Solid-state formation reactions of (Ba,Ca)(Zr,Ti)O3 piezoceramics

The lead-free piezoceramic (Ba,Ca)(Zr,Ti)O3 system has been a focus of scientific research due to its outstanding electromechanical properties, rivaling those of conventional lead-based materials. However, poor reproducibility and unwanted secondary phases are major obstacles to the further development of these materials. Here, we used thermal analysis and high-temperature in-situ X-ray diffraction to identify the chemical reactions taking place during the solid-state synthesis of (Ba,Ca)(Zr,Ti)O3. We identified the reaction sequence, discovered novel and formerly unknown intermediate phases, and defined the conditions for secondary phase formation. Strategies for the removal of the main secondary phases, namely CaTiO3 and a polytitanate phase, were proposed. This resulted in an increase of the small-signal piezoelectric coefficient d33 by 28%. The reaction sequence generated in this study will help to improve the processing conditions for this material system to allow for controlled microstructure engineering and enhanced electromechanical properties.