Optimization of sintering conditions depending on doping in BiNaTiO3 and KNaNbO3 based piezoelectric ceramics

A problem existing on piezoelectric materials which today's electronic industry use to manufacture many devices constitutes the main goal of this thesis. Several materials in solid solution form with perovskite structure such as lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT) and lead zinc niobate-lead titanate (PZN-PT) that are known and produced over five decades offer excellent piezoelectric and ferroelectric properties. These materials that have a wide range usage for both civilian and military applications such as ultrasonic transducer, SONAR, sensor, actuator, fuel injector and nano-positioner for scanning electron microscope contain lead (Pb) more than 60 percent by weight which is a toxic heavy metal. It has been revealed that lead can evaporate easily during the processing of these technologically essential materials at elevated temperatures and cause both severe environmental and health problems. For this reason, recently lead contained materials have been banned in European Union (EU) countries and current materials selection criteria for piezoelectric include not only superior properties but being environmentally friendliness. Today there is an increased demand for developing "lead-free piezoelectric materials". In recent years, a remarkable effort has been made to produce alternative materials for lead-based piezoelectric materials, especially PZT, and improve their properties. Among these materials, there are two main systems shined up: BiNaTiO3 (BNT) and KNaNbO3 (KNN). However, there are still many challenging problems to overcome on synthesis and improving properties. Some strategies have been pursued to overcome problems such as phase transformation under Curie temperature (Tc) in BNT, poor densification, temperature dependent properties and difficulties in controlling the stoichiometry due to volatility of alkalies in KNN. On the purpose of solving density problems, some techniques such as hot isostatic pressing (HIP), spark plasma sintering (SPS) have been studied and successful results were reported. However, it is clear that those techniques are not economic and practical for industry. Many modified systems with dopants still using conventional techniques offer quite good properties. The purpose of this study is to produce BNT and KNN-based environmental friendly lead-free piezoelectric ceramics using high-purity raw materials via solid-state method and measure their properties. Dopants used in both systems can alter sintering conditions that is the most critical step for obtaining superior material properties. In this respect, it is aimed to reveal systematical results by optimizing both thermodynamic and kinetic conditions taking effect on sintering.