Sodium niobate ceramics prepared by mechanical activation assisted methods

Sodium niobate is an interesting material that is nowadays considered to be used as a lead-free piezoelectric ceramic. However, it is very difficult to process fully dense ceramics of this composition starting from crystalline powdered precursors. It seems a priority to develop a new synthesis route for the processing of high quality ceramics. A new synthesis method based on high-energy milling, not yet explored for this type of materials, has been applied to obtain NaNbO3. Stoichiometric mixtures of analytical grade Na2CO3 and Nb2O5 were mechanically activated in a vibrating-type mill. A progressive broadening of the different X-ray diffraction peaks was observed when the milling time was increased. The starting products did not become amorphous. The thermal behaviour of the milled samples was studied by high temperature in situ X-ray powder diffraction and thermal analysis techniques. Ceramic materials were processed by natural sintering and hot-pressing or a combination of both. Ferro-piezoelectric properties were measured to assess their practical use as piezoceramics.