In this work, “lead free” 0.99K0.5Na0.5NbO3-0.01BiFeO3 (KNN–BF) piezoceramics were prepared by a combination of mechanochemical activation, Spark Plasma Sintering and post-annealing treatment. Results show that the annealing treatment causes important microstructural and electrical changes. The SPS sample was characterized by low electrical resistance, while the air annealed samples showed better insulating properties due to a partial compensation of the oxygen vacancy. The best piezoelectric properties were found for the samples annealed at 1000 and 1050 °C for 2h due to the optimum grain size and oxygen vacancy compensation achieved. A further enhancement of the dielectric and piezoelectric properties was achieved through a second annealing treatment in oxygen flux at 1050 °C for 30 min. Moreover, the toxicity of the pellets was evaluated through exposure experiments to the pulverized KNN–BF pellets, employing two widely used human and environmental cellular models.
