The high temperature behaviour of Pt/Ti base electrode bilayers is crucial for the deposition of ferro-electric thin films on top of such metal films. Therefore the microstructural development during annealing has to be considered. These parameters are studied by X-ray diffraction (XRD). Comparing the microstructure before and after thermal treatment significant differences could be found. Pt3Ti compound formation was observed in all coatings. The stress in the Pt phase changes from compressive to tensile during annealing. In contradiction the stress in the Pt3Ti phase is compressive after thermal treatment. From measurements of the total reflected signal an amount of TiO2 on the surface of the oxygen treated film could be found. A model based on diffusion of Ti along grain boundaries and considering thermodynamic aspects of stress development is predicted to describe the microstructural changes during annealing.