Effect of mechanochemical activation on the synthesis of NaNbO3 and processing of environmentally friendly piezoceramics

High-energy milling has been applied to obtain NaNbO3 ceramic precursor powders and dense ceramics by a one-step thermal treatment. Stoichiometric mixtures of Nb2O5 and different sodium reactants (Na2CO3, Na2O and NaOH) were mechanically activated. The obtained results are discussed regarding the starting reactants and the milling media. The evolution of the powder mixtures and the thermal behavior of the activated samples were investigated by X-ray powder diffraction and thermal analysis. The most crystalline NaNbO3 powders were obtained when a 2NaOH/Nb2O5 mixture was homogenized using a wet-chemistry technique followed by mechanochemical activation in a planetary mill and treated at 900 °C for 2 h. Dense ceramics were processed from the different precursors by conventional-sintering and hot-pressing and their microstructure and piezoelectric properties characterized.