Piezoelectric materials for transducer or actuator applications are nowadays still based on Pb(Zr,Ti)O3 (PZT) perovskite ceramics containing toxic lead. Alternative lead-free piezoelectrics are being developed while still not reaching the response values of PZT and imposing difficulties in the manufacturing processes, raising numerous development issues. Among the potential lead-free materials, K0.5Na0.5NbO3 (KNN) is one of the most promising piezoelectric systems that needs to be further improved to meet the industrial demands. Beside chemical modifications to produce high-quality ceramics, the alternative sintering technique of Spark Plasma Sintering is used to limit species volatilization, excessive grain growth and segregation of defects. The progress of this technique is crucial also from environmental stand-point as it represents a means of reducing energy consumption.
We have investigated selected lead-free KNN based compositions and their influence on ceramic’s structures, microstructures, densification, mechanical and functional properties.
Study and comparison of conventional sintering and spark plasma sintering and the complete characterization of the microstructures through SEM, EDX, Raman and XPS techniques has shown the high potential of spark plasma sintering technique. Emphasis is given to the effects of tantalum and lithium substitution, largely investigated in conventional sintering but with only few studies with Spark Plasma Sintering. Finaly upscaling of the ceramics’ dimensions and mechanical characterizations such as hardness and fracture toughness, will be also presented. Polarization and electromechanical characterization served as a quality check of functionalities of the produced piezoelectric components.

Barium titanate-based ceramics with Positive Temperature Coefficient of Resistance (PTCR) become increasingly important due to their unique possible applications e.g., as cabin heaters in electrical vehicles or as overcurrent protection devices in circuits. The change of operating conditions like the increase of board voltage in electric vehicles requires further adjustment of current PTCR materials. For this purpose, the whole manufacturing process must be considered, and the influence of the selected process parameters and chemical additives understood.
In our contribution, the process parameters of grinding, such as grinding medium and duration, and sintering, such as temperature and sintering time, are varied and their influence on microstructure and functional properties examined. In addition, influence of donor and acceptor dopant concentration on PTCR characteristics are investigated in detail.
The improvement of the dielectric strength of PTCR ceramics is especially essential if higher voltages are applied and is achieved by a defined addition of silicon dioxide. To evaluate the different impacts, microstructural studies are carried out using scanning electron microscopy and functional properties determined by characterization of breakdown voltage and temperature dependent measurement of the electrical resistance. The influence of additional process parameters like calcination temperature as well as heating and cooling rates are subject of ongoing investigations.