Solid-state formation reactions of Ba0.82Ca0.18Zr0.08Ti0.92O3 piezoceramics

The lead-free piezoceramic (Ba,Ca)(Zr,Ti)O ₃ 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 _0.82Ca _0.18Zr _0.08Ti _0.92O ₃. We identified the phase formation 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 CaTiO ₃ and a polytitanate phase, were proposed. This resulted in an increase of the small-signal piezoelectric coefficient d ₃₃ 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.