Base metal Co-fired (Na,K)NbO₃ structures with enhanced piezoelectric performance

A NaF-Nb₂O₅ flux doped (Na,K)NbO₃ (NKN) based lead-free ceramic was successfully co-fired with nickel inner electrodes in reduced atmospheres. No chemical reactions and/or inter-diffusion were detected at the interface between the nickel (Ni) electrodes and the NKN-based piezoelectrics. Dielectric, resistivity, and electromechanical performance were measured with processing under different firing conditions and flux additions to obtain high densities. Ceramics are obtained with submicron grain structures with the NaF-Nb₂O₅ sintering aids (2 and 4 wt%) fluxes, and high densities when firing at low pO₂ (10⁻¹⁰ atms) atmospheres at sintering temperatures ~1150 °C for 2 hours. High resistivities and low losses can be obtained through a second annealing condition at 850 °C and 10⁻⁷ atms at 8 hours. High d ₃₃ values (over 350 pm/V) determined under unipolar converse electromechanical measurements were obtained in the simple prototyped co-fired structures to show feasibility towards base metal electrodes in multilayer actuators.