Synthesis and sintering improvement of Aurivillius type structure ferroelectric ceramics by mechanochemical activation

An oxide mixture of composition 3Bi(2)O(3):Nb2O5:2TiO(2) has been mechanochemically activated in a laboratory mill for different times from 3 to 336 h. The as-milled powder and an unmilled mixture of identical composition were annealed at different temperatures up to the formation of the Aurivillius-type oxide Bi3NbTiO9,and examined by X-ray diffraction (XRD) and differential thermal analysis (DTA). The sample milled for 336 h shows complete amorphization. Its DTA curve exhibits two exothermic process at 370 and 560 degrees C, corresponding to the formation of a metastable fluorite phase and the Aurivillius-type oxide, respectively. The crystallization temperature of this Aurivillius phase from the unmilled oxide mixture is reported to be 1050 degrees C, whereas from the amorphous powder obtained by 336 h of mechanochemical activation this temperature becomes as low as 600 degrees C. Ceramics of this composition must be prepared by hot-pressing in order to obtain low porosities, owing to the lamellar morphology of the conventionally crystallized powder, which gives rise to textured anisotropic materials. Non-textured ceramics were obtained both from the conventionally crystallized and the amorphous powder by natural sintering at 1100 degrees C. Ceramics obtained From amorphous powder show lower porosity and higher electromechanical coupling factors.