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 mechanoch emically activated in a laboratory mill for different times from 3 to 336 h . The as-milled powder and an unmilled mixture of identical composition wer e annealed at different temperatures up to the formation of the Aurivillius -type oxide Bi3NbTiO9,and examined by X-ray diffraction (XRD) and different ial thermal analysis (DTA). The sample milled for 336 h shows complete amor phization. Its DTA curve exhibits two exothermic process at 370 and 560 deg rees C, corresponding to the formation of a metastable fluorite phase and t he Aurivillius-type oxide, respectively. The crystallization temperature of this Aurivillius phase from the unmilled oxide mixture is reported to be 1 050 degrees C, whereas from the amorphous powder obtained by 336 h of mecha nochemical activation this temperature becomes as low as 600 degrees C. Cer amics of this composition must be prepared by hot-pressing in order to obta in low porosities, owing to the lamellar morphology of the conventionally c rystallized 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 o btained From amorphous powder show lower porosity and higher electromechani cal coupling factors.