Origins and evolution of stress development in sol-gel derived thin layers and multideposited coatings of lead titanate

Stress development in thin layers of lead titanate prepared by sol-gel processing was monitored by in situ laser reflectance measurements. Layers were spin coated onto silicon substrates and thermally cycled to 500 °C. The shrinkage normal to the rigid substrate was determined by in situ ellipsometry. Changes that occurred on drying and firing, which related to densification and stress development, are reported. The observed changes were explained in terms of evaporation and solvent/polymeric network interactions at lower temperatures, and thermal expansion mismatch between the substrate and the coating after formation of the dense oxide. Crystallization into the perovskite structure occurred only in thicker or multideposited coatings, altering the state of stress from tensile, to progressively more compressive, on cooling. The importance of the choice of substrate material, deposition method and heat treatment conditions, in relation to stress development and dependent electrical properties, are discussed.