Low pO2 sintering and reoxidation of lead-free KNNLT piezoceramic laminates

We studied the sintering behavior under reducing conditions of laminates and the performance of the sintered monolithic samples of Li- and Ta-modified sodium potassium niobate (KNNLT) lead-free piezoceramics. Sintering under low pO2 allows co-firing with base metal electrodes, which is an important step towards competitive multilayer actuator fabrication technologies. We present results on phase composition, microstructure and electromechanical properties of KNNLT ceramics, obtained by sintering laminates under low oxygen partial pressure of 10−10 atm at temperatures from 970 °C to 1070 °C and reoxidized at 850 °C with pO2 between 10-9 atm and 10-1 atm. Sintered samples exhibit dense and fine-grained microstructures with low dielectric losses of 2%. A normalized strain coefficient d 33 * = 330 pm/V was obtained at 3 kV/mm for a sample reoxidized at 10-3 atm. Samples reoxidized at very low pO2 exhibit increased dielectric losses and leakage currents at 150 °C as signature of larger oxygen vacancy concentrations.