also found that the type of equipment used for firing the thin films had a significant effect on a crystallisation temperature of the required perovskite phase. The thin films fired on a hot plate crystallise at a temperature as low as 520 deg. C whilst these would normally crystallise at 700 deg C when fired in a tube furnace. However, the reason for this difference has not yet been identified. The addition of Pb excess was also investigated and it was shown that this has an important effect in promoting the crystal growth and the orientation of the perovskite phase; Pb excess also had the effect of depressing the unwanted intermediate pyrochlore phase. (author)