Properties improvement by microstructure control in lead-free piezoelectric ceramics

From past to present, most of the piezoelectric materials used in actuators, sensors, transducers, and generators contain lead-based compositions, which has superior piezoelectric properties but is harmful to nature and humans. Research and practice have initiated many new directions in many countries, including Turkey, about limiting the use of piezoelectric materials containing lead and converting it to clean content. Lead-free piezoelectric systems' development to provide superior performance proceeds intensively in today's world of materials science. There are ongoing studies on lead-free piezoceramics that can be stable for the usage temperature (100oC< T< 200oC) in areas such as the automotive sector, where the usage intensity is mainly considered. In these studies, sodium bismuth titanate (NBT) based ceramics are important alternatives to toxic lead-based ceramics due to their high piezoelectric performance and reproducibility. This study was carried out with anticipation is that potassium bismuth titanate (KBT) and barium titanate (BT) modification of NBT ceramics will result in superior electrical properties with relatively high phase transformation temperatures. Additionally, texturing ceramics with the desired crystallographic orientation is another approach to obtain significantly higher piezoelectric responses from NBT-based ceramics. Templated Grain Growth is a technique widely used to produce grain-oriented ceramics by the orientation of anisotropic shaped templates in coaxial matrix particles and subsequent heat treatments in which densification and grain orientation occur through the Ostwald ripening process. In this process, the development of lattice mismatches between cores and oriented grains can result in low phase transformation and depoling temperatures. In this study, to test this effect, plate-shaped NBT, BiT, and KBT templates that are considered to be compatible with the matrix were used to texture the KBT-BT-NBT ceramics. Homogeneous orientation amount analyzes of ceramics containing 0%, 5%, 10%, and 15% template produced by tape casting with Templated Grain Growth (TGG) method. It is designated as the lotgering factor. Microstructural development of sintered samples was observed by scanning electron microscope and electrical measurements of depolarization temperature (Td), hysteresis and piezoelectric coefficient (d33) were made.