Key steps in the processing of ferroelectrics: solid state synthesis of the perovskitic phase, cold consolidation and densification

The processing of bulk ferroelectric materials is based on several steps each of them with the potential of limiting the final properties of the materials, if not carefully addressed and optimized. The solid state synthesis is the most used method to produce the perovskitic phase , and the massively one chosen for the production of the commercial powder. It is based on the thorough mixing of the starting oxides or carbonates followed by solid-state reaction (SSR) at high temperatures. The successful production of powders depends on the control of the synthesis parameters and purity and morphology of the raw materials. The content of the perovskitic phase as well as the morphology and cold compaction behaviour of the powders strongly influence the behaviour of the powder during densification and the final microstructure of the sintered material. Milling steps introduced after SSR result of outmost importance in order to enhance the green density of the samples produced either by dry pressing or colloidal processing. The densification step is critical as the difficulty to achieve full density is associated with the easy of evaporation of elements of the composition and stoicheiometry loss. These issues will be addressed with focus on the optimization of the conventional and cheap processing techniques, with main reference to the PZT based compositions.