Lead scandium tantalate (PST) thin films have been deposited on a platinized silicon substrate with and without a buffer layer of MgO at the temperature of 525 degrees C. It was found that PST films on the substrate without a buffer layer were strongly (111) oriented perovskite, whilst films on the substrate with a buffer layer showed the presence of second-phase pyrochlore, and the films were (111) and (110) oriented. These structural differences were believed to result from the structural differences between the platinum layers immediately below the respective PST layers. The "lines" which divide PST into "network" of islands were found to be no more than wider grain boundaries, rather than "cracks" as believed previously. Micro-beam diffraction and energy dispersive X-ray analysis showed that grain boundaries were tantalum-rich and lead-deficient compared to perovskite grain centres. Electrical properties, such as relative permittivity and dielectric loss, for the films were also measured.